JPS63175237A - Optical head - Google Patents

Abstract

PURPOSE:To ensure the stabilized recording and reproducing actions with an optical head by setting the light emitting points of the semiconductor lasers excluding the one set on the optical axis of a collimator lens with prescribed level differences secured in the direction of the optical axis of the collimator lens against the light emitting point of the semiconductor laser set on the optical axis of the collimator lens. CONSTITUTION:The light emitting points 33a and 33c of laser diodes LD3a and 3c are set with level differences secured in the direction of an optical axis against the light emitting point 33b of an LD3b so that the bend of an image surface due to a focusing optical system is corrected. Both points 33a and 33c are not set on the optical axis of a collimator lens 4 and therefore the light beams emitted from the points 33a and 33c and transmitted through the lens 4 and a focusing lens 8 are made incident obliquely on the lenses to cause the bends of the image surfaces. These image surfaces, however, are connected to each other on the same plane of an optical disk 9 owing to a level difference (d). As a result, three beam spots sent from the points 33a-33c on the disk 9 are even to secure the stable recording and reproducing actions.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical head used in an optical information recording/reproducing device that records or reproduces information by converging a light beam onto a disc-shaped recording medium. Regarding.

[Conventional technology]

In an optical information recording/reproducing device (optical disk device) that records or reproduces information by converging a light beam onto a disk-shaped recording medium (optical disk), an optical head for recording or reproducing information is Usually one semiconductor laser (LD)
is used as a light source, but in cases where the purpose is to record or reproduce information at high speed, a method that uses multiple LDs to simultaneously record and reproduce information on multiple tracks is used. There are some. At this time, it is considered desirable to use a semiconductor laser array (LD array), which is constructed by integrating multiple LDs on the same semiconductor substrate, as a light source because it has fewer parts and is easier to adjust. . (See Japanese Patent Application No. 58-154576.) FIG. 3 is a block diagram showing an optical system of an example of a conventional optical head that irradiates a plurality of beams using an LD array as a light source.

(Refer to Japanese Patent Application Laid-Open No. 60-115033.) In FIG. 3, irradiated light (light beams) 100a, 100b and 100c from LDs 2a, 2b and 2C of light source 2 are collimated by collimating lens 4 and incident on polarizing beam splitter 5. be done. When recording or reproducing information in parallel by irradiating these three light beams onto three adjacent tracks on an optical disk, each light beam performs an information recording/reproducing operation on its corresponding track. At this time, one of the light beams 100c is used for servo and also for recording and reproducing information, or is used exclusively for servo, and the other two
The book beams 100a and 100b are used exclusively for recording or reproduction. The light beams 100a, 100b, and 100c from the LDs 2a, 2b, and 2c are P-polarized lights, so they travel straight through the polarization beam splitter 5 without being deflected, and pass through the quarter-wave plate 6, where they are converted into circularly polarized light. be done. Further, the light passes through a converging lens 8 attached to the actuator tough and is focused onto a recording medium (optical disc) 9.

The light beam reflected from the optical disk 9 travels along essentially the same optical path in the opposite direction and passes through the quarter-wave plate 6, where the circularly polarized light is changed from the polarization direction of the irradiated light from the LDs 2a, 2b, and 2c. The light becomes orthogonally polarized light (S-polarized light) and changes its course by 90 degrees at the polarizing beam splitter 5. The light beam that has changed its course is the light beam 1 that has passed through the lens 10.
01a, 101b and 101c are focused to a point at approximately the same distance from lens 10.

The servo light beam 101c passes through a light separation element 14 such as a pinhole or knife disposed at a convergence position.
The light beam is separated from other light beams and is incident on the detector 13. On the other hand, the other light beams 101a and 101b are detected by a photodetector 1 disposed at a convergence position on the light separation element 14.
1 and 12, and the three light beams 101a, 101b and 101c are detected independently.

[Problem that the invention seeks to solve]

In the optical head that irradiates multiple beams as described above, each of the multiple light beams is irradiated onto separate adjacent tracks on the optical disk, and recording or reproduction is performed simultaneously using the multiple light beams. In this operation, it is essential that all the plurality of light beams on the optical disk are uniformly converged to their diffraction limit. However, since the converging optical system uses one collimating lens and one converging lens, some of the multiple beams will be incident obliquely to the lens, as shown in Figure 4. A curvature of the image plane occurs due to the converging optical system as shown in . That is, as shown in FIG. 4, among the light beams emitted from the LDs 2a, 2b, and 2c located on the same light source surface 2h of the light source, the beams emitted from the LDs 2a and 2c are directed toward the collimating lens 4 and the converging lens 8. Because they are incident obliquely, their convergence points shift with respect to the optical disc surface (optical disc surface) 9a, and the best image plane 401a
And 401C is a position shifted from the best image plane 401b by LD2b. As a result, the positions of the focal planes of the spots of the plurality of light beams on the optical disk are different, and the overall depth of focus is reduced, making recording or reproducing operations unstable. The curvature of the image plane as described above can be improved by optimizing the shapes of the collimating lens 4 and the converging lens 8, but in this case, the shapes of the lenses become complicated and the size and weight of the optical head increases. This is not preferable because it increases the cost of the pod.

An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional optical head, and to eliminate the inability to properly converge the beams emitted from a plurality of semiconductor lasers onto the optical disk surface. An object of the present invention is to provide an optical head capable of recording or reproducing information without increasing size, weight, or cost.

[Means for solving problems]

The optical head of the present invention includes: a light source having a plurality of semiconductor lasers; an actuator having a collimating lens, a polarizing beam splitter, a quarter-wave plate, and a converging lens disposed between the light source and the optical disk; A light beam emitted from a light source and reflected from the optical disk is changed its course by the polarization boom splitter. A lens is disposed in the path of the reflected light beam, and the light passing through the lens is detected. In the optical head, the optical head includes a photodetector, a light separation element that separates a servo light beam from the reflected light beam, and a detector that detects the separated servo light beam. Among them, the light emitting points of the remaining semiconductor lasers excluding the semiconductor laser disposed on the optical axis of the collimating lens are the same as the light emitting points of the semiconductor lasers disposed on the optical axis of the collimating lens. It is arranged with a predetermined step in the direction of the optical axis.

[Effect]

In the optical head of the present invention, when a plurality of light beams irradiated from a plurality of LDs of one light source pass through a collimating lens and a converging lens to form a plurality of light beam spots on an optical disk, the optical head uses a converging optical system. In order to correct the curvature of the image plane caused by the system, the spots of the plurality of light beams on the optical disk are accurately focused on the optical disk by arranging the LD with a step in the optical axis direction. Can be done. This eliminates the curvature of the image plane, making it possible to perform stable recording or reproducing operations.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a configuration diagram showing an optical system according to an embodiment of the present invention.

In FIG. 2, a light source 3 is disposed facing a recording medium (optical disk) 9, and LDs 3a, 3b, and 3
It has c. Between the light source 3 and the optical disk 9, there are a collimating lens 4, a polarizing beam splitter, etc.
Actuator 7 having a four-wave plate 6 and a converging lens 8
The lens 10, the photodetectors 11 and 12, the detector 13, and the optical separation element 14 are connected to the optical disk 9.
The path of the light beam whose course is changed by the polarizing beam splitter 5 is disposed on the path of the light beam reflected from the polarizing beam splitter 5.

The configuration and operation of the other components except for the light source 3 are the same as the conventional example shown in FIG.
b and 3c irradiation light 102a and 102b and 1
02c is focused onto an optical disk 9 via a collimating lens 4, a polarizing beam splitter 5, a quarter-wave plate 6, and a converging lens 8. The reflected light beam from the optical disk 9 passes through the polarizing beam splitter 5 with a path of 90".
is transmitted through the lens 10 and the photodetectors 11 and 1
2 and the detector 13.

FIGS. 1(a) and (b) show a light source 3 having three LDs.
FIG. 2 is a plan view and a front view showing the same. In Figure 1, 3
1a, 31b, and 31c are positive electrodes, 32 is a negative electrode, 33a, 33b, and 33c are light emitting points, and by applying a predetermined voltage between the positive electrode 31a, 31b, or 31c and the negative electrode 32, the light emitting point is A light beam is irradiated from 33a, 33b, or 33c.

The light emitting points 33a and 33C of the LD3a and 3c are located at the LD3b in order to correct the curvature of the image plane caused by the convergent optical system.
The light emitting point 3b is disposed with a step (reference numeral d) in the optical axis direction. Light emitting point 3 of LD3a and 3c
3a and 33c are not located on the optical axis of the collimating lens 4, so the light beam irradiated from these and passing through the collimating lens 4 and the converging lens 8 enters the lens obliquely and the image plane is curved. However, since the light emitting points 33a and 33c have a step d with respect to the optical axis direction, the image planes on the optical disk 9 are aligned on the same plane. As a result, the same depth of focus as in the case of three lights on the optical disk 9 can be obtained. Therefore, all three beams can perform stable recording or reproducing operations.

Although the embodiment shown in FIG. 1 is an example in which a plurality of LDs are integrated on the same substrate, the same operation and effect can be obtained even if three single semiconductor lasers are arranged in the same way. It will be done. Further, even when four or more LDs are used, the same operation and effect can be obtained by providing each LD with a step according to its degree of curvature. The arrangement of the LD can be uneven or asymmetrical depending on the curvature of the image plane of the converging optical system.

〔Effect of the invention〕

As explained above, in the optical head of the present invention, the light beams irradiated from the plurality of semiconductor lasers in one light source correct the curvature of the image plane that occurs in the converging optical system, so that the image planes are on the same plane. By arranging the semiconductor lasers with steps in the optical axis direction, the slits of the light beams on the recording medium are made uniform, and all the light beams perform recording and reproducing operations simultaneously in parallel. Therefore, there is an effect that the recording or reproducing operation of an optical disk device using the present optical head can be performed at high speed and with excellent reliability.

[Brief explanation of the drawing]

1(a) and (b) are a plan view and a front view showing the structure of the light source of the embodiment of FIG. 2, FIG. 2 is a configuration diagram showing the optical system of one embodiment of the present invention, and FIG. 3 4 is a configuration diagram showing an optical system of an example of a conventional optical bed, and FIG. 4 is an optical path diagram for explaining the operation of the optical head shown in FIG. 3. 2.3...Light source, 4...Collimating lens, 5...
・Polarizing beam splitter, 6...1/4 wavelength plate, 7.
... Actuator, 8... Converging lens, 9... Optical disk, 11, 12... Photodetector, 13... Detector, 14... Light separation element, 2a, 2b-2cm3a-
3b-3c2b-2 Foil 1 Figure riz Figure 3%411] 7-De; Procedural amendment (voluntary) 63.1.29 Showa year, month, day 2, name of invention Optical head 3, make amendment Applicant: 5-33-1 Shiba, Minato-ku, Tokyo (423) NEC Corporation Representative: Tadahiro Sekimoto 4, Agent: Sumitomo Sanda Building, 37-8 Shiba 5-chome, Minato-ku, Tokyo 108
(Contact address: NEC Corporation Patent Department) 5. Detailed explanation of the invention in the specification to be amended 6. Contents of the amendment (1) "Unable to converge" on page 6, line 20 of the specification Correct this by saying that it can converge.

Claims (1)

[Scope of Claims] A light source having a plurality of semiconductor lasers, an actuator having a collimating lens, a polarizing beam splitter, a quarter wavelength plate, and a converging lens disposed between the light source and an optical disk, and the light source. a lens disposed in the path of the reflected light beam whose course is changed by the polarizing beam splitter, and a light beam that detects the light passing through the lens; An optical head comprising a detector, a light separation element that separates a servo light beam from the reflected light beam, and a detector that detects the separated servo light beam, wherein one of the plurality of semiconductor lasers The light emitting points of the remaining semiconductor lasers excluding the semiconductor laser disposed on the optical axis of the collimating lens are different from the light emitting points of the semiconductor lasers disposed on the optical axis of the collimating lens. An optical head characterized in that the optical head is arranged with a predetermined step in the axial direction.