# US 8,787,137 B2 · Optical pickup device and optical disc device

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- Number: US 8,787,137 B2
- Document ID: US8787137B2
- Status: Granted
- Kind: B2
- Application number: 13/978,160
- Filed: 2012-01-17
- Published: 2013-10-31
- Granted: 2014-07-22
- Earliest claimed: 2011-01-20
- Assignees: Mitsubishi Electric Corporation
- Applicants: Hironori Nakahara; Toshiya Matozaki; Nobuo Takeshita
- Inventors: Hironori Nakahara; Toshiya Matozaki; Nobuo Takeshita
- Web page: https://patentgrep.com/patent/US8787137B2

## CPC

- G11B 7/13927: {during transducing, e.g. to correct for variation of the spherical aberration due to disc tilt or irregularities in the cover layer thickness}
- G11B 7/1362: Mirrors
- G11B 7/1376: Collimator lenses {(collimators per se G02B27/30)}
- G11B 2007/0013: {for carriers having multiple discrete layers}
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)

## Abstract

An optical pickup device includes a laser light source 201, a collimating optical system 202 for converting laser light to parallel light, a focusing optical system 205 for focusing the parallel light onto an optical disc, a light detection unit for receiving returning light returning by reflection of the focused light from the optical disc 101 and outputting a detection signal, and a reflecting mirror 204 disposed between the collimating optical system and the focusing optical system. The reflecting mirror 204 has a reflective surface including three regions having different reflectances. The central region on the reflecting surface meets the other two regions, at positions illuminated by the light focused by the light focusing optical system, in boundary lines that are parallel to a radial direction on the optical disc 101. The reflectance of the central region is lower than the reflectances of the other two regions.

## Claims

### Claim 1

An optical pickup device comprising:
a laser light source;
a collimating optical system for converting laser light emitted from the laser light source to parallel light;
a focusing optical system for focusing the parallel light to which the laser light is converted onto an optical disc;
a light detection unit for receiving returning light returning by reflection, from the optical disc, of the light focused by the focusing optical system, and outputting a detection signal; and
a reflecting mirror disposed between the collimating optical system and the focusing optical system; wherein
the reflecting mirror has a reflecting surface, the reflecting surface having a central region and first and second outside regions located outside the central region;
the central region on the reflecting surface meets the first and second outside regions on the reflecting surface, at respective positions illuminated by the light focused by the focusing optical system, in two boundary lines parallel to a radial direction on the optical disc; and
a ratio of a reflectance of the central region to reflectances of the first and second outside regions is defined by the following mathematical expression:
Ri/Ro<0.44·ln(x)−0.70,
where Ri denotes the reflectance of the central region; Ro denotes the reflectances of the first and second outside regions; and x denotes a rim light intensity measured on a percentage basis, assuming that a value of Ri/Ro is equal to 1 with respect to a predetermined focused spot diameter on the optical disc.

### Claim 2 (depends on 1)

The optical pickup device of claim 1, wherein the two boundary lines are spaced apart by a quantity less than a lens pupil diameter of the focusing optical system.

### Claim 3 (depends on 1)

An optical disc device comprising:
the optical pickup device of claim 1; and
a signal reproduction circuit for reproducing information recorded on the optical disc on a basis of a signal output from the light detection unit in the optical pickup device.

### Claim 4 (depends on 1)

The optical pickup device of claim 1, wherein the mathematical expression is satisfied under a condition that:
the predetermined focused spot diameter is about 0.412 micrometers; and
a value of fh/φ is equal to about 0.5 where φ denotes a pupil diameter of a objective lens of the focusing optical system, and fh denotes a width of the central region in a direction perpendicular to the radial direction.