CA1116294A - Apparatus for reading an optical radiation-reflecting record carrier - Google Patents
Apparatus for reading an optical radiation-reflecting record carrierInfo
- Publication number
- CA1116294A CA1116294A CA299,001A CA299001A CA1116294A CA 1116294 A CA1116294 A CA 1116294A CA 299001 A CA299001 A CA 299001A CA 1116294 A CA1116294 A CA 1116294A
- Authority
- CA
- Canada
- Prior art keywords
- radiation
- focussing
- read
- spot
- detectors
- 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
- G11B7/08—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
- G11B7/0917—Focus-error methods other than those covered by G11B7/0909 - G11B7/0916
-
- 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
- G11B7/0917—Focus-error methods other than those covered by G11B7/0909 - G11B7/0916
- G11B2007/0924—Skewed beams methods (using an angled beam, i.e. a beam which is reflected from the disc at an angle different from 90°)
Abstract
ABSTRACT:
An apparatus is described for reading an optical radiation-reflecting information carrier, which apparatus com-prises an opto-electronic focussing error detection system. The radiation path of the read beam which is directed towards the information carrier includes a radiation deflecting element.
The focussing beam which is derived from the radiation beam by said element co-operates with two focussing detectors, the difference between the output signals of the focussing detector being determined by the degree of focussing of the read beam on the information structure.
An apparatus is described for reading an optical radiation-reflecting information carrier, which apparatus com-prises an opto-electronic focussing error detection system. The radiation path of the read beam which is directed towards the information carrier includes a radiation deflecting element.
The focussing beam which is derived from the radiation beam by said element co-operates with two focussing detectors, the difference between the output signals of the focussing detector being determined by the degree of focussing of the read beam on the information structure.
Description
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The invention relates to an apparatus for reading an optical radiation-reflecting information carrier, which apparatus comprises a radiation source which produces a read beam, an objective system for focussing the read beam to a read spot on the information structure of the information car~
rier and for imaging the read spot on a radiation-sensitive information detector whose output signal represents the infor-mation, and an opto-electronic focussing error detection system for determining a deviation between the desired and the actual position of the plane of focussing of the objective system, which focussing error detection system comprises two radiation-sensitive focussing detectors which co-operate with a narrow focussing beam, the difference in the output signals of the focussing detectors providing an indication about said deviation.
In this respect "focussing beam" is to be under-stood to mean an auxiliary beam with the aid of which the focussing errors of the read beam are detected. The "focuss-ing detectors" are radiation-sensitive detectors which co-operate with said auxiliary beam.
Such apparatus is described in Canadian Patent1,017,858 - Xramer et al September 20, 1977 - PHN 6295C.
This apparatus is for example used for reading an information carrier on which a (colour) television programme is stored.
The information structure then consists of a multitude of areas alternating with intermediate areas which are arranged in accordance with a spiral track, which areas and inter-mediate areas have a different influence on a read beam. The : 2 information is then for example contained in the lengths of the areas and those of the intermediate areas. To obtain a sufficiently long playing time the details of the information s~ructure will be very small for limited dimensions of the information carrier. For example, if a 30-minute television programme is stoxed on one side of a disc-shaped round infor-mation carrier in an annular area with an outer radius of approx. 15 cm and an inner radius of approx. 6 cm, the width of the tracks will be approx. 0.5/um and the average length of the areas and of the intermediate areas will be approxi-mately l/um.
- In order to enable such minute details to be read an objective system with a fairly large numerical aperture must be employed. However, the depth of focus of such an objective system is small. As in the read apparatus varia-tions in the distance between the plane of the information structure and the objective system may occur which are greater than the depth of focus, steps must be taken to enable these variations to be detected and to enable the focussing to be corrected.
In the apparatus in accordance with the said Canadian Patent a narrow beam is therefore split from the read beam before this beam enters the objective systemO The narrow beam passes obliquely through the objective system.
After this beam has been reflected by the information carrier, it traverses the objective system for a second time and then forms a radiation spot, the focussing spot, in the plane of the two focussing detectors. The symmetry of the focussing spot relative the focussing detectors then provides : .:
~7~ l7 an indication of the degree of focussing of the read beam on the information structure.
In the known read apparatus a number of additional e]ements are needed, such as a semitransparent mirror, a fully reflecting mirror for the formation of the focussing beam, and an additional lens for focussing the auxiliary beam in the focal plane of the objective system. The positions of the additional elements are very critical.
It is an object of the present invention to provide an apparatus of the type mentioned in the preamble in which a minimal number of additional elements is needed for focussing detection. The apparatus in accordance with the invention is characterized in that the radiation path of the - rèad beam on one side of the optical axis of the objective system includes a radiation-deflecting element whose surface area is substantially smaller than the cross-sectional area of the read beam.
Owing to the radiation-deflecting element a small portion of the read beam is given an other direction than the rest of the read beam. Thls portion is focussed on the focussing d~tectors by the objective system, the position of the radiation spot, whlch is formed in the plane of the focussing detectors, relative to the detectors being governed by the degree o`f focussing of the read beam on the in~ormation~
surface of the information carrier.
Preferably, the information detector and the focussing detectors are disposed in the same plane perpendicular to the optical axis.
The radiation~deflecting element may be constituted by an optical wedge or by a diffraction grating.
A first cmbodiment of an apparatus in accordance - ~4-,: , .
27.7.1"7 with the invention is characterized in that the radiation path of the radiation beam which is directed towards the informatlon carrier includes a radiation deflecting element, in such a way that the radiation which is incident on the radiation deflecting element forms an additional radiation spot on the information structure besides the read spot, which radiation spot i5 imaged on the focussing detectors by the objective system.
As a radiation source a gas laser may be used, such as a helium-neon laser. In that case the distance between the objective system and the plane of the detectors is comparatively great. The focussing spot is then situated at a comparatively great distance from the read spot image.
It is alternatively possible to employ a (semi-conductor) diode laser as radia-tion source. Such a laser may also be used as information detector. In that case the radiation which is reflected by the information carrier need not be separated from the radiation which is directed towards the information carrier. The optical read unit can then be kept simple and compact. Furthermore, the objective system may then have a low magnification. If in such a read apparatus a focussing beam is formed by means of a deflecting element, the focussing spot may be situated so closely to the image of the read spot that the focussing detectors cannot be arranged within the required distance to the diode laser. If - it were possible to arrange the focussing detectors in the desired position, a part o~ the read beam would already be incident on the focussing detectors in the case of a slight , focussing error of the read beam, resulting in an error in the focussing control signal.
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The invention relates to an apparatus for reading an optical radiation-reflecting information carrier, which apparatus comprises a radiation source which produces a read beam, an objective system for focussing the read beam to a read spot on the information structure of the information car~
rier and for imaging the read spot on a radiation-sensitive information detector whose output signal represents the infor-mation, and an opto-electronic focussing error detection system for determining a deviation between the desired and the actual position of the plane of focussing of the objective system, which focussing error detection system comprises two radiation-sensitive focussing detectors which co-operate with a narrow focussing beam, the difference in the output signals of the focussing detectors providing an indication about said deviation.
In this respect "focussing beam" is to be under-stood to mean an auxiliary beam with the aid of which the focussing errors of the read beam are detected. The "focuss-ing detectors" are radiation-sensitive detectors which co-operate with said auxiliary beam.
Such apparatus is described in Canadian Patent1,017,858 - Xramer et al September 20, 1977 - PHN 6295C.
This apparatus is for example used for reading an information carrier on which a (colour) television programme is stored.
The information structure then consists of a multitude of areas alternating with intermediate areas which are arranged in accordance with a spiral track, which areas and inter-mediate areas have a different influence on a read beam. The : 2 information is then for example contained in the lengths of the areas and those of the intermediate areas. To obtain a sufficiently long playing time the details of the information s~ructure will be very small for limited dimensions of the information carrier. For example, if a 30-minute television programme is stoxed on one side of a disc-shaped round infor-mation carrier in an annular area with an outer radius of approx. 15 cm and an inner radius of approx. 6 cm, the width of the tracks will be approx. 0.5/um and the average length of the areas and of the intermediate areas will be approxi-mately l/um.
- In order to enable such minute details to be read an objective system with a fairly large numerical aperture must be employed. However, the depth of focus of such an objective system is small. As in the read apparatus varia-tions in the distance between the plane of the information structure and the objective system may occur which are greater than the depth of focus, steps must be taken to enable these variations to be detected and to enable the focussing to be corrected.
In the apparatus in accordance with the said Canadian Patent a narrow beam is therefore split from the read beam before this beam enters the objective systemO The narrow beam passes obliquely through the objective system.
After this beam has been reflected by the information carrier, it traverses the objective system for a second time and then forms a radiation spot, the focussing spot, in the plane of the two focussing detectors. The symmetry of the focussing spot relative the focussing detectors then provides : .:
~7~ l7 an indication of the degree of focussing of the read beam on the information structure.
In the known read apparatus a number of additional e]ements are needed, such as a semitransparent mirror, a fully reflecting mirror for the formation of the focussing beam, and an additional lens for focussing the auxiliary beam in the focal plane of the objective system. The positions of the additional elements are very critical.
It is an object of the present invention to provide an apparatus of the type mentioned in the preamble in which a minimal number of additional elements is needed for focussing detection. The apparatus in accordance with the invention is characterized in that the radiation path of the - rèad beam on one side of the optical axis of the objective system includes a radiation-deflecting element whose surface area is substantially smaller than the cross-sectional area of the read beam.
Owing to the radiation-deflecting element a small portion of the read beam is given an other direction than the rest of the read beam. Thls portion is focussed on the focussing d~tectors by the objective system, the position of the radiation spot, whlch is formed in the plane of the focussing detectors, relative to the detectors being governed by the degree o`f focussing of the read beam on the in~ormation~
surface of the information carrier.
Preferably, the information detector and the focussing detectors are disposed in the same plane perpendicular to the optical axis.
The radiation~deflecting element may be constituted by an optical wedge or by a diffraction grating.
A first cmbodiment of an apparatus in accordance - ~4-,: , .
27.7.1"7 with the invention is characterized in that the radiation path of the radiation beam which is directed towards the informatlon carrier includes a radiation deflecting element, in such a way that the radiation which is incident on the radiation deflecting element forms an additional radiation spot on the information structure besides the read spot, which radiation spot i5 imaged on the focussing detectors by the objective system.
As a radiation source a gas laser may be used, such as a helium-neon laser. In that case the distance between the objective system and the plane of the detectors is comparatively great. The focussing spot is then situated at a comparatively great distance from the read spot image.
It is alternatively possible to employ a (semi-conductor) diode laser as radia-tion source. Such a laser may also be used as information detector. In that case the radiation which is reflected by the information carrier need not be separated from the radiation which is directed towards the information carrier. The optical read unit can then be kept simple and compact. Furthermore, the objective system may then have a low magnification. If in such a read apparatus a focussing beam is formed by means of a deflecting element, the focussing spot may be situated so closely to the image of the read spot that the focussing detectors cannot be arranged within the required distance to the diode laser. If - it were possible to arrange the focussing detectors in the desired position, a part o~ the read beam would already be incident on the focussing detectors in the case of a slight , focussing error of the read beam, resulting in an error in the focussing control signal.
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7 7.1~-~7~
2~
In order to avoid these problems, in accordance with a further characteris~ic feature of the first ernbodlment of the in~ention, in which the radiation-deflecting element is an optical wedge, a second optical we~ge may be included in the radiation pa-th of the sub-beam which is formed by the first optical wedge and which is reflected by the information carrier.
Preferably, the second optical wedge is then disposed - within the image of the first optical wedge which image is formed with the aid of the information carrier and the lens element of the objective system nearest the informa~on carrier. Thi$ means that the area of the second optical wedge - is smaller than or equal to the area of the first optical - wedge.
The objecti~e system may comprise a plurality of lens elements or one lens elcment. In the last mentioned case thel~ens element of the objective system nearest the information carrier" is the objective system itself.
The second optical wedge, whose angle of refraction is preferably greater than that of the first optical wedge, deflects the focussing beam reflected by the information carrier additi.onally relative to the read beam, so that the distance between the focusslng spot and the read spot increases.
In order to ensur0 that the second wedge always remains in the image of the first wedge independently of the position of the information carrier relative to the obJective system, the optical wedges, in accordance with a further characteristic feature of the lnvention, are disposed in the _6-, .. . :, . .
27.7.1~7l bac~ focal plane of the lens element of the objective system nearest the information carrier.
~ second embodiment of an apparatus in æccordance with the invention is characterized in that a radiation-de-flecting element is disposed in the path of the read beam - which is reflected by the information carrier and which originates from the read spot, in such a way that the radiation which is incident on the radiation deflecting element is deflected to the focussing detectors.
In accordance with a further characteristic feature of an apparatus in accordance with the invention the dividing line between the focussing detectors makes an acute angle with the direction in which the focussing spot moves owing to focussing errors. By means of this step it is avoided that the position of the focussing detector is very critical.
The radiation-deflecting elements which are used are substantially smaller than the cross-section of- the read beam. As a result of this the si~e of the read spot and thus - the actual information read-out is not affected significantlyO
The slight influence of the radiation-deflecting elements on.
the read-out can further be reduced by arranging for the line of interconnection between the optical axis of the objective system and the radiation-deflectlng element to make an angle of 45 with the direction in which an information track of ` the information carrier is read.
The invention will now be described in more detail~
on the basis of an apparatus which employs a dlode laser as radiati.on source and optical wedges as radiation~deflecting element. In this description reference is made to the ~7~
27.7.1~77 drawing, in which:
- Fig. 1 shows a firs-l; embodiment of an apparatus in accordance with the'invention, Figs. 2a,and 2b show different orientations of the focussing detectors relative to the directions of movement of the focussing spot, and ' ~igs. 3a and 3b show how,the focussing spot moves rela*ive to the focussing detectors when the optical wedges are rotated relative to the optical axis, and Fig. 4 shows a second embodiment of an apparatus in accordance with the invention.
Fig. 1 shows a part of a round disc-shaped informaticn carrier 1 in radial cross-section. The information structure is for example a phase structure and comprises a multitude of concentric or quasi-concentric tracks 2, which tracks consist of a sequence of areas and intermediate areas. The areas ma~
for example be situated at a different level in the information carrier than the intermediate areas. The information may for - example be a colour television programme, but it may alterna-tively be other information? such as a multitude of different images or digital information. Preferably, the information structure is situated at the back of the information carrier 1.
The information carrier is illuminated by a read beam 3 produced by a diode laser l~. An objective system, which consists of a single lens, or as shown in Fig. 1, of` two lenses ~1 and L2 focusses the read beam to a read spot ~i on the information structure. The read beam 3 is then reflected by the information s-tructure and upon rotation of the information carrier it is modulated in accordance with the information which is contained in a ~rack portion to be read.
Pl~L~I ~7~
4 27.'7.'1'~'7'7 - Af`ter reflection the read beam traverses the objecti~e system for a second time, an image ~'i being formed of' the read spot Vi. At the location of the radiation spot ~'i a'~detector is situated which converts the modulated read beam into an elec~rical signal Si.
If the radiation source is a diode laser it is possible, as is described in the published German Patent Application No. 2,2~4,119, to use this diode laser as a detector. Depending on the intensity of the reflected read beam ' the electrical resistance across the diode ]aser or the intensity of the radiation emit'ted from the rear of the diode laser will vary. When a diode laser is used as radiation source no beam-splitting element is necessary'to separate the , modulated read beam reflected by the information carrier from the unmodulated read beam which is dirccted towards i the information carrier.
' In accordance with the invention a small optical wedge 5 is disposed in the path of'the read beam 3. This wedge ' splits-off a sub-beam 6 (represented by dashed lines in Fig. 1) from the,read beam. This sub-beam is focussed to a radiation spot ~f on the information structure by the lens,L1. After ~
reflection at the information structure and a second passage through the objective system the focussing beam forms a radiation spot V'f(focussing spot) on an assembly of two focussing detec*ors 7 and 8. If the distance betwcen the plane of the tracks 2 and the objective system is correct, the focussing spot is symmetrical relative to the focussing detectors, so that both detectors receive an equal amo1lnt of radiatlon and -the output signals S7 and S~ are equal. If the plane o~ the information structure moves downwards relative _9_ 2~.7.1'377 to the objective system, the point where the principal ray of the reflected beam 6 enters the lens L1 will be shifted towards the optical axis 00~. The deflection of the beam 6 by the objective system is then slightly less and the focussing spot Vlf moves to the left. The detector 7 then receives more radiation than the detector ~. If the plane of the tracks 2 moves upwards, the reverse takes place, and the detector 7 receives less radiation than the detector 8.
The signals S7 and Sg from the detectors are applied to an electronic circuit 9. In this circuit the signals are subtracted from each other in a manner known per se. ~t the output of the circuit 9 a focussing control signal rf is then obtained with which the focussing of the objective system can be corrected, for example by moving this system along the optical axis 00'. If the radiation source is a diode laser, the optical read unit may also be moved along the optioal axis.
The optical wedge, or a diffraction grating, is disposed in the path of~the read beam which is directed towards the information carrier, and the focussing beam which passes through the lens L1 is narrow. Thus it is ensured that the spot Vf is appreciably larger than the spot Vi.
The details of the information structure then can not be distinguished with the focussing beam, so that the signals S7 and Sg will not exhibit any high-frequency variations.
For the sake of clarity the reflected focussing beam is shown to pass through the border of the lens L1 in ~ig. 1. In reality the point where the principal ray of this beam enters the lens L1 uill be nearer the optical axis.
.
.
-- I O--~7.7. I~77 2~
In the apparatus in accordance with the invention the focussing beam is formed with very simpLe means, namely with a wedge-shaped element only or a small diffraction grating only. The wedge of the diffraction grating may for ex~mple be mounted on a transparent plate. This plate may be fixed relative to the lens L1 in the direction of the optica]
-axis 00'.
The angle of refraction of the wedge 5 is subject ' to an upper limit, so that thisis also the case for the deflection of the fooussing beam by said wedge. It is desirable that the point of the information structure to which the focussing is adjusted is nearest the point of the information structure where read-out is effected. The distance between Vi and Vf is for example 100/um. In cases that the lnformation carrier is oblique relative to the optical axis or that variations in thicl~ness of the information carrier occur it is then also possible to main-tain a correct focussing of the read beam.' In order to have a sufficient distance between the focussing spot V'f and the read spot V'i de~lection by the wedge 5 alone suffices if'the magnification of the objeotive system is sufficiently high, or if the-radiation source does not at the same time constitute the information detec-tor, so that the radiation reflected by the record carrier can be mirror-di~erted and the detectors can be arranged at~a suitable distance from the information carrier.
When a diode laser is used as radlation source ~see Fi~. 1)'and an objective system which images the diode laser o~to the information structure with a ratio of 2-1, 27.7.i~j7 ~ ~ 6'~ ~
the distance between the objective system and the diode laser beilig preferably small, the distance as a result of the deflection by the wedge 5 between the spots V~i and V~f is too small. In that case it is possible in accordance with the invention to employ a second optical wedge 10. This~7edge is then disposed in the path of the reflected focussing beam. The wedge 10 may have a greater angle of refraction than the wedge 5, because it does not affect the distance between the spots Vi and Vf.
Also in the case that a satisfactory distance between the spots V'i and Vlf can be obtained with a wedge 5, a second wedge 10 may be used. By means of the second wedge it is then possible to prevent radiation of the read beam from being incident on the focussing detectors when the information structure is out of focus, resulting in the ` read spot V'i being "blown up".
The wedge 10 should then be disposed in the shadow of the wedge 5 or, in other words, thé wedges 5 and 10 must be imaged onto each other by the lens L1 via the information carrier. In Fig. 1 the marginal rays of said imaging are represented by dash-dot lines.
If the plane of the wedges were situated at an arbitrary height between the lenses L1 and I,2, the image of the wedge 5 would depend on the distance between the plane of the information s-tructure and the objective system. Therefore care is taken, in accordance with the invention, that the plane Or the wedges ooincide with tho focal plane F of th0 lens I,1.
In order to ensure -that all -the radiation which is deflected by the first wedge (5) passes through the second wedge (10), the second wedge wouLd ha~e to be slightly larg~er than the first wedge. Howe~er, a small portion of the read beam3 , - ... . - ~
2~.i.l'~l7 62~
itseif would then pass -through the second wedge and result in a separate racliation spot V on the surface of the detectors; compare the sma:Ll beam 3~ indicated by the un-interrupted lines in Fig. 1. In the sltuation of Fig. 1, in which the read beam is correctly focussed on the information structure the radiation spot Vn is situated closely to the focussing detectors. If the plane of the tracks 2 should then be moved upwards, the radiation spot V would even fall onto the detector 7 in the case of a small focussing error, thus giving rise to an erroneous signal rf.
~ Therefore, the area of the wedge lO should at the mos be equal to that of the wedge 5 and the wedge 10 is dispoeed in the shadow of the wedge 5. As a result of this, a part of the focussing beam, the beam 6' represented by the dashed lines, will not be incident on the detectors 7 and 8. However, this merely results in the signals S7 and S8 being slightly smaller. The sensitivity of the detection system for focussing errors is not significantly affected thereby.
Furthermore, care is taken that the distance d between the optical axis 00~ and the point where the focussing beam enters the lens L1 is approximately 0.7 times the radius r of the lens pupil. For the read method shown in Fig. 1, where the read beam traverses the information carrier twice, the influence of spherical aberration in the objective system on the shape of the spot Vi in the case of variations in the thickness of the informatlon carrier is then minimal for the focussing control method described.
In Figs. 2a and 2b the two focussing de-tectors 7 and 8 are shown with the focussing spot V~ projected thereon.
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It is assumed that in the case of a variation o r the focussing of the read beam the focussing spot V'f moves in the x direction.
- For an optimum sensitivity to focussing errors of the detection system the line separating -the detectors 7 and 8 should be perpendicular to the x-direction, as is shown in Fig. 2a.
However, the derived focussing control signa-L rf would then greatly depend on the position of the focussing detectors in the x-direction.
In accordance with the invention the cletectors 7 and 8 are arranged so that the line of separation ~ makes an aeute angle, for example 1~5, with the x-d:irection, as is shown in Fig. 2b. The zero passage of the signal rf can then be adjusted by rotating the wedge 5 or the wedges 5 and 10 about the optical axis 00'. In Figs. 3a and 3b the path des-cribed by the focussing spot Vlf if the wedges are rotated is represented by the curve c. In the case of ~ig. 3a, in which the detectors have the orientation of Fig. 2b, the radiation distribution over the focussing detectors will ehange when the focussing spot moves over the detectors in aceordanoe with the curve c. During assembly of the read apparatus, after the pl~e with the wedges has been mounted between the lenses L1 and L2 and the focussing has been adjusted correctly, the plates can then be rotated so that the focussing spot is symmetrical relative to the detectors 7 and 8. This is not possible if the focussing detectors have the orientation in aecordanee with Fig. 2a~ In that ease the radiation distribution over the focussing detectors cannot be inf~u~nced by rotating -the wedge plate through small angles. Compare Figure 3b.
PJl~i ~s i ~
2~.7.l977 If the focussing detectors have tlle orientation of Fig. 2b, moving the focussing spot Vlf in -the x-direction, i.e. a movement as a result of the focussing errors, will result in a smaller variation of the signals S7 and S8 then if these detectors were oriented in accordance with ~ig. 2a.
Consequently, the sensitivity of the detection system is reduced. However, this presents no problems. The sensitivity also remains adequate in the case of *he arrangement of ~igo 2b.
The advantage obtained in respect of the positional tolerance of the focussing detectors is then more importa~t than the loss of sensitivity.
` As a focussing beam is derived from the read beam, this beam will no longer fill the pupil of the lens L1 in an optimum manner. As a result, the radiation spot Vi will become slightly ]arger in the direction of the line connecting the optical axis 00' to the centre of the deflecting element (a wedge or a grating). The resolution of the read beam in this dirèction is then slightly reduced. The influence of this, in itself minor effect, may further be reduced by arranging the line which c~nnects the optical axis and the deflection element at an angle of approximately ~5 with the direction of a track portion to be read.
The two radiation-deflecting elemen~ 5 and 10 in Figure 1, which are necessary to obtain an adequate distance between the radiation spots V'i and V'f should correct]y bc aligned relative to each other. Moreover, the elements 5 and 10 together should correctly be aligned relative to the objective system. This is because the element 10 must be disposed in the shadow of the element 5.
Figure 4 shows an embodiment of an apparatus in 27.7.19i7 accordance with the inventin in which an adequate spacing is obtained between the focussing spot Vlf and the re-imaged read spot with the aid of only one radlation-deflecting element whose position is not very critical. In ~igure 4 the elements which correspond to those of Figure 1 bear the same reference numeral s .
In the arrangement of Figure 4 a small optical wedge 10 is disposed so that a sub-beam, or focussing beam 6 is deflect0d from the read beam which has been reflected by -the information carrier. The dashed lines in Figure 4 indicate which part of the read beam passes through the wedge. The lenses Ll and L2 ensure that the focussing beam 6 lS concentrated on the focussing detectors to a radiation spot, or focussing spot, V~f.
1~ Now only one radiation spot on the information structure is used for reading the information and for generating a focussing error signal. The area of -the information structure on which the read beam is focussed i.s thèn always the area which is belng read.
The wedge 10 also deflects a part from the read beam which is directed towards the information carrier. However, this part is focussed on the information structure to an additional radiation spot to the right of the read spot Vi.
The lens system Ll, L2 re-i1nages the additional radiation spot in a position to the left of the optical axis 00~, i.e. not on the focussing detectors.
The optical elements are allgned so that lf the distance between the plane of the information tracks 2 and the ob?ective system L1, L2 is correc-t, the radiation which is 27.7.1'J7~
incident on the optical -wedge is directed as inclicated by the dashed lines in Figure 4. The optical wedge then deflects the focussing beam 6 so that the focussing spot is symmetrical relative to the focussing detectors. These focussing c~tectors then receive the same amount of radiation, and the output signals S7 and S~ of the detectors 7 and 8 are then equal.
If the plane of the information structure moves relative to the objective system L1L2, the convergence of the - read beam which is reflected by the information carrier changesO As a result of this, that part of the read beam which is used as focussing beam will be incident on the wedge 10 at an angle which differs from that indicated in Figure 4. As a result of this the direction of the beam ~ which passes through the wedge 10 and thus the position of the focussing spot V'~
relative to the focussing detectors also changes. If the plane of the information structure moves towards the objective system, the detector 7 will receive more radiation than the detector 8. However, if the plane of the information structure moves away from the objective system, the detector 7 will receive less radiation than the detector 8~
The additional steps described with reference to Figure 1 may also be applied to the arrangement of Figure 4.
Preferably, the dlstance a between the centre of the wedge 10 and the optical axis 00~ is approximately 0.7 times the radius of the read beam at the location of the wedge. In the case of a variation in the thickness of the informatior carrier the influence of the spherical aberrations in the objective system on the shape of the spot V~i is then again minimal.
' 27.7.1'J/7 ~urthermore, the lille which sep~rates the focussing detectors preferably makes an acute angle, of for example 45, with the direction in which the radiation spot which is formed in the plane of the focussing detéctors moves upon a change in the position of the plane of the information structure.
Finally, the line which interconrlects the optical wedge 10 and the optical axis preferably makes an angle of approximately 45 with the direction of a track portion to be read.
Thefact that the invention has been described on the basis of a wedge as a radiation-deflecting element does not mean that the invention is limited to the use of such a wedg~e. Instead of a wedg~e it is alternatively possible to use any other radiation-deflecting element, such as a diffraction grating.
Steps may also be taken to deflect the focussing beam 6 in a direction opposite to that indicated in the Figures, so tha-t the focussing detectors can be arranged on the same side of the optical axis 00~ as the radiation~
deflecting element 10. ~or this purpose -the wedge 10 may for example be rotated 1~0 about its own axis.
.
-18s .
' '~; `, '., '.:
In order to avoid these problems, in accordance with a further characteris~ic feature of the first ernbodlment of the in~ention, in which the radiation-deflecting element is an optical wedge, a second optical we~ge may be included in the radiation pa-th of the sub-beam which is formed by the first optical wedge and which is reflected by the information carrier.
Preferably, the second optical wedge is then disposed - within the image of the first optical wedge which image is formed with the aid of the information carrier and the lens element of the objective system nearest the informa~on carrier. Thi$ means that the area of the second optical wedge - is smaller than or equal to the area of the first optical - wedge.
The objecti~e system may comprise a plurality of lens elements or one lens elcment. In the last mentioned case thel~ens element of the objective system nearest the information carrier" is the objective system itself.
The second optical wedge, whose angle of refraction is preferably greater than that of the first optical wedge, deflects the focussing beam reflected by the information carrier additi.onally relative to the read beam, so that the distance between the focusslng spot and the read spot increases.
In order to ensur0 that the second wedge always remains in the image of the first wedge independently of the position of the information carrier relative to the obJective system, the optical wedges, in accordance with a further characteristic feature of the lnvention, are disposed in the _6-, .. . :, . .
27.7.1~7l bac~ focal plane of the lens element of the objective system nearest the information carrier.
~ second embodiment of an apparatus in æccordance with the invention is characterized in that a radiation-de-flecting element is disposed in the path of the read beam - which is reflected by the information carrier and which originates from the read spot, in such a way that the radiation which is incident on the radiation deflecting element is deflected to the focussing detectors.
In accordance with a further characteristic feature of an apparatus in accordance with the invention the dividing line between the focussing detectors makes an acute angle with the direction in which the focussing spot moves owing to focussing errors. By means of this step it is avoided that the position of the focussing detector is very critical.
The radiation-deflecting elements which are used are substantially smaller than the cross-section of- the read beam. As a result of this the si~e of the read spot and thus - the actual information read-out is not affected significantlyO
The slight influence of the radiation-deflecting elements on.
the read-out can further be reduced by arranging for the line of interconnection between the optical axis of the objective system and the radiation-deflectlng element to make an angle of 45 with the direction in which an information track of ` the information carrier is read.
The invention will now be described in more detail~
on the basis of an apparatus which employs a dlode laser as radiati.on source and optical wedges as radiation~deflecting element. In this description reference is made to the ~7~
27.7.1~77 drawing, in which:
- Fig. 1 shows a firs-l; embodiment of an apparatus in accordance with the'invention, Figs. 2a,and 2b show different orientations of the focussing detectors relative to the directions of movement of the focussing spot, and ' ~igs. 3a and 3b show how,the focussing spot moves rela*ive to the focussing detectors when the optical wedges are rotated relative to the optical axis, and Fig. 4 shows a second embodiment of an apparatus in accordance with the invention.
Fig. 1 shows a part of a round disc-shaped informaticn carrier 1 in radial cross-section. The information structure is for example a phase structure and comprises a multitude of concentric or quasi-concentric tracks 2, which tracks consist of a sequence of areas and intermediate areas. The areas ma~
for example be situated at a different level in the information carrier than the intermediate areas. The information may for - example be a colour television programme, but it may alterna-tively be other information? such as a multitude of different images or digital information. Preferably, the information structure is situated at the back of the information carrier 1.
The information carrier is illuminated by a read beam 3 produced by a diode laser l~. An objective system, which consists of a single lens, or as shown in Fig. 1, of` two lenses ~1 and L2 focusses the read beam to a read spot ~i on the information structure. The read beam 3 is then reflected by the information s-tructure and upon rotation of the information carrier it is modulated in accordance with the information which is contained in a ~rack portion to be read.
Pl~L~I ~7~
4 27.'7.'1'~'7'7 - Af`ter reflection the read beam traverses the objecti~e system for a second time, an image ~'i being formed of' the read spot Vi. At the location of the radiation spot ~'i a'~detector is situated which converts the modulated read beam into an elec~rical signal Si.
If the radiation source is a diode laser it is possible, as is described in the published German Patent Application No. 2,2~4,119, to use this diode laser as a detector. Depending on the intensity of the reflected read beam ' the electrical resistance across the diode ]aser or the intensity of the radiation emit'ted from the rear of the diode laser will vary. When a diode laser is used as radiation source no beam-splitting element is necessary'to separate the , modulated read beam reflected by the information carrier from the unmodulated read beam which is dirccted towards i the information carrier.
' In accordance with the invention a small optical wedge 5 is disposed in the path of'the read beam 3. This wedge ' splits-off a sub-beam 6 (represented by dashed lines in Fig. 1) from the,read beam. This sub-beam is focussed to a radiation spot ~f on the information structure by the lens,L1. After ~
reflection at the information structure and a second passage through the objective system the focussing beam forms a radiation spot V'f(focussing spot) on an assembly of two focussing detec*ors 7 and 8. If the distance betwcen the plane of the tracks 2 and the objective system is correct, the focussing spot is symmetrical relative to the focussing detectors, so that both detectors receive an equal amo1lnt of radiatlon and -the output signals S7 and S~ are equal. If the plane o~ the information structure moves downwards relative _9_ 2~.7.1'377 to the objective system, the point where the principal ray of the reflected beam 6 enters the lens L1 will be shifted towards the optical axis 00~. The deflection of the beam 6 by the objective system is then slightly less and the focussing spot Vlf moves to the left. The detector 7 then receives more radiation than the detector ~. If the plane of the tracks 2 moves upwards, the reverse takes place, and the detector 7 receives less radiation than the detector 8.
The signals S7 and Sg from the detectors are applied to an electronic circuit 9. In this circuit the signals are subtracted from each other in a manner known per se. ~t the output of the circuit 9 a focussing control signal rf is then obtained with which the focussing of the objective system can be corrected, for example by moving this system along the optical axis 00'. If the radiation source is a diode laser, the optical read unit may also be moved along the optioal axis.
The optical wedge, or a diffraction grating, is disposed in the path of~the read beam which is directed towards the information carrier, and the focussing beam which passes through the lens L1 is narrow. Thus it is ensured that the spot Vf is appreciably larger than the spot Vi.
The details of the information structure then can not be distinguished with the focussing beam, so that the signals S7 and Sg will not exhibit any high-frequency variations.
For the sake of clarity the reflected focussing beam is shown to pass through the border of the lens L1 in ~ig. 1. In reality the point where the principal ray of this beam enters the lens L1 uill be nearer the optical axis.
.
.
-- I O--~7.7. I~77 2~
In the apparatus in accordance with the invention the focussing beam is formed with very simpLe means, namely with a wedge-shaped element only or a small diffraction grating only. The wedge of the diffraction grating may for ex~mple be mounted on a transparent plate. This plate may be fixed relative to the lens L1 in the direction of the optica]
-axis 00'.
The angle of refraction of the wedge 5 is subject ' to an upper limit, so that thisis also the case for the deflection of the fooussing beam by said wedge. It is desirable that the point of the information structure to which the focussing is adjusted is nearest the point of the information structure where read-out is effected. The distance between Vi and Vf is for example 100/um. In cases that the lnformation carrier is oblique relative to the optical axis or that variations in thicl~ness of the information carrier occur it is then also possible to main-tain a correct focussing of the read beam.' In order to have a sufficient distance between the focussing spot V'f and the read spot V'i de~lection by the wedge 5 alone suffices if'the magnification of the objeotive system is sufficiently high, or if the-radiation source does not at the same time constitute the information detec-tor, so that the radiation reflected by the record carrier can be mirror-di~erted and the detectors can be arranged at~a suitable distance from the information carrier.
When a diode laser is used as radlation source ~see Fi~. 1)'and an objective system which images the diode laser o~to the information structure with a ratio of 2-1, 27.7.i~j7 ~ ~ 6'~ ~
the distance between the objective system and the diode laser beilig preferably small, the distance as a result of the deflection by the wedge 5 between the spots V~i and V~f is too small. In that case it is possible in accordance with the invention to employ a second optical wedge 10. This~7edge is then disposed in the path of the reflected focussing beam. The wedge 10 may have a greater angle of refraction than the wedge 5, because it does not affect the distance between the spots Vi and Vf.
Also in the case that a satisfactory distance between the spots V'i and Vlf can be obtained with a wedge 5, a second wedge 10 may be used. By means of the second wedge it is then possible to prevent radiation of the read beam from being incident on the focussing detectors when the information structure is out of focus, resulting in the ` read spot V'i being "blown up".
The wedge 10 should then be disposed in the shadow of the wedge 5 or, in other words, thé wedges 5 and 10 must be imaged onto each other by the lens L1 via the information carrier. In Fig. 1 the marginal rays of said imaging are represented by dash-dot lines.
If the plane of the wedges were situated at an arbitrary height between the lenses L1 and I,2, the image of the wedge 5 would depend on the distance between the plane of the information s-tructure and the objective system. Therefore care is taken, in accordance with the invention, that the plane Or the wedges ooincide with tho focal plane F of th0 lens I,1.
In order to ensure -that all -the radiation which is deflected by the first wedge (5) passes through the second wedge (10), the second wedge wouLd ha~e to be slightly larg~er than the first wedge. Howe~er, a small portion of the read beam3 , - ... . - ~
2~.i.l'~l7 62~
itseif would then pass -through the second wedge and result in a separate racliation spot V on the surface of the detectors; compare the sma:Ll beam 3~ indicated by the un-interrupted lines in Fig. 1. In the sltuation of Fig. 1, in which the read beam is correctly focussed on the information structure the radiation spot Vn is situated closely to the focussing detectors. If the plane of the tracks 2 should then be moved upwards, the radiation spot V would even fall onto the detector 7 in the case of a small focussing error, thus giving rise to an erroneous signal rf.
~ Therefore, the area of the wedge lO should at the mos be equal to that of the wedge 5 and the wedge 10 is dispoeed in the shadow of the wedge 5. As a result of this, a part of the focussing beam, the beam 6' represented by the dashed lines, will not be incident on the detectors 7 and 8. However, this merely results in the signals S7 and S8 being slightly smaller. The sensitivity of the detection system for focussing errors is not significantly affected thereby.
Furthermore, care is taken that the distance d between the optical axis 00~ and the point where the focussing beam enters the lens L1 is approximately 0.7 times the radius r of the lens pupil. For the read method shown in Fig. 1, where the read beam traverses the information carrier twice, the influence of spherical aberration in the objective system on the shape of the spot Vi in the case of variations in the thickness of the informatlon carrier is then minimal for the focussing control method described.
In Figs. 2a and 2b the two focussing de-tectors 7 and 8 are shown with the focussing spot V~ projected thereon.
- -13~
~j.j.l'~7 6Z'~/~
It is assumed that in the case of a variation o r the focussing of the read beam the focussing spot V'f moves in the x direction.
- For an optimum sensitivity to focussing errors of the detection system the line separating -the detectors 7 and 8 should be perpendicular to the x-direction, as is shown in Fig. 2a.
However, the derived focussing control signa-L rf would then greatly depend on the position of the focussing detectors in the x-direction.
In accordance with the invention the cletectors 7 and 8 are arranged so that the line of separation ~ makes an aeute angle, for example 1~5, with the x-d:irection, as is shown in Fig. 2b. The zero passage of the signal rf can then be adjusted by rotating the wedge 5 or the wedges 5 and 10 about the optical axis 00'. In Figs. 3a and 3b the path des-cribed by the focussing spot Vlf if the wedges are rotated is represented by the curve c. In the case of ~ig. 3a, in which the detectors have the orientation of Fig. 2b, the radiation distribution over the focussing detectors will ehange when the focussing spot moves over the detectors in aceordanoe with the curve c. During assembly of the read apparatus, after the pl~e with the wedges has been mounted between the lenses L1 and L2 and the focussing has been adjusted correctly, the plates can then be rotated so that the focussing spot is symmetrical relative to the detectors 7 and 8. This is not possible if the focussing detectors have the orientation in aecordanee with Fig. 2a~ In that ease the radiation distribution over the focussing detectors cannot be inf~u~nced by rotating -the wedge plate through small angles. Compare Figure 3b.
PJl~i ~s i ~
2~.7.l977 If the focussing detectors have tlle orientation of Fig. 2b, moving the focussing spot Vlf in -the x-direction, i.e. a movement as a result of the focussing errors, will result in a smaller variation of the signals S7 and S8 then if these detectors were oriented in accordance with ~ig. 2a.
Consequently, the sensitivity of the detection system is reduced. However, this presents no problems. The sensitivity also remains adequate in the case of *he arrangement of ~igo 2b.
The advantage obtained in respect of the positional tolerance of the focussing detectors is then more importa~t than the loss of sensitivity.
` As a focussing beam is derived from the read beam, this beam will no longer fill the pupil of the lens L1 in an optimum manner. As a result, the radiation spot Vi will become slightly ]arger in the direction of the line connecting the optical axis 00' to the centre of the deflecting element (a wedge or a grating). The resolution of the read beam in this dirèction is then slightly reduced. The influence of this, in itself minor effect, may further be reduced by arranging the line which c~nnects the optical axis and the deflection element at an angle of approximately ~5 with the direction of a track portion to be read.
The two radiation-deflecting elemen~ 5 and 10 in Figure 1, which are necessary to obtain an adequate distance between the radiation spots V'i and V'f should correct]y bc aligned relative to each other. Moreover, the elements 5 and 10 together should correctly be aligned relative to the objective system. This is because the element 10 must be disposed in the shadow of the element 5.
Figure 4 shows an embodiment of an apparatus in 27.7.19i7 accordance with the inventin in which an adequate spacing is obtained between the focussing spot Vlf and the re-imaged read spot with the aid of only one radlation-deflecting element whose position is not very critical. In ~igure 4 the elements which correspond to those of Figure 1 bear the same reference numeral s .
In the arrangement of Figure 4 a small optical wedge 10 is disposed so that a sub-beam, or focussing beam 6 is deflect0d from the read beam which has been reflected by -the information carrier. The dashed lines in Figure 4 indicate which part of the read beam passes through the wedge. The lenses Ll and L2 ensure that the focussing beam 6 lS concentrated on the focussing detectors to a radiation spot, or focussing spot, V~f.
1~ Now only one radiation spot on the information structure is used for reading the information and for generating a focussing error signal. The area of -the information structure on which the read beam is focussed i.s thèn always the area which is belng read.
The wedge 10 also deflects a part from the read beam which is directed towards the information carrier. However, this part is focussed on the information structure to an additional radiation spot to the right of the read spot Vi.
The lens system Ll, L2 re-i1nages the additional radiation spot in a position to the left of the optical axis 00~, i.e. not on the focussing detectors.
The optical elements are allgned so that lf the distance between the plane of the information tracks 2 and the ob?ective system L1, L2 is correc-t, the radiation which is 27.7.1'J7~
incident on the optical -wedge is directed as inclicated by the dashed lines in Figure 4. The optical wedge then deflects the focussing beam 6 so that the focussing spot is symmetrical relative to the focussing detectors. These focussing c~tectors then receive the same amount of radiation, and the output signals S7 and S~ of the detectors 7 and 8 are then equal.
If the plane of the information structure moves relative to the objective system L1L2, the convergence of the - read beam which is reflected by the information carrier changesO As a result of this, that part of the read beam which is used as focussing beam will be incident on the wedge 10 at an angle which differs from that indicated in Figure 4. As a result of this the direction of the beam ~ which passes through the wedge 10 and thus the position of the focussing spot V'~
relative to the focussing detectors also changes. If the plane of the information structure moves towards the objective system, the detector 7 will receive more radiation than the detector 8. However, if the plane of the information structure moves away from the objective system, the detector 7 will receive less radiation than the detector 8~
The additional steps described with reference to Figure 1 may also be applied to the arrangement of Figure 4.
Preferably, the dlstance a between the centre of the wedge 10 and the optical axis 00~ is approximately 0.7 times the radius of the read beam at the location of the wedge. In the case of a variation in the thickness of the informatior carrier the influence of the spherical aberrations in the objective system on the shape of the spot V~i is then again minimal.
' 27.7.1'J/7 ~urthermore, the lille which sep~rates the focussing detectors preferably makes an acute angle, of for example 45, with the direction in which the radiation spot which is formed in the plane of the focussing detéctors moves upon a change in the position of the plane of the information structure.
Finally, the line which interconrlects the optical wedge 10 and the optical axis preferably makes an angle of approximately 45 with the direction of a track portion to be read.
Thefact that the invention has been described on the basis of a wedge as a radiation-deflecting element does not mean that the invention is limited to the use of such a wedg~e. Instead of a wedg~e it is alternatively possible to use any other radiation-deflecting element, such as a diffraction grating.
Steps may also be taken to deflect the focussing beam 6 in a direction opposite to that indicated in the Figures, so tha-t the focussing detectors can be arranged on the same side of the optical axis 00~ as the radiation~
deflecting element 10. ~or this purpose -the wedge 10 may for example be rotated 1~0 about its own axis.
.
-18s .
' '~; `, '., '.:
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An apparatus for reading an optical radiation-reflecting information carrier, which apparatus comprises a radiation source which produces a read beam, an objective system for focussing the read beam to a read spot on the information structure of the information carrier and for imaging the read spot on a radiation-sensitive information detector whose output signal represents the information and an opto-electronic focussing error detection system for determining a deviation between the desired and the actual position of the plane of focussing of the objective system, which focussing error detection system comprises two radia-tion-sensitive focussing detectors which co-operate with a narrow focussing beam, the difference in the output signals of the focussing detectors providing an indication of said deviation, characterized in that, in order to produce the focussing beam,which forms a radiation spot on the focussing detectors, the radiation path of the read beam on one side of the optical axis of the objective system includes a radi-ation-deflecting element, whose surface area is substantially smaller than the cross-sectional area of the read beam.
2. An apparatus as claimed in Claim 1, characterized in that the radiation deflecting element is constituted by a diffraction grating.
3. An apparatus as claimed in Claim 1, characterized in that the radiation-deflecting element is constituted by an optical wedge.
4. An apparatus as claimed in Claim 1, characterized in that the radiation path of the read beam which is directed to the information carrier includes a radiation-deflecting element which deflects part of the read beam in such a way that the radiation which is incident on the radiation-deflect-ing element forms an additional radiation spot on the inform-ation structure besides the read spot which radiation spot is imaged on the focussing detectors by the objective system.
5. An apparatus as claimed in Claim 4, the radiation-deflecting element being an optical wedge, characterized in that the radiation path of the sub-beam which is formed by the first optical wedge and which is reflected by the information carrier includes a second optical wedge.
6. An apparatus as claimed in Claim 5, characterized in that the second optical wedge is disposed within the image of the first optical wedge formed with the aid of the inform-ation carrier and the lens element of the objective system nearest the information carrier.
7. An apparatus as claimed in Claim 6, characterized in that the optical wedges are disposed in the back focal plane of the lens element of the objective system nearest the information carrier.
8. An apparatus as claimed in Claim 4, characterized in that the deflecting element is arranged so that the dis-tance between the optical axis of the objective system and the point where the focussing beam for the first time enters the lens element of the objective system nearest the inform-ation carrier equals approximately 0.7 times the radius of the pupil of said lens.
9. An apparatus as claimed in Claim 1, characterized in that a radiation-deflecting element is included in the path of the read beam which is reflected by the information carrier and which originates from the read spot, in such a way that the radiation which is incident on the radiation-deflecting element is deflected to the focussing detectors.
10. An apparatus as claimed in Claim 9, characterized in that the distance between the centre of the radiation-deflecting element and the optical axis is equal to approxi-mately 0.7 times the radius of the read beam at the location of the radiation-deflecting element.
11. An apparatus as claimed in Claim 1, 4 or 9, charac-terized in that the dividing line between the focussing detectors makes an acute angle with the direction in which the radiation spot formed in the plane of the focussing detectors moves as a result of focussing errors.
12. An apparatus as claimed in Claim 1, 4 or 9, charac-terized in that the connecting line between the optical axis of the objective system and the radiation-deflecting element makes an angle of approximately 45° with the direction in which an information track of the record carrier is read.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL7703123A NL7703123A (en) | 1977-03-23 | 1977-03-23 | DEVICE FOR READING AN OPTICAL RADIATION-REFLECTING REGISTRATION CARRIER. |
| NL7703123 | 1977-03-23 | ||
| NL7706753 | 1977-06-20 | ||
| NL7706753A NL7706753A (en) | 1977-03-23 | 1977-06-20 | DEVICE FOR READING AN OPTICAL RADIATION-REFLECTING INFORMATION CARRIER. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1116294A true CA1116294A (en) | 1982-01-12 |
Family
ID=26645307
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA299,001A Expired CA1116294A (en) | 1977-03-23 | 1978-03-15 | Apparatus for reading an optical radiation-reflecting record carrier |
Country Status (16)
| Country | Link |
|---|---|
| JP (1) | JPS6028055B2 (en) |
| AR (1) | AR217276A1 (en) |
| AT (1) | AT371275B (en) |
| AU (1) | AU516903B2 (en) |
| BE (1) | BE865140A (en) |
| BR (1) | BR7801692A (en) |
| CA (1) | CA1116294A (en) |
| DD (1) | DD135654A5 (en) |
| DE (1) | DE2810566A1 (en) |
| DK (1) | DK124478A (en) |
| ES (1) | ES468083A1 (en) |
| FR (1) | FR2385173A1 (en) |
| GB (1) | GB1589035A (en) |
| IT (1) | IT1093249B (en) |
| NL (1) | NL7706753A (en) |
| SE (1) | SE424677B (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL7809635A (en) * | 1978-09-22 | 1980-03-25 | Philips Nv | DEVICE FOR READING AN OPTICAL REGISTRATION CARRIER CONTAINING A RADIATION-REFLECTING INFORMATION STRUCTURE. |
| NL186353C (en) * | 1979-06-12 | 1990-11-01 | Philips Nv | DEVICE FOR IMAGING A MASK PATTERN ON A SUBSTRATE EQUIPPED WITH AN OPTO-ELECTRONIC DETECTION SYSTEM FOR DETERMINING A DEROGATION BETWEEN THE IMAGE OF A PROJECT SYSTEM AND THE SUBSTRATE PLATE. |
| FR2460523A1 (en) * | 1979-06-29 | 1981-01-23 | Thomson Csf | SEMICONDUCTOR LASER SOURCE OPTICAL READING HEAD AND DEVICE FOR REFLECTING AN INFORMATION MEDIUM COMPRISING SUCH AN OPTICAL HEAD |
| JPS5870434A (en) * | 1981-10-22 | 1983-04-26 | Toshiba Corp | Optical head |
| JPS57186240A (en) * | 1981-11-09 | 1982-11-16 | Teac Co | Optical reproducing device |
| JPS59119548A (en) * | 1982-12-25 | 1984-07-10 | Pioneer Electronic Corp | Optical pickup device |
| JPS59125727U (en) * | 1983-02-15 | 1984-08-24 | パイオニア株式会社 | Optical information pickup device |
| US4630927A (en) * | 1983-02-15 | 1986-12-23 | General Electric Company | Optical projector |
| JPS60197950A (en) * | 1984-03-22 | 1985-10-07 | Toshiba Corp | Optical head |
| JPH0626972Y2 (en) * | 1986-10-03 | 1994-07-20 | パイオニア株式会社 | Optical pickup device |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2313716A1 (en) * | 1975-06-03 | 1976-12-31 | Thomson Brandt | OPTICAL READING SYSTEM BY REFLECTION OF AN INFORMATION MEDIA |
-
1977
- 1977-06-20 NL NL7706753A patent/NL7706753A/en not_active Application Discontinuation
-
1978
- 1978-02-16 AR AR271114A patent/AR217276A1/en active
- 1978-03-11 DE DE19782810566 patent/DE2810566A1/en active Granted
- 1978-03-15 CA CA299,001A patent/CA1116294A/en not_active Expired
- 1978-03-20 GB GB10887/78A patent/GB1589035A/en not_active Expired
- 1978-03-20 AU AU34292/78A patent/AU516903B2/en not_active Expired
- 1978-03-20 BR BR7801692A patent/BR7801692A/en unknown
- 1978-03-20 SE SE7803140A patent/SE424677B/en not_active IP Right Cessation
- 1978-03-20 JP JP53032272A patent/JPS6028055B2/en not_active Expired
- 1978-03-20 DK DK124478A patent/DK124478A/en unknown
- 1978-03-20 DD DD78204290A patent/DD135654A5/en unknown
- 1978-03-20 IT IT21384/78A patent/IT1093249B/en active
- 1978-03-21 AT AT0200278A patent/AT371275B/en active
- 1978-03-21 BE BE186137A patent/BE865140A/en not_active IP Right Cessation
- 1978-03-21 ES ES468083A patent/ES468083A1/en not_active Expired
- 1978-03-22 FR FR7808297A patent/FR2385173A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| NL7706753A (en) | 1978-12-22 |
| BE865140A (en) | 1978-09-21 |
| ES468083A1 (en) | 1978-12-16 |
| DD135654A5 (en) | 1979-05-16 |
| GB1589035A (en) | 1981-05-07 |
| SE7803140L (en) | 1978-09-24 |
| ATA200278A (en) | 1982-10-15 |
| IT1093249B (en) | 1985-07-19 |
| SE424677B (en) | 1982-08-02 |
| JPS6028055B2 (en) | 1985-07-02 |
| DE2810566C2 (en) | 1988-01-21 |
| AU3429278A (en) | 1979-09-27 |
| AR217276A1 (en) | 1980-03-14 |
| DK124478A (en) | 1978-09-24 |
| BR7801692A (en) | 1979-01-02 |
| DE2810566A1 (en) | 1978-09-28 |
| AT371275B (en) | 1983-06-10 |
| AU516903B2 (en) | 1981-06-25 |
| JPS53118103A (en) | 1978-10-16 |
| FR2385173A1 (en) | 1978-10-20 |
| FR2385173B1 (en) | 1985-05-10 |
| IT7821384A0 (en) | 1978-03-20 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |