DE19631171A1 - Optical glass used in optical polarisation system - having specified photoelastic constant in specified wavelength region - Google Patents

Abstract

Optical glass has a photoelastic constant (C) in the region of zero in a wavelength region of 0.4-3.0 mu m. Prodn. of the optical glass is also claimed by changing the ratios of PbO in a Pb-contg. optical glass, in which its photoelastic constant C is controlled. Further claimed are: (i) a polarisation beam distributor; and (ii) an optical polarisation system.

Description

The present invention relates to an optical glass for a optical polarization system that can be suitably used is for an optical polarization system like one Polarization beam splitter and a spatial optical Modulation device to achieve Polarization modulation, and an extremely small one has photoelastic constant C, a method for Production of such an optical glass for an optical Polarization system, and an optical polarization system, in which such an optical glass is used.

In recent years, the use of "Polarization characteristic" as an optical information representing factor in various areas have been further developed, such as in the area of Liquid crystals. Examples of an optical element for Control of polarized light include the following: a polarized light-modulating spatial Light modulator (SLM) for spatial modulation of  polarized light, or a polarizing beam splitter Separation of P-polarized light and S-polarized Light, etc. . Some devices (such as Projection type display devices) in which such an optical Element used is already used in practice been.

Accompanying such a development in the use of Polarization characteristic has the meaning of High-precision control of the polarization characteristic, the optical information forms, in optical systems, the use polarized light, d. H. in an optical Polarization system, increasing from year to year. Because of there is an increase in the above meaning serious need for precision or accuracy in the Control of polarization characteristics continues to increase improve.

Among different optical elements or elements that represent an optical polarization system (like for example substrate and prism) it is common to use a To use material with optical isotropy, especially for some optical elements where the Preservation of polarization characteristics is required. Of the The reason for this is that when using an optical Element that is a material with an optical anisotropy includes the phase difference (optical path difference) between the ordinary ray and the extraordinary ray perpendicular to the ordinary jet during the passage is changed in terms of light by such a material, that was transmitted by the optical element, and therefore in such a case, the polarization characteristic not be preserved. In other words, even in that Case that an optical element or an optical  Component that forms a certain optical system in is able to precisely control polarized light, good Characteristics not with the entire optical system be achieved if the substrate or base material than that other component forming the optical system (which is the Polarization characteristics should be obtained) Polarization characteristics impaired.

In general, a glass has an adequate Has undergone annealing, optical isotropy and possesses also various characteristics that are better than those of other materials in terms of stability, Strength, permeability, refractive index, cost, etc. and therefore, such a glass is widely used for optical elements, the polarization characteristic should get. In particular borosilicate glass (for example a borosilicate glass made by Schott, Germany, trade name "BK7") is inexpensive and owns excellent durability and also low Dispersion. Therefore, borosilicate glass is used in many optical Polarization systems are widely used.

However, even when using the above conventional optical glass for the optical elements of optical polarization systems a certain optical Anisotropy due to a photoelastic effect in the optical element can be induced as in the application of external mechanical or thermal stress of the optical element. Accordingly, the Use of conventional optical glass for the optical element of an optical polarization system Polarization characteristic of optical information due to the "induced optical" described above Anisotropy ". Therefore it is in such a way  Case difficult that the optical polarization system has the desired quality.

It is believed that the external one described above mechanical or thermal stress predominantly in the following situation is trained.

So it is assumed that the "external mechanical stress" predominantly in a manufacturing step of a glass (like for example cutting, gluing or connecting the Glass with a different material, and film formation on the Surface of a glass), or often in one step of the Installation of a glass in an optical system (like holding of the glass with a jig or Holding device and the adhesion of the glass to another Component) is caused. In addition, it is believed that the "thermal stress" is caused by the Development of heat inside a glass (like for example heat generation through the absorption of Light energy) or the generation of heat outside of a Glases (for example due to heat development in one surrounding component). It is also believed that when a Glass is bonded with another material or in Contact device that has a different thermal Expansion coefficient than the glass shows, stress due to of the above heat generation is generated.

As described above, it is difficult if an optical Polarization system using an optical Element is formed, the effect of external mechanical stress or thermal stress completely prevent. Accordingly, it is at Use of conventional optical glass for one optical polarization system in such an optical  System extremely difficult, the induction of the optical Anisotropy due to the external mechanical mentioned above Avoid stress or thermal stress.

An object of the invention is the provision an optical glass for an optical polarization system, that is the polarization characteristic of optical information essentially not affected, not even under the Exposure to external mechanical stress or thermal stress.

Another object of the invention is Providing an optical glass for an optical Polarization system that is able to its To control the refractive index in the desired manner.

Another object of the invention is Provision of an optical polarization system with excellent characteristics.

As a result of serious investigations, the local ones Inventors found that the polarization characteristic of optical information in an optical glass for a optical polarization system (under the influence of a external mechanical stress or thermal Stress) can be determined in the desired manner by using a "photoelastic constant on the value of birefringence or birefringence (under the Application of a load), measured by a Photoelastic modulation method ". The invention optical glass for an optical polarization system based on the discovery above and is characterized by its photoelastic constant C in the range of im  essentially zero in a wavelength range from 0.4 µm to 3.0 µm.

Generally, when a force is applied to a transparent substance such as glass, the homogeneity and isotropy has, so that stress is generated therein, an optical Anisotropy induced in the transparent substance, and the transparent substance shows birefringent properties in similarly as in certain types of crystalline Substances. This phenomenon is called the photoelastic effect designated. The refractive index of a transparent substance, in which stress was developed can be represented by a so-called "(refractive) index ellipsoid", and the The main refractive index axis of the refractive index ellipsoid is coincident with the main load axis.

In general, when the main refractive indices as n₁, n₂ and n₃ are referred to, and the main loads as σ₁, σ₂ and σ₃ are designated (with the same indices the same Mean), satisfy these main refractive indices and Main strains the following relationship.

EQUATION 1:
n₁ = n₀ + C₁σ₁ + C₂ (σ₂ + σ₃)
n₂ = n₀ + C₁σ₂ + C₂ (σ₃ + σ₁)
n₃ = n₀ + C₁σ₃ + C₂ (σ₁ + σ₂).

Here are the above C₁ and C₂ constants, which of depend on the wavelength of light and the transparent substance and n₀ is the refractive index under stress-free Conditions.  

If light shines on a transparent substance with one Refractive index hits, and if a coordinate like that is defined that the direction of the incident light is identical to that of the above σ₃, so the incident Light split into two linearly polarized ones Light components, which are in σ₁- and σ₂-direction (So the components of linearly polarized light have vibration levels that are perpendicular to each other). If light, on the other hand, from the transparent substance emerges, so in the event that the refractive index in the respective directions of the main stresses (n₁, n₂) are different from each other, an optical path difference (Phase difference) ΔΦ between these two linear polarized light components caused by the following formula is shown.

EQUATION 2:
ΔΦ = (2 π / λ) (n₂-n₁) · 1
= (2 π / λ) (C₁-C₂) (σ2-σ1) · 1
= (2 π / λ) · C · (σ₂-σ₁) · 1

In Equation 2 above, λ gives the wavelength of the light and 1 ("el") the light transmission thickness of the transparent Substance. The constant C = C₁-C₂ in the above Equation is called the "photoelastic constant".

According to the present inventors, the value of the photoelastic constant C of conventional optical glasses used for optical polarization systems is large. For example, in the case of the commercially available borosilicate glass "BK7" (Schott Co.), a value for the above constant of C = 2.78 [10 ^-8 cm² / N] (wavelength λ = 633 nm) was obtained, as further is described below. In the case of a borosilicate glass with such a large photoelastic constant C, the optical anisotropy induced by thermal stress or external mechanical stress and the optical path difference ΔΦ, which is based on the anisotropy, reach certain values which are not negligible.

In contrast to this, in the case of the above-mentioned optical glass for the optical polarization system according to the invention, the photoelastic constant C is in the range of essentially zero in the wavelength range from 0.4 μm to 3.0 μm. The expression "a photoelastic constant C in the range of substantially zero" as used herein refers to conditions such that the influence of the optical path difference due to optical anisotropy that occurs when the glass is used for an optical polarization system is within a negligible extent with respect to the entirety of the above optical system. The photoelastic constant C may preferably range from -0.8 to 0.8 [10 ^-8 cm² / N], more preferably from -0.1 to 0.1 [10 ^-8 cm² / N] for incident light in the visible Range. It is particularly preferred that the photoelastic constant C is preferably in the range of -0.1 to 0.1 [10 ^-8 cm² / N] with incident light having a wavelength in the entire visible range (e.g. in a wavelength range from 0.4 to 0.7 µm).

If the photoelastic constant C is dependent on the Wavelength of the incident light varies, so be at least three specific wavelengths λ within the above said predetermined wavelength range selected (i.e. 0.4 µm to 3.0 µm, more preferably 0.4 µm to 1.0 µm, particularly preferably 0.4 to 0.7 µm) in such a way that in  there are substantially equal intervals between them, and the values of the photoelastic constant for these respective ones concrete wavelengths are averaged, whereby the above Value for the photoelastic constant C is obtained.

Fig. 1 is a graph showing the relationship between the fluorine-oxygen (F / O) ratio in an optical glass composition for an optical polarization system according to the present invention, wherein the photoelastic constant C for a wavelength of incident light (633 nm) becomes substantially zero, and the refractive index of the glass. Further, Fig. 2 is a graph showing the change of the photoelastic constant C as a function of the change of the above F / O ratio in the above-mentioned glass composition.

As shown in Figs. 1 and 2, a certain linearity can be established for the refractive index of the optical glass according to the present invention with respect to the F / O ratio, and it is observed that the photoelastic constant C of the glass is independent of the F / O Ratio becomes essentially zero. According to the present inventors, the photoelastic constant C depends on the lead ion content in the optical glass, but is not dependent on the amount of fluorine ions introduced into the glass, and it is therefore concluded that the phenomenon that the photoelastic constant C becomes essentially zero, is achieved in the glass composition according to the invention.

Fig. 3 is a graph showing transmission spectra of a series of the optical glass composition according to the invention in a depth of 10 mm shows. As shown in Fig. 3, it can be seen that the blue light transmittance is increased by introducing fluorine into the glass composition. According to the investigations of the present inventors, it can be seen that the tendency of the transmission of blue light to increase becomes apparent as the F / O ratio is increased, and at the same time as such an increase, the absorption edge (absorption limit towards shorter wavelengths) becomes ) is shifted towards shorter wavelengths.

As a result of further research based on the above The inventors mentioned have a glass found that have a specific compositional range and is capable of only a low platinum elution during the melting of the glass-forming materials cause, and that an improved permeability in the shorter visible wavelength range up to the UV range has and in this area a photo-elastic Constant of substantially zero.

The optical glass according to the invention for an optical Polarization system (second embodiment) is based on the discovery above and has the following composition in Specifications of oxide mol%:

B₂O₃: 0-57.0 mol%
Al₂O₃: 0-13.0 mol% (B₂O₃ + Al₂O₃: 0.1-57.0 mol%)
SiO₂: 0-54.0 mol% (SiO₂ + B₂O₃: 43.0-57.0 mol%)
PbO: 43.0-45.5 mol%
R₂O (R: Li, Na, K): 0-3.5 mol%
R′O (R ′: Mg, Ca, Sr, Ba): 0-12.0 mol%)
As₂O₃ + Sb₂O₃: 0-1.5 mol%; and

also contains fluorine in the following area:

F₂ / (F₂ + O₂): 0-0.1

The above optical glass can preferably be the following Composition in terms of oxide mol% have:

B₂O₃: 0-19.0 mol%
Al₂O₃: 0-13.0 mol% (B₂O₃ + Al₂O₃: 2.0-19.0 mol%)
SiO₂: 38.0-54.0 mol% (SiO₂ + B₂O₃: 43.0-57.0 mol%)
PbO: 43.0-45.5 mol%
R₂O (R: Li, Na, K): 0-3.5 mol%
R′O (R ′: Mg, Ca, Sr, Ba): 0-12.0 mol%
As₂O₃ + Sb₂O₃: 0-1.5 mol%; and

also contains fluorine in the following area:

F₂ / (F₂ + O₂): 0-0.1

(Here the wavelength of the incident light can affect the Glass according to the invention preferably in the range of 0.4 microns to 3.0 µm).

In general, when melting, one High quality glass used a platinum crucible opposite molten or liquid glass is stable. Dependent on However, the coloring of the composition of the glass of the resulting glass by removing platinum in a problem in some cases. Expressed differently it becomes significant even with leaded glasses that Coloring of the glass due to the removal of platinum  to suppress sufficiently to allow a glass to continue with improved permeability is obtained.

For a glass that contains only SiO₂ as the glass-forming oxide, there is the problem that the melting is high Temperature required. Accordingly, it is common that Viscosity of the molten glass by adding a Reduce alkali metal oxide, thereby reducing the Melting temperature is reduced. As a result of different However, the inventors here have chemical experiments found that the above removal of Platinum by an alkali metal oxide, etc., often called Flux for SiO₂ is used, greatly accelerated or is supported. Furthermore, the inventors here as Result of serious research found that the Content of alkali metal oxide, etc., can be reduced by replacing SiO₂ as a glass-forming oxide with a other glass-forming oxide from B₂O₃ and / or Al₂O₃, whereby the meltability of the glass is increased, and have that optical glass according to the invention (second embodiment), such as described above.

In addition, the local inventors have more as a result serious investigations for the purpose of finding a translucent material with sufficient Permeability that is particularly suitable for a high-precision optical polarization system that the uses the entire visible range or UV range, found that a fluoride / phosphate type optical glass with a specific refractive index n₁ and Abbe number ν not only has a photoelastic constant that is much less than that of ordinary ones optical glasses, as in conventional optical Polarization systems are used, but also a  has satisfactory permeability for different applications is suitable. Furthermore, the local inventors also found that an optical Fluoride / phosphate type glass has the property that it a slight change in the value of the photoelastic Constant depending on the wavelength of the used Light has compared to that of optical Glasses for an optical polarization system, the one contains a predetermined amount of lead ions.

For a glass with a large dispersion of photoelastic constant, such as lead glass, changes even if the glass has a composition in which the photoelastic constant is im substantial zero with respect to a specific Light wavelength is set, the photoelastic Constant depending on the wavelength in some Cases so that the resulting optical anisotropy, the by external mechanical stress or thermal Stress is a problem. On the other hand, the present inventors have found that not only a specific optical fluoride / phosphate type glass a low dispersion of the photoelastic constant owns, but also a small dispersion of photoelastic constant at any wavelength within a wide range of wavelengths and that it also little of the optical anisotropy caused by external mechanical load or thermal load is impaired.

The fluoride / phosphate type glass according to the invention is based on the above discoveries and has a refractive index n _d from 1.43 to 1.65 and an Abbe number ν _d from 62 to 96, the absolute value of the photoelastic constant C of the glass is 1, 0 × 10 ^-8 cm² / N or less at the light wavelength at which the glass is to be used.

The above photoelastic constant C dispersion was determined by forming a simple optical polarization system and determining the constant using the optical system. If the photoelastic constant value thus determined is 1 × 10 ^-8 cm² / N or less, such a glass can be practically used in an optical glass for an optical polarization system without causing problems. In particular, the change in the photoelastic constant C (dispersion in the values of the photoelastic constant C) can preferably be within 0.3 × 10 ^-8 cm² / N or less in the entire visible wavelength region of about 400 to 700 nm at which the optical glass to be used for an optical polarization system.

The present invention further provides:
an optical polarization system comprising:
at least one device generating polarization characteristics for generating polarization characteristics in the case of light emitted by a light source;
an analyzer for converting the polarization characteristic into light intensity information; and
an output device for outputting the light intensity information;
at least one element that the
The device generating polarization characteristics comprises an optical glass with a photoelastic constant C in the range of substantially zero in the wavelength range from 0.4 µm to 3.0 µm.

In the above polarization optical system in which the optical glass according to the invention can be used Factors capable of polarizing information to interfere with light before the light passes through the analysis unit happens to be removed as much as possible, and therefore can the polarization information precisely in Intensity information can be converted.

The further scope of the present invention will be can be seen from the detailed description below. However, it should be understood that the detailed Description and specific examples, the preferred Specify designs according to the invention, only illustrative Have purpose and various changes and modifications within the spirit and scope of the invention for the One skilled in the art can be seen from this detailed description will.

Fig. 1 is a graph showing the relationship between the F / O ratio in a composition of the glass of the present invention and the refractive index n _d as a change in the physical properties of the glass.

Fig. 2 is a graph showing the relationship between the F / O ratio in a composition of the optical glass of the present invention and a photoelastic constant C as a physical property of the glass.

Fig. 3 is a graph showing spectral transmission spectra of the optical glasses with a thickness of 10 mm, which were prepared in Examples 1, 3 and 5 as described later.

Fig. 4 is a schematic perspective view of an example of an optical system for measuring the photoelastic constant C of an optical glass according to the invention.

FIG. 5 is a schematic sectional view of an example of the holder for applying a load on a glass sample that can be used in the optical system in FIG. 4.

Fig. 6 is a schematic sectional view for illustrating a state of a light beam incident on the dielectric multilayer film which forms a polarizing beam splitter according to the invention.

Fig. 7 is a schematic sectional view showing an example of the structure of the polarizing beam splitter according to the invention.

Fig. 8 is a schematic sectional view according to the present invention shows an example of the structure of the first dielectric multilayer film 13 and the second dielectric multilayer film 23.

Fig. 9 is a graph for comparing transmittance characteristics based on the structures of conventional polarization beam splitters.

Fig. 10 is a schematic sectional view showing an example of the structure of the first dielectric multilayer film 13 and the second dielectric multilayer film 23 according to a third structural embodiment of the present invention.

Fig. 11 is a schematic sectional view showing an example of the structure of another polarizing beam splitter (fourth structural embodiment) according to the present invention.

Fig. 12 is a graph for illustrating the transmission characteristic of the dielectric multilayer film constituting the polarization beam splitter according to the first structural embodiment of the invention.

Fig. 13 is a graph illustrating the incident angle dependency of the transmittance characteristic of the dielectric multilayer film constituting the polarization beam splitter according to the first structural embodiment of the invention.

Fig. 14 is a graph for illustrating the transmittance characteristic of the dielectric multilayer film constituting the polarization beam splitter according to the second structural embodiment of the invention, with respect to the P-polarized light component.

Fig. 15 is a schematic sectional view showing an example of the structure of another polarizing beam splitter according to the present invention (third structural embodiment).

Fig. 16 (Table 1) is a table showing the compositions and data for various physical properties of optical glasses (Sample Nos. 1 to 4 ) for an optical polarization system according to the present invention, which were prepared in Example 1.

Fig. 17 (Table 2) is a table showing the compositions and data for various physical properties of optical glasses (Sample Nos. 5 to 8 ) for an optical polarization system according to the present invention, which were prepared in Example 1.

Fig. 18 (Table 3) is a table showing the compositions and data for various physical properties of optical glasses (Sample Nos. 9 to 12 ) for an optical polarization system according to the present invention, which were prepared in Example 1.

Fig. 19 (Table 4) is a table showing the compositions and data for various physical properties of optical glasses (Sample Nos. 13 to 14 ) for an optical polarization system according to the present invention, which were prepared in Example 1.

Fig. 20 (Table 5) is a table showing the refractive index data of optical glasses for an optical polarization system, etc., measured in Example 2 according to the present invention.

Fig. 21 (Table 6) is a table showing the data for the degree of birefringence of optical glasses for a polarization system according to the invention, etc. using a predetermined load, which were measured in Example 3.

Fig. 22 is a schematic view showing an example of the structure of a projector using a polarizing beam splitter according to the invention.

Fig. 23 is a schematic sectional view showing an example of the structure of an optical system for measuring the extinction ratio or illuminance nonuniformity of a polarizing beam splitter formed using the optical glass for an optical polarizing system according to the present invention.

Fig. 24 is a photograph showing the illuminance non-uniformity obtained when a polarizing beam splitter formed by using the optical glass for an optical polarization system according to the present invention was evaluated using the optical measuring system of Fig. 23.

Fig. 25 is a photograph showing the Beleuchtungsstärkenungleichförmigkeit obtained when a polarization beam splitter, which has been formed by using a conventional optical glass was evaluated using the optical measurement system of Fig. 23.

Fig. 26 (Table 7) is a table showing the compositions and data for various physical properties of optical glasses (Sample Nos. 21 to 24) for an optical polarization system according to the present invention, which were prepared in Example 1.

Fig. 27 (Table 8) is a table showing the compositions and data for various physical properties of optical glasses (Sample Nos. 25 to 27) for an optical polarization system according to the present invention, which were prepared in Example 1.

Fig. 28 is a graph showing the correlation between the lead oxide (PbO) content in the optical glass for an optical polarization system according to the invention from Example 1, and its photoelastic constant C.

Fig. 29 is a schematic sectional view showing an example of the basic structure of a projector system using a polarization beam splitter formed using the optical glass for an optical polarization system according to the present invention.

Fig. 30 is a block diagram showing an embodiment of the polarization optical system in which the optical glass of the present invention can be suitably used.

Fig. 31 is a block diagram showing an embodiment of an SLM (spatial light modulator) type projector as an example of the polarization optical system.

Fig. 32 is a block diagram showing an embodiment of a polarizing microscope as an example of the polarizing optical system.

Fig. 33 is a block diagram showing an embodiment of the polarization optical system having no polarizer.

Fig. 34 (Table 9) is a table showing the raw material compositions and optical characteristics of Sample Nos. 31, 32 and Comparative Sample (A) of Example 6.

Fig. 35 (Table 10) is a table which represents the raw material compositions and optical characteristics of the sample Nos. 33 to 35 of Example 6.

Fig. 36 (Table 11) is a table showing the raw material compositions and optical characteristics of Sample Nos. 36 to 38 in Example 6.

Fig. 37 is a graph showing the internal transmittance curves of the optical glasses of Sample Nos. 32, 35 and 36 and the comparative sample (A) at a depth of 10 mm, which were prepared in Example 6.

Fig. 38 (Table 12) is a table indicating the raw material composition of Sample No. 46 obtained in Example 7.

Fig. 39 (Table 13) is a table showing the optical characteristics of Sample Nos. 41 to 47, Comparative Sample (A) and the commercially available "BK7" optical glass from Example 7.

Fig. 40 is a graph indicating the relationship between Abbe numbers and photoelastic constants.

Fig. 41 is a graph indicating mm internal transmittance curves of the optical glasses of the respective samples at a depth of 10, which were prepared in Example 7.

Fig. 42 is a graph demonstrating the wavelength dependence of the sample Nos. 46, 41 and 47 and comparative sample (A) prepared in Example 7 glasses.

The present invention is detailed below described with reference to the accompanying Drawings where necessary.

Photoelastic constant C

The optical glass for the optical polarization system according to the invention is characterized in that its photoelastic constant C is in the range of essentially zero within a wavelength range of 0.4 µm to 3.0 µm. The photoelastic constant C can preferably be in the range from -0.8 to +0.8 (10 ^-8 cm² / N), more preferably in the range from -0.5 to +0.5 (10 ^-8 cm² / N), more preferably in the range from -0.1 to +0.1 (10 ^-8 cm² / N), particularly preferably in the range from -0.05 to +0.05 (10 ^-8 cm² / N).

In the present invention, the optical Path difference ΔΦ measured by measuring birefringence (or birefringence) using light with a known wavelength λ under conditions such that a known uniaxial load σ₂ on a sample with the known size l (el) is exercised so that the relationship σ₁ = σ₃ = 0 in (Equation 1) and (Equation 2) as above described is fulfilled. Based on the so determined optical path difference ΔΦ it is possible to photoelastic constant C = C₁-C₂ according to the above (Equation 2). Regarding the details of one such a method of measuring the "photoelastic Constants C "can be attached to an instruction manual a birefringence meter ADR-150LC as follows described, or on Etsuhiro Mochida "Optical Technique Contact, "Volume 27, No. 3, page 127 (1989) will.  

Fig. 4 is a schematic view showing the arrangement of optical elements in a measuring system for measuring the above photoelastic constant C (birefringence measuring device, trade name: ADR-150LC, manufactured by Oak Seisakusho Co.). In Fig. 4, the "Sample S" is enclosed and held by a sample holder for exerting a uniaxial load on the sample, as shown in the schematic sectional view in Fig. 5, whereby the birefringence can be measured while a predetermined load on the Sample is exercised. Referring to Fig. 5, the sample holder includes: a pair of metal blocks 37 a and 37 b (dimensions: (40 to 50 mm) × (30 to 40 mm), thickness: 25 to 30 mm) between which a sample 36 is held, and a load cell 38 (diameter 20 mm, thickness 9.5 mm, trade name: 9E01-L32-100K, manufactured by Nihon Denshi-Sanei KK), which is embedded in the metal block 37 a. When the load cell 38 is arranged in this manner, the value of the load to be applied to the sample can be tracked.

The dimensions of the above-mentioned sample 36 are 10 mm × 15 mm × 20 mm, the dimensions of the loading area are 10 mm × 20 mm, the dimensions of the light transmission area are 15 mm × 20 mm, and the length of the light transmission thickness is 10 mm.

Glass composition

In the optical glass for the optical according to the invention Polarization system is not an essential component of fluorine. However, the glass may preferably contain fluorine below the aspect of a large width, or the degree of freedom, the refractive index (a wide range in the selection of the  Refractive index) of a composition for provision a photoelastic constant C of essentially zero, and / or with respect to a relatively high permeability for Light in the range of shorter wavelengths (wavelength approx 400-480 nm).

Version that does not contain fluorine

The optical glass for the optical according to the invention Polarization system (in a version that does not contain fluorine contains) can preferably have the following composition have, stated in wt .-% of the oxides.

SiO₂: 17.0-27.0% (35.5-57.0 mol%) Li₂O + Na₂O + K₂O: 0.5-5.0% (0.7-20.0 mol%) PbO: 72.0-75.0% (39.1-45.0 mol%) As₂O₃ + Sb₂O₃: 0-3.0% (0.0-2.0 mol%).

The above amount of SiO₂ can more preferably 22.0-26.0% be. The amount of (Li₂O + Na₂O + K₂O) can be further preferred 0.5-3.0%. The amount of PbO can be further preferred 73.0-75.0% (39.6-45.0 mol%). The amount of (As₂O₃ + Sb₂O₃) can more preferably be 0.1-0.5% by weight.

In the optical glass for the optical according to the invention Polarization system (in a version that does not contain fluorine contains) are the above contents of the respective components preferred for the following reasons.

PbO

As described above, the photoelastic constant C of a glass tends to depend heavily on the PbO content. More specifically, there is a tendency that when the PbO content is increased, the value of the photoelastic constant C decreases and the value of the photoelastic constant C becomes zero at a certain content and then takes a negative value. If this characteristic of the PbO is used, the PbO content can preferably be used to regulate the value of the photoelastic constant C of the glass to substantially zero. According to the present inventors, the reason for the change in the photoelastic constant C as a function of the PbO content is that the coordination state of the lead ions changes with increasing PbO content. The expression "a photoelastic constant in the range of substantially zero" as used here refers to such a condition that the influence of the optical path difference due to optical anisotropy of the glass according to the invention, which is produced when the glass is for an optical Polarization system is used, is within a negligible extent with respect to the entirety of the above optical polarization system. More specifically, the photoelastic constant may preferably be in the range of -0.1 to 0.1 [10 ^-8 cm² / N] for light in a wavelength range of 500 to 650 nm. In order to obtain an optical glass with a photoelastic constant C in this range, it is preferred, for example, that the PbO content takes on a value in the range of 73-75% by weight.

According to the experiment of the local inventor found that the photoelastic constant C on can be brought to almost zero, even if one Glass composition is used that does not contain lead oxide contains. However, if such a glass composition, the contains no lead oxide, is caused to photoelastic constant C in the range of substantially Having zero, the resulting glass has a relative  large coefficient of thermal expansion and tends more to break, and therefore such a glass built into an optical polarization system with caution will.

SiO₂

SiO₂ is a glass-forming component in the optical glass according to the invention and is preferably in contain an amount of 17 wt .-%. If the SiO₂ content 27 wt .-%, there is a risk that the above PbO content decreases so far that it from its preferred salary range deviates and the photoelastic Constant C tends to be large.

Alkali metal component

The alkali metal component such as Na₂O, K₂O and / or Li₂O has the function of lowering the glass melting temperature and the Glass transition temperature and improving stability versus devitrification. From this point of view, the Alkali metal content (if two or more types of Alkali metal are included, the sum of these contents) is preferably 0.5% by weight or more. Exceeds the content on the other hand 5 wt .-%, the chemical Resistance of the glass can be considerably reduced.

Defoaming agent

As₂O₃, Sb₂O₃ or (As₂O₃ + Sb₂Q₃) that are capable of Defoamers can act in the Raw materials for the glass are added if this is is desired. If the defoamer content (if contain two or more types of defoaming agents  are the sum of these contents, for example the Total amount of (As₂O₃ + Sb₂O₃)) exceeds 3 wt .-%, so resistance to devitrification tends to Transmission spectrum characteristics, etc. of the glass to decrease. The amount of defoaming agent can continue preferably 0.2 to 0.5% by weight.

Fluorine version

The optical glass for the optical according to the invention Polarization system (in a fluorine-containing version) can preferably have the following composition, if the information is given in mol%.

SiO₂: 40.0-54.0 mol%
R₂O (R: alkali metal): 0.5-9.0 mol%
PbO: 43.0-45.5 mol%
As₂O₃ + Sb₂O₃: 0-1.5 mol%
Fluorine / Oxygen (F / O) ratio: 0.1-18.0%.

The optical glass for the optical according to the invention Polarization system (in a fluorine-containing version) can also have the following composition if they are in mol% is expressed.

SiO₂: 40.0-54.0 mol%
R₂O (R: alkali metal): 0.5-9.0 mol%
RF: 0-16.0 mol%
R₂SiF₆: 0-3.3 mol%
PbO + PbF₂: 43.0-45.5 mol%
PbF₂: 0-10.0 mol%
As₂2O₃ + Sb₂O₃: 0-1.5 mol%
Fluorine / Oxygen (F / O) ratio: 0.1-18.0%.

In the optical glass for the optical according to the invention Polarization systems are the above levels of each Components preferred for the following reasons.

Lead ion

The lead ion can preferably be used for the purpose to set the photoelastic constant C. in the in general, the photoelastic constant C tends to one Glass composition containing lead ions from which Lead ion content. A value for the Can be substantially zero photoelastic constant C can be easily obtained if the lead ion content (calculated in units of PbO) 43.0-45.50 mol% (more preferred 44.0-45.5 mol%).

fluorine

It is observed that when fluorine is of the invention optical glass composition is added to the Refractive index of the glass decreases and the Absorption edge of the transmission spectrum in the direction of shorter wavelengths is shifted.

The way of introducing fluorine into a glass composition is not particularly restricted. For example it is possible fluorine by using a fluoride (for example KF, K₂SiF₆ and / or PbF₂) as a raw material for the glass to introduce into the glass composition. After this Knowledge of the local inventor can fluorine into the glass in an amount of 16.0 mol%, 3.3 mol% and 10.0 mol%, respectively be introduced when KF, K₂SiF₆ and PbF₂ alone can be used as raw material for the glass. If the crowd of such a component exceeds the amount that  can be suitably introduced into the glass, so precipitated due to excess fluorine crystals will. On the other hand, it is different when using Varieties of fluorides as raw material for the glass in one Mixture or combination possible, the fluorine / oxygen (F / O) ratio to increase to 18.0%. The (F / O) ratio may more preferably be 5.0-18.0%.

SiO₂

SiO₂ is a glass-forming oxide in the invention optical glass. In the optical glass according to the invention can the SiO₂ content is preferably 40.0 mol% or more be. So that the lead ion content to achieve a preferred photoelastic constant C does not decrease, so that it deviates from its preferred range is the SiO₂ content, on the other hand, preferably 54.0 mol% or fewer. The SiO₂ content can more preferably 45-53 mol% or less.

Alkali metal oxide

An alkali metal oxide such as Li₂O, Na₂O and / or K₂O shows that Effect of lowering the melting temperature and the Glass transition temperature of a glass and the improvement of the Stability of the glass against devitrification. So that the above Effect is sufficiently pronounced, its content (if several types of alkali metal oxides contained in the glass are the total content thereof, for example total amount Li₂O + Na₂O + K₂O) preferably 0.5 mol% or more be. On the other hand, if the Alkali metal oxide content of 9.0 mol% the decrease in chemical resistance of the glass clearly. Of the  Alkali metal oxide content can preferably be 2.0-9.0 mol% be.

Refining agents

As₂O₃, Sb₂O₃ or (As₂O₃ + Sb₂O₃) that are able to Defoaming agents can, if desired, be used Raw materials for the glass can be added. If the Defoamer content (if two or more types defoamers are included, the total amount these contents, for example the total amount of (As₂ZO₃ + Sb₂O₃)) exceeds 1.5 mol%, the resistance tends versus devitrification that Transmission spectrum characteristics, etc. of the glass, to be belittled. The amount of defoaming agent can more preferably 0.1 to 1.5 mol%.

production method

As described above, the present invention can optical glass for an optical polarization system provide that a photoelastic constant C im Essentially zero range for incident light and has a wavelength in the visible range. As above described, it is possible to choose the refractive index as desired adjust as long as the glass composition within the preferred range above.

The process for producing the optical glass for the optical polarization system according to the invention is not particularly limited. For example, the optical Glass for the optical polarization system according to the invention easily by using oxide, fluoride, carbonate, nitrate, etc. as raw materials according to the above  Components are made by weighing and mixing the components Components to produce a formulated Raw material, heating the formulated raw material to 1000 up to 1300 ° C with melting and refining of the formulated Raw material and stirring for homogenization, pouring the resulting mixture in a preheated metal mold and then gradually cooling or annealing (annealing) the resulting mixture. However, if too during this time an excess amount (for example 5.0 mol% in Information on its content) of the nitrate is used, so the effect described above tends to introduce fluorine to decrease in the present invention.

Optical glass of the second embodiment

In the optical glass (second embodiment) for that optical polarization system according to the invention are Reasons for preferred composition ranges of the respective Components based on various chemical experiments were determined as follows.

The oxides that are able to glass according to this To form embodiment, SiO₂, B₂O₃ and Al₂O₃. If the total content of these components is below 43 mol% the resulting glass tends to devitrification. On the other hand, if the above total content is 57.0 mol% exceeds the lead ion content described below to a value outside of a predetermined one Range and it becomes difficult to get the one you want To achieve the value of the photoelastic constant C.

The above B₂O₃ is a glass-forming oxide and has good meltability. If the content of it however Exceeds 57.0 mol%, the one described below tends  Lead ion content to a value outside of a predetermined range and it becomes difficult the desired value of the photoelastic constant C. achieve. Furthermore, given the resulting chemical stability of the B₂O₃ content preferably 19.0 mol% or less.

The above Al₂O₃ is an intermediate oxide and is in able to form a glass. This oxide is used for the purpose used to replace SiO₂ so that the meltability is increased. If the Al₂O₃ content exceeds 13.0 mol%, so may in some cases be due to platinum leaching a decrease in the resulting permeability was observed will.

If the SiO₂ is replaced by B₂O₃ and / or Al₂O₃, it is possible, compared to SiO₂, the melting temperature diminish without increasing the stability of the glass affect. In addition, the Melting operation in a platinum crucible Prevents platinum, thereby improving resulting permeability of the glass is made possible. The B₂O₃ and Al₂O₃ can be added to the glass until the Total amount reached 57.0 mol%. So the effect of these components occurs completely, is the total amount preferably 2.0 mol% or more. If the total Exceeds 19.0 mol%, the chemical stability of the resulting glass significantly impaired.

If the SiO₂ content exceeds 54.0 mol%, then the resulting meltability of the glass. To achieve good formability (or castability) and chemical Stability is an SiO₂ content of 38.0 mol% or more prefers.  

As described above, PbO can be used for the purpose of controlling the Photoelastic constant C can be used. If the Lead ion content is 43.0 to 45.5 mol%, so the value the photoelastic constant C is largely zero.

Alkali metal oxides, such as Li₂O, Na₂O and K₂O, can be used for Lowering the melting temperature and the Glass transition temperature of the glass as well as to increase the Stability of the glass against devitrification used will. However, if the content thereof exceeds 3.5 mol% the coloring of the glass is achieved by removing platinum noticeably promoted.

Similarly, alkaline earth metal oxides such as MgO, CaO, SrO and BaO, for lowering the melting temperature and the Glass transition temperature of the glass and to increase the Stability of the glass used with regard to devitrification will. In addition, these oxides can also be extracted support from platinum. However, the effect of these oxides is weaker than that of the alkali metal oxides, and therefore can these oxides to the glass up to a content of 12.0 mol% be added.

(As₂O₃ + Sb₂O₃) as a refining agent can be added to the glass if desired. If the content of it however Exceeds 1.5 mol%, the Resistance to devitrification, the Spectral transmission characteristics, etc., of the glass be affected.

It is also when fluorine is introduced into the above Glass composition possible, the absorption edge on the Side of short wavelengths of the spectral transmission curve  continue to shift towards short wavelengths. The Fluorine can be added to the glass by using a fluoride such as for example KF, K₂SiF₆ and PbF₃ can be added. If that Ratio F₂ / (F₂ + O₂) in which the corresponding oxide is replaced by the fluoride, but exceeds 0.1, so can affect the stability of the glass, causing for example, devitrification is caused.

As described above, according to the invention, an optical Glass provided for an optical polarization system, which is a photoelastic constant C in the range of largely zero with respect to the wavelength of incident Has light.

The process for producing the optical glass for the optical polarization system according to the embodiment is not particularly limited. For example, the optical Glass for the optical polarization system according to the invention can be easily manufactured using oxide, fluoride, Carbonate, nitrate, etc., as raw materials, according to the above components that the respective Form glass compositions, their weighing and mix together in a box in which the temperature is up Room temperature is set, creating the desired Mixing ratios can be set and a formulated Raw material is provided. Then the resulting formulated raw material at 1000 to 1300 ° C in one Platinum crucible using an electric furnace in the vicinity of Atmospheric air is heated, thereby melting it Refined and homogenized in the usual way Stirred way, and then into a metal mold (made of stainless Steel) which has been preheated to 300 to 450 ° C and the resulting mixture is slowly cooled or annealed, creating an optical glass for a  optical polymerization system according to the invention provided.

Optical glass for the optical polarization system of the third embodiment

In general optical oxide type glasses the shows photoelastic constant C has a relatively high value. It will assumed that the reason for this was mainly from the Binding properties between those contained in the glass Depends on atoms. For example, a bond with a relatively high covalent property, such as a Si-O bond in strongly localized in an oxide type glass and has electrons with anisotropic expansion. Accordingly, such electronic structure due to heavy use is influenced and therefore the photoelastic constant C also great. On the other hand is in a bond with strong ionic properties the localization of electrons low and the electron structure is soft or flexible, and therefore the distortion of the electronic structure is due to Small stress. In addition, the photoelastic shows Constant C is a low value because the symmetry is high.

From this point of view, in an oxide type optical glass, a larger amount of a modification oxide, such as an alkali metal oxide and an alkaline earth metal oxide, in the glass be included, whereby the photoelastic constant C is reduced. In such a case, however, the salary reduced on glass-forming oxide and the glass stability therefore decreases extremely. According to the results of the local PbO is a special component in so far as it is an inventor Modification oxide represents, and yet in one particular large amount can be contained in the glass. Furthermore is only  PbO is able to measure the photoelastic constant C of the glass to reduce it to the range of essentially zero.

On the other hand, it is about the anion to lower the photoelastic constant C effective, a halogen atom, which in is able to bind with stronger ionic To form properties instead of an oxygen atom use. With regard to an industrially producible Optical glass is particularly a system, the F atoms are able to add the photoelastic constant C belittling. The stability of a pure fluoride glass (i.e. a glass that does not contain oxygen atoms as anions contains), is compared with that of the oxide type glass significantly worse, and therefore a fluoride / phosphate type Glass as an optical glass for general use suitable.

Fig. 40 shows the relationship between the refractive indices n₁, the Abbe numbers ν₁ of any optical fluoride / phosphate type glasses and their photoelastic constants C at the wavelength used (633 nm). In this figure, the numbers 41 to 46 each indicate the sample number of the optical glasses obtained in the following examples. From Fig. 40 above, it can be seen that the photoelastic constant C of the glass of the present invention is much smaller than that of the commercially available "BK7" optical glass manufactured by Schott Co. which has been widely used for general purposes.

Furthermore, FIG. 41 shows the spectral transmission curves of the above-mentioned optical glass samples according to the invention at a depth of 10 mm (internal transmittance of 10 mm thick samples), together with that of a reference example. Regarding the transmittance at a depth of 10 mm, it can be seen that the fluoride / phosphate type optical glass of the present invention is superior to the optical glass (A) for the optical polarization system containing lead ions.

Further, FIG 42 shows. The wavelength dependency of the photoelastic constant C of the optical glass sample according to the invention together with that of the reference example. It can be seen from these two figures that the glass according to the invention is superior to an optical glass (A) for an optical polarization system, which contains a certain amount of lead ions, in terms of transmittance in the short-wave visible range and in the UV range and can also be used for many optical elements is because it has little dispersion of the photoelastic constant with respect to the light wavelength. In particular, the glass according to the invention can be used for an optical polarization system with a large optical transmission thickness, such as, for example, a large-format polarization beam splitter, in which it is particularly necessary to achieve high-precision control of the polarization characteristic and which must have excellent transmission.

For example, the polarization beam splitter comprises two dielectric multilayer films formed between two transparent substrates, as shown in FIG. 7. In Fig. 7, the two prisms ( 1 ) and ( 2 ) are formed as substrates from a translucent material using an optical glass for the optical polarization system of the present invention, and dielectric multilayer films ( 3 ) and ( 4 ) are formed by an adhesive layer ( 5 ) held between the two prisms.

The optical loss due to absorption, scattering, etc. at the time light passes through a glass increases as the optical transmission thickness of the prisms ( 41 ) and ( 42 ) increases. Therefore, the fluoride / phosphate type optical glass of the present invention, which has low optical loss, is suitably used for such a polarizing beam splitter with a large optical transmission thickness. In addition, even if the polarizing beam splitter is used within a wide wavelength range, the glass of the present invention can provide a uniform and high-precision characteristic for each wavelength in such a range because the wavelength dependency of its photoelastic constant is small.

As described above, the present invention can an optical fluoride / phosphate type glass for an optical Polarization system with excellent permeability and low photoelastic constant C with respect to used light wavelength are provided.

The process for producing the optical glass for the optical polarization system according to the invention is not particularly limited. For example, the optical Glass for the optical polarization system according to the invention can be easily manufactured using Metaphosphoric acid salt, fluoride, oxide, carbonate, nitrate, etc., as raw materials according to the above Components, weighing and mixing, creating a formulated Raw material provided with predetermined ratios heating the formulated raw material to 900 to 1300 ° C, whereby it is melted, refining the formulated raw material and stirring for homogenization,  Pour the resulting mixture into a preheated one Metal mold, and then slow cooling or Annealing the resulting mixture.

The above fluoride / phosphate type optical glass according to the present invention has a large Abbe number ν _d compared to that of an oxide type glass such as "BK7" or an optical glass for an optical polarization system containing a predetermined amount of lead ions, and further has a low dispersion. Therefore, the glass of the present invention can provide low chromatic aberration in an optical element in which the above optical glass is used for an optical polarization system. As a result, according to the invention, it is possible to reduce the necessary amount of optical design for other elements positioned before or after the above-mentioned optical element in an optical system, so that the glass according to the invention can improve the quality of the entire optical system and can help reduce its cost.

The above optical glass for the optical polarization system of the present invention can be applied to many optical elements by taking advantage of its characteristics. The range of application of the optical glass for the optical polarization system according to the invention is not particularly restricted, but the optical glass can be used particularly preferably for an optical element or an optical polarization system which must have high-precision polarization characteristics, such as polarization beam splitters and a transparent readout substrate for one spatial light modulator. Here, "optical polarization system" means an optical system in which the polarization information is passed on in the form of intensity information of the light. In general, as shown in the block diagram in Fig. 30, the polarization optical system includes an optical information source ( 71 ) for outputting (polarization) information, an analyzer unit ( 72 ) for converting the polarization state or condition in the polarization information into intensity information of light, and an output unit ( 73 ) for receiving the "intensity information of light" (if the light source to be observed itself has polarization characteristics as shown in Fig. 33), the above-mentioned optical information source ( 71 ) can be omitted in the polarization optical system In such an optical polarization system, since the polarization information needs to be precisely converted into the intensity information, a factor capable of interfering with the polarization information of the light should be removed as much as possible before the polarization information by the analyzer unit ( 72 ) happens.

Accordingly, the above optical glass is for one optical polarization system according to the invention in particular effective for the purpose of preventing Turbulence in the polarization information of light before it passes through the analyzer unit. Under this One aspect is the optical glass according to the invention, for example suitably usable for an optical element such as for example a polarizer, a wave plate, a Phase compensator, PBS and transparent readout substrates for SLM. 15  

SLM projector

Fig. 31 is a block diagram illustrating an embodiment of an SLM (spatial light modulator) type projector as an example of an optical polarization system as described above. Referring to Fig. 31, in the optical information source ( 71 ) constituting this SLM projector, light from a light source ( 74 ) is converted into linearly polarized light by means of a polarization beam splitter (PBS) ( 76 ), which is a transmission type polarizer ( 75 ) and a reflection type analyzer ( 72 a), converted, and further the resulting polarized light is subjected to polarization modulation using an SLM ( 77 ), whereby spatial information is communicated to the phase of the polarized light.

In the system shown in Fig. 31, the light emerging from the above SLM is again passed through the PBS (ie, the reflection type analyzer ( 72 a)) so that the light is converted into intensity information, and is further converted into an optical projection type. System ( 78 ) (and a screen ( 79 )), which corresponds to an output unit ( 73 ).

In the SLM projector in FIG. 31, the image information with a spatial intensity distribution is directed onto the screen ( 79 ). The wavelength of the light to be processed in this system can be extended to the visible range. More precisely, for example, color image information can be processed in this system by dividing the light band into the three colors red, green and blue.

Polarizing microscope

Fig. 32 is a block diagram illustrating an embodiment of a polarization microscope, as another example of the polarizing optical system. Referring to Fig. 32, in the optical information source ( 71 ) constituting this polarizing microscope, light from a light source ( 80 ) is passed through a polarizer ( 81 ) and then strikes a sample ( 82 ), thereby subjecting the light to polarization modulation becomes. In the embodiment in Fig. 32, the light transmitted through the sample ( 82 ) is observed. In addition, it is also possible to observe the light reflected by the sample ( 82 ) in the same way.

In Fig. 32, the polarization-modulated image information output from the sample ( 82 ) is passed through an analyzer ( 72 b), thereby converting it into intensity information, and is further conducted into an eyepiece lens system ( 83 ) and a human eye (not shown). In the analysis unit ( 72 ) shown in Fig. 32, it is also possible to give the light different intensities according to its respective wavelength by inserting a phase compensator (not shown) into the analysis unit. In other words, it is also possible to convert the polarization distribution into different colors and light intensities.

System without polarizer

Fig. 33 is a block diagram showing an embodiment of the polarization optical system having no polarizer. In this in Fig. System shown 33 light is, for example, emitted from a light source (84), the polarization information has (such as a star as a light source) is (c 72) (if desired, through an analyzer after the light, not shown, through a Telescope was sent), whereby it is converted into intensity information, and output to an output unit ( 73 ). It is possible to use a detector, a camera, an eye, a screen, etc. as the output unit in FIG. 33. The system shown in FIG. 33 can also be used for a telescope or microscope for observing light sources or reflected light with polarization information.

In the event that such a system is used in combination with an object to be observed or a light source or reflected light with linear polarization characteristics, the polarization information can be converted into intensity information by setting up a deflection unit as an analyzer. In the case of circularly polarized light, it is difficult to distinguish such light from non-polarized light. Accordingly, in such a case, it is possible that the circularly polarized light is converted into linearly polarized light by means of a λ _1/4 plate, etc. and then passed through a deflection unit, whereby the light information can be converted into intensity information.

Beam splitter

A specific embodiment is described below, wherein the optical glass for the optical according to the invention Polarization system is applied in one Polarization beam splitter.  

The above polarization beam splitter typically contains Designs as described below.

Version 1

A polarizing beam splitter comprising a multilayer dielectric film formed on a transparent substrate (or base material), wherein:
the above dielectric multilayer film comprises a first dielectric multilayer film and a second dielectric multilayer film, each having two different selected reference reference wavelengths (λ₁ and λ₂);
both the first and second multilayer dielectric films comprise a periodically changing layer each comprising a laminate (or multilayer structure) comprising a basic two-layer cycle comprising a high refractive index substance and a low refractive index substance having an optical film thickness of λ₁ / 4 or λ₂ / 4 at each reference wavelength includes λ₁ or λ₂ which is repeatedly deposited or formed in n cycles (n: an arbitrary integer); and a thin film adjusting layer applied on both sides of the periodically changing layer and comprising both (each one of) the high refractive index substance and the low refractive index substance having an optical film thickness of λ₁ / 8 or λ₂ / 8; and
the alternating layer of the first dielectric multilayer film and the alternating layer of the second dielectric multilayer film each comprise combinations of different substances.

Version 2

A polarization beam splitter according to embodiment 1 above, wherein the periodically changing layer of the first dielectric multilayer film a combination of TiO₂ as a substance with a high refractive index and SiO₂ as a substance with low refractive index, and which are periodic changing layer of the second dielectric multilayer film comprises a combination of TiO₂ as a substance with high Refractive index and Al₂O₃ as a substance with a low Refractive index.

Version 3

A polarization beam splitter according to embodiment 1 above, wherein the periodically changing layer of the first dielectric multilayer film a combination of TiO₂ as a substance with a high refractive index and SiO₂ as a substance with low refractive index, and which are periodic changing layer of the second dielectric multilayer film includes a combination of ZrO₂ as a substance with high Refractive index and MgF₂ as a substance with low Refractive index.

Version 4

A polarization beam splitter according to embodiment 1 above, wherein the alternating layer of the first dielectric Multi-layer film and the periodically changing layer of the second dielectric multilayer film or are largely deposited in a liquid medium  has the same refractive index as the translucent Substrate.

In the polarization beam splitter according to the invention with the Above structure is an arrangement as well as to be used Substances for the layer with high refractive index and the Layer with low refractive index, which is periodic form changing layer of the dielectric multilayer film, selected so that it is the bandwidth of the one to be used Do not narrow the wavelength range, even if the Angle of incidence of a light beam on the dielectric Multilayer film something is changed.

In general, it is to carry out the Polarization separation over a wide range preferably the bandwidth for separating a P- polarized light component and an S-polarized Light component in terms of the wavelength of a Light beam on a polarization separation film noticeable to increase. To meet this condition it is preferred that the incident light beam in Compliance with Snell's law on the Polarization separation film strikes so that a Design angle of incidence in the area of the Brewster angle reached which is the angle to achieve the maximum Polarization separation between P-polarized Light component and S-polarized light component represents.

The above dielectric multilayer film structure includes the first and second dielectric multilayer films, the each different design Design reference wavelengths exhibit. Such a structure is generally so  designed that different angles of incidence for light rays be achieved, respectively on the first and second dielectric multilayer film. In addition it is preferred, the substance with high refractive index and the Low refractive index substance, the first and the form second dielectric multilayer film, so select the following Brewster conditions (1) and (2) be different from each other. For example it is preferred that one of the periodically changing layers of the dielectric multilayer film is a combination of TiO₂ as a substance with a high refractive index and SiO₂ as Includes low refractive index substance, and the other of the periodically changing layers of the dielectric Multilayer films comprises a combination of TiO₂ as Substance with a high refractive index and Al₂O₃ as a substance low refractive index.

For the respective design reference wavelengths λ₁, λ₂ (λ¬λ) and the design reference angle of incidence Θ the corresponding angles of incidence are referred to as Θ₁ and Θ₂. For each set of the above conditions, the Brewster's condition represented by the following formula (1 or 2):

λ₁ <λ₂
λ₁, Θ₁; nH₁, COSΘH₁ = nL₁ COSΘL₁ (1)
λ₂, Θ₂; nH₂, COSΘH₂ = nL₂ COSΘL₂ (2)

Θ₁ angle of incidence when the light emerging from the translucent substrate 1 is incident at the interface between the first dielectric multilayer film and the translucent substrate.

Θ₂ incident angle when the light exiting from the light-transmissive substrate 2, is incident at the interface between the second dielectric multilayer film and the light-transmissive substrate. 2

nH₁, nL₁ refractive indices of the substance with high Refractive index and the substance with a low refractive index, the periodically changing layer of the first dielectric multilayer film with a design Form reference wavelength λ₁.

nH₂, nL₂ refractive indices of the substance with high Refractive index and the substance with low refractive index, the periodically changing layer of the second dielectric multilayer film with a design Form reference wavelength λ₂.

ΘH₁, ΘL₁ angle of incidence of light coming from each of the layers the substance with a high refractive index and the layer of Substance with a low refractive index emerges, and at the Interface occurs in the periodically changing Layer of the first dielectric multilayer film with a Design reference wavelength λ₁.

ΘH₂, ΘL₂ angle of incidence of light coming from each of the layers the substance with a high refractive index and the layer of Substance with a low refractive index emerges and at the Interface occurs in the periodically changing Layer of the second dielectric multilayer film with a design reference wavelength λ₂.

Fig. 6 is a view illustrating the moment of incidence of a light beam incident on the above multilayer dielectric film as it emerges from the high refractive index substance layer and the low refractive index substance layer and is incident at the interface. In Fig. 6, Θ₁, ΘH _i and ΘL _i correspond to the first and second dielectric multilayer films (i = 1 and 2).

It is preferred that the film thickness of the layer of substance with a high refractive index, the layer of the substance with low refractive index, and the alignment layer, which for the periodically changing layer of the invention dielectric multilayer film can be used, respectively λ / 4, λ / 4 and λ / 8. The ones actually to be formed However, film thicknesses can also be experimentally and error procedures can be determined, and therefore these Thicknesses differ slightly from the above design values.

The above "alignment layer" is a layer that has the function has to reduce the ripple in the Permeability of the P-polarized light component occur can. If there is a large curl, the Wavelength range in which the polarization beam splitter can be used, be undesirably restricted.

In order to compare the above embodiment of the polarization beam splitter according to the invention with another one, the transmission characteristic of another polarization beam splitter will be briefly described. Such a polarizing beam splitter has substantially the same structure as shown in Fig. 7, wherein the periodically changing layers of the first and second multilayer dielectric films use the same combinations of a layer of a high refractive index substance made of TiO₂ and a layer of a low refractive index substance made of SiO₂ . Fig. 9 is a graph showing the angle of incidence dependency of the transmission characteristic of such a polarization beam splitter.

Referring to Fig. 9, in the case of a design reference incident angle of 45 degrees, the band in which the P / S polarization separation ratio is high is 160 nm (indicated by the solid line in Fig. 9). On the other hand, if the angle of incidence is shifted by ± 2.5 degrees to 42.5 degrees or 47.5 degrees, the bandwidth becomes 90 nm (denoted by the dotted line in FIG. 9 and an alternately long and short dashed line). As shown in Fig. 9, a polarization beam splitter comprising a multi-layer dielectric film comprising only one combination can allow a wide range of wavelengths to be used, within which S and P polarized light components can be separated. In such a structure, however, the desired wavelength bandwidth is extremely narrowed when the angle of incidence of the light incident on the dielectric multilayer film is shifted by only a small amount.

In contrast, in the polarization beam splitter according to the embodiment of the invention described above the bandwidth that can be used for this is extremely widened while the separation ratio between the P-polarized Light component and the S-polarized light component is maintained even if the angle of incidence of a Light beam on the dielectric multilayer film comes up with something that is postponed or distracted. In addition it is possible to change the latitude or the degree of freedom in the Arrangement of an optical system in which the Polarization beam splitter was installed to increase.  

Process for forming the multilayer dielectric film

The following is a method for forming the dielectric multilayer film of the invention Polarization beam splitter described.

FIG. 7 shows a structure in which a first dielectric multilayer film 3 and a second dielectric multilayer film 4 are each formed or deposited on a prism 1 and 2 as transparent substrates, and are bonded to each other by means of an adhesive layer 5 .

In the structure shown in FIG. 8, a first dielectric multilayer film 13 and a second dielectric multilayer film 23 are successively deposited or formed on a transparent substrate 1 . Another translucent substrate is also glued to its top.

The loss of light due to absorption, scattering, etc. at the time of the passage of light through a glass becomes larger as the optical transmission thickness of the prisms ( 1 ) and ( 2 ) increases. Accordingly, the optical glass according to the invention for an optical polarization system which is improved in terms of its transmissivity can be used in a suitable manner for such a polarization beam splitter with a large optical transmission thickness.

Fig. 11 shows a structure in which dielectric multilayer films 3 and 4 are deposited on both sides of a flat glass plate 2 as a transparent substrate, and further the resultant laminate is immersed in a liquid medium 6 which has largely the same refractive index as the glass. If such a structure is adopted, essentially the same quality as that of the structure in FIG. 7 can be achieved.

Execution of the structure of the polarization beam splitter

It will be a first execution of the structure of the described polarization beam splitter according to the invention.

Fig. 7 shows a structure of a polarization beam splitter, in which a prism 1 (on which a laminate of an alignment layer IC and a periodically changing layer 13 of a first dielectric multilayer film 3 is deposited, as shown in Fig. 8) with the prism 2 (on which Laminate of an alignment layer 2 C and an alternating layer 23 of a second dielectric multilayer film 4 is deposited, as shown in Fig. 8) is connected by an optical adhesive 5 .

In this structure, prisms 1 and 2 have a refractive index n₂ = 1.84. Furthermore, the optical adhesive has a refractive index n _b = 1.52. Fig. 7 shows the reflected light R and the transmitted light T when a light beam is incident at an angle of 45 degrees. The transmitted light T includes an S-polarized light component T _s and a P-polarized light component T _p .

Referring to Fig. 10, the periodically changing layer 13 of the first dielectric multilayer film has a design reference wavelength λ₁ = 680 nm and has such a structure that a TiO₂ layer 11 as a high refractive index substance with nH₁ = 2.38 and an Al₂O₃ -Layer 12 as a substance with a low refractive index with nL₁ = 1.65 are alternately deposited in an optical film thickness of λ₁ / 4.

On the other hand, the periodically changing layer 23 of the second dielectric multilayer film has a design reference wavelength λ₂ = 420 nm and has such a structure that a TiO₂ layer 21 as a substance with a high refractive index of nH₂ = 2.38 and a SiO₂ layer 22 as Substance with a low refractive index of nL₁ = 1.47 are alternately deposited in an optical film thickness of λ₂ / 4.

In addition, an alignment layer 1 C or 2 C with a film thickness of λ₁ / 8 or λ₂ / 8 is deposited between the above-mentioned periodically changing layer 13 or 23 of the first or second dielectric multilayer film 2 and the prism 1 or prism 2 .

In the polarizing beam splitter with the above structure the case is assumed that the angle of incidence of a Light beam by ± 2.5 degrees from the design reference angle of 45 degrees shifted or distracted.

In this case, the low refractive index substance 12 and the high refractive index substance 11 in the periodically changing layer 13 of the first multilayer dielectric film correspond to the larger angle side (ie, corresponding to the side 48264 00070 552 001000280000000200012000285914815300040 0002019631171 of 00004 4814 shorter wavelength compared to the wavelength to be used) are selected so that the above-mentioned Brewster condition (1) is fulfilled at an angle of Θ₁ = 47.5 degrees, at which a light beam emerging from the transparent substrate 1 emerges at the interface between the transparent substrate 1 and the first dielectric multilayer film 12 . In this structural design, TiO₂ was selected as layer 11 with a high refractive index and Al₂O₃ as layer 12 with a low refractive index as the combination of materials or substances which form the periodically changing layer 13 of the first dielectric multilayer film.

On the other hand, the low refractive index substance 22 and the high refractive index substance 21 contained in the periodically changing layer 23 of the second multilayer dielectric film correspond to the lower angle side (ie, corresponding to a longer wavelength side compared to that to be used Wavelength) selected so that the above-mentioned Brewster condition (2) is fulfilled at an angle of 01 = 42.5 degrees, at which a light beam emerging from the transparent substrate 2 at the interface between the transparent substrate 2 and the first dielectric multilayer film 23 is incident. In this structural design, TiO₂ was selected as the high refractive index layer 21 and SiO₂ was selected as the low refractive index layer 12 , as the combination of materials or substances which they form periodically changing layer 23 of the second dielectric multilayer film.

Fig. 12 is a graph of _P, the permeability characteristics T, _s T of the P-polarized light component and S-polarized light component in the dielectric multi-layer film structure of the above-mentioned structure design is shown, as well as the permeability characteristics at incident angles of 42.5 degrees, 45 degrees and 47 ,5 degrees.

In the following, the incidence angle dependency of the transmittance for P- and S-polarized light components in the polarization beam splitter with the above-mentioned structure of the dielectric multilayer of the first structural embodiment is compared with that of a polarization beam splitter (comparative example) which has the characteristics as described above in FIG. 9 are shown.

Referring to Fig. 9, in a case where the multilayer film structure of the comparative example is used, the angle of incidence is shifted a few degrees (e.g., about ± 2.5 degrees) from the design reference angle in the wavelength range from 480 nm to 570 nm, its bandwidth X 90 nm, which is a very narrow band.

In contrast, in the first embodiment of the structure according to the invention, the characteristics of which are shown in FIG. 12, a high polarization separation capacity (T _s / T _p ) of 0.1% or less is achieved in the wavelength range from 460 nm to 620 nm. In this embodiment, the bandwidth λ is maintained in a wide band of 160 nm, even if the angle of incidence is shifted by ± 2.5 degrees from the design reference angle of incidence.

Fig. 13 is a graph of the λ, the incident angle dependence of the transmittance of P-polarized light components at a longer wavelength = 620 nm in the above-mentioned structure according to the invention the first embodiment FIG.

As shown in Fig. 13, in the polarization beam splitter of this structure, the bandwidth of the transmission characteristic can be widened considerably even considering the angle of incidence thereof, as compared with that of the polarization beam splitter of the comparative example, which has the characteristic as shown in Fig. 9, wherein TiO₂ and SiO₂ can be used for the combination of the same kind of substances as periodically changing layers that form the first and second dielectric multilayer films.

To the best of our knowledge, the local inventor is believed that the reason for providing such a good one Characteristic in the present invention is that the film-forming substances for the respective dielectric multilayer films are selected so that the periodically changing layer of the first dielectric Multilayer film that is able to decrease the Permeability of the P-polarized light component in the longer wavelength region, the Brewster Condition (1) at 47.5 degrees is met and that the periodically changing layer of the first second dielectric Multilayer film that is able to decrease the Permeability in the shorter wavelength region too cause the Brewster condition (2) to be met at 42.5 degrees.

Therefore, when using the polarizing beam splitter, which has the structure according to the invention, possible Bandwidth of the wavelength to be used increases considerably widen and a polarization beam splitter to provide a high degree of freedom with regard to Has light incidence angle.

Second structural version of the polarization beam splitter

A second version of the structure of the described polarization beam splitter according to the invention.  

The dielectric multilayer film structures of the second Structural execution is basically the same as that the first structural execution, with the difference that the Combination of substances for the dielectric Multilayer film is used by those working in the first version used is different.

Referring to FIGS. 7 and 8, the second structural embodiment, a polarization beam splitter structure in which a light transmitting substrate 1 on which a laminate of a mandrel layer 1C and a periodically changing layer 13 is applied from a first dielectric multilayer film 3, light-transmissive with a Substrate 2 , to which a laminate of an alignment layer 2 C and a periodically changing layer 23 of a second dielectric multilayer film 4 is applied, is connected by means of an optical adhesive 5 . The transparent substrates 1 and 2 have a refractive index n _s = 1.52.

In this structural design, the periodically changing layer 13 of the first dielectric multilayer film has a design reference wavelength λ₁ = 700 nm and has a structure in which a TiO₂ layer as a substance with a high refractive index of nH₁ = 2.38 and an SiO₂ layer as a substance with a low refractive index of nL₁ = 1.47 each alternately deposited in an optical film thickness of λ₁ / 4.

The periodically changing layer 23 of the second dielectric multilayer film has a design reference wavelength of 430 nm and has a structure in which a ZrO₂ layer as a substance with a high refractive index of nH₂ = 2.02 and a MgF₂ layer as a substance with a low refractive index of nL₂ = 1.37 each alternately deposited in an optical film thickness of λ₂ / 4.

In addition, an alignment layer 1 C or 2 C with a respective film thickness of λ₁ / 8 or λ₂ / 8 is deposited between the above-mentioned periodically changing layer 13 or 23 of the first or second dielectric multilayer film and the prism 1 or 2 .

In the polarizing beam splitter of the above structure, when the angle of incidence of an incident light beam is shifted or deflected by ± 4 degrees around the design reference angle of 52 degrees, the substance 12 with a low refractive index and the substance 11 with a high refractive index which are periodically changed changing layer 13 of the first dielectric multilayer film corresponding to the higher angle side (ie corresponding to the shorter wavelength side compared to the wavelength to be used) is selected so that the above-mentioned Brewster condition (1) is at an angle of incidence of 56 ° as the angle of a light beam with respect to the perpendicular of the film surface is fulfilled. In this embodiment of the structure, TiO₂ was selected as the high refractive index layer 11 and SiO₂ was selected as the low refractive index layer 12 as the combination of materials or substances that form the periodically changing layer 13 of the first dielectric multilayer film.

On the other hand, the low refractive index substance 22 and the high refractive index substance 21 contained in the periodically changing layer 23 of the second multilayer dielectric film correspond to the smaller angle side (ie, corresponding to a longer wavelength side compared to that wavelength to be used), are selected so that the above-mentioned Brewster condition ( 2 ) is met at an angle of incidence of a light beam of 48 °. In this embodiment of the structure, ZrO₂ was selected as layer 21 with a high refractive index and MgF₂ as layer 22 with a low refractive index as the combination of materials or substances which they form periodically changing layer 23 of the second dielectric multilayer film.

Fig. 14 is a graph showing the transmittance characteristics of the P-polarized light component and the S-polarized light component in the dielectric multi-layer film structure of the above first structural embodiment, and the transmittance characteristics at angles of incidence of 48 °, 52 ° and 56 °.

In the following, the incidence angle dependency of the transmittance of the P- and S-polarized light components in the polarization beam splitter with the above-mentioned structure of the dielectric multilayer of the second structure embodiment of the present invention is compared with that of the above-mentioned polarization beam splitter (comparative example), which has the characteristic as shown in FIG. 9 shown.

Referring to Fig. 9, in the case that the multilayer film structure of the comparative example is used, the angle of incidence is shifted a few degrees (e.g., about ± 2.5 degrees) from the design reference angle in a wavelength range of 480 nm to 570 nm its bandwidth X 90 nm, which is a very narrow band that can be used.

In contrast, in the second structural embodiment according to the invention, the characteristic of which is shown in FIG. 14, a high polarization separation is achieved between the P-polarized light component and the S-polarized light component in the wavelength range from 460 nm to 620 nm. In this embodiment, the bandwidth X is maintained within a wide band of 170 nm, even if the angle of incidence is shifted by ± 4 degrees from the design reference angle of incidence.

As shown in Fig. 14, in the polarizing beam splitter of this structure, the bandwidth of the transmission characteristic can be widened considerably even considering the angle of incidence thereof, compared to the polarizing beam splitter of the comparative example, in which TiO₂ and SiO₂ is used for the combination of the same kind of substances as that periodically changing layers that form the first and second multilayer dielectric films.

According to the present inventors, it is believed that the reason for providing such a good characteristic in the present invention is that the film-forming substances for the respective dielectric multilayer films are selected so that the periodically changing layer of the first dielectric multilayer film capable of causing a decrease in the transmittance of the P-polarized light component on the longer wavelength side meets the Brewster condition (1) at 56 degrees and that the periodically changing layer of the first multilayer dielectric film used in the It is capable of causing a decrease in the transmittance on the shorter wavelength side that Brewster's condition ( 2 ) fulfills at 48 degrees.

Therefore, it is possible if the design reference wavelengths and the combination of the high refractive index substance and the low refractive index substance which is the first and form second dielectric multilayer film, from each other be made different, the range of usable To broaden the wavelength considerably and a High bandwidth polarization beam splitter ready to provide a high degree of freedom regarding the Light incidence angle and a high one Polarization separation ratio S / P has.

Third embodiment of the structure of the polarization beam splitter

FIGS. 15 and 10 show a third embodiment of the structure of the polarization beam splitter according to the invention.

This structural design is an example of the modification of the polarization beam splitter according to the invention with regard to its arrangement. Referring to Fig. 15, a first multi-layer dielectric film 3 and a second multi-layer dielectric film 4 are sequentially deposited or laminated on a transparent substrate 1 , and another transparent substrate 2 is applied thereon by means of an adhesive layer 5 .

The structure in Fig. 15 has the advantage that film formation of the low refractive index layer and the high refractive index layer can be accomplished simultaneously or in one batch. In other words, using the structure arrangement of the third embodiment of the polarization beam splitter enables film formation of the dielectric multilayer film to be achieved all at once or in one batch, and the resulting productivity can therefore be increased.

Fourth embodiment of the structure of the polarization beam splitter

The above-mentioned FIG. 11 shows a fourth embodiment of the structure of the polarization beam splitter according to the invention.

Referring to Fig. 11, the polarizing beam splitter of this structure has a structure in which a substrate made of a transparent flat plate 2 is used as a transparent substrate, a first dielectric multilayer film 3 and a second dielectric multilayer film 4 are formed on both sides of the substrate from a transparent flat plate 2 is applied, and the resulting laminate is further immersed in a liquid medium 6 which largely has the same refractive index as the substrate from the transparent flat plate 2 . For example, it is preferable to use ethylene glycol (refractive index = 1.43), benzene (refractive index = 1.51), etc.

In general, when using a prism as translucent substrate the possibility that Birefringence due to the non-uniformity of the Material that forms the inside of the prism can occur. It is also known that a case may arise in which the polarization state changed and the characteristic of linearly polarized light deteriorates when a  Beam of light through a translucent substrate passes through. In such a case, the problem of This causes birefringence in the translucent substrate resolved that a structure is adopted in which like in the above structure, a liquid medium is used.

In addition, it is not necessary in the Polarizing beam splitter with the above structure an expensive prism to this fourth structure use. As a result, it is possible to structure a simplify optical system and its cost too decrease etc.

The meanings of the reference numbers used in Figs. 6 to 15 above are as follows.

• 1 .: First translucent substrate (prism).
• 2 .: Second translucent substrate (prism).
• 3 .: First dielectric multilayer film.
• 4 .: Second dielectric multilayer film.
• 5 .: Adhesive layer.
• 6 .: Liquid medium.
• 11: Substance with a high refractive index with an optical Film thickness of λ₁ / 4.
• 12 .: Substance with a low refractive index with a optical film thickness of λ₁ / 4.
• 13 .: Periodically changing layer comprising one Substance with a high refractive index and a substance with low refractive index, each an optical Have film thickness of λ₁ / 4.
• 1C: alignment layer with an optical film thickness of λ₁ / 8.
• 21: Substance with a high refractive index with an optical Film thickness of λ₂ / 4.  
• 22: Low refractive index substance with a optical film thickness of λ₂ / 4.
• 23: Periodically changing layer comprising one Substance with a high refractive index and a substance with low refractive index, each an optical Have film thickness of λ₂ / 4.
• 2C: alignment layer with an optical film thickness of λ₂ / 8.

Application example for the polarization beam splitter

An example is described below in which the polarization beam splitter according to the invention in one Projector is applied.

Fig. 22 is a schematic view showing an example of the structure of a multi-color or full-color projector using a polarizing beam splitter 40 according to the present invention (for details of such a projector, refer to U.S. Patent No. 4,127,322, for example). A projector of this type is required to have the characteristic of providing an image with a high contrast. In order that a high contrast can be achieved in a simple manner, it is particularly preferred to use a polarization beam splitter 40 which has a high extinction ratio and is able to suppress the occurrence of non-uniform illuminance (i.e. a polarization beam splitter which uses an optical glass according to the invention , which has a photoelastic constant C of substantially zero). The meanings of the reference numbers used in Fig. 22 are as follows:

• 15A, 15B, 15C: optical valve (e.g. Liquid crystal device).  
• 24A, 24B, 24C: CRT.
• 40: polarization beam splitter.
• 41, 42: dichroic mirror.
• 43: lens.
• 44: screen.
• 45: arc tube.
• 46: Spherical lens.
• 47: condenser / collimator lens
• 48: First optical axis.
• 49: Glass cube.
• RA, RB, RC: The respective colors.

Fig. 29 is a schematic sectional view showing a basic example of the structure of the projector system in which the polarizing beam splitter (PBS) according to the present invention is used. In this embodiment of Fig. 29, along the optical path is a lamp as a light source, an IR cut filter, an UV cut filter, a condenser lens, the above-mentioned PBS, a liquid crystal (LC) device, (PBS), a projection lens and a screen arranged.

The present invention will now be described with reference specifically described on examples to which the present invention is not to be considered.

Examples EXAMPLE 1

Corresponding oxides, carbonates, nitrates, etc. were provided as the respective raw materials for forming the respective glass compositions. After these raw materials were conventionally highly refined, they were weighed in a can (total weight of each batch: 100 to 500 g), the temperature of which was set at room temperature, and mixed together, thereby providing the appropriate ratios (% by weight) were as in Fig. 26 (Table 7) and Fig. 27 (Table 8) (wt% in the above Figs. 26 to 28 were 100% in total).

The raw materials formulated in this way were combined in one Platinum crucible at 1000 to 1300 degrees using a electric furnace melted in an air atmosphere and the resulting mixture was then clarified and for the purpose of homogenization in the usual way touched. The resulting mixture was then mixed in a metal mold (made of stainless steel) poured, which was previously preheated to 300 to 450 degrees, and then gradually cooled or annealed, whereby seven types of optical glasses (sample glass nos. 21 to 27) for the optical polarization system were manufactured.

A photoelastic constant C for light with a wavelength of λ = 633 nm and a linear expansion coefficient were measured for each of the glasses thus prepared (No. 21 to 27). At this time, the photoelastic constant C was obtained by the above photoelastic modulation method using light with a wavelength of λ = 633 nm, and the respective glass sample had a light transmission thickness of 1 (el) = 10 mm as in the above equations (1) and (2) are shown. The results thus obtained are shown in Figs. 26 to 28 (Tables 7 to 8).

As shown in the tables above, this example presented optical glasses ready for the optical polarization system,  the different types of compositions for Providing a photoelastic constant of im have substantially zero (C = -0.12 to 0.41).

Fig. 28 is a graph in which the abscissa represents the lead oxide (PbO) content and the ordinate represents the photoelastic constant C for each of the glasses described above (Nos. 21 to 27). Regarding the graph in Fig. 28, it can be understood that the photoelastic constant C decreases almost linearly with the increase in the lead oxide content and the constant becomes zero at a certain point and then takes a negative value.

Regarding a borosilicate glass "BK7" as a comparative example which has been widely used for conventional optical systems, the ratios of the components and the measurement results of the photoelastic constant C for light with a wavelength of λ = 633 nm, as well as the linear expansion coefficient in Fig. 27 (Table 8) shown.

With regard to these FIGS. 26 to 28 (Table 7-8), these can be understood such that the photoelastic constant C of the optical glass according to the invention (sample no. 21 to 27) is substantially smaller than that of the conventional "BK7" glass, and in particular the glasses with the numbers 24 to 26 had photoelastic constants in an extremely small range (-0.07 to +0.10).

in addition, the linear expansion coefficients of the glasses according to the invention with the numbers 21 to 27 are essentially of the same order of magnitude as that of "BK7". Accordingly, it can be understood that even when using the glasses according to the invention with the numbers 21 to 27 instead of "BK7" holder for holding the optical glass or other optical elements are not adversely affected by a difference between their thermal expansion coefficients.

EXAMPLE 2

The degree of birefringence of the sample glass numbers. 22, 24 and 25 made in Example 1 and the commercially available borosilicate glass BK7 (manufactured by Schott Co., Germany) were made using an apparatus shown in Figs. 4 and 5 using a load of about 30 N / cm² measured.

More specifically, a sample of each glass with a known size l (el) = 10 mm was used for the measurement, and its birefringence was measured using light with a known wavelength of λ = 633 nm using a known uniaxial load σ2 for Establishing a relationship of σ1 = σ3 = 0 in the above equations (1) and (2), whereby an optical path difference ΔΦ (nm / cm) per 1 cm of the sample glass was obtained. The measurement results obtained in this way are shown in FIG. 21 (Table 6) and in the following table:

Glass sample number: No. 24
Load: 31.0 N / cm²
Extent of birefringence: 3.10 nm / cm.

As shown in Fig. 21 (Table 6) above, the optical glass for the polarization optical system shows an extremely small value compared to that of the commercially available borosilicate glass BK7.

EXAMPLE 3

The refractive indices of those prepared in Example 1 Glass Samples Nos. 21 to 27 and the commercially available BK7 borosilicate glass (manufactured by Schott Co., Germany) were used commercially available device for measuring the refractive index at Using light with a wavelength of λ = 587.6 nm and a sample of each glass with one Light transmission thickness of l (el) = 10 mm measured.

The measurement results thus obtained are shown in Fig. 20 (Table 5).

EXAMPLE 4

Corresponding oxides, carbonates, nitrates, etc. were provided as the respective raw materials for forming the respective glass compositions. After these raw materials were highly refined in the usual manner, they were weighed in a can (total weight of each batch: 100 to 500 g), the temperature of which was set at room temperature, thereby providing the appropriate ratios (% by weight) as shown in Fig , thereby obtaining a formulated raw material. 16 (Table 1), Fig. 17 (Table 2), Fig. 18 (Table 3) and Fig. 19 (Table 4) shown and mixed together. The above Figs. 16 to 19 (Tables 1, 2, 3 and 4) show ratios of the respective components calculated in units of mol% and% by weight (the percentages as shown in the respective batches were total 100%).

The raw materials formulated in this way were combined in one Platinum crucible at 1000 to 1300 degrees using a electric furnace melted in an air atmosphere and the resulting mixture was then clarified subjected and in the usual way for the purpose of Homogenization stirred. Then the resulting mixture into a metal mold (made stainless steel), previously at 300 to 450 degrees was preheated, poured and then gradually cooled or annealed, whereby 14 types of optical glasses (glass sample no. 1 to 14) for an optical polarization system were.

A refractive index n _d , a transmission spectrum at a thickness of 10 mm (wavelength corresponding to a transmittance of 80%) and a photoelastic constant C for light with a wavelength of λ = 633 were used for each of the glasses thus produced (nos. 1 to 14) nm measured. At this time, the photoelastic constant C was calculated using the birefringence using a load obtained by the above photoelastic modulation method using light with a wavelength of λ = 633 nm and the respective glass samples having a light transmission thickness of l (el ) = 10 mm as shown in equations (1) and (2) above. The results thus obtained are shown in Figs. 16 to 19 (Tables 1, 2, 3 and 4).

As shown in the tables above, this example represents optical glasses ready for an optical polarization system, that different types of compositions for Providing a photoelastic constant C of im have substantially zero (C = +0.01 to 0.04).  

EXAMPLE 5

A polarization beam splitter (as shown in Fig. 7, first embodiment of the structure) formed using the optical glass for the optical polarization system (Sample No. 24) manufactured in Example 1 as the material for the prisms 1 and 2 was evaluated using an optical evaluation system as shown in the schematic view of FIG. 23. The polarizing film of the polarizing beam splitter used here was designed to provide a central wavelength of λ = 540 nm, which corresponds to a wavelength in the green range.

More specifically, a polarization beam splitter 61 was illuminated with the light emitted from a xenon lamp 62 as a light source, the image of the xenon lamp 62 was projected onto a screen 64 by means of a mirror 63 , and the resulting nonuniformity of the illuminance on the screen 64 was recorded with a camera Photograph evaluated. The results of the evaluation are shown in the photograph in FIG. 24, in which an interference image can be seen. As shown in Fig. 24, very little non-uniformity was observed when the polarizing beam splitter was used by using the optical glass of the invention with a photoelastic constant C of substantially zero.

On the other hand, in the same manner as in the above procedure, the non-uniformity was measured using a polarizing beam splitter having the same structure as that described above, with the difference that a conventional optical glass (borosilicate glass BK7, manufactured by Schott Co.) instead of the above optical glass according to the invention was used. As a result, a marked nonuniformity in illuminance was observed as shown in the photograph in FIG. 25.

EXAMPLE 6

Corresponding oxides, fluorides, carbonates, nitrates, etc. have been provided as the respective raw materials for forming the respective glass compositions. These raw materials were weighed in a box whose temperature was set at room temperature (total weight of each batch 100 to 500 g) and then mixed together so that the ratios as in Fig. 34 (Table 9), Fig. 35 (Table 10) and Fig. 36 (Table 11).

The raw materials formulated in this way were combined in one Platinum crucible at 1000 to 1300 degrees using a electric furnace melted in atmospheric air and the resulting mixture was then refined and to Homogenization stirred in the usual way. Subsequently the resulting mixture was made into a metal mold (made of stainless steel) that previously cast on 300 to 400 degrees was heated, and then slowly cooled or annealed, creating eight types of optical glasses for an optical polarization system.

The above Fig. 34 (Table 9), Fig. 35 (Table 10) and Fig. 36 (Table 11) show the ratios of the respective raw materials, which were converted into mol% and wt% (which in the above Fig. 34 to 36 ratios shown were 100% in total).

For each of these glasses thus produced, the refractive index n _d , the wavelength at which the transmittance at a depth of 10 mm (the internal transmittance of a 10 mm thick sample) became 80%, and the photoelastic constant C for light with a wavelength of λ = 633 nm measured. At this time, the photoelastic constant C was determined using light with a wavelength of λ = 633 nm, and corresponding glass samples with a light transmission thickness of l (el) = 10 mm, as in the above-mentioned equations (1) and (2) shown.

The results thus obtained are shown in Fig. 34 (Table 9), Fig. 35 (Table 10) and Fig. 36 (Table 11). Fig. 34 (Table 9) also shows the raw material ratios for an optical glass (A) for an optical polarization system containing a predetermined amount of lead ions (as a reference sample) and the results measured therefor, as described above. In addition, Fig. 37 is a graph showing the respective spectral transmission curves of Sample Nos. 32, 35 and 36 and the reference sample (A) at a depth of 10 mm.

EXAMPLE 7

As respective raw materials for the formation of Fluoride / phosphate type glasses for an optical Polarization system with predetermined refractive indices and Abbe numbers were corresponding metaphosphoric acid salts, Fluorides, oxides, carbonates, nitrates, etc. are provided.  

These raw materials were weighed and so together mixed that the respective conditions were achieved. The raw materials so formulated were at 900 to 1300 degrees melted in an electric furnace and the resulting mixture was refined and with stirring homogenized. Then the resulting mixture poured into a metal mold that was previously heated, and then subsequently cooled or annealed, creating optical Glasses made for an optical polarization system were.

The above Fig. 38 (Table 12) shows the ratios of the respective raw materials. Accordingly, the glasses of samples (41) to (46) were manufactured as shown in Fig. 39 (Table 13).

For each of the glasses thus produced, the photoelastic constant C for light with a wavelength of λ = 633 nm, the refractive index n _d and the transmittance at a depth of 10 mm (ie the wavelength at which the transmittance became 80%) were measured. The results thus obtained are shown in Fig. 39 (Table 13).

At this time, the photoelastic constant C was obtained using light with a wavelength of λ = 633 nm and the respective glass samples with a light transmission thickness of l (el) = 10 mm, as in the above-mentioned equations (1) and (2) shown. The results thus obtained are shown in Fig. 39 (Table 13). This Fig. 39 (Table 13) also shows corresponding measurement results for "BK7" from Schott Co., and for an optical glass (A) for an optical polarization system which contains a predetermined amount of lead ions (as reference samples).

Fig. 40 is a graph showing the relationships between the refractive indices, the Abbe numbers, and the photoelastic constants of the respective samples in this example. Fig. 41 is a graph showing the spectral transmission curves of the respective sample glasses from this example at a depth of 10 mm. Further, FIG. 42 is a graph indicating the wavelength dependency of the photoelastic constant C in the samples Nos. 46, 41 and 47 (and in sample (A) for comparison purposes) of the respective obtained in this example glass samples.

As described above, it can be seen from the above data that the optical glass of the present invention has photoelastic constants C which are substantially smaller than those of the comparative glass sample "BK7", and that it is also the optical glass for an optical polarization system which has a predetermined amount contains lead ions, are superior in terms of permeability in the shorter-wave visible range and in the UV range, and that they have Abbe numbers ν _d , which are considerably larger than those of the lead-containing glass.

As described above, the present Invention an optical glass for an optical Polarization system with a photoelastic constant C im Range of substantially zero in the wavelength range from 0.4 µm to 3.0 µm.

As described above, the optical glass for the optical polarization system according to the invention in so far excellent characteristic than that there is essentially none optical path difference causes on an optical Anisotropy is based even if an external mechanical  Stress or thermal stress occurs. Accordingly, when using the invention Glases in an optical element for an optical Polarization system the polarization characteristic of the optical information by largely eliminating the External mechanical stress or effect thermal load can be maintained well.

In an embodiment in which the optical glass for the optical polarization system according to the invention no fluorine contains an optical glass for an optical Polarization system with a photoelastic constant C from essentially zero easily by selecting the PbO composition ratio can be achieved. Accordingly, it is for the glass according to the invention possible, essentially no optical anisotropy deliver, even if an external mechanical load or thermal stress occurs in the glass.

In addition, it is according to the present invention Selection of the fluorine / oxygen (F / O) ratio possible optical glass for an optical polarization system that is capable of producing its refractive index increase or decrease within a predetermined range decrease, while the photoelastic constant C at im remains essentially zero. As described above, it is possible according to the invention, a simple optical Glass or an optical element (or an optical Component) by using such a component Glases, which has a refractive index for its Use is appropriate, being a good one Polarization characteristic is maintained. Accordingly in the present invention, the degree of freedom or Possibility of optical design greatly enlarged.  

In the present invention, the width in the selection of an "optical thin film" based on to determine the refractive index of the glass, broadened, and the selection of the optical thin film is facilitated. In addition, the present invention enables Improvement of transparency (or extent of coloring) at a wavelength corresponding to visible light, and therefore the optical glass can be in a larger number of optical elements can be used. The Optical glass according to the invention can be particularly preferred can be used for an optical polarization system or a polarization beam splitter or a transparent one Readout substrate for a spatial light modulator, in which a high-precision polarization characteristic is required is.

The present invention further provides an optical glass ready for an optical polarization system that the has the following composition in terms of oxide mol%:

B₂O₃: 0-57.0 mol%
Al₂O₃: 0-13.0 mol% (B₂O₃ + Al₂O₃: 0.1-57.0 mol%)
SiO₂: 0-54.0 mol% (SiO₂ + B₂O₃: 43.0-57.0 mol%)
PbO: 43.0-45.5 mol%
R₂O (R: Li, Na, K): 0-3.5 mol%
R′O (R ′: Mg, Ca, Sr, Ba): 0-12.0 mol%)
As₂O3 + Sb₂O₃: 0-1.5 mol%; and

also contains fluorine in the following area:

F₂ / (F₂ + O₂): 0-0.1

The present invention also provides an optical glass ready for an optical polarization system that the has the following composition in terms of oxide mol%:

B₂O₃: 0-19.0 mol%
Al₂O₃: 0-13.0 mol% (B₂O₃ + Al₂O₃: 2.0-19.0 mol%)
SiO₂: 38.0-54.0 mol% (SiO₂ + B₂O₃: 43.0-57.0 mol%)
PbO: 43.0-45.5 mol%
R₂O (R: Li, Na, K): 0-3.5 mol%
R′O ′ (R ′: Mg, Ca, Sr, Ba): 0-12.0 mol%
As₂O₃ + Sb₂O₃: 0-1.5 mol%; and

also contains fluorine in the following area:

F₂ / (F₂ + O₂): 0-0.1

In the above glass for an optical according to the invention Discoloration was due to polarization Removal of platinum during the melting operation can be done in a platinum crucible compared to that in the case of a conventional optical glass for an optical polarization system reduced, so that Permeability within the entire visible area was improved. Therefore, such an optical glass is in many optical elements applicable. In particular that is above optical glass suitable for a transparent Readout substrate for a spatial light modulator or a polarization beam splitter that is highly precise Polarization characteristics required.  

According to the invention, an optical fluoride / phosphate type glass for an optical polarization system is also provided, which has a refractive index n _d from 1.43 to 1.65 and an Abbe number ν _d from 62 to 96, and its absolute value for the photoelastic constant C has 1.0 x 10 ^-8 cm² / N or less at the wavelength at which the glass is used.

The above optical fluoride / phosphate type glass for one optical polarization system according to the invention has a extremely small optical path difference due to optical Anisotropy (birefringence) even if there is one possible mechanical external stress and thermal Is exposed to stress, and furthermore the Wavelength dependency thereof is also low. Accordingly is in when using the glass according to the invention in a practical optical system, the effect an undesirable optical path difference (birefringence), the unintentional in the case of conventional glass can occur minimized as much as possible. In addition, according to the invention provided a material that a excellent permeability in the shorter-wave visible Range and in the UV range compared to the conventional optical glass for an optical polarization system having. Therefore, it becomes possible to opt To develop and manufacture polarization system that has excellent optical properties.

According to the invention, an optical polarization system is also provided, which comprises the following:
at least one polarization characteristic generating device for generating a polarization characteristic in the case of light emitted by a light source;
an analyzer device for converting the polarization characteristic into light intensity information; and
a readout device for outputting the light intensity information;
at least one element which forms a polarization characteristic generating device, comprising an optical glass with a photoelastic constant C in the range of substantially zero in a wavelength range of 0.4 µm to 3.0 µm.

In the polarization optical system in which the above optical glass according to the invention is used Factors that are able to To disrupt polarization information as completely as possibly removed before it passes the analyzer unit. Therefore, it is possible to get the polarization information exactly in Convert intensity information.

The present invention further provides a polarization beam splitter comprising a transparent substrate and a dielectric multilayer film applied to the substrate;
wherein the dielectric multilayer film comprises at least a first dielectric multilayer film and a second dielectric multilayer film, each having two design reference wavelengths λ₁ and λ₂, which are different from each other;
each of these first and second multilayer dielectric films includes: a periodically changing layer including n cycles (n: an integer) of a basic cycle laminate having a two-ply structure of a high refractive index layer and a low refractive index layer each have an optical film thickness of λ₁ / 4 or λ₂ / 4 at each of the reference wavelength λ₁ or λ₂; and a thin film alignment layer each comprising a high refractive index layer and a low refractive index layer each having an optical film thickness of λ₁ / 8 or λ₂ / 8 and deposited on both sides of the periodically changing layer;
and the periodically changing layers of the first and second dielectric multilayer films each comprise different combinations of substances.

After the polarization beam splitter according to the invention with the structure above based on the combination of the substance with high refractive index and the substance with low Refractive index, or on the structure comprising the first and second dielectric multilayer films with based on different design reference wavelengths, it is possible a high degree of freedom regarding the Achieve angle of incidence and high separation and / or composition between the P-polarized Light component and the S-polarized light component to be achieved within a large wavelength range.

From the invention described above, it is apparent that it can be modified in many ways. Such Variations are not a departure from the mind and realm view of the invention, and all such modifications  are, as far as they are obvious to the expert, than in Include the scope of the following claims.

Claims (24)

1. Optical glass for an optical polarization system with a photoelastic constant C in the range of im essentially zero in a wavelength range of 0.4 µm to 3.0 µm. 2. Optical glass for an optical polarization system according to claim 1, characterized in that the photoelastic constant C is in the range of -0.8 to +0.8 (10 ^-8 cm²N). 3. Optical glass for an optical polarization system according to claim 2; characterized in that the photoelastic constant C is in the range of -0.1 to +0.1 (10 ^-8 cm² / N). 4. Optical glass for an optical polarization system according to claim 1, characterized in that it has the following composition in units of% by weight of the oxides:
SiO₂: 17.0-27.0% (35.5-57.0 mol%)
Li₂O + Na₂O + K₂O: 0.5-5.0% (0.7-20.0 mol%)
PbO: 72.0-75.0% (39.1-45.0 mol%)
As₂O₃ + Sb₂O₃: 0-3.0% (0.0-2.0 mol%). 5. Process for producing an optical glass for a optical polarization system, wherein an optical glass for an optical polarization system with a photoelastic constant C in the range of im essentially zero in the wavelength range from 0.4 µm to 3.0 µm is provided by changing the Ratio of PbO in a leaded optical  Glass, whereby its photoelastic constant C is controlled. 6. Optical glass for an optical polarization system according to claim 1, characterized in that it has the following composition in units of mol%:
SiO₂: 40.0-54.0 mol%
R₂O (R: alkali metal): 0.5-9.0 mol%
PbO: 43.0-45.5 mol%
As₂O₃ + Sb₂O₃: 0-1.5 mol%; and
also contains fluorine within the following range in units of mol%:
Fluorine / oxygen (F / O) ratio: 0.1-18.0 mol%. 7. Optical glass for an optical polarization system according to claim 1, characterized in that it has the following composition in units of mol%:
SiO₂: 40.0-54.0 mol%
R₂O (R: alkali metal): 0.5-9.0 mol%
RF: 0-16.0 mol%
R₂SiF₆: 0-3.3 mol%
PbO + PbF₂: 43.0-45.5 mol%
PbF₂: 0-10.0 mol%
As₂O₃ + Sb₂O₃: 0-1.5 mol%; and
also contains fluorine in units of mole% in the following range:
Fluorine / oxygen (F / O) ratio: 0.1-18.0 mol%. 8. Process for producing an optical glass for a optical polarization system, thereby characterized in that an optical glass for a optical polarization system with a photoelastic Constant C in the range of essentially zero in one Wavelength range from 0.4 µm to 3.0 µm provided is changed by changing the fluorine / oxygen (F / O) - Ratio of a fluorine-containing optical glass, thereby controlling its photoelastic constant C. becomes. 9. polarization beam splitter, characterized in that it comprises a transparent substrate and a dielectric multilayer film deposited on the substrate,
the dielectric multilayer film comprises at least a first dielectric multilayer film and a second dielectric multilayer film, each having two design reference waves λ₁ and λ₂, which are different from one another,
each of the first and second multilayer dielectric films includes: a periodically changing layer comprising an n-cycle (n: integer) laminate of a base cycle of a two-layer structure of a high refractive index layer and a low refractive index layer, each have an optical film thickness of λ₁ / 4 or λ₂ / 4 at the respective reference wavelength λ₁ or λ₂; and a thin film alignment layer each comprising a high refractive index layer or the low refractive index layer having an optical film thickness of λ₁ / 8 or λ₂ / 8 applied on both sides of the periodically changing layer;
the periodically changing layers of the first and second dielectric multilayer films each comprise different combinations of substances. 10. polarization beam splitter according to claim 9, characterized characterized that the translucent An optical glass substrate for an optical Polarization system that includes a photoelastic Constant C in the range of substantially zero within a wavelength range from 0.4 µm to 3.0 µm. 11. polarization beam splitter according to claim 9, characterized characterized in that the periodically changing Layer of the first dielectric multilayer film one Combination comprises a substance made of TiO₂ high refractive index and a substance made of SiO₂ low refractive index, and that periodically changing layer of the second dielectric Multilayer films a combination of one substance made of TiO₂ with a high refractive index and a substance Al₂O₃ includes low refractive index. 12. polarization beam splitter according to claim 9, characterized characterized in that the periodically changing Layer of the first dielectric multilayer film one Combination of a substance with high TiO₂ Refractive index and a substance made of SiO₂ with low Refractive index includes, and that the periodically  changing layer of the second dielectric Multilayer films a combination of one substance ZrO₂ with a high refractive index and a substance MgF₂ includes low refractive index. 13. polarization beam splitter according to claim 9, characterized characterized in that the first and second dielectric multilayer films are arranged in a liquid medium that is essentially the same Refractive index shows like the translucent Substrate. 14. Optical, glass for an optical polarization system according to claim 1, which has the following composition in terms of oxide mol%:
B₂O₃: 0-57.0 mol%
Al₂O₃: 0-13.0 mol% (B₂O₃ + Al₂O₃: 0.1-57.0 mol%)
SiO₂: 0-54.0 mol% (SiO₂ + B₂O₃: 43.0-57.0 mol%)
PbO: 43.0-45.5 mol%
R₂O (R: Li, Na, K): 0-3.5 mol%
R′O (R ′: Mg, Ca, Sr, Ba): 0-12.0 mol%)
As₂O₃ + Sb₂O₃: 0-1.5 mol%; and
also contains fluorine in the following area:
F₂ / (F₂ + O₂): 0-0.1. 15. Optical glass for an optical polarization system according to claim 1, which has the following composition in terms of oxide mol%:
B₂O₃: 0-19.0 mol%
Al₂O₃: 0-13.0 mol% (B₂O₃ + Al₂O₃: 2.0-19.0 mol%)
SiO₂: 38.0-54.0 mol% (SiO₂ + B₂O₃: 43.0-57.0 mol%)
PbO: 43.0-45.5 mol%
R₂O (R: Li, Na, K): 0-3.5 mol%
R′O (R ′: Mg, Ca, Sr, Ba): 0-12.0 mol%
As₂O₃ + Sb₂O₃: O-1.5 mol%; and
also contains fluorine in the following area:
F₂ / (F₂ + O₂): 0-0.1. 16. Optical glass for an optical polarization system according to claim 14 or 15, which is a photoelastic Constant C in the range of substantially zero regarding light incident on the glass with a Has a wavelength of 0.4 to 3.0 microns. 17. Optical fluoride / phosphate type glass for an optical polarization system with a refractive index n _d from 1.43 to 1.65, an Abbe number ν _d from 62 to 96 and an absolute value of the photoelastic constant C of the glass of 1.0 × 10 ^-8 cm² / N or less at the wavelength of the light used in the glass. 18. Optical fluoride / phosphate type glass for an optical A polarization system according to claim 17, wherein the Wavelength is in the range from 0.3 to 3.0 µm. 19. The fluoride / phosphate type optical glass for an optical polarization system according to claim 17, wherein the change in the photoelastic constant C in the wavelength range of 0.4 to 0.7 µm is 0.3 × 10 ^-8 cm² / m or less. 20. A polarization beam splitter comprising a substrate which is transparent with respect to the wavelength to be used and a dielectric multilayer film applied to the substrate, the substrate comprising an optical fluoride / phosphate-type glass with a refractive index n _d of 1.43 to 1.65 and an Abbe number ν _d of 62 to 96, and the absolute value of the photoelastic constant C of the glass is 1.0 × 10 ^-8 cm² / N or less at the wavelength of the light to be used for the glass. 21. Optical polarization system comprising:
at least one polarization characteristic generating device for generating polarization characteristics in the case of light emitted by a light source;
an analyzer device for converting the polarization characteristic into light intensity information; and
a readout device for outputting the light intensity information;
at least one element which forms the polarization characteristic generating device comprises an optical glass with a photoelastic constant C in the range of substantially zero for a wavelength in the range of 0.4 to 3.0 µm. 22. The optical polarization system according to claim 21, wherein the optical element that the Polarization characteristic generating device is a polarizer. 23. An optical polarization system according to claim 21, wherein the polarization characteristic generating device a light source, a transmission type polarizer and a spatial light modulator (SLM), and optical system the function of an SLM projector owns. 24. The optical polarization system according to claim 21, wherein the polarization characteristic generating device a light source, a polarizer and one too observing object, and the optical System functions as a polarizing microscope.