JPH03292644A - Optical pickup device - Google Patents

Abstract

PURPOSE:To reduce an unnecessary signal due to outgoing diffracted light by providing a lens area on the outside of a diffraction area for the generation of a tracking error signal and the focus error signal of a translucent type hologram. CONSTITUTION:A diffraction area A for the generation of the tracking error signal and the focus error signal is disposed in the center part of the translucent type hologram 4, and a lens area B which refracts the light made incident on an area other than the diffraction area A among the rays of light reflected from a recording medium 8 outward is disposed on the outside of the area A. Light 9 which is diffracted toward a point 7a of a focus lens 7 at an intersection 4b and becomes 1st-order light among the rays of the light radiated from a semiconductor laser 1 is reflected at a reflection point 8c on the recording medium 8, and the reflected light passes a point 7b of the focus lens 7 and reaches a point 4d. It is refracted outward by the action of a convex lens, and light is not made incident on a photodetector. Thus, unnecessary light is refracted to reduce the noise and the offset of the regenerative signal of an essential error signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical pickup device for an optical disc device.

Conventional technology Fig. 5 is a block diagram of an optical pickup device using a conventional hologram ram, Fig. 6 is a plan view of a conventional hologram ram, and Fig. 7 shows how light emitted from a semiconductor laser returns. FIG.

In FIG. 5, 1 is a semiconductor laser that emits light, 2 is a photodetector for monitoring the output of the semiconductor laser 1,
3, a stem for fixing and cooling the semiconductor laser l;
Reference numeral 4 denotes a hologram ram that is reflected by the sphere distribution medium 8 and separates the modulated light from the optical axis to generate a focus error signal and a tracking error signal. 5 is a light for detecting the light separated by the hologram ram. A photodetector for detecting focus and tracking error signals is configured on the photodetector 5 . 6 is a semiconductor laser 1, a photodetector 2. Stem 3. A hologram unit that integrates a hologram ram 4 and a photodetector 5; 7 is a round focus lens that focuses on a recording medium 8; 8a;
is a bit.

In FIG. 6, a diffraction beam 11I which generates a tracking error signal and a focus error signal is disposed in the center of the hologram ram 4, and no hologram ram is formed on the outside so that light can pass therethrough.

In FIG. 7, 4a and 4c are the intersection points on the hologram ram 4 when looking into the aperture of the focus lens 7 from the semiconductor laser 1, and 4b is the intersection point when looking into the aperture of the focus lens 7 from a point 5a on the photodetector 5. The intersection point %4d on the hologram ram 4 is the point 7a where the light is reflected from the recording medium 8, returns and passes through the hologram ram 4, assuming that the light is emitted from the point 5a on the photodetector 5. , 7c Id When it is assumed that the light is emitted from the point 5a on the photodetector 5, the 0 point 7b at both ends of the aperture of the focus lens 7 is the recording medium 8.
It is assumed that the light is emitted from the point 8b which is emitted from the semiconductor laser l and focused on the recording medium 8, and the point 8c is the point 5a on the photodetector Ja5. This is the reflection point on the recording medium B at that time.

Note that the diffraction @BinA that generates the tracking error signal and focus error signal on the ram 4 of the hologram is composed of a spherical wave diverging from each detection point on the photodetector 5 and a spherical wave diverging from the position of the semiconductor laser l. Corresponds to the tidal stripes.

In the conventional optical pickup device configured as described above, the light emitted from the semiconductor laser 1 is divided by the ram 4 of the hologram into 0th-order light that travels straight and diffracted light of ±1st-order light or higher. Among them, the zero-order light enters the focus lens 7 and focuses on the recording medium 8. It is modulated and reflected by the hologram's ram 4. Follow the opposite route until then. The returned light is collected and focused by the hologram ram 4 on a photodetector for detecting a tracking error signal and a focus error signal, and an error signal is obtained. Further, light emitted from the surface of the hologram of the semiconductor laser 1 opposite to the ram 4 is detected by the photodetector 2, and the light output of the semiconductor laser 1 is controlled to be constant.

Next, the optical path will be explained in detail using FIG. 7.

The focus lens 7 uses the light emitted from the semiconductor laser l.
The zero-order light passing through a point 7a at one end of the aperture reaches a focal point 8b on the recording medium 8 and is reflected. The reflected light is from the focus lens 7
The +1st-order light passes through point 7c at the other end of the aperture, returns to the ram 4 of the hologram, and is diffracted at the intersection 4b, reaching a point 51 on the photodetector 5. Therefore, the number of outgoing 0th-order light emitted from the semiconductor laser 1 that is not diffracted by the ram 4 of the hologram is 2! A focal point 8b is placed on the recording medium 8. On the return trip, the light reflected by the recording medium 8 is diffracted by the hologram ram 4 and reaches a point 5a K on the photodetector 5:
JI is illuminated.

On the other hand, among the light emitted from the semiconductor laser, the intersection point 4
At b, the light beam 9#i is diffracted in the direction of the point 7a of the focus lens 7 and becomes the first-order light beam 9#i, which is transmitted to the point ScK on the recording medium 8 and reflected. The reflected light passes through points 7b and 4d and reaches point 5a on photodetector 5. Therefore, among the light emitted from the semiconductor laser l, the angle θ of the 11th order light diffracted by the hologram J-4 from the point 5a on the photodetector 5 to the points 7a and 7b of the aperture of the focus lens 7 is The incident light is focused on a point 5a on the photodetector 5.

Problem II to be Solved by the Invention Originally, information should be extracted by focusing the focal point 8b on the recording medium 8, but information from the reflection point 8c is simultaneously detected by the photodetector 5 due to a portion of the 1st-order light on the outgoing path. Resulting in.

The alternating current component of the signal from the reflection point 8c becomes jitter in the reproduced signal. Further, the DC component becomes an offset of the tracking error signal and the focus error signal, making the control unstable.

In view of the points related to the present invention, it is an object of the present invention to provide an optical pickup device that reduces unnecessary signals due to diffracted light on the outward path.

Means for Solving the Problems In order to solve this problem, the optical pickup device of the present invention has an optical pickup device in which the light flux emitted from the light source that emits light to the recording medium is limited by the aperture of the focus lens, and a focus error signal and a tracking error are generated. A diffraction region A for generating a signal, a hologram ram with another optical element formed outside the diffraction region A, and a diffraction fR of the hologram ram A
and a photodetector that detects the light separated by.

Effect of the present invention With the above-described configuration, the light emitted from the light source is diffracted by the diffraction beam WA of the hologram ram, and the 1st-order light of the diffracted light enters the aperture of the focus lens and is reflected by the recording medium. , the light that has returned to the outside of the diffraction region A is refracted or diffracted by an optical element separate from the diffraction region A, thereby reducing unnecessary light entering the photodetector.

Embodiments Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 1 is a plan view of the hologram ram of the optical pickup device in the first embodiment of the present invention, and FIG. 2 is an optical path diagram of the optical pickup device. This is the same as the conventional example, and the same members are designated by the same reference numerals.

In FIG. 1, a diffraction area A that generates the same tracking error signal and focus error signal as in the conventional example is arranged in the center of the ram 4 of the hologram, and outside of the diffraction area A, part of the light reflected from the recording medium 8 is disposed. A lens region B is provided that refracts light incident on sources other than the diffraction beam EA in the outer circumferential direction so as not to enter the photodetector. The other configurations are the same as those of the conventional example.

The operation of the optical pickup device of this embodiment equipped with the hologram ram 4t as described above will be explained with reference to FIG.

The focus lens 7 uses the light emitted from the semiconductor laser l.
The zero-order light passing through the aperture point 71 reaches the focal point 8b[Jl[I] on the recording medium 8 and is reflected, as in the conventional example.

The reflected light modulated by the bit at the focal point 8b returns to the hologram ram 4 through a point 7C, and the +1st-order light diffracted by the hologram ram 4 reaches a point 5aK on the photodetector 5.
@reached and detected.

On the other hand, out of the light emitted from the semiconductor laser l.

At the intersection 4b, the light 9 that is diffracted in the direction of the focus lens 70 point 7a and becomes the 1st-order light is reflected at a reflection point 8c on the recording medium 8.
K @reach and reflect. Reflected light is focused lens 70
It passes through point 7b and reaches point 4clK. At point 4d, the light is refracted toward the outer circumference due to the action of the convex lens, and the light no longer enters the photodetector 5.

As described above, according to this embodiment, by providing the lens area B outside the diffraction area A for generating tracking error signals and focus error signals of the ram 4 of the hologram, the 1st-order light on the outgoing path is directed to the recording medium 8. The unnecessary light that is reflected by and returns to the lens area B is refracted and sent to the photodetector 5.
The influence of this unnecessary light can be eliminated.

Although the lens region B in this embodiment is made up of convex lenses, the same effect can be obtained with concave lenses. Also,
Although the lens f[J[B was formed on one side.

It goes without saying that it may be formed on both sides.

Next, the 25th j! of the present invention! An example will be explained.

FIG. 3 is a plan view of a hologram ram in an optical pickup device according to a second embodiment of the present invention, and FIG. 4 is an optical path diagram of the same optical pickup device. This is the same as the conventional example.

In FIG. 3, a diffraction area A that generates the same tracking error signal and focus error signal as in the conventional example is disposed in the center of the ram 4 of the hologram, and a diffraction area outside of the diffraction area A that generates the tracking error signal and focus error signal as in the conventional example. A concentric diffraction area C is provided that diffracts light incident on a person other than a person.

One example of the optical pickup device of this embodiment equipped with the hologram ram 4 as described above will be described with reference to FIG. 4, 1jt.

The focus lens 7 uses light emitted from the semiconductor laser l.
The zero-order light passing through the point 7a1 of the aperture reaches a focal point 8bK on the recording medium 8 and is reflected, as in the conventional example.

The reflected light modulated by the bit at the focal point 8b passes through the point 7c and returns to the ram 4 of the hologram, and the +1st order light diffracted by the ram 4 of the hologram reaches the point 5a on the photodetector 5 and is detected.

On the other hand, out of the light emitted from the semiconductor laser 1.

At the intersection 4b, the light 9 that is diffracted in the direction of the focus lens 70 point 7a and becomes the 1st-order light is reflected at a reflection point 8c on the recording medium 8.
reach and reflect. The reflected light is a focus lens with 70 points 7
Passing through b, the point Ad K j! do. At point 4d, the light is diffracted by the diffraction area C in the inner and outer circumferential directions.

As described above, according to the main dormitory example, by providing other diffraction types M and C outside the diffraction area A for generating tracking error signals and focus error signals of the ram 4 of the hologram, The light is reflected by the distribution medium 8,
The unnecessary light returning to the diffraction region B is diffracted and dispersed, and this influence can be reduced.

Note that the same effect can be obtained even if the ram pattern of the hologram of the diffraction type w:, C is not concentric, but radial or parallel.

Further, by disposing diffraction talc on both sides of the ram 40 of the hologram, it is possible to diffract the light twice and further attenuate unnecessary light.

Moreover, the lens area B of the first projecting embodiment and the second!
i! ! It goes without saying that the diffraction type vcC of the embodiment may be combined.

Effects of the Invention As described above, according to the present invention, by forming another optical element outside the diffraction region A that generates the tracking error signal and the focus error signal, unnecessary light is refracted or diffracted and the original light is not reflected. It is possible to reduce the error signal, noise and offset of the reproduced signal.

Also, the lens area B of the ram 4 of the hologram according to the invention
Since the diffraction filtration region B can be formed simultaneously with the diffraction region A, a replica can be obtained on the container, which is suitable for mass production, and has great practical effects.

[Brief explanation of drawings]

FIG. 1 is a plan view of a hologram ram of an optical pickup device according to a first embodiment of the present invention, FIG. 2 is an optical path diagram of the same pickup device, and FIG. 3 is an optical pickup device according to a second embodiment of the present invention. 4 is a plan view of the hologram ram, FIG. 4 is an optical path diagram of the same pickup device, FIG. 5 is a configuration diagram of an optical pickup device using a conventional hologram ram, and FIG. 6 is a conventional optical pickup device FIG. 7 is a plan view of a hologram ram, and FIG. 7 is an optical path diagram of a conventional optical pickup device. l... Semiconductor laser, 2... Photodetector, 4... Hologram ram, 4a to 4C... Intersection %4d... Point, A... Diffraction area, B... Lens area , C... Diffraction area, 5... Photodetector, 5a... Point, 6... Hologram unit, 7... Focus lens, 7a~
7c...Point, 8...Note [11,8b...Focus, 8
c...Reflection point. Figure 1 Δ Figure 2 Yoshihiro Morimoto Figure 3 Figure 4 Figure j

Claims (1)

[Scope of Claims] 1. An optical pickup device comprising: a light source that emits light to a recording medium; and a focus lens that focuses a beam of light emitted from the light source onto the recording medium, the optical pickup device comprising: a diffraction region A located between the medium and the light source, in which the light flux emitted from the light source is limited by the aperture of the focus lens to generate a focus error signal and a tracking error signal; and a diffraction region A outside the diffraction region A. An optical pickup device comprising: a transmission hologram in which another optical element is formed; and a photodetector that detects light separated by a diffraction area A of the transmission hologram.