KR20030006537A - Method for compensating birefringence and a optical pickup apparatus adopting it - Google Patents
Method for compensating birefringence and a optical pickup apparatus adopting it Download PDFInfo
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- KR20030006537A KR20030006537A KR1020010042349A KR20010042349A KR20030006537A KR 20030006537 A KR20030006537 A KR 20030006537A KR 1020010042349 A KR1020010042349 A KR 1020010042349A KR 20010042349 A KR20010042349 A KR 20010042349A KR 20030006537 A KR20030006537 A KR 20030006537A
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- optical disk
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- 230000003287 optical effect Effects 0.000 title claims abstract description 84
- 238000000034 method Methods 0.000 title claims abstract description 14
- 230000000694 effects Effects 0.000 abstract description 2
- 230000005855 radiation Effects 0.000 abstract 4
- 230000001172 regenerating effect Effects 0.000 abstract 1
- 230000010287 polarization Effects 0.000 description 12
- 238000004519 manufacturing process Methods 0.000 description 3
- 238000001746 injection moulding Methods 0.000 description 2
- 239000011347 resin Substances 0.000 description 2
- 229920005989 resin Polymers 0.000 description 2
- 230000007423 decrease Effects 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 230000000593 degrading effect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229920000515 polycarbonate Polymers 0.000 description 1
- 239000004417 polycarbonate Substances 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
Classifications
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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
- G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/02—Details
- G01J1/04—Optical or mechanical part supplementary adjustable parts
- G01J1/0407—Optical elements not provided otherwise, e.g. manifolds, windows, holograms, gratings
- G01J1/0429—Optical elements not provided otherwise, e.g. manifolds, windows, holograms, gratings using polarisation elements
-
- 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
- G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
- G11B7/126—Circuits, methods or arrangements for laser control or stabilisation
- G11B7/1263—Power control during transducing, e.g. by monitoring
-
- 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
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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
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1372—Lenses
- G11B7/1374—Objective lenses
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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
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1395—Beam splitters or combiners
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B2220/00—Record carriers by type
- G11B2220/20—Disc-shaped record carriers
- G11B2220/25—Disc-shaped record carriers characterised in that the disc is based on a specific recording technology
- G11B2220/2537—Optical discs
Abstract
Description
본 발명은 광디스크의 복굴절 보상 방법 및 이를 채용한 광픽업 장치에 관한 것으로, 특히 광디스크에서 복굴절되는 광에 의한 영향을 최소화하여 보다 신뢰성 있는 재생신호를 얻을 수 있도록 한 광디스크의 복굴절 보상 방법 및 이를 채용한광픽업 장치에 관한 것이다.The present invention relates to a method for compensating a birefringence of an optical disc and an optical pickup device employing the optical disc. In particular, a method for compensating a birefringence of an optical disc and minimizing the influence of light birefringent on the optical disc to obtain a more reliable playback signal and an optical disc having the same It relates to a pickup device.
광디스크는 이론적으로 그 기판이 폴리카보네이트(Polycarbonate) 재질로 되어 있어 모든 방향에 대해 굴절률이 동일한 등방성 구조로 되어 있다. 그런데, 실제로는 광디스크는 그 제조 과정에서 응력(stress)을 받게 되어 등방성이 깨지는 경우, 방향에 따라 굴절률이 달라지게 되어 입사광을 복굴절 시키게 된다. 즉, 광디스크는 사출 성형에 의하여 기판을 제작하게 되는데, 사출 성형시 고온의 레진(resin)이 금형 내로 주입되면서 응고되는 과정에서 인장 또는 압축 응력을 받아 복굴절이 발생된다.The optical disk is theoretically made of polycarbonate, so that the optical disk has an isotropic structure with the same refractive index in all directions. In reality, however, when the optical disk is subjected to stress in the manufacturing process and the isotropy is broken, the refractive index is changed depending on the direction to birefringe the incident light. That is, the optical disk is to produce a substrate by injection molding, the birefringence is generated by the tensile or compressive stress in the process of solidifying the injection of a high temperature resin (resin) into the mold during injection molding.
이와 같이, 광디스크에 복굴절이 존재하면 광픽업 장치를 이루는 광학요소의 편광 특성에 의한 영향으로 신호 레벨이 변하게 되어 재생 신호가 열화된다.As such, when the birefringence is present on the optical disk, the signal level is changed due to the polarization characteristic of the optical element constituting the optical pickup device, thereby degrading the reproduction signal.
도 1을 참조하면, 종래의 광픽업장치는 광을 출사하는 광원(10)과, 상기 광원(10)에서 출사된 광이 입사되어 반사 및/또는 투과되는 빔스프리터(15)와, 이 빔스프리터(15)에서 반사된 광을 디스크(50)에 집속시키는 대물 렌즈(45)를 포함한다. 그리고, 상기 디스크(50)에서 반사된 후, 상기 빔스프리터(15)를 투과하여 광검출기(60)에 수광된다. 여기서, 상기 빔스프리터(15)와 디스크(50) 사이의 광경로 상에는 광원(10)에서 출사된 광의 경로를 변환시키는 반사미러(35), 광을 평행한 상태로 만들어 주는 콜리메이팅 렌즈(40)가 배치된다.Referring to FIG. 1, a conventional optical pickup apparatus includes a light source 10 for emitting light, a beam splitter 15 through which light emitted from the light source 10 is incident, reflected and / or transmitted, and the beam splitter. The objective lens 45 which focuses the light reflected by the 15 at the disk 50 is included. After the light is reflected by the disk 50, the light is transmitted through the beam splitter 15 and received by the photodetector 60. Here, on the optical path between the beam splitter 15 and the disk 50, the reflection mirror 35 for converting the path of the light emitted from the light source 10, the collimating lens 40 to make the light in a parallel state Is placed.
여기서, 상기 빔스프리터(15)와 광검출기(60) 사이에는 수속렌즈(55)가 구비될 수 있다.Here, a converging lens 55 may be provided between the beam splitter 15 and the photodetector 60.
한편, 상기 광원(10)은 소정 편광모드 예컨대, TE모드(transverse electricmode)의 광을 조사한다. TE모드는 상기 광원(10)을 이루는 반도체 물질층의 적층방향으로 p편광이 진동하고, 수평방향으로 s편광이 진동하는 모드를 말한다.On the other hand, the light source 10 irradiates light of a predetermined polarization mode, for example, a TE mode (transverse electric mode). The TE mode refers to a mode in which p-polarized light vibrates in the stacking direction of the semiconductor material layer constituting the light source 10 and s-polarized light vibrates in the horizontal direction.
이 광은 상기 콜리메이팅렌즈(40) 및 대물렌즈(45)를 경유하여 광디스크(50)에 도달하게 된다. 여기서, 상기 광디스크(50)는 그 제조과정에서 상술한 바와 같이 등방성이 깨지면 광의 편광 상태에 따라 굴절률이 달라지는 복굴절 성질을 가지게 된다.This light reaches the optical disc 50 via the collimating lens 40 and the objective lens 45. Here, the optical disk 50 has a birefringence property in which the refractive index varies depending on the polarization state of light when the isotropy is broken as described above in the manufacturing process.
상기 광디스크(50)에 입사되는 광의 편광 상태와 복굴절의 방향에 따라서 광량이 감소되고, 이에 따라 광검출기(60)에 수광되는 신호 레벨이 변하게 된다. 따라서, 종래의 광픽업 장치는 편광상태에 따라 투과율 편차가 크게 나타나므로 광디스크의 복굴절 특성에 따라 광검출기에 수광되는 신호 레벨이 변함으로써, 정보의 정상적인 재생이 곤란하다는 문제점이 있다.The amount of light decreases according to the polarization state of the light incident on the optical disk 50 and the direction of birefringence, thereby changing the signal level received by the photodetector 60. Therefore, in the conventional optical pickup apparatus, since the transmittance variation is large depending on the polarization state, the signal level received by the photodetector is changed according to the birefringence characteristic of the optical disk, thereby making it difficult to reproduce the information normally.
본 발명은 상기한 문제점을 해결하기 위하여 안출된 것으로서, 편광기를 이용하여 광디스크의 복굴절 특성을 검출하고, 그 검출 데이터를 광원에 피드백시켜 복굴절에 의한 영향을 보상할 수 있도록 한 광디스크의 복굴절 보상 방법 및 이를 채용한 광픽업 장치를 제공하는데 그 목적이 있다.SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the method of compensating the birefringence of the optical disk to detect the birefringence characteristics of the optical disk using a polarizer, and to feed back the detection data to the light source to compensate for the effects of the birefringence, and An object of the present invention is to provide an optical pickup apparatus employing the same.
도 1은 종래의 광픽업 장치의 개략적인 배치도이다.1 is a schematic layout view of a conventional optical pickup apparatus.
도 2는 본 발명에 따른 광픽업 장치의 개략적인 배치도이다.2 is a schematic layout view of an optical pickup apparatus according to the present invention.
도 3은 본 발명에 따른 광픽업 장치의 광디스크 복굴절 보상 방법을 구현하기 위한 흐름도이다.3 is a flowchart for implementing an optical disc birefringence compensation method of an optical pickup apparatus according to the present invention.
<도면 중 주요 부분에 대한 부호의 설명><Explanation of symbols for main parts of the drawings>
10...광원 25...광분할기10 ... light source 25 ... light splitter
30...편광기 40...콜리메이팅 렌즈30 ... polarizer 40 ... collimating lens
45...대물 렌즈 50...광디스크45 objective lens 50 optical disc
60...광검출기60.Photodetector
상기한 문제점을 해결하기 위하여 본 발명에 따른 광디스크의 복굴절 보상 방법은, 광원에서 출사된 광의 광량을 측정하는 단계; 상기 광원에서 출사된 광을 광분할기와 대물 렌즈를 통해 광디스크에 집속시키는 단계; 상기 광디스크에서 반사된 광이 편광기를 통과한 후의 광량을 측정하는 단계; 상기 광원에서의 광량과 상기 편광기를 통과한 후의 광량을 비교하여 광원의 파워를 조절하는 단계;를 포함하는 것을 특징으로 한다.In order to solve the above problems, the birefringence compensation method of an optical disk according to the present invention comprises the steps of measuring the amount of light emitted from the light source; Focusing the light emitted from the light source to the optical disc through a light splitter and an objective lens; Measuring an amount of light after the light reflected from the optical disk passes through the polarizer; And comparing the amount of light from the light source with the amount of light after passing through the polarizer to adjust power of the light source.
상기한 문제점을 해결하기 위하여 본 발명에 따른 광픽업 장치는, 광원, 상기 광원으로부터의 광을 반사 또는 투과시키는 광분할기, 상기 광분할기에서 나온 광을 광디스크에 집속시키는 대물 렌즈, 상기 광디스크에서 반사된 광이 상기 대물 렌즈와 광분할기를 경유하여 수광되는 광검출기를 포함하는 광픽업 장치에 있어서,In order to solve the above problems, an optical pickup apparatus according to the present invention includes a light source, an optical splitter for reflecting or transmitting light from the light source, an objective lens for condensing light emitted from the optical splitter, onto an optical disk, and reflected from the optical disk. An optical pickup apparatus comprising a photodetector in which light is received via the objective lens and a splitter,
상기 광분할기와 상기 광검출기 사이의 광경로상에 편광기를 배치하여 광디스크의 복굴절에 의한 영향을 측정할 수 있도록 된 것을 특징으로 한다.The polarizer may be disposed on an optical path between the optical splitter and the photodetector to measure the influence of birefringence of the optical disk.
이하 첨부 도면을 참조하여 본 발명에 따른 광디스크의 복굴절 보상 방법 및 이를 채용한 광픽업 장치에 대해 상세히 설명한다.Hereinafter, a birefringence compensation method of an optical disc and an optical pickup apparatus employing the same will be described in detail with reference to the accompanying drawings.
도 2를 참조하면, 본 발명에 따른 광픽업 장치는, 광원(10)과, 상기 광원(10)으로부터의 광을 반사 또는 투과시키는 광분할기(25), 상기 광분할기(25)에서 나온 광을 광디스크(50)에 집속시키는 대물 렌즈(45), 상기 광디스크(50)에서 반사된 광이 상기 대물 렌즈(45)와 광분할기(25)를 경유하여 수광되는 광검출기(60)를 포함한다. 그리고, 상기 광디스크(50)의 복굴절에 의한 영향을 측정할 수 있도록 상기 광분할기(25)와 상기 광검출기(60) 사이의 광경로상에 편광기(30)를 배치한다. 여기서, 도 1에 도시된 광픽업 장치와 동일한 참조 번호를 사용하는 구성 요소는 동일한 기능, 동일한 구성을 가지므로 그 자세한 설명은 생략하기로 한다.Referring to FIG. 2, the optical pickup apparatus according to the present invention includes a light source 10, a light splitter 25 that reflects or transmits light from the light source 10, and light emitted from the light splitter 25. The objective lens 45 to focus on the optical disk 50, and the photodetector 60 that the light reflected from the optical disk 50 is received via the objective lens 45 and the optical splitter 25. The polarizer 30 is disposed on the optical path between the optical splitter 25 and the photodetector 60 so as to measure the influence of the birefringence of the optical disk 50. Here, the components using the same reference numerals as those of the optical pickup apparatus shown in FIG. 1 have the same function and the same configuration, and thus detailed description thereof will be omitted.
상기 편광기(30)는 s편광 또는 p편광 중 일 편광 성분만을 투과시키는 것으로, 상기 광원(10)에서 출사된 광량과 상기 편광기(30)를 통과한 후의 광량을 비교함으로써 상기 광디스크(50)의 복굴절로 인한 광량 감소를 측정할 수 있다. 한편, 상기 광분할기(25)는 예를 들어 빔스프리터, 편광 방향에 따라 투과 및 반사시키는 편광 빔스프리터일 수 있다. 편광 빔스프리터를 사용하는 경우에는 1/4 파장판(미도시)을 더 구비한다.The polarizer 30 transmits only one polarization component of s-polarized light or p-polarized light, and compares the amount of light emitted from the light source 10 with the amount of light after passing through the polarizer 30 to birefringence of the optical disc 50. Can reduce the amount of light due to. On the other hand, the light splitter 25 may be, for example, a beam splitter, a polarizing beam splitter that transmits and reflects according to the polarization direction. When using a polarizing beam splitter, a quarter wave plate (not shown) is further provided.
본 발명에 따른 광디스크의 복굴절 보상 방법은, 도 3에 도시된 바와 같이 광원(10)에서 출사된 광의 광량을 측정하는 단계(S5); 광원(10)에서 출사된 광을 광분할기(25)와 대물 렌즈(45)를 통해 광디스크(50)에 집속시키는 단계(S10); 상기 광디스크(50)에서 반사된 광이 편광기(30)를 통과한 후의 광량을 측정하는 단계(S15);를 포함한다.Birefringence compensation method of an optical disk according to the present invention, as shown in Figure 3, the step of measuring the amount of light emitted from the light source 10 (S5); Concentrating the light emitted from the light source 10 to the optical disc 50 through the light splitter 25 and the objective lens 45 (S10); And measuring the amount of light after the light reflected by the optical disk 50 passes through the polarizer 30 (S15).
상기 광원(10)에서 출사된 광은 선형 편광되어 있어 광원을 고정시키는 방향에 따라 s편광과 p편광의 비율을 조절할 수 있다. 이러한 광이 상기 광분할기(25)를 통과하면서 편광 상태에 따른 반사율 차이로 인해 편광비가 변하게 된다. 이어서, 상기 광디스크(50)에서 반사될 때 복굴절 특성으로 인해 일편광 상태의 광이 다른 편광 상태의 광으로 변하게 되어 편광비에 편차가 더욱 커지게 된다. 이러한 변화를 측정하기 위해 상기 광분할기(25)와 광검출기(60) 사이에 상기 편광기(30)를 배치하고, 이 편광기(30)를 통과한 후의 광량을 측정한다. 상기 편광기(30)는 s편광 또는 p편광 중 어느 한 편광만을 투과시키는 것으로, 상기 광디스크(50)로부터 반사된 광이 상기 편광기(30)를 통과하면 일편광의 광만이 존재한다. 그리고,일편광의 광이 광검출기(60)에 수광되어 디스크에 기록된 신호를 재생하게 된다. 한편, 상기 광검출기(60)에 의해 검출된 광의 광량을 측정하여 상기 광원(10)에서 출사된 광의 광량과 비교한다. 이 비교치에 의해 상기 광디스크(50)의 복굴절에 의한 광 감소량을 알 수 있다.The light emitted from the light source 10 is linearly polarized to adjust the ratio of s-polarized light and p-polarized light according to the direction in which the light source is fixed. As the light passes through the light splitter 25, the polarization ratio is changed due to the difference in reflectance according to the polarization state. Subsequently, when the light is reflected from the optical disc 50, the light in one polarization state is changed to light in another polarization state due to the birefringence characteristic, so that the deviation in polarization ratio is further increased. In order to measure such a change, the polarizer 30 is disposed between the light splitter 25 and the photodetector 60, and the amount of light after passing through the polarizer 30 is measured. The polarizer 30 transmits only one of s-polarized light and p-polarized light. When light reflected from the optical disk 50 passes through the polarizer 30, only one polarized light exists. Then, light of one polarized light is received by the photodetector 60 to reproduce the signal recorded on the disk. Meanwhile, the amount of light detected by the photodetector 60 is measured and compared with the amount of light emitted from the light source 10. This comparison value shows the amount of light reduction due to birefringence of the optical disc 50.
이 비교치를 반영하여 상기 광원(10)의 광량을 조절(S25)함으로써 상기 광디스크(50)의 복굴절로 인한 광량 감소를 보상할 수 있다.The amount of light due to birefringence of the optical disc 50 can be compensated by adjusting the amount of light of the light source 10 by reflecting the comparison value (S25).
상기와 같은 과정을 반복하여 검출한 광량 감소량만큼 상기 광원(10)의 파워를 높임으로써 상기 광디스크(50)의 복굴절에 의한 광량 감소를 보상한다. 이와 같이 하여 보다 신뢰성 있는 재생 신호를 얻을 수 있다.By repeating the above process by increasing the power of the light source 10 by the amount of light reduction is detected to compensate for the reduction in the amount of light due to the birefringence of the optical disk 50. In this way, a more reliable reproduction signal can be obtained.
본 발명에 따른 광디스크의 복굴절 보상 방법 및 이를 채용한 광픽업 장치에 의하면, 편광기를 이용하여 광디스크의 복굴절에 의한 영향으로 광검출기에 수광되는 광의 감소량을 측정하고 이 측정 결과를 이용하여 광파워를 조절함으로써 양호한 재생 신호를 얻을 수 있도록 한다. 또한, 광디스크의 제조 조건에 따라서 광디스크의 복굴절 특성에 차이가 생기게 되는데 본 발명의 원리를 이용하여 광검출기에서 검출되는 광량의 변화를 통하여 광디스크의 복굴절량을 측정함으로써 불량 광디스크를 판별할 수 있다.According to the birefringence compensation method and the optical pickup device employing the optical disk according to the present invention, by using a polarizer to measure the amount of light received by the photodetector under the influence of the birefringence of the optical disk and using the measurement results to adjust the optical power By doing so, a good reproduction signal can be obtained. In addition, there is a difference in the birefringence characteristics of the optical disc according to the manufacturing conditions of the optical disc. By using the principle of the present invention, the defective optical disc can be determined by measuring the birefringence amount of the optical disc through the change of the amount of light detected by the photodetector.
Claims (2)
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH02304729A (en) * | 1989-05-18 | 1990-12-18 | Olympus Optical Co Ltd | Optical information recording and reproducing device |
| US5644562A (en) * | 1996-02-28 | 1997-07-01 | Zygo Corporation | Method and apparatus for measuring and compensating birefringence in rotating disks |
| JPH09282658A (en) * | 1996-04-08 | 1997-10-31 | Sony Corp | Surface defect detector for disk |
| KR19990030279U (en) * | 1997-12-30 | 1999-07-26 | 윤종용 | Abnormality Detection Device in Optical Recording Device |
| JP2000268398A (en) * | 1999-03-18 | 2000-09-29 | Pioneer Electronic Corp | Optical pickup, information recording device, and information reproducing device |
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2001
- 2001-07-13 KR KR1020010042349A patent/KR20030006537A/en not_active Application Discontinuation
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH02304729A (en) * | 1989-05-18 | 1990-12-18 | Olympus Optical Co Ltd | Optical information recording and reproducing device |
| US5644562A (en) * | 1996-02-28 | 1997-07-01 | Zygo Corporation | Method and apparatus for measuring and compensating birefringence in rotating disks |
| JPH09282658A (en) * | 1996-04-08 | 1997-10-31 | Sony Corp | Surface defect detector for disk |
| KR19990030279U (en) * | 1997-12-30 | 1999-07-26 | 윤종용 | Abnormality Detection Device in Optical Recording Device |
| JP2000268398A (en) * | 1999-03-18 | 2000-09-29 | Pioneer Electronic Corp | Optical pickup, information recording device, and information reproducing device |
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