JPH0713060Y2 - Optical pickup device - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an optical pickup device, and more particularly to improvement of a pickup device for reading optical information.

[Technical background of the device and its problems]

An optical pickup device of this type is shown in FIGS. 6 and 7.

In FIG. 6, the information reading light emitted from the laser light source 1 is incident on the objective lens 3 via the half prism 2 as a light splitting element and converged on the recording surface of the recording disk 4.

The reflected light from the recording disk 4 is again made incident on the objective lens 3 to become parallel rays, and is made incident on the half prism 2. In the half prism 2, the light reflected in the direction orthogonal to the light emitted from the light source 1 reaches the light receiving surface of the light receiving element 5 and is converted into an electric signal.

In FIG. 7, light from the light source 1 becomes so-called P-polarized light and S-polarized light in different directions by the Wollaston prism 6, and one light, for example, P-polarized wave passes through the λ / 4 wave plate 7. It becomes circularly polarized light and enters the objective lens 3.

The convergent light from the objective lens 3 is incident on the disc 4, and the reflected light from the disc 4 passes through the objective lens 3 and is again λ.
S-polarized light is obtained by passing through the / 4 wavelength plate 7.

This S-polarized wave is introduced into the Wollaston prism 6, its direction is changed, and reaches the light receiving element 5.

In the examples shown in FIGS. 6 and 7, prisms are used as the light splitting elements for separating the light emitted from the light source and the light reflected from the disk.

However, this prism has a large light splitting angle, and particularly in a half prism, the light splitting angle is approximately 90 °, which is a factor that prevents miniaturization of the pickup.

Further, since the Wollaston prism is expensive, there is a drawback that the cost is increased.

It is possible to use a diffraction grating as the light splitting means in order to eliminate such a defect. However, the irradiation light may enter the diffraction grating after passing through a collimator lens as a collimator optical member for obtaining parallel rays. In addition, when the collimator lens is located between the light source and the diffraction grating, the entire optical path length becomes long, and the miniaturization of the entire pickup cannot be achieved.

[Purpose of device]

In order to eliminate such a defect, the present invention uses a diffraction grating as a light splitting means for separating irradiation light and reflected light, and devises the arrangement and structure of this diffraction grating to provide a laser light source. It is an object of the present invention to achieve miniaturization and cost reduction of a pickup without deteriorating the performance of the optical system while eliminating the aberration of the virtual image caused by the difference in the incident angle of the irradiation light incident from.

[Example of device]

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 2 shows the state of light incident on the diffraction grating.
When the incident angle is θi, the wavelength is λ, and the grating interval is d, the diffraction angle θd is represented by Sinθd−sinθi = m (λ / d) (m = 0, ± 1, ± 2 ...).

FIG. 3 shows that a diffraction grating 13 is used for the light beam splitter,
The collimator lens 12 is installed between the light source 11 and the light source 11, and the light rays incident on the diffraction grating 13 are parallel rays, and the incident angle of the light rays incident on the diffraction grating 13 is made constant, and no aberration occurs in the virtual image. It was done like this.

However, this method requires a viewing angle due to the length of the entire optical path and the performance of the collimator lens.

On the other hand, in the embodiment of the present invention shown in FIG. 1, the distance between the collimator lens 12 and the objective lens 14 can be minimized and the viewing angle of the collimator lens 12 is not necessary.

In this case, the collimator lens and the objective lens can be integrated.

That is, in FIG. 1, 11 is a light source, for example, a laser diode, 13 is a diffraction grating in which the grating spacing varies depending on the location, 12 is a collimator lens, 14 is an objective lens, 15 is a disk, and 16 is a photoelectric converter. Is.

The light diverging from the light source 11 is incident on the diffraction grating 13 and diffracted, and if the focused order (± 1st order and + 1st order in this case is focused, the solid line is the + 1st order and the broken line is the − 1
(Shown below) creates a virtual image of the light source P at P '.

This light is collimated by the collimator lens 12, condensed by the objective lens 14, reflected by the disk 15, passes through the objective lens 14 again, and becomes collimated light directed to P ′ by the collimator lens 12.

In this way, the light entering the diffraction grating 13 is diffracted again, and is divided into the −1st-order light directed to P and the light directed to the photoelectric converter 16, and the light directed to the photoelectric converter 16 becomes P ″. Collected.

However, in the case of such a configuration, the diffraction grating 13
The angle of incidence of the light incident on is different depending on the location, and therefore θi in equation 1 changes.

This means that the incident angle θi, that is, the diffraction angle θd changes depending on the location of the diffraction grating 13.

FIG. 4 schematically shows this, and the light diverged from O (in this case, divergent light, but it is the same when the focused light is used as the optical path) is, for example, OB light. When the incident angle is θiB and the angle COB is θ ₀ , the diffraction angles (only one of the first-order diffraction angles (−) is considered.) Θd _B and θd _C are θd _B = sin ⁻¹ (sin θi _B −λ / d). 2 θd _C = sin ⁻¹ (sin [θi _B + θ ₀ ] −λ / d) 3

The angle of the light after passing through the diffraction grating 13 is sin θi _B = λ / d ... 4 when λ / d is taken so that θd _B = 0.

The diffraction angle θ d _{C of} OC is subtly changed by the change of θ _{0 when} λ / d = constant when comparing equations 3 and 4, and therefore it is produced by the diffraction grating as shown in Fig. 4. The resulting virtual image will have aberrations.

In order to prevent this aberration from occurring, as shown in FIG.
The diffraction angle d _C of must be equal to θ ₀ .

Therefore, it is necessary to satisfy Sin (θi _B + θ ₀ ) −λ / d = sin θ ₀ ... 5 from the three equations.

For this reason, d defined by the equation 4 and d satisfying the equation 5 are different.

As described above, the diffraction grating used in the pickup of the present invention must have different distances between the diffraction gratings at points D, E, F, etc. of FIG. Although it was performed only on one side, by doing so, the aberration of the virtual image due to a certain order of the diffraction grating can be eliminated.

[Effect of device]

The present invention uses a diffraction grating as a light splitting means for separating the light emitted from the laser light source and the light reflected from the recording disk. The diffraction grating is arranged between the laser light source and the collimator optical member, and Since the grating has different grating intervals depending on the grating position so as to correct the aberration of the virtual image caused by the difference in the incident angle of the irradiation light incident from the laser light source, the irradiation light incident from the laser light source is incident. It is possible to reduce the size and cost of the optical pickup without deteriorating the performance of the optical system while removing the aberration of the virtual image caused by the difference in the angle.

[Brief description of drawings]

FIG. 1 is an optical path diagram of an embodiment of the present invention, FIG. 2 is a schematic diagram of the principle of a diffraction grating, FIG. 3 is an optical path diagram in which a diffraction grating is provided after a collimator lens, and FIG. FIG. 5 is an explanatory diagram of the occurrence of aberrations, FIG. 5 is an explanatory diagram in which the grating spacing is changed and no aberration occurs, and FIGS. 6 and 7 are optical path diagrams of the conventional optical pickup device. 11 ... Light source, 12 ... Collimator lens, 13 ... Diffraction grating, 14 ... Objective lens, 15 ... Disc.

Claims (1)

[Scope of utility model registration request] 1. A collimator optical member converts irradiation light emitted from a laser light source into parallel light rays, which is then condensed and irradiated onto a recording surface of a recording disk by an objective lens, and reflected light from the recording surface is converted into light. In an optical pickup device in which a splitting means is used to separate in a direction different from the irradiation light of the laser light source, and the separated reflected light is received by a light receiving means, in order to separate the irradiation light and the reflected light A diffraction grating is used as the light splitting means, and the diffraction grating as the light splitting means is disposed between the laser light source and the collimator optical member, and the diffraction grating is different depending on the incident angle of the irradiation light incident from the laser light source. An optical pickup device characterized in that the lattice spacing is varied according to the lattice position so as to correct the aberration of the virtual image that occurs.