WO2008128678A1

WO2008128678A1 - Device and method for coupling light in a fiber

Info

Publication number: WO2008128678A1
Application number: PCT/EP2008/002987
Authority: WO
Inventors: Bernd Offenbeck; Wladimir Tschekalinskij; Stephan Junger; Norbert Weber
Original assignee: Fraunhofer Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2007-04-18
Filing date: 2008-04-15
Publication date: 2008-10-30
Also published as: DE102007018354A1

Abstract

The invention relates to a device (200) for coupling light in a fiber (120), comprising a light source (100) for generating a light beam (202) and an optical arrangement (20A) comprising a plurality of laterally adjacent beam shaping units (206; 306), forming a lens array (306-1,..., 306-N) on the fiber side for generating from the light beam (202) a plurality of convergent or divergent beam bundles (208) that can be coupled in the fiber (120).

Description

Device and method for coupling light into a

fiber

description

The present invention relates to devices and methods for coupling light into a fiber, such as may be used to increase eye safety in optical data transmission.

Fig. 6 shows schematically a typical coupling of light beams into an optical waveguide and m an optical fiber.

In the case of an optical fiber coupling, a light beam of a point light source 100 is typically collimated with a launching optics 110 and optionally refocused, as shown in FIG. 6, in order to couple as much light as possible into an optical fiber 120. That is, a classical coupling optics 110 includes, for example, a collimating lens and possibly also a condensing lens. A direct, mostly magnifying, image of the light source 100 on the fiber 120 is often used. In price-sensitive applications, a so-called blunt coupling between the fiber 120 and a light-emitting component is often used (shock coupling). This means that when the light from the light-emitting component 100 is transferred onto the fiber 120, an end face of the light-emitting component 100 and an end face of the optical fiber 120 directly oppose each other

If an optical fiber 120 is not connected to an optical transmitter or a light source, or if an optical connection between transmitter (eg light source) and a corresponding fiber leading to a corresponding receiver (eg photodiode) has been unintentionally interrupted, for example the coupling technologies mentioned above pose significant risks to eye safety. If, for example, an optical continuous wave power of more than 1 mW from the transmitter strikes the retina of the human eye, (in the case of visible radiation) not only glare but also lasting damage must be expected. Since lasers and laser diodes in optical transmission systems emit such power, protective measures must be taken. The measures to be taken depend on the respective laser protection class, which in turn depends on the emitted power and the wavelength.

An illustration of a point light source 100 on the retina of a viewer is sketched schematically in FIG.

FIG. 7 shows a point light source 100 whose light radiation passes through the classic emitter optics 110 and has the intensity distribution shown in FIG. 7 in its focal plane 150. From the focal plane 150, the concentrated radiation emerges in the form of divergent radiation beams and finally strikes an eye 160 of an observer, where the light beams are re-focused and thereby depict the point light source 100 to scale on the retina of the eye 160.

It may therefore be an acute Personengefahrdung under circumstances, as in the case of transmitting side solved fiber connectors or fallen fiber cable ends or even in cases sendah interrupted fiber lines used a point light source, such as a laser scale on the retina of an observer can be mapped in the Transmitter or the coupling Opt ik looks. In order to reduce such a risk of personal injury, for example, the power of a laser can be reduced, which, however, leads to performance losses of the optical transmission path, since thus only smaller distances can be crossed. The publication DE 4229511 A1 describes a shading device or a plug-in connection for optical waveguide plug-in connections, with which shading of a laser radiation by a mechanism can be achieved as soon as a coupled fiber is drawn off. However, this means increased mechanical complexity, such as complex mechanical locking mechanisms.

The laid-open specification DE 4231919 A1 describes an electrical protection circuit for switching off an electro-optical transducer, e.g. a laser diode, with no optical fiber connected.

The published patent application DE 4414862 A1 discloses an optical waveguide connector with monitoring device, wherein the connector is equipped with an optical transmitting and / or receiving element. This element is coupled to the receiver or transmitter connected to the connector and arranged such that it is optically covered when the connector is produced. This will determine if the fiber optic cable is connected or not, or if the connector is installed incorrectly or incompletely.

DE 4444569 A1 discloses an electro-optical module with a transmitter which emits energy-rich radiation when electrically driven and with a receptacle into which a connecting part for coupling a coupling element to the transmitter can be introduced. A light barrier beam of a light barrier penetrates the receptacle in such a way that the light barrier beam is interrupted when the connecting element is inserted. The control of the transmitter is only enabled when the light beam is interrupted.

To protect against personal injury, for example, the breakage of laserlichtfuhrenden optical waveguides, a laser safety shutdown is usually provided on the Counter direction of the Ubertragungsstrecke is controlled, and in the absence of signal in the opposite direction also shuts off the laser in the transmitter direction. Directed operation lacks a jerk channel. In this case, the patent EP 0296427 A1 proposes optically coupling a monitor photodiode to a fiber piece (pigtail) of a laser diode via an optical feeder whose output current, after comparison with a reference current, actuates a controlled switch when a predetermined limit value of the light output is exceeded so that the supply current for the laser diode interrupts. These protective mechanisms have a considerable additional electronic expenditure in common. By interposing a fiber stucco (micropigtail), the structural size is partly increased considerably.

From German Offenlegungsschπft DE 19654600 Al a laser diode with an annular active Abstrahlflache is known, which is acted upon by such a drive current, that the emitted light has an annular intensity profile with low Lichtmtensitat in the center. A change in the radiating laser aperture requires a special laser design and has, for example, adverse effects on the bandwidth.

There are a number of other known protective devices in optical Datenubertragungsemrichtungen with which the eye safety can be ensured.

It would be desirable to improve the eye safety without complicated and complicated mechanical connectors and electronic protection circuits.

The object of the present invention is therefore to provide an apparatus and a method for improving the eye safety in a light coupling into optical fibers. This object is achieved by a device having the features of patent claim 1 and a method according to claim 12.

The present invention is based on the finding that the eye safety can be improved in a light coupling into optical fibers by the light from a light source, in particular from a point light source, is divided into a plurality of individual beam sources. That is, a light beam emanating from a light source, instead of being directly or bundled into an optical fiber, e.g. a polymer fiber or a polymer optical fiber, to be coupled, previously transformed into a plurality of separate beam bundles, which are then coupled into the optical fiber. Thus, a total radiation power can be distributed to a plurality of beam sources, so that the light output can be increased as a whole, wherein a single light power each of verre. - Th rays sources is eye safe. As a result, a higher eye safety can be achieved with staked optical fiber, without significantly affecting the efficiency of the light coupling into the light guide.

According to exemplary embodiments, an optically transparent component is used whose one side, which faces the optical fiber, comprises an arrangement of optical beam forming units, which can be defined or regularly arranged and / or arranged in a completely random or irregular manner. According to one embodiment, the optical arrangement is a lens array, in particular a microlens array, ie the beam shaping units are lenses. According to exemplary embodiments, the side of the optical component facing the light source can be designed as a converging lens in order to maximize a coupling efficiency between the light source and the fiber and to compensate for lateral alignment tolerances. The side facing the light source can also be structured as a plane or otherwise. According to exemplary embodiments, the optical component can also be part of a housing of a light source or a larger unit, or cast on a side facing the fiber of a potting compound, such as plastic Sprit, be structured, wherein in the potting compound, the light source and optionally other components are included ,

An advantage of the present invention is that with a Faspr not connected to the light source and a view into the plurality of light beams, no single light spot can be imaged on the retina of an eye, so that a harmful effect is considerably lower than with a point light source. Thus, the eye safety can be increased.

A further advantage of the present invention is that a higher total optical power can be used and thus the range of a transmission link can be increased while at the same time guaranteeing eye safety directly at the light source.

Preferred embodiments of the present invention will be explained in more detail below with reference to the accompanying drawings. Show it:

1 shows a schematic flow diagram of a method for coupling light into a fiber according to an exemplary embodiment of the present invention;

2 shows a device for coupling light into a fiber according to an embodiment of the present invention; 3a-c embodiments of optical components according to embodiments of the present invention;

4a is a schematic representation of a coupling of a plurality of light beams in an optical fiber according to an exemplary embodiment of the present invention;

4b is a schematic representation of a coupling of a plurality of light beams in a multi-core optical fiber according to an embodiment of the present invention;

Fig. 5 is a schematic representation of an image of the plurality of light rays on the retina of an eye;

Fig. 6 is a schematic representation of a conventional fiber coupling with high Augengefahrdung; and

7 is a schematic representation of a scaled image of a point light source on the retina of an eye.

With regard to the following description, it should be noted that in the case of the different embodiments, identical or identically functioning functional elements have the same reference symbols, and thus the descriptions of these functional elements in the various exemplary embodiments illustrated below are interchangeable.

Fig. 1 shows a schematic flow diagram of a method for coupling light into a fiber according to one. Embodiment of the present invention. In a first step Sl, a light beam or a radiation beam is generated by means of a light source. In a second step S2, a plurality of radiation beams is generated from the one beam bundle, which can be coupled into the optical fiber. In a third step S3, the plurality of radiation beams are coupled into the optical fiber.

A device 200 for coupling light into a fiber, which can be used to carry out the method described with reference to FIG. 1, is shown schematically in FIG.

The device 200 has a light source 100 for generating a light beam or a beam bundle 202. Further, the apparatus 200 includes an optical assembly 204 having a plurality of laterally adjacent beam forming units 206-1 through 206-N for generating the plurality of beam bundles 208-1 through 208-N from the light beam 202, the beam bundles 208-1 to 208-N can be coupled into an optical fiber.

According to exemplary embodiments, the light source 100 is a point light source, such as a laser.

The beamforming units 206-1 through 206-N of the device 200 face the optical fiber (not shown). According to embodiments ^h, the beam-shaping units 206-1 to ^"1" ^, N are lenses, in particular converging lenses, which are designed to form a collimated light beam in a radius of beam bends 208-1 to 208 -N divide. in this case, the condenser lenses may be arranged completely arbitrarily defined 206-1 to 206-N or aui ^μ i. According to a preferred exemplary embodiment, the lenses 206-n (n = l, ..., N) in the form of a planar Lens arrays or Mi krol i nsenarrays arranged. According to exemplary embodiments, the light source 100 facing side of the optical arrangement 204 as a lens, in particular condenser lens, can be configured to collimate the divergent light beams of the radiation beam 202 and the coupling efficiency between the light source 100 and the fiber, in particular in the case of light beams emanating divergently from the light source 100 (not shown) to maximize and compensate for lateral adjustment tolerances. Meet on the light source 100 side facing the optical assembly 204 by way of example already collimated light rays on the optical assembly 204, the light source side facing may also be structured as a transparent plane. The impingement of already collimated beams is, however, not mandatory, although this may be advantageous in terms of the coupling-in effectiveness.

Embodiments of the optical arrangement 204 are shown schematically in FIGS. 3a and 3b.

3a shows the transparent optical arrangement 204 in the form of a one-piece optical component with a first side 302, which is formed as a plane, and a second side 304, which lies opposite the first side and in which a plurality of adjacent beamforming units or lenses Elementals 306-1 to 306-N are formed. Although only four laterally arranged elementary arms 306-n are shown in FIG. 3a, it will be clear to a person skilled in the art that this is merely a schematic side view of a lens array which can have a multiplicity of lenses arranged in a plane, in particular converging lenses , These may be, for example, square, round or hexagonal microlenses. The beam shaping units 306-1 to 306-N have mutually laterally spaced optical axes, which may for example run parallel to each other. Further, beam forming units 306-1 through 306-N may be formed to be along a plane parallel to their optical Axis have a shorter focal length than in a plane perpendicular thereto. A same focal length is of course also possible. Advantageously, the beamforming units 306-1 through 306-N cover the majority of the lateral dimension of the assembly 204 in a laterally flat fashion. Expressed differently, the lateral dimensions of the beam-forming units 306-1 to 306-N are, for example, maximally selected in order to find space next to one another.

A front view of the second side 304 of the optical assembly 204 shown in FIG. 3a is shown in FIG. 3b.

Fig. 3b shows by way of example a 4 x 3 lens array with four rows and three columns. In this case, for example, it has a total of N = 12 lens elements 306-n (n = 1,..., 12). Again, of course, that the number and also the regularity of the arrangement of the lens elements is merely exemplary in nature.

An embodiment of the first side 302 of the optical arrangement 204 as a plane is advantageous, for example, when collimated light beams from the direction of the light source 100 (not shown) strike the component or the optical arrangement 204. The collimated light beams are split by the lenses 306-1 to 306-N into N beam bundles, which for example can be coupled into an optical fiber.

FIG. 3 c shows an optical component 204 according to a further exemplary embodiment of the present invention.

In this embodiment is in the first page

(302), i. the light source 100 side facing, a converging lens 308 is formed to collimate outgoing from the light source 100 divergent rays and a

To maximize coupling efficiency between light source and fiber. For this purpose, light source 100 is in a focal plane of Conveying lens 308 arranged. Furthermore, lateral adjustment tolerances can thus be compensated.

According to exemplary embodiments, lenslets 306-n (n = 1,..., N) of the second side 304 each have a maximum lateral extent that is less than one-third of the maximum lateral extent of the first-lenslamping lens 308. Lateral in this context means perpendicular to the light propagation direction. In other words, a diameter of an elementary lens 306-n (n = 1,..., N) of the second side 304 is, for example, at most one half or alternatively even at most one third of the diameter of the lens 308 of the first side 302.

The components 204 shown in FIGS. 3a-c can be implemented, for example, in plastic injection molding, so that the optical components 204 can be realized relatively inexpensively. The lens 308 and / or the lens ray from the lenses 306-n (n = 1,..., N) can be applied to the front and rear sides of a transparent, planar plastic part by means of injection molding, for example Fig. 3a and 3c is indicated by the dashed lines. Of course, a monolithic production of the component 204 is conceivable. For the application düng in laser technology, the optical assembly 204 according to exemplary embodiments of glass, in particular quartz glass, consist. The lenslets 306-1 through 306-N may be fabricated using microfabrication techniques such as photolithography and high optical vibration etching techniques. For laser applications in the ultraviolet, visible and near-infrared wavelength range, for example, synthetic quartz glass or calcium fluoride can be used as the lens material.

A typical application example of embodiments of the present invention is high speed data transmission over polymer optical fibers or multi-core optical fibers. Such fibers generally have a relatively large core diameter or fiber diameter (usually greater than 100 microns, typically, for example, 1 mm), so that the fiber itself provides a relatively high eye safety (large radiating surface with large numerical aperture). However, if, for example, a laser with a small radiating surface (for example 1 to 3 μm) is required for fast data transmission, then the power of the laser must be selected so low that eye safety is maintained even when the fiber is staked and the laser is sighted , This may mean, for example, that a fiber may carry up to 4 mW (milliWatts) of optical power in order to be classified in laser protection class 1, but the laser may radiate a maximum of 0.39 mW in order to be classified in this class. the.

FIG. 4a shows a coupling of a plurality of radiation beams 208-1 to 208-3 into an optical fiber line 120 according to an embodiment of the present invention.

The light or the light beam 202 from the laser 100 is collimated by the first converging lens 308 on the first side 302 of the optical component 204 and again by the lens array 306-n on the second side 304 of the component 204 at N locations through lens elements 306-n. 1 to 306-N are converted into convergent beams 208 of short focal length. Due to the size and numerical aperture of the lens array, the coupling of the light source 100 to the optical fiber 120 can be optimized.

Alternatively, the optical member or lens array may be configured to convert the light beam 202 into divergent rays on the fiber side, i. The lens array can have scattering lenses.

When looking directly into the light source with the eye but also when looking into the light source via another image end optics, such as a burning glass, this, according to embodiments, distributed to many apparent sources light 202 of the light source can not be mapped to a single point on the retina. This connection is sketched schematically in FIG.

5 shows an apparatus 200 for coupling light into a fiber having a laser 100 and an optical assembly 204, wherein a plurality of radiation beams 208 are imaged onto the retina of an eye 160. For an exemplary 3 × 3 lens array on the second side of the component 204, an intensity distribution is obtained in a focal plane 550 of the elementary lenses 306-1 through 306-N, as shown schematically in FIG. 5.

By a large number of the lenslets 306-1 to 306-N, the light output of the radiation beam 202 is distributed (aperture judgment) so that even when using an external imaging optics, the total beam power can not be collected in one point. In the simple case, the distribution can take place in individual points, circular rings or even arbitrary patterns. When the fiber is not connected, therefore, when looking into the beams 208, with or without additional optics, no single spot can be imaged on the retina of the eye 160, so that the harmful effect of the light beams 208 is significantly lower than with a point light source , Due to the laser protection zverordruig DIN EN 60825-1 / VDE0837-1, "safety of laser devices", the entire structure can now be considered in the ideal case, so with a sufficiently large distance of the lenslets 306-1 to 306-N as a variety of individual sources so that a multiple of the optical power can now also be emitted in comparison with a single point source If the lenslets 306-1 to 306-N are very close to one another, the combination of the lenslets 306-1 to 306 may also have to be considered in terms of eye safety -N, but which still allows higher performance than a single source. By a higher optical power, a range of an optical transmission link can be increased, while ensuring eye safety directly at the light source. Furthermore, by changing the numerical aperture, ie the size and shape of the two optical surfaces or sides 302 and 304, the optical coupling of the optical arrangement 204 to the fiber 120 and the light source 100 can be adjusted so that the achieved coupling efficiency can be similarly good like a conventional fiber optic. The optical arrangement or the optical component 204 can, as has already been described above, be realized, for example, in plastic injection molding, so that the optical component can furthermore also be very cost-effective.

Although it has been described above that a plurality of beam bundles 208 are coupled into one and the same fiber 120, it should be noted that this may in particular mean that the beam bundles 208 are coupled to one and the same fiber core 122, which is surrounded by a jacket 124 and together with this forms the fiber 120.

Furthermore, it is of course also conceivable that the fiber 120 comprises a plurality of fiber cores 402, which in turn may each have a fiber core diameter D. Such a multi-core fiber is used as a single core fiber, i. the light is coupled in at the end face of the fiber 120 without specific assignment to the cores.

4b shows an optical arrangement 204 with the plurality of laterally adjacent beamforming units 306, which form a lens array on the fiber side, for producing a plurality of convergent or divergent bundles of rays 208 from the light beam 202 of the light source 100, which is in the fiber 120 a plurality of fiber cores 402 can be coupled. Optical axes 307 of the lenses 306 are opposite optical axes or axes of symmetry 403 of the lenses Serkerne 402 arranged uncorrelated with respect to their spatial position. Light, starting from the lenses or beam shaping units 306, is coupled into the fiber cores 402 at the end face of the fiber 120 without specific association between the beam shaping units 306 and the fiber cores 402. That is, in general, optical axes 307 of the beamforming units 306 and axes of symmetry 403 of the fiber cores 402 do not coincide, so that accurate tuning of the optical assembly 204 to the fiber 120 is not necessary. According to embodiments, the optical axes 307 of the lenses 306 may even be outside of the lenses (random) associated fiber cores 402. That is to say, a distance d between some optical axes 307 of the lenses 306 and some axes of symmetry 403 of the fiber cores 402 is greater than a radius D / 2 of the fiber cores 402. This does not necessarily apply to the spatial position of all the optical axes 307 and symmetry axes 404 , a mean distance d 'between an optical axis 307 of a beam shaping unit 306 and an optical axis 403 of a (randomly) associated fiber core 402 according to embodiments is smaller than D / 2, for example in a range between D / 8 and D / 4 , ie D / 8 <d '<D / 4.

In general, therefore, light is not imaged onto specific fibers or fiber cores or segments of a fiber end surface with the optical arrangement 204. On the contrary, the aim of some exemplary embodiments is to form light beams 202 from a (point) light source 100 in such a way that on the one hand a good coupling efficiency to one or more fiber cores 402 is achieved, ie numerical aperture and diameter of the optical arrangement 204 and beam shaping units 306 are adapted to the fiber, but on the other hand, when viewed accidentally in a light beam manipulated by the optical arrangement 204 when the fibers are staked off, focusing on a point and thus on an eye is excluded. For the homogenization of light beams, so-called honeycomb condensers for slide and film projections are used, for example, in projection and microscopy. However, the task of a honeycomb condenser is completely different from that of a device according to exemplary embodiments of the present invention, namely the homogenization of light and imaging in an entrance pupil of a projection optics, for example, to illuminate a screen evenly without depicting the structure of the light source (eg Gluhwendel) - the. The eye safety of the system is not in the foreground with honeycomb condensers and is not necessarily ensured by a honeycomb condenser, depending on the design. In embodiments of the present invention, the homogenization of light is not necessary, but the priority is the distribution of light on many individual sources. A honeycomb condenser is also relatively complicated, consisting of at least three optical components, constructed and its dimensions are relatively large, which is very unfavorable in the fiber coupling, especially in optical transceivers. In addition, an adjustment of the components to each other is necessary, which makes a honeycomb condenser generally very expensive. As already described above, however, an optical arrangement 204 or an optical component according to exemplary embodiments only consists of a structured optical part.

Finally, it should be pointed out that the present invention is not limited to the respective components of the device or the explained procedure, since these components and methods may vary. The terms used herein are intended only to describe particular embodiments and are not used in a limiting sense. When the singular or indefinite articles are used in the specification and claims, these also refer to the majority of these elements unless the context clearly makes otherwise clear. The same applies in the opposite direction.

Claims

claims

1. Device (200) for coupling light into a fiber (120), with

a light source (100) for generating a light beam (202); and

an optical assembly (204) having a plurality of laterally adjacent beamforming units (206; 306) forming a lens array (306-1, ..., 306-N) on the fiber side for generating a plurality of convergent or divergent beam bundles (208). from the light beam (202) which can be coupled into the fiber (120).

2. Device according to claim 1, wherein the light source

(100) comprises a laser.

3. Device according to claim 1 or 2, wherein the fiber

(120) is an optical waveguide with a diameter greater than 50 microns.

4. Device according to one of the preceding claims, wherein the optical arrangement (204) light source side forms a converging lens (308), in whose focal length, the light source (100) is arranged.

5. Device according to one of the preceding claims, wherein the optical arrangement (204) is formed of a transparent plastic.

6. Device according to one of the preceding claims, wherein the optical assembly (204) is integrally formed.

7. Apparatus according to claim 5 or 6, wherein the optical assembly (204) is made by injection molding technique.

A device according to any one of the preceding claims, wherein the fiber is a polymer fiber.

9. Device according to one of the preceding claims, wherein the optical arrangement (204) is formed as a one-piece optical component.

10. Device according to claim 9, wherein the optical arrangement (204) has a first side (302) facing the light source (100), in which a first collection lens (308) is formed, and

a second side (304) facing the fiber (120) facing the first side (302) and in which a plurality of second adjacent collection lenses (306) are formed, one lateral

Dimension of the first converging lens (308) is greater than a lateral dimension of the second converging lenses

(306).

The device of claim 10, wherein the second collection lenses (306) each have a maximum lateral extent that is less than one half the maximum lateral extent of the first collection lens (308).

12. A method for coupling light into a fiber (120), comprising the following steps:

Arranging a plurality of laterally adjacent beamforming units (206; 306) which form a lens array (306-1, ..., 306-N) on the fiber side;

Generating a light beam (202); and Generating, with the plurality of laterally adjacent beamforming units (206; 306), a plurality of convergent or divergent beam bundles (208) from the light beam (202) that are injectable into the fiber (120).