US20010024416A1 - Optical information detection apparatus - Google Patents
Optical information detection apparatus Download PDFInfo
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- US20010024416A1 US20010024416A1 US09/772,659 US77265901A US2001024416A1 US 20010024416 A1 US20010024416 A1 US 20010024416A1 US 77265901 A US77265901 A US 77265901A US 2001024416 A1 US2001024416 A1 US 2001024416A1
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- optical
- optical beam
- phase compensation
- prism
- detecting apparatus
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- 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
- G11B7/13—Optical detectors therefor
- G11B7/131—Arrangement of detectors in a multiple array
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
- G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
- G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
- G11B11/10532—Heads
- G11B11/10541—Heads for reproducing
- G11B11/10543—Heads for reproducing using optical beam of radiation
-
- 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
- G11B7/1356—Double or multiple prisms, i.e. having two or more prisms in cooperation
-
- 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
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- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Head (AREA)
- Optical Recording Or Reproduction (AREA)
Abstract
An optical information detecting apparatus includes a first optical system focusing an optical beam on a recording surface of a recording medium and a second optical system directing a reflection optical beam produced as a result of reflection of the optical beam by a recording surface of the recording medium to a photodetection unit, wherein the second optical system including a beam dividing element disposed so as to intercept the reflection optical beam and divide the reflection beam into a plurality of optical beam elements traveling generally parallel with each other in the reflection optical beam, such that the plurality of optical beam elements reach the photodetection unit along respective optical paths.
Description
- 1. Field of the Invention
- The present invention generally relates to reading of information from an optical recording medium and more particularly to a compact and high-density optical information detection apparatus capable of reproducing information from a high-density optical recording medium in which information is recorded on both a land and a groove that define a track. More specifically, the present invention relates to an optical information detection apparatus in which cross-talk between the information read out from the land and read out from the groove is minimized and wherein the resolution at the time of detection of the recorded information is improved.
- Optical disks are used extensively as the recording medium of various information including audio and visual data. In relation to the art of high-density rewritable recording of information, intensive efforts are being made particularly with regard to the development of rewritable optical disks such as a magneto-optical disk or a phase transition disk.
- In order to increase the recording density of such optical disks, it is desired to decrease the wavelength of the optical beam used for information detection or to increase the numerical aperture of the objective lens such that the beam spot of the optical beam on the recording medium is reduced.
- Further, there is a proposal to use an MSR (magnetic super-resolution) technology. It should be noted that the MSR technology attempts to increase the recording density of a magneto-optical recording medium while using the optical beam of the same spot size, by suppressing the cross-talk between the tracks or between the recording marks aligned in the tangential direction of the track as much as possible. However, the MSR technology still includes various problems related to resolution which appear conspicuously when the track pitch is reduced, such as the decrease of tracking performance or the increase of the crosstalk. In the case of a rewritable optical disk such as a magneto-optical disk, the cross-erasing of information becomes also a serious problem.
- Meanwhile, there is a proposal of so-called land-groove recording technology that increases the effective track recording density twice as compared with the conventional land recording technology or groove recording technology. In the conventional land recording technology or groove recording technology, the information is recorded only on the land or on the groove that defines a track, while the information is recorded both on the land and the groove in the land-groove recording technology.
- In the land-groove recording technology, in which lands and grooves are separated three-dimensionally, the problem of cross-erasing of information is effectively suppressed as a result of the spatial separation of the lands and the grooves. Thus, the land-groove recording technology is thought an effective approach to increase the recording density of optical disks including rewritable optical disks. In order to reduce this promising technology into practice, however, it is necessary to device a method of suppressing the cross-talk further.
- 2. Description of the Prior Art
- Conventionally, there is a proposal to reduce the cross-talk as described in the Japanese patent application 9-16134, wherein this prior application achieves the desired suppressing of the cross-talk between the lands and the grooves by applying a phase compensation to the optical signals produced by the lands and produced by grooves of the optical recording medium independently. When the desired increase of the line recording density is to be achieved according to this prior application while using the same spot size for the optical beam, on the other hand, there is a need of a further process for compensating for the decrease of the reproduced signal output. It should be noted that such a decrease of the reproduced signal output is caused by the interference of the recording marks aligned on a track.
- With regard to the improvement of resolution of the reproduced signal output for the recording marks aligned on a track, there is a proposal of optical super-resolution by Milster, T. D., et al., Japanese J. Appl. Phys. vol.32, 1993, pp.5397-5401, in which a shading band is provided in the optical path which is used for detecting the information from an optical disk. Thereby, the shading band functions as an optical equalizer.
- Further, in view of the recent trend of technology that targets an integrated optical head carrying a hologram, it is desired that the high-density recording method is compatible with the construction of such integrated optical heads.
- Furthermore, there is a proposal of optical information detection method as disclosed in the Japanese Laid-Open Patent Publication 9-128825, in which simultaneous detection of different information is achieved by dividing a reflected optical beam into several optical beams by using one or more optical beam splitters. It should be noted that the process of this prior art achieves the optical beam splitting with respect to the entirety of the optical beam, by disposing the optical beam splitter so as to intercept the entire optical beam that is reflected by the optical recording medium and traveling toward an optical detection system.
- With regard to the process of the Japanese patent application 9-16134 noted before, it is confirmed that the MSR process is an effective approach for suppressing the cross-talk between the tracks and the interference between the recording marks aligned on a track. On the other hand, the process of the foregoing prior application has a drawback in that it requires at least two magneto-optical layers on the magneto-optical recording medium and that a high optical power has to be used for the optical beam used for reading information. Further, there is an additional drawback in that an exact control the of the optical beam power is necessary such that the optical beam power falls within a narrow tolerance range.
- In addition to the foregoing, the process of the Japanese patent application 9-16134 has a drawback in that, while the problem of the cross-talk between the tracks may be successfully reduced, the reproduced optical beam tends to have an ecliptic polarization state due to the admixing of polarization components having a mutual phase offset corresponding to twice the depth of the groove, into the reflected optical beam. It should be noted that such an admixing of the polarization component occurs as a result of the reflection of the optical beam at the land and the groove adjacent thereto. When this occurs, the output of the reproduced signal is deteriorated inevitably. In order to avoid this problem, it is necessary to provide an appropriate optical phase compensation process.
- It is possible to achieve the desired increase of the track recording density and the linear recording density without using the MSR technology, by combining the optical super-resolution of the Milster et al., op. cit., which uses a shading band, with the optical phase compensation process applied separately to the optical beams reflected from the lands and reflected from the grooves. However, such a process requires a construction in which the optical shading band and the optical phase compensation device are provided for each of the optical beams reflected by the lands and the grooves, and the construction of the optical system becomes inevitably bulky and complex.
- In the process of Japanese Laid-Open Patent Publication 9-128825, which divides the reflected optical beam into a plurality of optical beam elements, on the other hand, there has been a problem in that it is difficult to construct the optical information detection apparatus to have a compact size, due to the fact that the beam splitting is applied to the entirety of the reflected optical beam at several locations of the optical path of the reflected optical beam and that it is necessary to provide a detection optical system to each of the optical beam thus divided.
- Accordingly, it is a general object of the present invention to provide a novel and useful optical information detection apparatus wherein the foregoing problems are eliminated.
- Another and more specific object of the present invention is to provide a compact and efficient optical information detection apparatus that is capable of detecting various different information recorded on an optical recording medium.
- Another object of the present invention is to provide an optical information detection apparatus, comprising:
- a turn-table adapted for holding an optical disk thereon rotatably, said optical disk including a land and an adjacent groove formed on a surface thereof, both of said land and groove carrying respective information;
- a motor connected to said turn-table so as to rotate said turn-table;
- an optical source emitting an optical beam;
- a first optical system directing said optical beam from said optical source to said optical disk held in a state that said optical disk is held on said turn-table;
- a second optical system collecting and guiding a reflection optical beam produced by a reflection of said optical beam at said surface of said optical disk in a state that said optical disk is held on said turn-table;
- a beam dividing element dividing said reflection optical beam into a plurality of optical beam elements each corresponding to a part of said reflection optical beam and traveling side by side in said reflection optical beam; and
- a plurality of photodetection devices respectively detecting said plurality of optical beam elements.
- According to the present invention, the reflection optical beam is divided into a plurality of optical beam elements each corresponding to a part of the reflection optical beam and traveling generally side by side as forming the reflection optical beam, wherein the plurality of optical beam elements carry respective, specific information such as tracking error information, focusing error information, the recorded information recorded on the groove, and the recorded information recorded on the land. Thereby, it is possible to extract various optical information from the reflection optical beam by a simple construction and the size of the optical information detection apparatus can be reduced successfully.
- Other objects and further features of the present invention will become apparent from the following detailed description when read in conjunction with the attached drawings.
- FIG. 1 is a diagram showing the construction of an optical information detection apparatus according to an embodiment of the present invention;
- FIG. 2 is a diagram showing the construction of an optical recording medium used in the optical information detection apparatus of FIG. 1;
- FIG. 3 is another diagram showing the construction of the optical recording medium of FIG. 2 in detail;
- FIGS. 4A and 4B are diagrams showing a composite optical element used in the optical information detection apparatus of FIG. 1;
- FIG. 5 is a diagram showing the composite optical element of FIGS. 4A and 4B in an exploded view;
- FIG. 6 is a diagram showing the construction of a photodetector array used in the optical information detection apparatus of FIG. 1;
- FIG. 7 is a circuit diagram showing a detection circuit used in the optical information detection apparatus of FIG. 1 for reading the information from the optical recording medium;
- FIG. 8 is another circuit diagram showing another detection circuit used in the optical information detection apparatus of FIG. 1 together with the circuit of FIG. 7;
- FIG. 9 is a diagram showing a diffraction pattern of a reflection optical beam obtained by the composite optical element of FIGS. 4A and 4B; and
- FIG. 10 is a diagram showing a jitter of a recording mark formed on the optical recording medium used in the optical information detection apparatus of FIG. 1 for various recording optical power.
- FIG. 1 shows the construction of an optical information recording and reproducing apparatus in which an optical information detection apparatus of the present invention is used.
- Referring to FIG. 1, there is provided a
laser diode 1 that produces an optical beam, wherein the optical beam is converted, after passing through a collimator lens 2 and abeam shaping prism 3, to a parallel optical beam L1 having a circular beam cross-section. The optical beam L1 is then directed to apolarization beam splitter 4 that divides the optical beam L1 to form an optical beam L2 and an optical beam L3, wherein the optical beam L2 is directed to aphotodetector 5 for automatic optical power control. - On the other hand, the optical beam L3 is directed to a magneto-
optical disk 7 and is focused on a surface thereof by anobjective lens 6. It should be noted that the magneto-optical disk 7 is held on a turn-table by a chuck mechanism CH and is rotated by a spindle motor SP at a high speed. Further, it should be noted that theobjective lens 6 is held movably on a biaxial actuator not illustrated such that the objective lens is movable in a radial direction of thedisk 7 and further in a direction to and from thedisk 7. As noted already, the objective lens focuses the optical beam L3 to a desired point on a recording surface of the magneto-optical recording disk 7 on which concentric or spiral-shaped guide tracks are formed. - FIG. 2 shows the construction of the magneto-
optical recording disk 7. - Referring to FIG. 2, the magneto-
optical recording disk 7 has acentral hub 7 b and is accommodated in a case 7 a, wherein a spiral track TR is formed on a recording surface of thedisk 7 that faces theobjective lens 3 for a tracking servo control of theobjective lens 6. The spiral track TR is defined by a spiral-shaped or concentric-shaped groove and an adjacent, spiral-shaped or concentric-shaped land. - FIG. 3 shows the recording surface of the magneto-
optical recording disk 7 in an enlarged scale. - Referring to FIG. 3, each of the tracks TR is defined by a
groove 7 e and aland 7 e, and the surface of thedisk 7 is covered by amagnetic recording film 7 f. Further, a floatingmagnetic head 8 is disposed at the opposite side of the recording surface of the magneto-optical disk 7 as indicated in FIG. 1. - In a write mode operation of the optical recording and reproducing apparatus of FIG. 1, the
magnetic recording film 7 f is heated locally by the optical beam L3 that is focused on the recording surface of thedisk 7 with a large optical power. As a result of such a localized heating, the direction of magnetization of themagnetic film 7 f is rotated according to the magnetic field of themagnetic head 8 and the writing of the information is achieved thereby. - In a read mode operation, on the other hand, the optical beam L3 is focused on the recording surface of the magneto-
optical disk 7 with a reduced optical power, and the plane of polarization of the optical beam. L3 is rotated according to the direction of magnetization of themagnetic film 7 f as the optical beam L3 is reflected by themagnetic film 7 f. The optical information recording and reproducing apparatus of FIG. 1 thereby detects the content of the recorded information by detecting the polarization state of the reflected optical beam. - More specifically, a reflected optical beam L4 thus produced as a result of the reflection of the optical beam L3 at the magneto-
optical disk 7 returns to thepolarization beam splitter 4 after passing through theobjective lens 6 in a reverse direction, wherein thepolarization beam splitter 4 reflects the reflection optical beam L4 thus returned thereto to a compositeoptical element 9 as a reflection optical beam L5. See FIG. 1. - As will be described below, the composite
optical element 9 decomposes the reflection optical beam L5 into respective optical beam elements representing the recorded information, focusing error information and tracking error information, wherein the optical beam elements thus produced are focused by alens 10 on aphotodetector array 11. - FIGS. 4A and 4B show the construction of the composite
optical element 9 respectively in a front view and a side view. The same compositeoptical element 9 is shown also in FIG. 5 in an exploded view. - Referring to FIGS. 4A and 4B, the composite
optical element 9 includesretardation plates retardation plates first Wollaston prism 14 a and asecond Wollaston prism 14 b respectively. As indicated in FIG. 4A, theretardation plates optical beam 18 which corresponds to the reflection optical beam L5, and the Wollaston prisms 14 a and 14 b are separated from each other in a lateral direction of theoptical element 9 with a distance d1. TheWollaston prism 14 a carries awedge prism 15 a thereon and theWollaston prism 14 b carries awedge prism 15 b. - Further, there is disposed a double-wedge prism17 formed of
wedge prisms 17 a and 17 b, wherein thewedge prisms 17 a and 17 b have respective prism surfaces inclined in mutually opposite directions on a substrate formed by the foregoingretardation plates wedge prisms - As indicated in FIGS. 4A and 4B, the incident
optical beam 18 corresponding to the reflection optical beam L5 is directed to the bottom of the substrate formed of theretardation plates retardation plate 12 applies an optical phase compensation to anoptical beam element 18A reflected by theland 7 d of theoptical disk 7 of FIG. 1 and forming a part of theoptical beam 18 such That the pertinentoptical beam element 18A has a predetermined optical phase. On the other hand, theretardation plate 13 applies an optical phase compensation to anoptical beam element 18B reflected by thegroove 7 e of theoptical disk 7 of FIG. 1 and forming a part of theoptical beam 18, wherein it should be noted that the optical phase compensation achieved by theretardation plate 13 has a magnitude substantially identical to the optical phase compensation achieved by theretardation plate 12 but the direction of the optical phase compensation of theretardation plate 13 is set opposite to the direction of the optical phase compensation achieved by theretardation plate 12. - The
optical beam element 18A thus passed through theretardation plate 12 is then caused to enter theWollaston prism 14 a, wherein theoptical beam element 18A, the optical phase of which is compensated by theretardation plate 12, experiences a deflection, inside theWollaston prism 14 a, in one of the B1- and B2-directions depending on the polarization state of the optical beam element. Similarly, theoptical beam element 18B passed through theretardation plate 13 enters theWollaston prism 14 b and experiences a deflection inside theWollaston prism 14 b in one of the B1- and B2-directions depending on the polarization state of the optical beam element. See FIG. 4B. - The
optical beam element 18A thus deflected by theWollaston prism 14 a is then caused to pass through thewedge prism 15 a, wherein thewedge prism 15 a, having a prism surface inclined in the A1-direction, refracts theoptical beam element 18A in the A1-direction. Similarly, theoptical beam element 18B thus deflected by theWollaston prism 14 b is caused to pass through thewedge prism 15 b, and thewedge prism 15 b, having a prism surface inclined in the A2-direction, refracts theoptical beam element 18B in the A2-direction. - In addition, the
wedge prism 16 a deflects amarginal ray 18 a included in the reflectionoptical beam 18 in the B1-direction and an oppositemarginal ray 18 b also included in the reflectionoptical beam 18 in the B2-direction. Themarginal rays wedge prisms lens 10 and focused on thephotodetector array 11 for the detection of a push-pull tracking error signal. Further, theoptical beam elements lens 10 and are focused on thephotodetector array 11 for differential detection of the recorded magneto-optical information signal. - The double-wedge prism17 is disposed so as to intercept the core part of the reflection
optical beam 18. As noted already and as indicated in FIG. 5, the double-wedge prism 17 is formed of twowedge prisms 17 a and 17 b disposed side by side, wherein thewedge prisms 17 a and 17 b have respective, mutually oppositely inclined prism surfaces. - More specifically, the
first wedge prism 17 a is disposed on theretardation plate 12 in alignment with the edge thereof at the side of the A2-direction, while the second wedge prism 17 b is disposed on theretardation plate 13 in alignment with the edge thereof at the side of the A1-direction. Thereby, thewedge prism 17 a causes a deflection of an incident optical beam in the B1-direction while the wedge prism 17 b causes a deflection of an incident optical beam in the B2-direction. - Thus, the double wedge prism17 decomposes a
core part 19 of the reflectionoptical beam 18 into twooptical beam elements 19 a and 19 b, wherein theoptical beam elements 19 a and 19 b are forwarded to thephotodetection array 11 via thelens 10 for extracting a focusing error signal by a double Foucault process. - As noted already, the optical beam element forming the reflection
optical beam 18 at the side of thecore part 19 is subjected to an optical phase compensation process achieved independently by theretardation plate 12 and theretardation plate 13, and each of the optical beam elements is deflected in one of the B1-B2-directions by theWollaston prism photodetector array 11 at thewedge prism - Hereinafter, the reflection occurring at the magneto-
optical recording medium 7 will be explained. - As described previously, the optical beam L3 illuminates both the
land 7 d and thegroove 7 e adjacent to theland 7 e, and thus, theoptical beam 18 corresponding to the reflection optical beam H4 inevitably includes a cross-talk component. - In the case of the magneto-
optical disk 7, theland 7 d and thegroove 7 e are formed with a step height corresponding to one-eighth the wavelength of theoptical beam 18, such that there appears a phase offset corresponding to one-quarter the wavelength between theoptical beam element 18A reflected by theland 7 d and theoptical beam element 18B reflected by thegroove 7 e. Because of the superposition of theoptical beam components optical beam 18, there inevitably appears a cross-talk between theoptical beam components optical beams optical beam component 18A becomes opposite to that of theoptical beam component 18B. This also means that it is possible to suppress the detection of unwanted optical beam component by setting theretardation plates land 7 d and thegroove 7 e. - Thus, in the present embodiment, the
retardation plate 12 is set such that the cross-talk of theoptical beam component 18B to theoptical beam component 18A becomes minimum and theretardation plate 13 is set such that the cross-talk of theoptical beam component 18A to theoptical beam component 18B becomes minimum. - It should be noted that the composite
optical element 9 of FIGS. 4A and 4B merely represents an example, and the compositeoptical element 9 may be formed as an integral unitary body. - Hereinafter, the construction of the
photodetector array 11 will be described with reference to FIG. 6. - Referring to FIG. 6, the
photodetector array 11 is formed on a common substrate 11 a that carries thereon first through seventh optical detectors 20-26, wherein theoptical detectors optical detector 20 is disposed so as to receive theoptical beam component 18B deflected by theWollaston prism 14 b in the B1-direction, while theoptical detector 21 is disposed so as to receive theoptical beam component 18B deflected by theWollaston prism 14 b in the B2-direction. - Further, it can be seen that the substrate11 a of the
photodetector array 11 carries thereon theoptical detectors optical detector 22 is disposed so as to receive theoptical beam component 18A deflected by theWollaston prism 14 a in the B1-direction, while theoptical detector 23 is disposed so as to receive theoptical beam component 18A deflected by theWollaston prism 14 a in the B2-direction. - Further, the substrate11 a of the
photodetector array 11 carries thereon acentral photodetection part 24 at the central part of the substrate 11 a, wherein thephotodetection part 24 includes fourphotodetection regions 24 a-24 d in correspondence to four quadrants. - Furthermore, the substrate11 a of the
photodetector array 11 carries thereonphotodetectors central photodetection part 24 in the B1-B2-directions, wherein thephotodetector 25, located at the side of the B1-direction of thecentral photodetection part 24, detects the optical beam deflected by thewedge prism 16 a in the B1-direction. Further, thephotodetector 26 at the B2-side of thephotodetection part 24 detects the optical beam deflected by thewedge prism 16 b in the B2-direction. - In the
photodetector array 11 of FIG. 6, it should be noted that the information recorded on theland 7 d of theoptical disk 7 is reproduced by obtaining a difference between a detection signal detected by thephotodetector 20 and a detection signal detected by thephotodetector 21. On the other hand, the information recorded on thegroove 7 e of the optical disk is reproduced by obtaining a difference between a detection signal detected by thephotodetector 22 and a detection signal thephotodetector 23. - On the other hand, a focusing error signal is obtained by applying a predetermined operation to be described below to the detection signals obtained by the
photodetectors 24 a-24 d forming the central photodetection part. Further, a tracking error signal is obtained by obtaining a difference between the detection signal detected by thephotodetector 25 and the detection signal detected by thephotodetector 26. - Hereinafter, a more detailed description will be made on the construction for reproducing the recorded information from the
land 7 d and from thegroove 7 e of theoptical disk 7 as well as the construction for extracting the tracking error signal and the focusing error signal. - FIG. 7 shows the construction for reproducing the recorded information from the
land 7 d and thegroove 7 e as well as the construction for obtaining the tracking error signal. - Referring to FIG. 7, there is provided a first differential amplifier Amp1 such that a non-inverting input terminal thereof is connected to the
first photodetector 20 and an inverting input terminal thereof connected to thesecond photodetector 21. Thereby, the differential amplifier Amp1 produces an information signal corresponding to the information recorded on theland 7 d of theoptical disk 7 as the difference between the output of thephotodetector 20 and thephotodetector 21. It should be noted that thephotodetectors optical beam element 18A of which optical phase is compensated by theretardation plate 13 such that the cross-talk from thegroove 7 e is minimized. - Further, there is provided a second differential amplifier Amp2 such that a non-inverting input terminal thereof is connected to the
photodetector 22 and an inverting input terminal thereof connected to thephotodetector 23. Thereby, the differential amplifier Amp2 produces an information signal corresponding to the information recorded on thegroove 7 e of theoptical disk 7 as the difference between the output of thephotodetector 22 and thephotodetector 23. It should be noted that thephotodetectors optical beam element 18B of which optical phase is compensated by theretardation plate 12 such that the cross-talk from theland 7 d is minimized. - FIG. 7 further shows another differential amplifier Amp3 having an inverting input terminal connected to the
photodetector 25 and a non-inverting input terminal connected to thephotodetector 26, wherein the differential amplifier Amp3 produces the tracking error signal as a difference between the output of thephotodetector 26 and the output of thephotodetector 25. It should be noted that thephotodetectors land 7 d and thegroove 7 e, wherein thephotodetectors land 7 d and thegroove 7 e. In such a case of ideal tracking, thephotodetectors differential amplifier Amp 3 becomes zero. - When there is a deviation in the tracking, on the other hand, there appears a difference in the optical beam intensity between the optical beam received by the
photodetector 25 and the optical beam received by thephotodetector 26. For example, the intensity of the optical beam received by thephotodetector 26 may decrease when the intensity of the optical beam received by thephotodetector 25 is increased, or vice versa. Thus, when the output of thephotodetector 25 is increased, the output of thephotodetector 26 is decreased and the differential amplifier Amp3 produces a negative output. In the opposite case, the differential amplifier Amp3 produces a positive output. Thus, the differential amplifier Amp3 produces an output signal indicative of the tracking state as the tracking error signal. - FIG. 8 shows a construction used for detecting a focusing error signal.
- Referring to FIG. 8, there is provided a summation amplifier Amp4 connected across the
photodetector 24 a and thephotodetector 24 c aligned in a diagonal direction in thecentral photodetection part 24, and anothersummation amplifier Amp 5 is connected across thephotodetector 24 b and thephotodetector 24 d aligned also in another diagonal direction of thecentral photodetection part 24. Wherein the summation amplifiers Amp4 and Amp5 produce an output indicative of a summation of the input signals supplied thereto. Further, there is provided a differential amplifier Amp6 having a non-inverting input terminal to which the output of the summation amplifier Amp4 is supplied and an inverting input terminal to which the output of the output of the summation amplifier Amp5 is supplied, wherein the summation amplifiers Amp4 and Amp5 carry out, together with the differential amplifier Amp6, a focusing detection according to a double Foucault process. - More in detail, the double Foucault process utilizes the nature of the reflection optical beam that the reflection optical beam has a circular beam shape when the optical beam is focused properly on the reflection surface. In such a properly focused state, therefore, the
photodetectors 24 a-24 d produce a generally identical output and the differential amplifier Amp6 produces a zero output. - When the focusing state of the optical beam is offset from the properly focused state, on the other hand, there is a tendency that the
photodetectors photodetectors - FIG. 9 shows a diffraction pattern obtained in the reflection optical beam L4 reflected by the
optical disk 7. Because of the presence of the land and grooves repeated with a periodical pitch, it should be noted that the optical beam L3 focused on the recording surface of theoptical disk 7 experiences a diffraction and the reflection optical beam L4 produced as a reflection of the optical beam L3 shows the diffraction pattern as indicated in FIG. 9. - Referring to FIG. 9, the diffraction pattern includes a band-shaped zeroth-
order diffraction beam 27 having awidth 30 and two first-order diffraction beams 28 and 29 at both sides of the zeroth-order beam 27, wherein the zeroth-order beam 27 does not carry information of the recording mark in the optical recording and reproducing apparatus of FIG. 1 in which the recording mark has a length smaller than the size of the beam spot. Thus, the resolution of the optical information detection in the optical recording and reproducing apparatus of FIG. 1 can be improved by cutting off the zeroth-order diffraction beam 27. - In the present invention, rather than providing a shading band contrary to the teaching of Milster et al., op cit., the Wollaston prisms14 a and 14 b are separated from each other with the separation d1 set coincident with the zeroth-
order diffraction beam 27, and the first-order diffraction beams 28 and 29 are processed by the Wollaston prisms 14 a and 14 b and directed to thephotodetectors photodetectors order beam 27 is used also effectively for the tracking control and the focusing control explained before, by providing thewedge prisms th order beam 27. - In the construction of the magneto-optical recording and reproducing apparatus of FIG. 1, it should be noted that a laser diode producing an output optical beam with a wavelength of650 nm is used for the
laser diode 1, and a lens having a numerical aperture of 0.6 is used for theobjective lens 6. Further, the direction of polarization of the reflection optical beam H4 reflected by theoptical disk 7 is set generally parallel to the elongating direction of theland 7 d and hence thegroove 7 e. In the case the direction of polarization is set perpendicular to the elongating direction of theland 7 d and thegroove 7 e, a 1/T wavelength plate may be used for rotating the polarization plane by 90° in the optical detection system. - In the magneto-
optical disk 7, a glass disc having a thickness of 0.6 mm may be used for the substrate 7 c, and theland 7 d and thegroove 7 e may be formed with a tack pitch of 1.2 μm (effective track pitch of 0.6 μm) by using a photo-polymer forming process. On the substrate 7 c, therecording film 7 f is formed as a four-layer stacking structure including a dielectric layer, a magneto-optical recording layer, another dielectric layer and a metal reflection layer. Therecording film 7 f may be formed by a sputtering process and is covered by a protective film of a UV-cure resin with a thickness of several microns. As described previously, thegroove 7 e is formed to have a depth corresponding to one-eighth (⅛) the wavelength of the laser beam used for reading information. - It should be noted that the material of the substrate7 c is by no means limited to a glass disc noted above but an injection molded plastic disc of polycarbonate, and the like, may also be used as long as the plastic disc has a small warp and little birefringence.
- In the present embodiment, the
recording film 7 f may include an amorphous alloy film of TbFeCo as the magneto-optical recording layer. When the TbFeCo alloy is used for the magneto-optical recording layer, therecording film 7 f provides a Kerr rotation angle of 0.9°, a Kerr ellipticity of 0° and a reflectance of 18%, including the contribution from the four-layer structure. Further, a multilayer film for MSR be used for the magneto-optical film 7 f. - The writing of information onto the magneto-
optical disk 7 may be achieved by using a floating magnetic head that creates a modulation magnetic field in combination with a pulse-assisted magnetic modulation process in which a laser pulse is applied in synchronization with the writing of information. While it is possible to carry out the recording of information by a magnetic field modulation process that uses a DC laser beam or by an optical modulation process, the use of the pulse-assisted magnetic modulation process is preferred in view of improved quality of reproduced signal output. - In FIG. 4A, it should be noted that the width d1 of the composite
optical element 9 is optimized in the state that theretardation plates - Further, it should be noted that the optimum value of the retardation of the
retardation plates land 7 d and thegroove 7 e while changing the retardation variously by using a Babinet-Soleil compensator. - In the present embodiment, a wavelength plate having a retardation value of 0.07 wavelength is used for the
retardation plates retardation plate 12 and theretardation plate 13. Thereby, an optical phase compensation of +0.07 wavelength is achieved for theland 7 d and an optical phase compensation of −0.07 wavelength is achieved for thegroove 7 e. An optically uniaxial crystal such as calcite, quartz or LiNbO3 may be used for theretardation plates - TABLE I below shows the result of measurement of CNR (carrier-noise ratio) and the cross-talk for the magneto-optical recording and reproducing apparatus of the present invention.
TABLE I present invention comparative exp. CNR land 45.3 dB 42.1 dB groove 45.8 dB 42.3 dB Cross-talk land −30.2 dB −10.3 dB groove −30.0 dB −11.1 dB - Referring to TABLE I, the measurement was made by first erasing information from a selected
land 7 d and twoadjacent grooves 7 e at both sides of the selectedland 7 d, writing information onto the selectedland 7 d, and reading the information by using the detection system for the land. The measurement for thegroove 7 e is conducted similarly, by exchanging theland 7 d and thegroove 7 e. In the measurement, the magneto-optical disk 7 is driven at a linear velocity of 5 m/sec and a laser power of 1.5 mW was used on therecording medium 7. In the recording of information, a recording mark having a length of 0.45 μm was recorded under the existence of modulation magnetic field of ±15000e, by irradiating a laser beam having a pulse duty of 40% and an optical power of 7.5 mW in synchronization with the modulation magnetic field. - In the experiment of TABLE I, the measurement of cross-talk was conducted as follows.
- In the case of measuring the cross-talk on the signal recorded on a selected lank7 d, the information on the selected
land 7 d as well as the information recorded on thegrooves 7 e at both sides of the selectedland 7 d are first erased, and recording of information is conducted on the selectedland 7 d. Next, a measurement is made on a signal output level CL reproduced by the signal detection system for the land, while tracking theland 7 d on which the recording of the information has been made previously. It should be noted that the signal detection system for the land includes thephotodetectors - Next, a tracking is made for each of the
adjacent grooves 7 e, and a measurement is made on a signal output level CR reproduced by the signal detection system for the groove, for each of theadjacent grooves 7 e. It should be noted that the signal detection system for the groove includes thephotodetectors groove 7 e that provides a larger output level CR is used in the foregoing calculation of the cross-talk. Further, the measurement of the cross-talk for agroove 7 e is conducted similarly as above, by exchanging theland 7 d and thegroove 7 e. - In the foregoing measurement of the cross-talk, it should be noted that a recording mark having a length of 1.35 μm is used. Otherwise, the measurement was conducted similarly to the measurement of the CNR.
- Further, TABLE I above includes result also for a comparative experiment, in which the
retardation plates optical element 9. - Referring to TABLE I, it can be seen that the present invention achieves an increase of the CNR of +3 dB as compared with the comparative experiment, wherein the increase of +2 dB is attributed to the contribution of the elimination of the zeroth-
order beam 27 shown in FIG. 9, while the increase of +1 dB is attributed to the increase of the carrier level in the reproduced signal as a result of the optical phase compensation. - Further, TABLE I indicates that the cross-talk is suppressed to −30 dB.
- Next, a description will be made on the recoding and playback margin for the magneto-optical recording apparatus of the present invention.
- FIG. 10 shows the relationship between the Jitter and the optical power used for writing information, wherein FIG. 10 represents the result of measurement of the jitter of a 2T signal for the case in which a random signal of the RLL1-7 format is recorded both on a
land 7 d and anadjacent groove 7 e with a minimum mark length of 0.45μ. In the measurement of FIG. 10, it should be noted that the linear velocity of the magneto-optical disk 7 is set to 5 m/sec at the time of reading of the information, and the reading of the information is achieved by setting the laser power to 1.5 mW on thedisk 7. - As can be seen in FIG. 10, a jitter of less than about 8% is achieved when the write optical power is set to a range between 7 mW and 10 mW. The result of FIG. 10 indicates that a recording density of 3.2 Gbit/inch2 can be achieved by the magneto-optical information recording and reproducing apparatus of the present invention.
- Thus, the present invention provides a magneto-optical information recording and reproducing apparatus as well as an optical information detection system used therein wherein the cross-talk between the lands and grooves on the magneto-optical recording disk is minimized and wherein the interference between the recording marks aligned on a track is also minimized.
- Further, it should be noted that, while the present invention has been described for a magneto-optical information recording and reproducing apparatus, the present invention is by no means limited to such a specific apparatus but is applicable also to ROM disks, write-once-read-many disks and phase transition disks in which phase pits are formed.
- Further, the present invention is not limited to the embodiments described heretofore, but various variations and modifications may be made without departing from the scope of the invention.
- The present application is based on Japanese priority application No. 10-23147 filed on Feb. 4, 1998, the entire contents of which are hereby incorporated by reference.
Claims (19)
1. An optical information detecting apparatus optically detecting information recorded on a recording medium, said optical information detecting apparatus being adapted to hold said recording medium and comprising:
a beam source;
a first optical system focusing an optical beam produced by said beam source on a recording surface of said recording medium;
a photodetection unit; and
a second optical system directing an optical beam, produced as a result of irradiation of said optical beam on said recording surface, to said photodetection unit,
said second optical system including a beam dividing element disposed so as to incident said produced optical beam, said beam dividing element extracting, from said produced optical beam, a plurality of optical beam elements traveling generally parallel with each other in said reflection optical beam, by dividing said produced optical beam such that said plurality of optical beam elements reach said photodetection unit along respective optical paths.
2. An optical beam detecting apparatus as claimed in , wherein said photodetection unit includes first and second photodetectors on respective optical paths of first and second optical beam elements included in said produced optical beam for detecting an information signal recorded on a land formed on said recording surface of said recording medium and wherein said photodetection unit includes third and fourth photodetectors on respective optical paths of third and fourth optical beam elements includes in said produced optical beam for detecting an information signal recorded on a groove formed on said recording surface of said recording medium.
claim 1
3. An optical information detecting apparatus as claimed in , wherein said beam dividing element has a unitary body.
claim 1
4. An optical information detecting apparatus as claimed in , wherein said beam dividing element applies a first optical phase compensation to a first optical beam element included in said plurality of optical beam elements and a second optical phase compensation to a second, different optical beam element included in said plurality of optical beam elements.
claim 1
5. An optical information detecting apparatus as claimed in , wherein said first optical phase compensation and said second optical phase compensation act oppositely and have the same magnitude.
claim 4
6. An optical information detecting apparatus as claimed in , wherein said first optical phase compensation includes an optical phase shift to said first optical beam element by +0.07 times a wavelength of said reflection optical beam and wherein said second optical phase compensation induces an optical phase shift to said second optical beam element by −0.07 times a wavelength of said reflection optical beam.
claim 5
7. An optical information detection apparatus as claimed in , wherein said beam dividing element includes a first optical phase compensation plate of an optically uniaxial crystal and a second optical phase compensation plate of an optically uniaxial crystal, said first optical phase compensation plate and said second optical phase compensation plates being disposed such that an optical axis of said first optical phase compensation plate and an optical axis of said second optical phase compensation plate intersect perpendicularly.
claim 4
8. An optical information detecting apparatus as claimed in , wherein said first optical phase compensation plate and said second optical phase compensation plate are jointed side by side.
claim 7
9. An optical information detecting apparatus as claimed in , wherein said first optical phase compensation compensates for an optical phase of said first optical beam element produced by a land formed on said recording surface and wherein said second optical phase compensation compensates for an optical phase of said second optical beam element produced by a groove formed on said recording surface adjacent to said land.
claim 4
10. An optical information detecting apparatus as claimed in , wherein said beam dividing element further includes a first polarization beam divider provided on said first optical phase compensation plate and a second polarization beam divider provided on said second optical phase compensation plate, said first polarization beam divider switching an optical path of said first optical beam element between a first optical path and a second optical path in response to a polarization state of said first optical beam element, said second polarization beam divider switching an optical path of said second optical beam element between a third optical path and a fourth optical path in response a polarization state of said second optical beam element.
claim 7
11. An optical beam detecting apparatus as claimed in , further including a first differential amplifier connected to said first and second photodetectors for detecting a difference in output of said first and second photodetectors as said information signal recorded on said land and a second differential amplifier connected to said third and fourth photodetectors for detecting a difference in output of said third and fourth photodetectors as said information signal recorded on said groove.
claim 2
12. An optical beam detecting apparatus as claimed in , wherein said first polarization beam divider and said second polarization beam divider are disposed with a separation from each other.
claim 10
13. An optical beam detecting apparatus as claimed in , wherein said first and second polarization beam splitters are separated with a distance corresponding to a zeroth-order diffraction beam produced by said land and groove on said recording surface of said recording medium and forming a part of said reflection optical beam.
claim 12
14. An optical beam detecting apparatus as claimed in , wherein said first and second polarization beam splitters are disposed so as to intercept two first-order diffraction beams produced in said reflection optical beam at both sides of said zeroth-order diffraction beam.
claim 13
15. An optical beam detecting apparatus as claimed in , further comprising a prism structure between said first and second polarization beam dividers for directing said zeroth-order beam to said photodetection unit for a servo control of said first and second optical systems.
claim 10
16. An optical beam detecting apparatus as claimed in , wherein said prism structure includes a first wedge prism having a first prism surface and a second wedge prism having a second prism surface disposed with a mutual separation such that said first and second prism surfaces are in a mutually inclined relationship, said first and second prism surfaces directing said zeroth-order beam respectively to a corresponding fifth photodetector and a corresponding sixth photodetector of said photodetection unit along fifth and sixth optical paths for a tracking servo control of said first and second optical systems.
claim 15
17. An optical beam detecting apparatus as claimed in , further including a third wedge prism having a third prism surface and a fourth wedge prism having a fourth prism surface disposed side by side in a state that said third and fourth prism surfaces are inclined in mutually opposite directions, said third and fourth prism surfaces directing said zeroth-order beam to a photodetector array of said photodetection unit including four photodetectors arranged in a four-quadrant formation for a focusing servo control of said first and second optical systems.
claim 16
18. An optical beam detecting apparatus as claimed in , wherein said beam dividing element includes: first and second optical phase compensation plates disposed side by side to form a unitary substrate; first and second Wollaston prisms provided on said first and second optical phase compensation plates respectively with a mutual separation from each other in a first direction; first and second wedge prisms respectively provided on said first and second Wollaston prisms, said first and second wedge prisms having respective prism surfaces inclined with each other; third and fourth wedge prisms disposed on said unitary substrate between said first and second Wollaston prisms with a separation from each other in a second direction perpendicular to said first direction, said third and fourth wedge prisms having respective, mutually inclined third and fourth prism surfaces; and fifth and sixth wedge prisms provided on said unitary substrate between said third and fourth wedge prisms, said fifth wedge prism having a fifth prism surface inclined to said third wedge prism, said sixth wedge prism having a sixth prism surface inclined to said fourth wedge prism.
claim 1
19. An optical beam detecting apparatus as claimed in , wherein said recording medium is a magneto-optical disk, and wherein said optical beam detecting apparatus further includes: a turn-table adapted to hold said magneto-optical disk thereon; a spindle motor rotating said turn-table; and a magnetic head disposed adjacent to said magneto-optical disk at a side opposite to said recording surface.
claim 1
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/772,659 US6359851B2 (en) | 1998-02-04 | 2001-01-30 | Optical information detection apparatus |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP10-023147 | 1998-02-04 | ||
JP02314798A JP3708320B2 (en) | 1998-02-04 | 1998-02-04 | Optical information detector |
US09/138,633 US6212152B1 (en) | 1998-02-04 | 1998-08-24 | Optical information detection apparatus |
US09/772,659 US6359851B2 (en) | 1998-02-04 | 2001-01-30 | Optical information detection apparatus |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US09/138,633 Division US6212152B1 (en) | 1998-02-04 | 1998-08-24 | Optical information detection apparatus |
Publications (2)
Publication Number | Publication Date |
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US20010024416A1 true US20010024416A1 (en) | 2001-09-27 |
US6359851B2 US6359851B2 (en) | 2002-03-19 |
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Application Number | Title | Priority Date | Filing Date |
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US09/138,633 Expired - Lifetime US6212152B1 (en) | 1998-02-04 | 1998-08-24 | Optical information detection apparatus |
US09/772,659 Expired - Fee Related US6359851B2 (en) | 1998-02-04 | 2001-01-30 | Optical information detection apparatus |
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US09/138,633 Expired - Lifetime US6212152B1 (en) | 1998-02-04 | 1998-08-24 | Optical information detection apparatus |
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EP (1) | EP0935244B1 (en) |
JP (1) | JP3708320B2 (en) |
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Cited By (1)
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US9769934B2 (en) | 2014-07-16 | 2017-09-19 | Seiko Epson Corporation | Package base, package, electronic device, electronic apparatus, and moving object |
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US7548370B2 (en) | 2004-06-29 | 2009-06-16 | Asml Holding N.V. | Layered structure for a tile wave plate assembly |
KR102527672B1 (en) | 2018-04-06 | 2023-04-28 | 에이에스엠엘 네델란즈 비.브이. | Inspection device with non-linear optical system |
Family Cites Families (18)
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JPS57167145A (en) | 1981-04-07 | 1982-10-14 | Toshiba Corp | Optical information reproducing device |
NL8403034A (en) * | 1984-10-05 | 1986-05-01 | Philips Nv | OPTO-ELECTRONIC FOCUS ERROR DETECTION SYSTEM. |
JPH0682473B2 (en) | 1986-05-16 | 1994-10-19 | 株式会社日立製作所 | Optical information reproducing device |
JP2538214B2 (en) | 1986-08-11 | 1996-09-25 | 松下電器産業株式会社 | Optical information recording / reproducing device |
JPH0770068B2 (en) | 1986-08-11 | 1995-07-31 | 松下電器産業株式会社 | Optical information recording / reproducing device |
JPH0487042A (en) * | 1990-07-31 | 1992-03-19 | Sony Corp | Optical pickup device |
EP0630005B1 (en) * | 1993-06-21 | 2001-08-29 | Fujitsu Limited | Optical information recording/reproducing apparatus |
DE4322149A1 (en) * | 1993-06-21 | 1994-12-22 | Fujitsu Ltd | Optical information recording/reproducing device |
JP3541893B2 (en) * | 1993-08-06 | 2004-07-14 | ソニー株式会社 | Magneto-optical recording medium reproducing device |
US5491675A (en) * | 1994-06-14 | 1996-02-13 | Eastman Kodak Company | Single return path orthogonally-arranged optical focus and tracking sensor system |
JPH08221820A (en) * | 1995-02-13 | 1996-08-30 | Hitachi Ltd | Magneto-optical disk device and magneto-optical recording medium and optical head |
US5784347A (en) * | 1995-02-13 | 1998-07-21 | Hitachi, Ltd. | Optical disk device having optical phase compensator |
JPH08329470A (en) * | 1995-05-31 | 1996-12-13 | Nikon Corp | Method and device for reproducing and optical disk |
JPH0935284A (en) * | 1995-07-17 | 1997-02-07 | Fujitsu Ltd | Optical disk device |
JP3857339B2 (en) | 1995-10-27 | 2006-12-13 | 富士通株式会社 | Optical information detector |
JP3645020B2 (en) * | 1995-12-12 | 2005-05-11 | 富士通株式会社 | Optical information detector |
JPH09212928A (en) | 1996-02-08 | 1997-08-15 | Dainippon Ink & Chem Inc | Magneto-optical recording medium and optical information detector |
US5761162A (en) * | 1996-10-31 | 1998-06-02 | Eastman Kodak Company | Multi-element prism for optical heads |
-
1998
- 1998-02-04 JP JP02314798A patent/JP3708320B2/en not_active Expired - Fee Related
- 1998-08-19 DE DE69837964T patent/DE69837964T2/en not_active Expired - Lifetime
- 1998-08-19 EP EP98115608A patent/EP0935244B1/en not_active Expired - Lifetime
- 1998-08-24 US US09/138,633 patent/US6212152B1/en not_active Expired - Lifetime
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Cited By (1)
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US9769934B2 (en) | 2014-07-16 | 2017-09-19 | Seiko Epson Corporation | Package base, package, electronic device, electronic apparatus, and moving object |
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EP0935244A2 (en) | 1999-08-11 |
US6212152B1 (en) | 2001-04-03 |
US6359851B2 (en) | 2002-03-19 |
DE69837964D1 (en) | 2007-08-02 |
JPH11224437A (en) | 1999-08-17 |
DE69837964T2 (en) | 2007-10-25 |
JP3708320B2 (en) | 2005-10-19 |
EP0935244A3 (en) | 2000-09-20 |
EP0935244B1 (en) | 2007-06-20 |
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