JP2763174B2 - Optical pickup device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for an optical disk device.

2. Description of the Related Art FIG. 5 is a block diagram of an optical pickup apparatus using a conventional transmission hologram, FIG. 6 is a plan view of a conventional transmission hologram, and FIG. 7 is a state in which light emitted from a semiconductor laser returns. FIG.

In FIG. 5, reference numeral 1 denotes a semiconductor laser that emits light;
Is a photodetector for monitoring the output of the semiconductor laser 1, 3 is a stem for fixing and cooling the semiconductor laser 1, 4 is reflected by the recording medium 8, separates modulated light from the optical axis, and A transmission hologram 5 for generating an error signal and a tracking error signal is a photodetector 5 for detecting light separated by the transmission hologram, and a photodetector 5 for detecting a focus and a tracking error signal is provided on the photodetector 5. Are configured. 6 is a semiconductor laser 1, a photodetector 2, a stem 3, a transmission hologram 4,
A hologram unit with an integrated photodetector 5; a focus lens 7 for focusing on a recording medium 8;
Is a pit.

In FIG. 6, a diffraction area A for generating a tracking error signal and a focus error signal is provided at the center of the transmission hologram 4, and the transmission hologram is not formed outside the transmission area so that light is transmitted.

In FIG. 7, reference numerals 4a and 4c denote intersections on the transmission hologram 4 when the opening of the focus lens 7 is viewed from the semiconductor laser 1, and reference numeral 4b denotes an opening of the focus lens 7 from a point 5a on the photodetector 5. The intersection point 4d on the transmission type hologram 4 at the time of expectation is reflected on the recording medium 8 and returns to pass through the transmission type hologram 4, assuming that light is emitted from a point 5a on the photodetector 5. The points 7a and 7c are points 7b at both ends of the opening of the focus lens 7, and assuming that light is emitted from the point 5a on the photodetector 5, the light is reflected back from the recording medium 8 and returned to the focus lens 7. 7b, a focus 8b emitted from the semiconductor laser 1 and focused on the recording medium 8, and 8c a photodetector 5
Recording medium 8 assuming that light was emitted from point 5a above
The upper reflection point.

The circuit area A for generating the tracking error signal and the focus error signal on the transmission hologram 4 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 1. This corresponds to interference fringes.

In the conventional optical pickup apparatus configured as described above, the light emitted from the semiconductor laser 1 is divided by the transmission type hologram 4 into 0th-order light traveling straight and diffracted light of ± 1st-order light or more. The zero-order light among them enters the focus lens 7 and focuses on the recording medium 8. The spot of light converged on the recording medium 8 is modulated and reflected by the pit 8a. Thereafter, the light follows the reverse path to the transmission type hologram 4. The returned light is separated and condensed by the transmission type hologram 4 to photodetectors for tracking error signal detection and focus error signal detection, and an error signal is obtained. The transmission hologram 4 of the semiconductor laser 1
Light emitted from the opposite surface is detected by the photodetector 2 and is controlled so that the optical output of the semiconductor laser 1 becomes constant.

Next, the optical path will be described in detail with reference to FIG. The zero-order light, which is emitted from the semiconductor laser 1 and passes through the point 7a at one end of the opening of the focus lens 7, reaches the focal point 8b on the recording medium 8 and is reflected. The reflected light returns to the transmission hologram 4 through the point 7c at the other end of the opening of the focus lens 7, and the + 1st-order light diffracted at the intersection 4b reaches the point 5a on the photodetector 5. Accordingly, the zero-order light on the outward path which is not diffracted by the transmission hologram 4 with the light emitted from the semiconductor laser 1 is focused on the recording medium 8. On the return path, the light reflected by the recording medium 8 is diffracted by the transmission hologram 4 and condensed at a point 5 a on the photodetector 5.

On the other hand, of the light emitted from the semiconductor laser 1,
At 4b, diffracted in the direction of point 7a of the focus lens 7-
The light 9 serving as the primary light reaches the point 8c on the recording medium 8 and is reflected. The reflected light reaches the point 5a on the photodetector 5 through the lights 7b and 4d. Accordingly, of the light emitted from the semiconductor laser 1, the −1st-order light diffracted by the transmission hologram 4 from the point 5 a on the photodetector 5 to the point 7 of the aperture of the focusing lens 7.
Light entering the angle θ for viewing a and 7b is focused on a point 5a on the photodetector 5.

Although the information should be originally extracted by focusing on the recording medium 8 at the focal point 8b, the information from the reflection point 8c is also detected by the photodetector 5 by a part of the -1st-order light on the outward path. At the same time. The AC component of the signal from the reflection point 8c becomes a jitter of the reproduced signal. In addition, the DC component becomes an offset of the tracking error signal and the focus error signal, and makes the control unstable.

SUMMARY OF THE INVENTION In view of the foregoing, an object of the present invention is 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, an optical pickup device according to the present invention is arranged such that a light beam emitted from a light source that emits light to a recording medium is limited by an aperture of a focus lens, and a focus error signal and A diffraction area A for generating a tracking error signal, a transmission hologram in which an optical element area for refracting or diffracting unnecessary light outside the diffraction area A is formed, and light separated by the diffraction area A of the transmission hologram. And a photodetector for detecting unnecessary light, so that unnecessary light incident outside the diffraction area A is refracted or diffracted by the optical element area so as not to enter the photodetector.

According to the present invention, the light emitted from the light source is diffracted by the diffraction area A of the transmission hologram, and the -1st-order light of the diffracted light enters the opening of the focus lens and is recorded on the recording medium. Accordingly, the light reflected and returned to the outside of the diffraction area A is refracted or diffracted by the optical element area outside the diffraction area A, and unnecessary light entering the photodetector is reduced.

Examples Hereinafter, examples of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view of a transmission hologram of an optical pickup device according to a first embodiment of the present invention, and FIG. 2 is an optical path diagram of the optical pickup device. It is the same as the conventional example, and the same members are denoted by the same reference numerals.

In FIG. 1, a diffraction area A for generating the same tracking error signal and focus error signal as the conventional example is disposed at the center of the transmission hologram 4, and the diffraction area A of the light reflected from the recording medium 8 is provided outside the diffraction area A. A lens area B is provided to refract light incident to areas other than A in the outer peripheral direction so as not to enter the photodetector. Other configurations are the same as those of the conventional example.

The operation of the optical pickup device of this embodiment having the above-described transmission hologram 4 will be described with reference to FIG.

The zero-order light, which is emitted from the semiconductor laser 1 and passes through the opening 7a of the focus lens 7, reaches the focal point 8b on the recording medium 8 and is reflected as in the conventional example. The reflected light modulated by the pit at the focal point 8b returns to the transmission hologram 4 through the point 7c, and the + 1st-order light diffracted by the transmission hologram 4 reaches the point 5a on the photodetector 5 and is detected. You.

On the other hand, of the light emitted from the semiconductor laser 1,
At 4b, diffracted in the direction of point 7a of the focus lens 7-
The light 9 serving as the primary light reaches the reflection point 8c on the recording medium 8 and is reflected. The reflected light passes through the point 7b of the focus lens 7 and the point 4d
Reach At the point 4d, the light is refracted in the outer peripheral direction by the action of the convex lens, so that light does not enter the photodetector 5.

As described above, according to the present embodiment, the transmission hologram 4
By providing the lens area B outside the diffraction area A for generating the tracking error signal and the focus error signal, unnecessary light returning to the lens area B is reflected by the recording medium 8 on the outward path. The light is refracted and does not enter the photodetector 5, so that the influence of the unnecessary light can be eliminated.

Although the lens area B in the present embodiment is formed of a convex lens, the same effect can be obtained with a concave lens. Further, although the lens area B is formed on one side, it is needless to say that the lens area B may be formed on both sides.

 Next, a second embodiment of the present invention will be described.

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

In FIG. 3, a diffraction area A for generating the same tracking error signal and focus error signal as that of the prior art is provided at the center of the transmission hologram 4, and the diffraction area of the light reflected from the recording medium 8 is provided outside the diffraction area A. A concentric diffraction region C for diffracting incident light other than A is provided.

The operation of the optical pickup device of this embodiment having the above-described transmission hologram 4 will be described with reference to FIG.

The zero-order light, which is emitted from the semiconductor laser 1 and passes through the opening 7a of the focus lens 7, reaches the focal point 8b on the recording medium 8 and is reflected as in the conventional example. The reflected light modulated by the pit at the focal point 8b passes through the point 7c, returns to the transmission hologram 4, and the + 1-order light diffracted by the transmission hologram 4 reaches the point 5a on the photodetector 5 and is detected. .

On the other hand, of the light emitted from the semiconductor laser 1,
At 4b, diffracted in the direction of point 7a of the focus lens 7-
The light 9 serving as the primary light reaches the reflection point 8c on the recording medium 8 and is reflected. The reflected light passes through the point 7b of the focus lens 7 and the point 4d
Reach At the point 4d, the light is diffracted in the inner and outer peripheral directions by the diffraction area C.

As described above, according to the present embodiment, the transmission hologram 4
By providing another diffraction area C outside the diffraction area A for generating the tracking error signal and the focus error signal, the -1st-order light on the outward path is reflected by the recording medium 8,
Unnecessary light returning to the diffraction region B is diffracted and dispersed, and this effect can be reduced.

The same effect can be obtained even if the transmission hologram pattern in the diffraction region C is not concentric but radial or parallel.

Further, diffraction regions C are provided on both surfaces of the transmission hologram 4 and are diffracted twice so that unnecessary light can be further attenuated.

It goes without saying that the lens area B of the first embodiment and the diffraction area C of the second embodiment may be combined on the same surface.

As described above, according to the present invention, an optical element region for refracting or diffracting unnecessary light is formed outside a diffraction region A for generating a tracking error signal and a focus error signal. Unnecessary light incident on the outside can be refracted or diffracted in the optical element region so as not to enter the photodetector, so that the error signal and the reproduction signal noise and offset destabilize the control as in the related art. Can be reduced.

Further, since the lens area B and the diffraction area B of the transmission type hologram 4 according to the present invention can be formed simultaneously with the diffraction area A,
A replica can be easily obtained and suitable for mass production, and its practical effect is great.

[Brief description of the drawings]

FIG. 1 is a plan view of a transmission hologram of an optical pickup device according to a first embodiment of the present invention, FIG. 2 is an optical path diagram of the optical pickup device, and FIG. 3 is an optical pickup device according to a second embodiment of the present invention. FIG. 4 is an optical path diagram of the optical pickup apparatus, FIG. 5 is a configuration diagram of an optical pickup apparatus using a transmission hologram in a conventional example, and FIG. 6 is an optical pickup apparatus in a conventional example. FIG. 7 is a plan view of a transmission type hologram, and FIG. 7 is an optical path diagram of a conventional optical pickup device. 1 ... Semiconductor laser, 2 ... Photodetector, 4 ... Transmission hologram, 4a-4c ... Intersection, 4d ... Point, A ... Diffraction area, B ... Lens area, C ... Diffraction area, 5 photodetector, 5a point, 6 hologram unit, 7 focus lens, 7a to 7c point, 8 recording medium, 8b
Focus, 8c …… Reflection point.

Claims (1)

(57) [Claims] 1. An optical pickup device comprising: a light source that emits light to a recording medium; and a focus lens that focuses a light beam emitted from the light source on the recording medium. Between the light sources, a light flux emitted from the light source is limited by an opening of the focus lens, a diffraction area A for generating a focus error signal and a tracking error signal, and unnecessary light outside the diffraction area A. A transmission hologram having an optical element region to be refracted or diffracted, and a photodetector for detecting light separated by the diffraction region A of the transmission hologram are provided, and unnecessary light incident on the outside of the diffraction region A is provided. An optical pickup device configured to be refracted or diffracted in the optical element region so as not to enter the photodetector.