JPH0640398B2 - Optical pickup device - Google Patents

Description

The present invention relates to an optical pickup device for recording / reproducing information on / from an optical video disc, a digital audio disc or the like.

[Outline of Invention]

The present invention includes a light source, an objective lens that converges incident light emitted from the light source and incident on a disc onto the disc,
A light receiving element for receiving at least a part of the reflected light reflected by the disk, and arranged in the optical path of the incident light and the reflected light,
The depth of the groove is set to about ½ of the wavelength of the light emitted from the light source, and an optical pickup device having a diffracting means for diffracting the incident light into ± first-order diffracted light at a predetermined diffraction angle is used. At least one of the + 1st-order diffracted light and the -1st-order diffracted light becomes a substantially aberration-free light by means of the means, and the substantially-aberration first-order diffracted light is applied to the disk through the objective lens and diffracted by the diffraction means. One of the first-order diffracted light components of the reflected light is received by the light-receiving element, and a semiconductor laser having two or more peaks of the oscillation spectrum is used as a light source, and the diffracting means is arranged in a direction parallel to the track formed on the disk. They are arranged so as to be vertical so that crosstalk from adjacent tracks is reduced or a good S / N in the time axis direction is obtained.

[Conventional technology]

In the case of optically recording / reproducing information on / from a disc, it is necessary to separate incident light and reflected light from each other so that recording / reproducing light such as laser light is incident on the disc and the reflected light is received. As such a separating means, a half mirror, a combination of a quarter wavelength plate and a polarizing prism, etc. have been proposed, but when these are used, there is a drawback that the device becomes large. As a means for solving this, it is conceivable to use a diffraction grating as a separating means, as disclosed in, for example, JP-A-56-57013 and JP-A-59-119548.

FIG. 3 is a schematic plan view of a conventional optical pickup device when a diffraction grating is used as a separating means.
In the figure, 1 is a light source such as a semiconductor laser or a gas laser which emits a recording / reproducing light having a predetermined wavelength λ. Reference numeral 2 is a phase type diffraction plate (diffraction grating) that diffracts incident light. The distribution state of the diffracted light is determined by the depth, spacing, and orientation of the grooves of the phase type diffraction plate 2. The depth is set to about 1/2 of the wavelength λ, and only the first-order diffracted light is provided. Is to be derived. Reference numeral 3 denotes an objective lens, which is driven by a focus motor (not shown) or the like so as to converge the light on the disk 4. A light receiving element 5 receives the reflected light reflected by the disk 4 and outputs a focus error signal and a reproduction signal of information recorded on the disk 4.

The light emitted from the light source 1 is diffracted by the phase type diffraction plate 2. Since the depth of the groove is set to about 1/2 of the wavelength λ of light, almost only the + 1st order diffracted light and the −1st order diffracted light are derived at this time. The phase type diffraction plate 2 is set so as to diffract, for example, only the −1st order diffracted light (or the + 1st order diffracted light) with almost no aberration, and the −1st order diffracted light enters the objective lens 3 as incident light, 4 is converged and irradiated (the 1st-order diffracted light is not shown).
The reflected light reflected by the disk 4 and incident on the objective lens 3 is further incident on the phase type diffraction plate 2 and is again diffracted into + 1st-order diffracted light and −1st-order diffracted light. And among them, + 1st order diffracted light (or -1st order diffracted light) with almost no aberration
Is returned to the light source 1, and the −1st-order diffracted light (or the + 1st-order diffracted light) having astigmatism is applied to the light receiving element 5. Therefore, the light receiving element 5 is divided into four, focus error control can be performed by a so-called astigmatism method, and a reproduction signal of recorded information can be obtained from the sum signal.

[Problems to be solved by the invention]

By the way, the multimode semiconductor laser has several peak wavelengths within a length of 1 nm, as shown in FIG. As described above, the semiconductor laser having two or more peaks of the oscillation spectrum is used as the light source 1, and the phase type diffraction plate 2 is used.
As shown in FIG. 5, a plurality of similar first-order diffracted lights of relatively large level are derived when the light is incident on the light at an incident angle α. For example, the incident angle α is about 9 degrees, and the phase type diffraction plate 2 is 1
Assuming that there are about 200 diffraction gratings per mm,
1st-order diffracted light L ₁ with a wavelength of 785 nm and ₁ with a wavelength of 784 nm
_Second-order diffracted light L ₂ (or first-order diffracted light L ₃ having a wavelength of 786 nm)
The angle θ formed by is about 0.007 degrees. The distance between the light source 1 and the phase type diffraction plate 2 (the distance between the intersection P of the phase type diffraction plate 2 and the optical axis and the light source 1) is 5 mm, the distance between the phase type diffraction plate 2 and the objective lens 3 is 5 mm, and the objective Assuming that the focal length of the lens 3 is 2 mm, the first-order diffracted light with a wavelength of 785 nm is at point Q on the disk 4, and the first-order diffracted light with a wavelength of 784 nm is at point R.
Each of them is converged, and the distance between points Q and R is about 0.256 μm
Becomes

That is, when a semiconductor laser having two or more oscillation spectrum peaks is used as the light source 1, the converged light spread in the diffraction direction of the phase type diffraction plate 2 is irradiated onto the disk 4. Therefore, there are drawbacks that crosstalk from the adjacent tracks on the disk 4 increases and the S / N in the time axis direction of the same track deteriorates.

[Means for solving problems]

1 and 2 are schematic perspective views of the optical pickup device of the present invention. The structure of the present invention is basically the same as that shown in FIG. However, in the present invention, a multimode semiconductor laser is used as the light source 1. Furthermore, the phase type diffraction plate 2 has its diffraction grating 11
Is arranged so as to have a specific relationship (vertical (FIG. 1) or parallel (FIG. 2)) with respect to the track 12 of the disk 4. In addition, laser light emitted from the light source 1 is incident on the phase type diffraction plate 2, and of the first-order diffracted light diffracted therein, almost diffracted light is incident on the objective lens 3 and converged on the disc 4. That is how it is done. Further, the reflected light from the disk 4 is applied to the light receiving element 5 via the objective lens 3 and the phase type diffraction plate 2 as in the case of FIG.

[Action]

Then, the operation will be explained. The light emitted from the light source 1 is diffracted in a direction substantially parallel to the y-axis direction because the diffraction grating 11 of the phase type diffraction plate 2 is substantially parallel to the x-axis direction. The phase type diffraction plate 2 is, for example, −1st order diffracted light (or +
It is designed to diffract only the (first-order diffracted light) with almost no aberration, and the -1st-order diffracted light with no aberration is made incident on the objective lens 3 as incident light, converged and irradiated on the disk 4. The reflected light reflected by the disk 4 and incident on the objective lens 3 is further incident on the phase type diffraction plate 2, where it is again diffracted (separated) into the + 1st order diffracted light and the −1st order diffracted light in the direction parallel to the y axis. It Then, one first-order diffracted light is returned to the light source 1, and the other first-order diffracted light is incident on the light receiving element 5. If one having astigmatism is selected as the first-order diffracted light incident on the light receiving element 5, focus error control can be performed by the so-called astigmatism method (of course, focus error control can be performed by other methods as well. ).

On the other hand, the reproduction signal of the information recorded on the track 12 formed on the disk 4 can be obtained from the output of the light receiving element 5. When the disc 4 is, for example, a video disc and a predetermined signal (video signal) is frequency-modulated and recorded, as shown in FIG. It is preferable that the direction) be substantially parallel to the direction of the track 12. By doing so, the beam spread of the multi-mode semiconductor laser becomes parallel to the track 12, and it is possible to prevent an increase in crosstalk from an adjacent track.

Further, when the predetermined signal (audio signal) is digitally modulated such as EEM modulation as in the case where the disk 4 is an optical digital audio disk, as shown in FIG. It is preferable that the (y-axis direction) is substantially perpendicular to the direction of the track 12. In this way, the beam of the multimode semiconductor laser spreads in the direction perpendicular to the track 12 and does not spread in the time axis direction of the same track.
It is possible to prevent / N from deteriorating.

〔effect〕

As described above, the present invention includes a light source, an objective lens that converges incident light emitted from the light source and incident on the disc onto the disc, and a light receiving element that receives at least a part of the reflected light reflected by the disc. And the depth of the groove disposed in the optical paths of the incident light and the reflected light is approximately 1 of the wavelength of the light emitted by the light source.
It is set to / 2 and the incident light is ± 1 at a predetermined diffraction angle.
In an optical pickup device having a diffracting means for diffracting to a diffracted light of at least one order, at least one of the + 1st order diffracted light and the -1st order diffracted light is made to be a substantially aberration-free light by the diffractive means. Folding light is applied to the disk through an objective lens, one first-order diffracted light of the reflected light diffracted by the diffracting means is received by a light receiving element, and a semiconductor laser having two or more peaks of an oscillation spectrum is used as a light source. Since the diffractive means is arranged such that its diffracting direction is parallel or perpendicular to the tracks formed on the disk, it is possible to prevent an increase in crosstalk from adjacent tracks and to suppress S / in the time axis direction. It is possible to prevent N from deteriorating.

[Brief description of drawings]

1 and 2 are schematic perspective views of an optical pickup device of the present invention, FIG. 3 is a schematic plan view of a conventional optical pickup device, and FIG. 4 is a spectrum diagram of a multimode semiconductor laser. FIG. 5 is a schematic optical path diagram of a conventional optical pickup device. 1 ... Light source, 2 ... Phase type diffraction plate 3 ... Objective lens, 4 ... Disk 5 ... Light receiving element, 11 ... Diffraction grating 12 ... Track

Claims (1)

[Claims] 1. A light source, an objective lens for converging incident light emitted from the light source and incident on a disc onto the disc, and a light receiving element for receiving at least a part of reflected light reflected by the disc. And the depth of the groove disposed in the optical paths of the incident light and the reflected light is approximately 1 of the wavelength of the light emitted by the light source.
It is set to / 2 and the incident light is ± 1 at a predetermined diffraction angle.
In an optical pickup device having a diffracting means for diffracting into a diffracted light of at least one order, at least one of the + 1st order diffracted light and the -1st order diffracted light is made to be a substantially aberration-free light by the diffractive means. The first-order diffracted light of the above is applied to the disk through the objective lens, one of the first-order diffracted light of the reflected light diffracted by the diffracting means is received by the light-receiving element, and the peak of the oscillation spectrum is obtained as the light source. An optical pickup device characterized in that a semiconductor laser having two or more of the above is used, and the diffracting means is arranged so that its diffracting direction is parallel or perpendicular to a track formed on the disk.