CA1183260A - Partial beam focus sensing in an optical recording system - Google Patents
Partial beam focus sensing in an optical recording systemInfo
- Publication number
- CA1183260A CA1183260A CA000413900A CA413900A CA1183260A CA 1183260 A CA1183260 A CA 1183260A CA 000413900 A CA000413900 A CA 000413900A CA 413900 A CA413900 A CA 413900A CA 1183260 A CA1183260 A CA 1183260A
- Authority
- CA
- Canada
- Prior art keywords
- light
- lens
- detector array
- focus
- condition
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1381—Non-lens elements for altering the properties of the beam, e.g. knife edges, slits, filters or stops
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/40—Optical focusing aids
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
- G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B7/0908—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
- G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B7/0908—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only
- G11B7/0916—Foucault or knife-edge methods
Abstract
ABSTRACT OF THE DISCLOSURE
Focus sensing using a light detector array is accomplished in an optical recording system using the light beam returned from the recording media through the objective focusing lens by passing the beam through a spherical focussing lens using a mask such as a knife edge which only passes a portion of the beam to the light detector array. The light detector array is matched to the mask and detects the different partial image patterns formed as a result of the close to focus condition with the recording media too far away from the objective lens and the near to focus condition with the media too close to the objective lens. In the focused condition, the light detector array receives a comparatively fine focused spot of light. Alternative embodiments of the present invention may use a cylindrical lens which in the focused condition creates a longitudinal bar of light. Further alternative embodiments may be made with a spherical Fresnel lens or a cylindrical Fresnel lens which create larger areas of light, round and bar shaped, respectively, in the focused condition.
Focus sensing using a light detector array is accomplished in an optical recording system using the light beam returned from the recording media through the objective focusing lens by passing the beam through a spherical focussing lens using a mask such as a knife edge which only passes a portion of the beam to the light detector array. The light detector array is matched to the mask and detects the different partial image patterns formed as a result of the close to focus condition with the recording media too far away from the objective lens and the near to focus condition with the media too close to the objective lens. In the focused condition, the light detector array receives a comparatively fine focused spot of light. Alternative embodiments of the present invention may use a cylindrical lens which in the focused condition creates a longitudinal bar of light. Further alternative embodiments may be made with a spherical Fresnel lens or a cylindrical Fresnel lens which create larger areas of light, round and bar shaped, respectively, in the focused condition.
Description
3~
This invention relates to op~ical recording systems. In particularJ
this invention relates to the foousing detection systems to be used ~ith op~ical media recording systems.
It is well known that optical recording systems require a very pre-cisely focused condition of the light beam through an objective lens onto the recording media. The light beam f'ocused on the media is, typically, reflected back thxough the objective lens and used in the sys~em to read information on the mediaO The reflected light beam is typically divided into additional parts includi,ng a part~ typically, used eor focus detection information and to operate a ~ocusing control system for a movable objective lens.
In optical recording technology, various focusing and light beam handling systems are known. In United States Patent Number 3,97~,327 a schematic diagram is shown of a light beam being returned directly from an objective lens to a light detector array from which a particular focusing s,ystem operatesO A mirror which is partially reflecting and partially trans-parent Tnay be used to control the splitting of the light beam into various ele-en~s for ~arious purposes. United States Patent Number 4,123,652 shows the use of partially reflecting and partially transparent mirrors or beam splitters to di~ide a light beam into various components in connection with both an ~0 ineormation reading detector for one bea~ element and a focusing light detector ax~ay ~or another beam element. United States Patent Number ~,123,652 shows what is known as the astigmatic focusing system whereby an image is distorted in a first directlon in a first out of focus condition with respect to the recording media and in a second direction in a second out of focus condition ~ith respect to the recording mediaO The two out of focus conditions with res-pect to the recording media are thos,e involving the objective lens being too close to the media and too far from the mediaO It i5 noted that Figure 7 of that patent shows a cylindrical lens element in connection with the focusing of a light beam on the light detector array. Ilowever, this patent is related to astigmatic focusing systems rather than partial beam focusing systems.
Also known to applicant are United States Patent Numbers 3,969,576 and 4,143,402 relating to partial beam focusing sys~ems.
In United States Patent Number 3,969,576, separate light detecting elements are arranged to receive a portion of a light beam for use in reading information and another light detecting element is disposed at a different location to receive a light beam for purposes of operating a focusing system.
The focusing beam is referred to in that patent as an auxiliary beam while the bea~ from which information is read i5 referred to as the read beamO A radia-tion absorbing knife is disposed between the radiation source and a Wollaston prism to block a portion of the auxiliary beam but which is so disposed with respect to the source and the prism that none of the read beam is blocked. As explained in the patent, the auxiliary beam is returned to the focusing light detector array as only a partial beam~ In the focused condition, a comparatively small ocused point of light exists on a pair of light detector elements~ In ono out o~ focus condition, a partial light beam, sometimes referred to as a h~lf-moon, is focused on one-half or one element of the light detector array an~ in the other out of focus condition a partial light beam image or half-moon is shown on the other light detector element of the light detector array. This p~tent therefore represents the basic half-moon or partial light beam focusing system which is now comparatively well known~
United States Patent Number ~,143,402 shows another half-moon focus-ing ~ystem in which the light ~rom a source is only partially returned to a ~3Z~.;!3 focusing detector ~ystem and in which the half-moon light spot returned to the focus,ing s,ource occurs on one half or one portion of the light detec~or array for one out of focus condition and on the other portion of the ligh~ de~ector array for the other out of focus conditionO In that patent, a prism is shown which reflects one-half of a portion of the light beam returned from the media to the focusing detector array while not affecting the other half of the light beam. The prism is disposed in such a fashion that it does not use all of the relected light from the media for focusing on the detector array but allows a portion of the original beam to pass to an information reading detector array.
Roth o the aforementioned partial beam focusing detection system patents show a means for forming a partial light beam which is also disposed in the path rom the light source to the media and is not disposed so as to only aect light being reflected from the mediaO In systems adapted for read-ing from the media o.lly, these systems, are not as critical as to light lost in the partial beam systemu ~ loweverJ or systems, in which data is to be both read and written, p~rtial beam system or system in which the light beam traveling towards the ~edia may be reduced in strength have a critical disadvantage. In systems in whichthe media is to be written, it is important to conserve the power of the writing beam so that only a minimum power writing source may be provided. If the systems shown i.n the aforementioned partial beam patents were to be used in a reading and writing system, they would suffer at least one of several poss-il~le disadvantages such that there would be less power in the writing beam, larger spot size on the media than desired because of necessary additional optical elements interposed in the writing beam or comparatively complex or large siæed lenses; all as compared to a system without such partial beam ele-~ 3 -3~
~ents interposed in the writing beamO
Thereore, in systems in which focus is to be maintained during writing on the media, it is clear that it is necessary to provide a focus detection system which does not require the provision of any additional optical elements which may interfere with the writing beam. Also, the aforementioned patents result in an extremely critical physical rela~ionship between the par-tial beam creating device, the knie in the one patent or the prism in the other patent, and the light detecting elementO If there should be any mis-alignment between the focusing light detector array and the prism or the knife, 1~ then the focusing system will not work as intended. It is therefore desirable to provide a focusing system having a somewhat less cri~ical relationship be-t~een the partial beam transmitting means and the focusing light detector array.
With respect to the astigmatic focusing system as shown in United States Patent Number 4,123,652, it is noted tha~ the astig~atic focusing system re~uires t~o cylinder lenses or one cylinder lens and one spherical lens or some other combination of multiple optical elements in order to create the astigmatic focusing pattern. Therefore, these additional optical elements create additional optical complexity or else cause loss of light between the media and the foc-using detector array.
Z~ It i5 clear that it ~ould be desirable to provide a focusing detec-tion system ha~ing some of the advantages of both the astigmatic focusing system and of the knife edge focus detecting systemO
In the present invention an optical me~ory system is provided with kno~l optical ~ystem for separating the reflected beam returning from the media 50 that it passes into an optical partial beam focusing system according to the p~esent inventionO Typically, such an optical system would use a polarizing z~;~
beam splitter and a quarter wave plate or a semi-transparent reflecting mirror to create a reflected beam portion which is separated from the line of tra-vel of the transmitted beam portionO The system according to ~he present invention would have particular application to an optical recording system in which in-formation i5 both written and read on the optical mediaO
Therefore, an input beam which represents a reflected light beam f~m th~ media and Whichis separated from the path of travel of the transmitled beaJn passes into an optical system according to the present invention in a coll-imated cross section, which may typically be circularO The collimated circu-lar light beam passes ~o a spherical, in one embodiment of the invention, read-out lens ~hich focuses the light beam on the focusing light detector array. A
~ask such as a knife edge cuts the lower or upper portion of the collimated keam, leaving a partial beam in what may be referred to as a half-moon shapeO
This knife edge mask is disposed in close ph~sical position to the spherical lens or it may even be attached to ito The knife edge may typically be placed in front of the spherical readout lens but may be behind it if it is physically close to the lens.
The half-moon light beam image ta~es one orientation on a focusing li~ht detector array ~hich matches the mask when the objective lens is focused ~Q in a near to focus but too close to the media positiohO The half-moon image appears in the other and opposite orientation when the near to focus condition ~laces the objective lens in a relationship too far from the media. This is ~ecause the light pattern makes a center sylnmetric inversion in the plane of the detector array at the in focus condition.
The present invention has the advantage that it does no~ detract f~a~ the light beam energ~ impingent upon the media in a writing mode for a 32i~
systeln which both reads and writes;O
An alternative embodiment of the present invention involves the use of a spherical Fresnel lens instead of the spherical lens in connection ~ith the knife edge to focus the light beam on the light detecting array. The spher-ical Fresnel lens causes the light spot on the light detector array to be com-paratively larger than it would be with the spherical lensO In a perfect spherical lens, when the optical system would have the oojective lens in a per-~ectly focused condition on the optical media, the light impinging on the foc-using light detector array would tend to converge to a vanishingly small spotO
~he detector array then would most advantageously detect the ouk of focus half-moon image condition but would have a minimally small light detecting signal QUtpUt in the ocused condition, This minimally small light detecting signal output would be subject to noise distu~banceO However, the use of the Fresnel spherical lens would leave a larger light spot in the focused condition which wquld be symmetrical on both sides of the light detector axis so that the light detecting elements in the light detector array would produce a balanced output representative of some light strengthO This balanced output signal would be comparatively free of noise disturbanceO
Another embodiment of the present invention would use a cylindrical
This invention relates to op~ical recording systems. In particularJ
this invention relates to the foousing detection systems to be used ~ith op~ical media recording systems.
It is well known that optical recording systems require a very pre-cisely focused condition of the light beam through an objective lens onto the recording media. The light beam f'ocused on the media is, typically, reflected back thxough the objective lens and used in the sys~em to read information on the mediaO The reflected light beam is typically divided into additional parts includi,ng a part~ typically, used eor focus detection information and to operate a ~ocusing control system for a movable objective lens.
In optical recording technology, various focusing and light beam handling systems are known. In United States Patent Number 3,97~,327 a schematic diagram is shown of a light beam being returned directly from an objective lens to a light detector array from which a particular focusing s,ystem operatesO A mirror which is partially reflecting and partially trans-parent Tnay be used to control the splitting of the light beam into various ele-en~s for ~arious purposes. United States Patent Number 4,123,652 shows the use of partially reflecting and partially transparent mirrors or beam splitters to di~ide a light beam into various components in connection with both an ~0 ineormation reading detector for one bea~ element and a focusing light detector ax~ay ~or another beam element. United States Patent Number ~,123,652 shows what is known as the astigmatic focusing system whereby an image is distorted in a first directlon in a first out of focus condition with respect to the recording media and in a second direction in a second out of focus condition ~ith respect to the recording mediaO The two out of focus conditions with res-pect to the recording media are thos,e involving the objective lens being too close to the media and too far from the mediaO It i5 noted that Figure 7 of that patent shows a cylindrical lens element in connection with the focusing of a light beam on the light detector array. Ilowever, this patent is related to astigmatic focusing systems rather than partial beam focusing systems.
Also known to applicant are United States Patent Numbers 3,969,576 and 4,143,402 relating to partial beam focusing sys~ems.
In United States Patent Number 3,969,576, separate light detecting elements are arranged to receive a portion of a light beam for use in reading information and another light detecting element is disposed at a different location to receive a light beam for purposes of operating a focusing system.
The focusing beam is referred to in that patent as an auxiliary beam while the bea~ from which information is read i5 referred to as the read beamO A radia-tion absorbing knife is disposed between the radiation source and a Wollaston prism to block a portion of the auxiliary beam but which is so disposed with respect to the source and the prism that none of the read beam is blocked. As explained in the patent, the auxiliary beam is returned to the focusing light detector array as only a partial beam~ In the focused condition, a comparatively small ocused point of light exists on a pair of light detector elements~ In ono out o~ focus condition, a partial light beam, sometimes referred to as a h~lf-moon, is focused on one-half or one element of the light detector array an~ in the other out of focus condition a partial light beam image or half-moon is shown on the other light detector element of the light detector array. This p~tent therefore represents the basic half-moon or partial light beam focusing system which is now comparatively well known~
United States Patent Number ~,143,402 shows another half-moon focus-ing ~ystem in which the light ~rom a source is only partially returned to a ~3Z~.;!3 focusing detector ~ystem and in which the half-moon light spot returned to the focus,ing s,ource occurs on one half or one portion of the light detec~or array for one out of focus condition and on the other portion of the ligh~ de~ector array for the other out of focus conditionO In that patent, a prism is shown which reflects one-half of a portion of the light beam returned from the media to the focusing detector array while not affecting the other half of the light beam. The prism is disposed in such a fashion that it does not use all of the relected light from the media for focusing on the detector array but allows a portion of the original beam to pass to an information reading detector array.
Roth o the aforementioned partial beam focusing detection system patents show a means for forming a partial light beam which is also disposed in the path rom the light source to the media and is not disposed so as to only aect light being reflected from the mediaO In systems adapted for read-ing from the media o.lly, these systems, are not as critical as to light lost in the partial beam systemu ~ loweverJ or systems, in which data is to be both read and written, p~rtial beam system or system in which the light beam traveling towards the ~edia may be reduced in strength have a critical disadvantage. In systems in whichthe media is to be written, it is important to conserve the power of the writing beam so that only a minimum power writing source may be provided. If the systems shown i.n the aforementioned partial beam patents were to be used in a reading and writing system, they would suffer at least one of several poss-il~le disadvantages such that there would be less power in the writing beam, larger spot size on the media than desired because of necessary additional optical elements interposed in the writing beam or comparatively complex or large siæed lenses; all as compared to a system without such partial beam ele-~ 3 -3~
~ents interposed in the writing beamO
Thereore, in systems in which focus is to be maintained during writing on the media, it is clear that it is necessary to provide a focus detection system which does not require the provision of any additional optical elements which may interfere with the writing beam. Also, the aforementioned patents result in an extremely critical physical rela~ionship between the par-tial beam creating device, the knie in the one patent or the prism in the other patent, and the light detecting elementO If there should be any mis-alignment between the focusing light detector array and the prism or the knife, 1~ then the focusing system will not work as intended. It is therefore desirable to provide a focusing system having a somewhat less cri~ical relationship be-t~een the partial beam transmitting means and the focusing light detector array.
With respect to the astigmatic focusing system as shown in United States Patent Number 4,123,652, it is noted tha~ the astig~atic focusing system re~uires t~o cylinder lenses or one cylinder lens and one spherical lens or some other combination of multiple optical elements in order to create the astigmatic focusing pattern. Therefore, these additional optical elements create additional optical complexity or else cause loss of light between the media and the foc-using detector array.
Z~ It i5 clear that it ~ould be desirable to provide a focusing detec-tion system ha~ing some of the advantages of both the astigmatic focusing system and of the knife edge focus detecting systemO
In the present invention an optical me~ory system is provided with kno~l optical ~ystem for separating the reflected beam returning from the media 50 that it passes into an optical partial beam focusing system according to the p~esent inventionO Typically, such an optical system would use a polarizing z~;~
beam splitter and a quarter wave plate or a semi-transparent reflecting mirror to create a reflected beam portion which is separated from the line of tra-vel of the transmitted beam portionO The system according to ~he present invention would have particular application to an optical recording system in which in-formation i5 both written and read on the optical mediaO
Therefore, an input beam which represents a reflected light beam f~m th~ media and Whichis separated from the path of travel of the transmitled beaJn passes into an optical system according to the present invention in a coll-imated cross section, which may typically be circularO The collimated circu-lar light beam passes ~o a spherical, in one embodiment of the invention, read-out lens ~hich focuses the light beam on the focusing light detector array. A
~ask such as a knife edge cuts the lower or upper portion of the collimated keam, leaving a partial beam in what may be referred to as a half-moon shapeO
This knife edge mask is disposed in close ph~sical position to the spherical lens or it may even be attached to ito The knife edge may typically be placed in front of the spherical readout lens but may be behind it if it is physically close to the lens.
The half-moon light beam image ta~es one orientation on a focusing li~ht detector array ~hich matches the mask when the objective lens is focused ~Q in a near to focus but too close to the media positiohO The half-moon image appears in the other and opposite orientation when the near to focus condition ~laces the objective lens in a relationship too far from the media. This is ~ecause the light pattern makes a center sylnmetric inversion in the plane of the detector array at the in focus condition.
The present invention has the advantage that it does no~ detract f~a~ the light beam energ~ impingent upon the media in a writing mode for a 32i~
systeln which both reads and writes;O
An alternative embodiment of the present invention involves the use of a spherical Fresnel lens instead of the spherical lens in connection ~ith the knife edge to focus the light beam on the light detecting array. The spher-ical Fresnel lens causes the light spot on the light detector array to be com-paratively larger than it would be with the spherical lensO In a perfect spherical lens, when the optical system would have the oojective lens in a per-~ectly focused condition on the optical media, the light impinging on the foc-using light detector array would tend to converge to a vanishingly small spotO
~he detector array then would most advantageously detect the ouk of focus half-moon image condition but would have a minimally small light detecting signal QUtpUt in the ocused condition, This minimally small light detecting signal output would be subject to noise distu~banceO However, the use of the Fresnel spherical lens would leave a larger light spot in the focused condition which wquld be symmetrical on both sides of the light detector axis so that the light detecting elements in the light detector array would produce a balanced output representative of some light strengthO This balanced output signal would be comparatively free of noise disturbanceO
Another embodiment of the present invention would use a cylindrical
2~ lens together with the knife edge to produce a half-moon image which in the ~cus~d condition would tend to go to a thin bar shape or a line shape rather than to a point shape as is the case with the spherical lens. Again, this would have the advant~ge of being detected by ~he light detector array better than a vanishingly small spotO Yet another embodiment of the present invention would use a cylindrical Fresnel lens which would, in the focused condition, tend to go to a longitudinal wide bar s~hape on the focusing detector array
3~
which ~ouldbe sY~metrical about the axis of the light detector array.
In accordance with a broad aspect of the invention, there is pro-vided a partial beam focus sensing system in optical recordin~ comprising;
lens element for receiving a collimated light beam in an optical recording 5y5~
tem representative of light reflected from optical recording rnedia, a centrallysymmetric mask element proxima.te to said lens element for eliminating a portionof s.aid light beam and transmitting a partial light beam, and a light detector array comprising at least two light detecting elements matched to said mask element and disposed to receive said partial beam from said lens elementO
~he invention will now be further described in conjunction with the accompanying drawings, in which: Figure 1 shows a first embodiment of the pres.ent invention using a spherical lens and a knife edgeO Figure 2 is an illustr~tion ofanother embodiment on the present invention using a knife edge and a cylindrical lensO Figure 3 is a showing of another embodiment of the present invcntion using a cylindrical Fresnel lens. Figure 4a is a side plan view o~ the embodiment of the invention shown in Figure 3 to illustrate the generation of a bar pattern by the cylindrical Fresnel lensO Figure 4b is a top view of the embodiment of the invention shown in Figure 3~ Figure 5 shows ~ central symmetric mask element.
Referring now to Figure 1, an embodiment 10 of the present invention i~s shown using a collimated circular light beam 12 passing into the system as 5hown sche~atically at 1~. A mask such as knife edge element 16 partially ob-structs a portion of the beam creating a half-moon image l~ on the knife edge element. ~he knife edge element may be placed on a spherical lens element 20 or in front of it or behind it, but, it is most desirable that it be placed in a proximate position with respect to the spherical lens element 20~ Other mask 32~
patterns than the simple knife edge are possible within the scope of the pre-sent invention so long as the mask pattern is center symmetric. The knife edge pattern shown in Figure l i5 center symmetricO
The half-moon image passing through the spherical lens element 20 is shown diagrammatically at 220 A ha].f moon image at 24 and an upside do~,m half-moon image at 28 illustrate the pre and post focused images formed by the par-tial or half-beam passing through the spherical lens element 2Q to illustrate the shape of the image generated on the partial ~eam, light detector array 260 The detector array has detector elem~nts in a pattern to match the maskO In a focused condition, as; shown, the detector array 26 receives an lmage converging nearly to a pointO The detector array 26 is divided.into a top half 26a and a bottom half 26b by a line 26c whlch represents the act that the detector array consists of light detecting elements at 26a and 26b, respectivelyO
An alternative embodiment of the present invention would replace the spherical lens element 20 with a spherical Fresnel lens eiement 3~0 In the near to focus, pre and post focus conditions, half-moon images resembling the symbolic images at 2~ and 2~ would exist on the focusing light detector array 26.
~lowever~ at a focused condition~ a round image would be formed, shown by a d~tted line~ at 26d~ This would allow a greater amount of light to fall on the 2~ two detector elements 26a and 26b to produce a stronger and balanced indication of light output on the detector array which would allow the focusing detector sys.tem to work in a balanced but comparatively noise free condition when the recording media is in a focused condition with respect to the objective lens.
Referring now to ~igure 2, another embodiment of the invention is ~hown in which a light beam 12 enters the system in a collimated condition, shown symbolically at l~o The beam impinges on a knife edge 16 where a partial beam is formed with the portion of the image blocked by the knife edge sho~m illustratively at 180 This embodiment is different from the previous embodi-ment in that a cylindrical lens 40 forms ~he optical element of the systemO A
half-moon image is shown symbolically at 42 to illustrate ~he partial light beam traversing through the cylindrical lens element 400 An image at 44 and an image at 48 illustrate the pre and post focus image conditions in the near out of focus condition using a cylindrical lens. The beam still has a half-moon shape, although it is in a slightly flattened condition because of use of the cyli.ndrical lens 40 as compared to the true half-moon shape of the images shownlq at 24 and 2~ as a resu].t of using the spherical lens 20, as shown in Figure lo A split detector array at 46 having a pair of light detecting elements 46a and 46b receives the light beam in the systemO In the focused condition, the cylindrical lens forms a bar shaped light element at 52. Because the bar shaped light element or image 52 in the focused condition would tend to fall between the two light detecting elements at 46a and 46b, the light detecting array 46 is disposed at an angle, shown schematically at 50, with respect to the vertical axis of the cylindrical lens 40 which generatas the bar shaped light element or image 520 The result of this is that the bar shaped light image then tends to fall symmetrically 0l1 both light detecting elements 46a andZ0 46b, ~'hllS, the output signals from light detecting elements 46a and 46b would b~ in a balanced condition representative of an approximately equal amount of l.ight. alling on both light detector elementsu However, the result is also that in the out of focus conditiong the half-moon image falling on the light detec-tor array 46 also tends to have some of the half-moon image fall on the unde-sired light detector elementO However, the majority of the light beam still impinges on the desired light detector element so that the out of focus condi-2~
tion can be easily detected by the strong imbalance in the output of the light detector elements indicating an imbalance condition of the light beam falling on the elementsO
Referring now to Figure 3, another embodiment of the invention is shown using a cylindrical Fresnel lens element 700 The cylindrical Fresnel lens element is characterized by having individual Fresnel lens elements 72 longi~
tudinal].y displaced in the same axis as the axis of the cylindrical Fresnel lens. The result of using a cylindrical Fresnel lens element 70 is similarly the creation of half-moon shaped partial beam images at 74 and 80 sho~ling, respectively, a pre and post focus condition of the objective lens element with respect to the optical mediaO ~owever~ the in focus light beam produces a wider light bar element or image 78 as a result of using the cylindrical Fres-nel lens 70 than the light bar element or image 52, shown in Figure 2 with the conventiona.l cylindrical lens elementO Figure ~a illustrates the system of the embodiment shown in Figure 3 with the cylindrical Fresnel lens element 70 hav-ing individual elements 720 The light beam coming from an individual Fresnel lens 72 arrives on the light detector array 76 in a focused condition to pro-~uce a comparatively wide bar light image shown at 78.
It i5 noted that the half-moon or partial beam focusing system of the present invention only needs a split or dual light detector and not a quad-rature light detector which represents an advantage in detector simplicity. It~s also noted that the half~moon or partial beam focusing system needs only a single focusing lens in connection with the detector array and the knife edge elementO Thus, the knife edge element or opaque material which creates the partial beam is clearly a more simple optical element than the provision of the present additional lenses needed with astig~atic focusingO Thus, the present half-moon focusing system may work with only a single lens and a ~nife edge ~32~i~
rather than with the two lenses needed for astig~atic focusing~
The present invention operates accordlng to certain ~eneral prin-ciples Q~optical physics and, accordingly, there are many alternative embodi-ments within the scope of the present inventionO In the illustrative embodi-ment of the invention using half-moon focus sensing, the incoming light beam is simply divided into top and bottom halves. Focus sensing according to the present invention works because the focus sensing beam performs a center sym-metric inversion in the plane of the detector array when the system is in focus.
The center symmetric inversion of the focus sensing light beam is always pres-lQ ent but, if the system is out of focus the detector array is on one side or the other of th0 center symmetric inversionO In general~ the most basic embodi-ment of the invention is to place a mask with a pattern having central symme-try in an incoming collimated focus sensing light beam. Then a detector array that matches the mask pattern is plaGed in the expected focal plane for the in ~qcus condition~ The detector array elements are then used to produce a differ-ontial signal when the light pattern reverses itselfO
Examples of appropriate central symmetry mask patterns would be those using centrally radiating spokes including those with symmetric patterns of curved spoke~u Various patterns including symmctry about concentric circles can be superimposed on appropriate spoke patterns. The spoke patterns can create $eg~ents whi!ch may be two in number, as in half-moon focusing, or 6, 10, 1~ etc.
The segments need not be the same size~ just centrally symmetric. Of rourse numerous other centrally symmetric patterns can be used for a mask~
The various mask patterns have different advantages and disadvantages.
The half-moon ~ask pattern is probably the simplest to implement and allows the detector array electronics to be simpleO llowever, a disadvantage can be that F~
align,m,ent of the detector array is s,ensitive in the direction perpendicular to the line or terminator separating the halves of the "moon". This sensitivity is because of the small light spot size at focus and is one of the reasons for employing the Fresnel lens embodimentO Thus, a more complex segmen~ed mask pattern could also be desirable because it would be less sensitive to linear motion than the half-moon embodiment and would have a larger in focus light spot becaus;e of internal beam diffraction from the maskO
For example, Figure 5 sho~s a centrally symmetric mask pattern 100 which would be suitable according to the present invention when used with a matching light detector patternO ~his mask has ten segments or pie-shaped slices every other one of which blocks or masks lighto
which ~ouldbe sY~metrical about the axis of the light detector array.
In accordance with a broad aspect of the invention, there is pro-vided a partial beam focus sensing system in optical recordin~ comprising;
lens element for receiving a collimated light beam in an optical recording 5y5~
tem representative of light reflected from optical recording rnedia, a centrallysymmetric mask element proxima.te to said lens element for eliminating a portionof s.aid light beam and transmitting a partial light beam, and a light detector array comprising at least two light detecting elements matched to said mask element and disposed to receive said partial beam from said lens elementO
~he invention will now be further described in conjunction with the accompanying drawings, in which: Figure 1 shows a first embodiment of the pres.ent invention using a spherical lens and a knife edgeO Figure 2 is an illustr~tion ofanother embodiment on the present invention using a knife edge and a cylindrical lensO Figure 3 is a showing of another embodiment of the present invcntion using a cylindrical Fresnel lens. Figure 4a is a side plan view o~ the embodiment of the invention shown in Figure 3 to illustrate the generation of a bar pattern by the cylindrical Fresnel lensO Figure 4b is a top view of the embodiment of the invention shown in Figure 3~ Figure 5 shows ~ central symmetric mask element.
Referring now to Figure 1, an embodiment 10 of the present invention i~s shown using a collimated circular light beam 12 passing into the system as 5hown sche~atically at 1~. A mask such as knife edge element 16 partially ob-structs a portion of the beam creating a half-moon image l~ on the knife edge element. ~he knife edge element may be placed on a spherical lens element 20 or in front of it or behind it, but, it is most desirable that it be placed in a proximate position with respect to the spherical lens element 20~ Other mask 32~
patterns than the simple knife edge are possible within the scope of the pre-sent invention so long as the mask pattern is center symmetric. The knife edge pattern shown in Figure l i5 center symmetricO
The half-moon image passing through the spherical lens element 20 is shown diagrammatically at 220 A ha].f moon image at 24 and an upside do~,m half-moon image at 28 illustrate the pre and post focused images formed by the par-tial or half-beam passing through the spherical lens element 2Q to illustrate the shape of the image generated on the partial ~eam, light detector array 260 The detector array has detector elem~nts in a pattern to match the maskO In a focused condition, as; shown, the detector array 26 receives an lmage converging nearly to a pointO The detector array 26 is divided.into a top half 26a and a bottom half 26b by a line 26c whlch represents the act that the detector array consists of light detecting elements at 26a and 26b, respectivelyO
An alternative embodiment of the present invention would replace the spherical lens element 20 with a spherical Fresnel lens eiement 3~0 In the near to focus, pre and post focus conditions, half-moon images resembling the symbolic images at 2~ and 2~ would exist on the focusing light detector array 26.
~lowever~ at a focused condition~ a round image would be formed, shown by a d~tted line~ at 26d~ This would allow a greater amount of light to fall on the 2~ two detector elements 26a and 26b to produce a stronger and balanced indication of light output on the detector array which would allow the focusing detector sys.tem to work in a balanced but comparatively noise free condition when the recording media is in a focused condition with respect to the objective lens.
Referring now to ~igure 2, another embodiment of the invention is ~hown in which a light beam 12 enters the system in a collimated condition, shown symbolically at l~o The beam impinges on a knife edge 16 where a partial beam is formed with the portion of the image blocked by the knife edge sho~m illustratively at 180 This embodiment is different from the previous embodi-ment in that a cylindrical lens 40 forms ~he optical element of the systemO A
half-moon image is shown symbolically at 42 to illustrate ~he partial light beam traversing through the cylindrical lens element 400 An image at 44 and an image at 48 illustrate the pre and post focus image conditions in the near out of focus condition using a cylindrical lens. The beam still has a half-moon shape, although it is in a slightly flattened condition because of use of the cyli.ndrical lens 40 as compared to the true half-moon shape of the images shownlq at 24 and 2~ as a resu].t of using the spherical lens 20, as shown in Figure lo A split detector array at 46 having a pair of light detecting elements 46a and 46b receives the light beam in the systemO In the focused condition, the cylindrical lens forms a bar shaped light element at 52. Because the bar shaped light element or image 52 in the focused condition would tend to fall between the two light detecting elements at 46a and 46b, the light detecting array 46 is disposed at an angle, shown schematically at 50, with respect to the vertical axis of the cylindrical lens 40 which generatas the bar shaped light element or image 520 The result of this is that the bar shaped light image then tends to fall symmetrically 0l1 both light detecting elements 46a andZ0 46b, ~'hllS, the output signals from light detecting elements 46a and 46b would b~ in a balanced condition representative of an approximately equal amount of l.ight. alling on both light detector elementsu However, the result is also that in the out of focus conditiong the half-moon image falling on the light detec-tor array 46 also tends to have some of the half-moon image fall on the unde-sired light detector elementO However, the majority of the light beam still impinges on the desired light detector element so that the out of focus condi-2~
tion can be easily detected by the strong imbalance in the output of the light detector elements indicating an imbalance condition of the light beam falling on the elementsO
Referring now to Figure 3, another embodiment of the invention is shown using a cylindrical Fresnel lens element 700 The cylindrical Fresnel lens element is characterized by having individual Fresnel lens elements 72 longi~
tudinal].y displaced in the same axis as the axis of the cylindrical Fresnel lens. The result of using a cylindrical Fresnel lens element 70 is similarly the creation of half-moon shaped partial beam images at 74 and 80 sho~ling, respectively, a pre and post focus condition of the objective lens element with respect to the optical mediaO ~owever~ the in focus light beam produces a wider light bar element or image 78 as a result of using the cylindrical Fres-nel lens 70 than the light bar element or image 52, shown in Figure 2 with the conventiona.l cylindrical lens elementO Figure ~a illustrates the system of the embodiment shown in Figure 3 with the cylindrical Fresnel lens element 70 hav-ing individual elements 720 The light beam coming from an individual Fresnel lens 72 arrives on the light detector array 76 in a focused condition to pro-~uce a comparatively wide bar light image shown at 78.
It i5 noted that the half-moon or partial beam focusing system of the present invention only needs a split or dual light detector and not a quad-rature light detector which represents an advantage in detector simplicity. It~s also noted that the half~moon or partial beam focusing system needs only a single focusing lens in connection with the detector array and the knife edge elementO Thus, the knife edge element or opaque material which creates the partial beam is clearly a more simple optical element than the provision of the present additional lenses needed with astig~atic focusingO Thus, the present half-moon focusing system may work with only a single lens and a ~nife edge ~32~i~
rather than with the two lenses needed for astig~atic focusing~
The present invention operates accordlng to certain ~eneral prin-ciples Q~optical physics and, accordingly, there are many alternative embodi-ments within the scope of the present inventionO In the illustrative embodi-ment of the invention using half-moon focus sensing, the incoming light beam is simply divided into top and bottom halves. Focus sensing according to the present invention works because the focus sensing beam performs a center sym-metric inversion in the plane of the detector array when the system is in focus.
The center symmetric inversion of the focus sensing light beam is always pres-lQ ent but, if the system is out of focus the detector array is on one side or the other of th0 center symmetric inversionO In general~ the most basic embodi-ment of the invention is to place a mask with a pattern having central symme-try in an incoming collimated focus sensing light beam. Then a detector array that matches the mask pattern is plaGed in the expected focal plane for the in ~qcus condition~ The detector array elements are then used to produce a differ-ontial signal when the light pattern reverses itselfO
Examples of appropriate central symmetry mask patterns would be those using centrally radiating spokes including those with symmetric patterns of curved spoke~u Various patterns including symmctry about concentric circles can be superimposed on appropriate spoke patterns. The spoke patterns can create $eg~ents whi!ch may be two in number, as in half-moon focusing, or 6, 10, 1~ etc.
The segments need not be the same size~ just centrally symmetric. Of rourse numerous other centrally symmetric patterns can be used for a mask~
The various mask patterns have different advantages and disadvantages.
The half-moon ~ask pattern is probably the simplest to implement and allows the detector array electronics to be simpleO llowever, a disadvantage can be that F~
align,m,ent of the detector array is s,ensitive in the direction perpendicular to the line or terminator separating the halves of the "moon". This sensitivity is because of the small light spot size at focus and is one of the reasons for employing the Fresnel lens embodimentO Thus, a more complex segmen~ed mask pattern could also be desirable because it would be less sensitive to linear motion than the half-moon embodiment and would have a larger in focus light spot becaus;e of internal beam diffraction from the maskO
For example, Figure 5 sho~s a centrally symmetric mask pattern 100 which would be suitable according to the present invention when used with a matching light detector patternO ~his mask has ten segments or pie-shaped slices every other one of which blocks or masks lighto
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A partial beam focus sensing system in optical recording comprising:
a lens element for receiving a collimated light beam in an optical recording system representative of light reflected from optical recording media, a cen-trally symmetric mask element proximate to said lens element for eliminating a portion of said light beam and transmitting a partial light beam, and a light detector array comprising at least two light detecting elements matched to said mask element and disposed to receive said partial beam from said lens element.
a lens element for receiving a collimated light beam in an optical recording system representative of light reflected from optical recording media, a cen-trally symmetric mask element proximate to said lens element for eliminating a portion of said light beam and transmitting a partial light beam, and a light detector array comprising at least two light detecting elements matched to said mask element and disposed to receive said partial beam from said lens element.
2. The system of claim 1 in which said lens element is, a spherical Fresnel lens.
3. The system of claim 1 in which said lens element is a cylindrical lens.
4. The system of claim 3 in which said light detector array is disposed at an angle with respect to the vertical axis of said cylindrical lens.
5. The system of claim 1 in which said lens element is a cylindrical Fresnol lens.
6. The system of claim 5 in which said light detector array is disposed at an angle with respect to the vertical axis of said cylindrical Fresnel lens.
7. The system of claim 1, 2 or 3 in which said mask element is a knife edge.
8. The system of claim 4, 5 or 6 in which said mask element is a knife edge.
9. The system of claim 1, 2 or 3 in which said mask element has a plurality of spokes radiating from the center to divide the light beam into a number of segments, every other one of which blocks light.
10. The system of claim 4, 5 or 6 in which said mask element has a plurality of spokes radiating from the center to divide the light beam into a number of segments, every other one of which blocks light.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US342,459 | 1982-01-25 | ||
| US06/342,459 US4441175A (en) | 1982-01-25 | 1982-01-25 | Partial beam focus sensing in an optical recording system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1183260A true CA1183260A (en) | 1985-02-26 |
Family
ID=23341921
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000413900A Expired CA1183260A (en) | 1982-01-25 | 1982-10-21 | Partial beam focus sensing in an optical recording system |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4441175A (en) |
| EP (1) | EP0084703B1 (en) |
| JP (1) | JPS58130447A (en) |
| AU (1) | AU549758B2 (en) |
| CA (1) | CA1183260A (en) |
| DE (1) | DE3279403D1 (en) |
Families Citing this family (19)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3219503C2 (en) * | 1982-05-25 | 1985-08-08 | Ernst Leitz Wetzlar Gmbh, 6330 Wetzlar | Device for automatic focusing on objects to be viewed in optical devices |
| US4684799A (en) * | 1983-09-19 | 1987-08-04 | Ricoh Company, Ltd. | Focus detection method involving cutting more than half of light beam reflected from disc |
| US4670869A (en) * | 1984-01-03 | 1987-06-02 | Magnetic Peripherals Inc. | Switching laser beam apparatus with recombined beam for recording |
| EP0180767B1 (en) * | 1984-10-11 | 1990-01-31 | Hitachi, Ltd. | Optical lens device |
| US4672188A (en) * | 1985-08-05 | 1987-06-09 | International Business Machines Corporation | Focus detector for optical apparatus |
| EP0283002B1 (en) * | 1987-03-17 | 1994-02-16 | Matsushita Electric Industrial Co., Ltd. | Optical head |
| EP0334601B1 (en) * | 1988-03-25 | 1994-09-07 | Tosoh Corporation | Error detecting device for optical head |
| JPH01311428A (en) * | 1988-06-09 | 1989-12-15 | Matsushita Electric Ind Co Ltd | Optical head device and optical information device using the same |
| US5036185A (en) * | 1988-12-27 | 1991-07-30 | Kabushiki Kaisha Toshiba | Optical apparatus for detecting a focusing state |
| JPH02201741A (en) * | 1989-01-31 | 1990-08-09 | Toshiba Corp | Focus detector |
| US4998011A (en) * | 1989-11-17 | 1991-03-05 | Applied Magnetics Corporation | Flat plate focus sensing apparatus |
| GB2248989B (en) * | 1990-10-15 | 1995-05-24 | Applied Magnetics Corp | Focus sensing apparatus and method |
| US5245174A (en) * | 1990-10-15 | 1993-09-14 | Applied Magnetics Corporation | Focus sensing apparatus utilizing a reflecting surface having variable reflectivity |
| US5255139A (en) * | 1991-03-18 | 1993-10-19 | Applied Magnetics Corporation | Ferrite capped Winchester-style slider |
| US5210929A (en) * | 1991-03-18 | 1993-05-18 | Applied Magnetics Corporation | Method of making a ferrite capped Winchester-style slider |
| US5331622A (en) * | 1991-05-28 | 1994-07-19 | Applied Magnetics Corporation | Compact optical head |
| US5646778A (en) * | 1991-05-28 | 1997-07-08 | Discovision Associates | Optical beamsplitter |
| SE520605C2 (en) * | 2001-06-29 | 2003-07-29 | Flir Systems Ab | Optical system comprising a detector and a mixer with decentering function |
| US10746905B1 (en) * | 2019-09-23 | 2020-08-18 | Rosemount Aerospace Inc. | Optical systems with toroidal fresnel lenses |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL7414776A (en) * | 1974-11-13 | 1976-05-17 | Philips Nv | DEVICE FOR READING A REGISTRATION CARRIER WITH AN OPTICAL INFORMATION STRUCTURE. |
| NL182257C (en) * | 1974-12-23 | 1988-02-01 | Philips Nv | DEVICE FOR READING A FLAT REFLECTING REGISTRATION CARRIER TO WHICH INFORMATION HAS BEEN APPLIED IN AN OPTICALLY READABLE STRUCTURE. |
| FR2313716A1 (en) * | 1975-06-03 | 1976-12-31 | Thomson Brandt | OPTICAL READING SYSTEM BY REFLECTION OF AN INFORMATION MEDIA |
| FR2325953A1 (en) * | 1975-09-29 | 1977-04-22 | Thomson Brandt | OPTICAL FOCUSING SENSOR AND FOCUSING DEVICE INCLUDING SUCH A SENSOR |
| JPS5328404A (en) * | 1976-08-27 | 1978-03-16 | Mitsubishi Electric Corp | Optical information re producer |
| NL7703077A (en) * | 1977-03-22 | 1978-09-26 | Philips Nv | DEVICE FOR READING A RADIATION-REFLECTING RECORD CARRIER. |
| JPS54116904A (en) * | 1978-03-03 | 1979-09-11 | Nippon Telegr & Teleph Corp <Ntt> | Optical information reader |
| JPS5746217A (en) * | 1980-09-03 | 1982-03-16 | Matsushita Electric Ind Co Ltd | Light beam focusing device |
| JPS57108811A (en) * | 1980-12-26 | 1982-07-07 | Hitachi Ltd | Optical focus position detector |
| US4521680A (en) * | 1981-07-20 | 1985-06-04 | Tokyo Shibaura Denki Kabushiki Kaisha | System for focusing a light beam on a light reflecting surface |
-
1982
- 1982-01-25 US US06/342,459 patent/US4441175A/en not_active Expired - Fee Related
- 1982-10-21 CA CA000413900A patent/CA1183260A/en not_active Expired
- 1982-11-11 DE DE8282306027T patent/DE3279403D1/en not_active Expired
- 1982-11-11 EP EP82306027A patent/EP0084703B1/en not_active Expired
- 1982-11-17 JP JP57200493A patent/JPS58130447A/en active Pending
- 1982-11-29 AU AU90961/82A patent/AU549758B2/en not_active Ceased
Also Published As
| Publication number | Publication date |
|---|---|
| DE3279403D1 (en) | 1989-03-02 |
| EP0084703A3 (en) | 1985-10-16 |
| JPS58130447A (en) | 1983-08-03 |
| EP0084703B1 (en) | 1989-01-25 |
| AU549758B2 (en) | 1986-02-13 |
| AU9096182A (en) | 1983-08-04 |
| EP0084703A2 (en) | 1983-08-03 |
| US4441175A (en) | 1984-04-03 |
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