JPH011126A - Optical pickup device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup device used for reproducing optical discs, etc., and particularly relates to detection of focus errors in the optical pickup device.

[Summary of the invention]

The present invention allows reflected light from a recording medium obtained through a lens system to be incident on an optical path length difference generating means formed by laminating glass and a uniaxial crystal material having an optical axis in a predetermined direction. Of the two lights with different optical path lengths output from the optical path length difference generating means, the first light is made to enter the first focus error photodetector ahead of its focused point, and the second light is made to enter the first focus error photodetector before its focused point. A second focus error photodetector disposed further rearward and substantially on the same plane as the first focus error photodetector.
By making the light incident on the focus error photodetector, an optical pick-up device is provided which is small and has excellent mechanical precision.

[Conventional technology]

A conventional optical pickup device used for reproducing optical discs is constructed as shown in FIG.

In FIG. 3, a laser beam from a laser diode 1 has its traveling direction changed by 90 degrees by a beam splitter 2, is converted into a parallel beam by a collimator lens 3, and is further focused onto a recording surface 5a of an optical disk 5 by an objective lens 4. I feel anxious. The reflected light from the optical disk 5 enters the objective lens 4 again, passes through the collimator lens 3, the beam splitter 2, and the beam splitter 6, and then reaches the first photodetector 7.
is irradiated to form a spot. At the same time, the light that has passed through the beam splitter 2 is changed in its traveling direction by 90 degrees by the beam splitter 6 and is irradiated onto the second photodetector 8 to form a spot. In this case, the light incident on the first photodetector 7 has a focal point 9 behind the first photodetector 7.
exists.

Further, the light incident on the second photodetector 8 has its focal point IO in front of the second photodetector 8.

The first photodetector 7 has three photodetection areas A, B, and C as shown in FIG. 4A, and is configured so that a light spot 11 is formed approximately in the middle thereof. ing. The second photodetector 8 has a photodetection area a divided into three as shown in FIG.
, b, and c, and a light spot 12 is formed approximately in the middle thereof.

According to the above configuration, when the recording surface 5a of the optical disc 5 moves away from the focal point of the objective lens 4, the diameter of the spot 11 formed on the first photodetector 7 becomes smaller, and the spot 11 formed on the second photodetector 8 becomes smaller. The diameter of the spot 12 that is formed becomes larger. At this time, regarding the amount of light irradiated to each photodetection area A% B, C, a, b, c, PE= (B-(A+C)) (b-(a+c))
By performing the calculation, the focus error PE can be obtained. Therefore, by controlling the position of the objective lens 4 in the focus direction so that this focus error PE becomes zero, the focused point of the objective lens 4 and the recording surface 5 can be adjusted.
A can be defeated once.

As described above, in the conventional optical pickup device, the beam splitter 7 separates the reflected light from the beam splitter 2 into two beams whose directions differ by 90'' from each other, and a first beam is placed in front of the focal point 9 of one of the beams. By arranging a photodetector 7 and a second photodetector 8 behind the focal point 10 of the other light, the two lights reach the first and second photodetectors 7.8. The optical path lengths up to the point are made to differ.

[Problem that the invention seeks to solve]

Conventional optical pickup devices use a beam splitter 6 and arrange first and second photodetectors 7.8 on two mutually orthogonal surfaces in order to provide the above-mentioned optical path length difference. The space for arranging the beam splitter 6 and the first and second photodetectors 7.8 becomes large, resulting in an increase in the size of the apparatus. In order to solve this problem, the first and second photodetectors 7.8 are placed on the same plane, and a prism is placed in close contact with the same plane. A device that captures light has been proposed, but the processing accuracy of the prism,
This has been extremely difficult to realize due to problems such as the need for strict mounting accuracy when bonding the prisms on the same plane.

[Means for solving problems]

In the present invention, instead of the beam splitter 2.6, an optical path length difference generating means is used, which is formed by laminating glass and a uniaxial crystal material such as crystal having an optical axis in a predetermined direction. The first and second photodetectors are arranged on the same plane, and the first light output from the optical path length difference generating means is made to enter the first focus error photodetector in front of the focused point thereof, and The second light is made to enter the second focus error photodetector at a position behind the focused point.

[Operation] When light passes through the laminated structure of glass and uniaxial crystal material, two lights with different optical path lengths are obtained, so the first and second photodetectors should be arranged on the same plane. Can be done.

〔Example〕

FIG. 1 shows an embodiment of the present invention, and parts corresponding to those in FIG. 3 are given the same reference numerals, and their explanation will be omitted.

In this embodiment, an optical path length difference generating means 13 is provided in place of the beam splitter 2.6 in the prior art shown in FIG. By providing it above, they are placed on the same plane.

As shown in FIG. 2, the optical path length difference generating means 13 has a laminated structure in which glass 15 and crystal 16 are bonded together via an adhesive layer and a vapor-deposited dielectric multilayer film 17. crystal 1
No. 6 is used in which the optical axis 16a when viewed from the front is inclined at 45° as shown in the figure, and the optical axis 16b when viewed from the side is inclined at 45°. In addition, a uniaxial crystal material such as calcite may be used in place of the crystal 16. In that case, the optical path length of the two output lights increases as the -axial anisotropy and thickness increase. The difference can be increased.

The optical path length difference generating means 13 having the above structure is arranged at the position shown in FIG. The function is to allow the reflected light from 3 to pass through and irradiate the first and second photodetectors 7.8. When the optical path length difference generating means 13 passes the reflected light from the collimator lens 3, the light that has passed through the glass 15 is separated into an ordinary ray and an extraordinary ray in the process of passing through the crystal 16, and the light is divided into an ordinary ray and an extraordinary ray according to their respective refractive indexes. Therefore, a difference occurs in the optical path lengths of the two output lights.

The first light having a long optical path length is then incident on the first photodetector 7, and a focused point 9 is obtained behind the first photodetector 7.

Further, the second light having a short optical path length is incident on the second photodetector 8, and a focused point 10 is created in front of the second photodetector 8.

Therefore, spots 11.12 are formed on the first and second photodetectors 7.8, respectively, as shown in FIG. The focus error PE in this case can be obtained by calculating PR=(B-(A+C))-(b-(a+c)) in the same way as described above.

According to this embodiment, since the optical path length difference generating means 13 can obtain two substantially parallel beams having a difference in optical path length, the first and second photodetectors 7.8 can be mounted on the same substrate. 14
3, and the beam splitter 2.6 of FIG. 3 can be omitted. Therefore, the space for arranging the first and second photodetectors 7.8 is small, and the optical pick amplifier device can be made compact. Further, since there is no need to bond a prism or the like onto the substrate 14, particularly strict precision is not required.

Note that if coma aberration or the like occurs in the optical system due to the provision of the optical path length difference generating means 13, a coma aberration correction plate may be provided between the optical path length difference generating means 13 and the substrate 14.

〔Effect of the invention〕

According to the present invention, two photodetectors can be arranged on the same plane, and the beam splitter that was conventionally used can be omitted, so the optical pickup device can be made smaller than the conventional one. . Further, it does not require particularly high mechanical precision and can be manufactured at low cost.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an optical pickup device showing an embodiment of the present invention, FIG. 2 is a perspective view showing an embodiment of the optical path length difference generating means, and FIG. 3 is a schematic diagram of a conventional optical pickup device. FIG. 4 is a diagram for explaining a photodetector. In addition, in the symbols used in the drawings, 1.
・−・−・−−−1−−−−−−−・・Collimator lens 4−・−・−・−・−・−・1 Objective lens 5−・・−
−−−−−・・・−・−Optical disc 7−−−・・
・−・−・・−First photodetector 8・・−・−−−−−・
------------Second photodetector 9.10--
...-Focal point 13---------- Optical path length difference generating means 15---------Glass 16--
−−−・−・−It is crystal.

Claims (1)

[Claims] Focusing light from a light source onto a recording medium through a lens system,
In an optical pickup device configured to detect reflected light from the recording medium through the lens system, the reflected light obtained through the lens system is detected by laminating glass and a uniaxial crystal material having an optical axis in a predetermined direction. The first light outputted from the optical path length difference generating means is made to enter the first focus error photodetector in front of the focused point thereof, and the The second light outputted from the optical path length difference generating means is incident on a second focus error photodetector arranged substantially on the same plane as the first focus error photodetector behind the focused point. An optical pickup device characterized in that: