JPH0520697A - Optical pickup device - Google Patents

Abstract

PURPOSE:To stably detect a tracking error signal with a three beams method by converging a recording medium reflecting light on a spatial filter and contriving the pattern of this spatial filter. CONSTITUTION:A reflected light from a recording medium 7 is reflected by a polarizing beam splitter 4 and converged to a spatial filter 8 through a 1/4 wavelength plate 5. Except the side robe component of a main beam is transmitted, and received by a tripartite photodetector 9, a regenerating signal and the tracking error signal are detected. A part of the side robe components are reflected, transmits through the polarizing beam splitter 9, are received by a bisected photodetector 10, and a focus error signal is detected. Thus, the stable tracking error signal is detected by ultra-resolution constitution and the three beams method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device used in an information input / output device for recording / reproducing information using light.

[0002]

2. Description of the Related Art It is effective to reduce the number of light spot systems on a recording medium in order to improve the recording density of an optical disk. As a means for reducing the beam diameter, there is a means for obtaining a main lobe with a small diameter by the effect of super-resolution by using a spatial filter that reduces the intensity near the center of the light incident on the condenser lens. However, the more the intensity decreases near the center, the smaller the main lobe diameter becomes, but the larger the side lobe becomes. The same effect can be obtained with a spatial filter that changes the phase of transmitted light instead of decreasing the intensity.

FIG. 5 shows an example of an optical pickup device utilizing super-resolution. Light emitted from the semiconductor laser 1 is reduced in intensity near the center by the super-resolution spatial filter 2.
The light is condensed as a super-resolution spot on the recording medium 7 by the condenser lens 4 via the polarization beam splitter 4 and the quarter-wave plate 5. The reflected light from the recording medium is reflected by the polarization beam splitter 4 and is condensed again via the quarter wavelength plate 5. Only the main lobe component is extracted by the spatial filter 16 placed at the condensing point and is received by the two-divided photodetector 10. From this detector, a reproduction signal and a track error signal by the push-pull method can be obtained. By using such a detection system, it is possible to obtain a reproduction signal that is less affected by side lobes.

FIG. 6 shows the structure of the spatial filter 16. Of the light intensity distribution 23, the side lobe component on one side is the absorption portion 2
2 is absorbed, and only one component is reflected by the reflector 21. The reflected component is transmitted through the polarization beam splitter 4, and the focus error signal is detected by the two-division type photodetector 10 based on the knife-edge method principle.

[0005]

High density recording can be realized even in such a conventional optical pickup device. However, this optical system can detect the track error signal only by the push-pull method. In the case of a read-only compact disc or the like, a sufficient signal may not be obtained depending on the pit depth on the recording medium.

An object of the present invention is to provide a three-beam type optical pickup device which does not cause the above problems.

[0007]

An optical pickup device of the present invention separates a converging optical system for converging light emitted from a laser light source as a minute spot on a recording medium, and reflected light from the recording medium. In an optical pickup device equipped with a detection optical system for detecting by means of: a diffraction grating for dividing a spot on a recording medium into a main spot and two side spots in the focusing optical system; And a spatial filter that includes a resolution spatial filter, refocuses the recording medium reflected light in the detection optical system, and selectively transmits the remaining components except the side lobe component of the main spot of the focused spots. An optical system for detecting a focus error from the side lobe component is provided.

Further, the optical pickup device of the present invention includes a condensing optical system for condensing the light emitted from the laser light source as a minute spot on the recording medium, and a detection for separating and detecting the reflected light from the recording medium. In an optical pickup device including an optical system, a diffraction grating that divides a spot on a recording medium into a main spot and two side spots in the condensing optical system, and a super-resolution spatial filter that reduces the condensing spot beam system. In the detection optical system, the recording medium reflected light is converged again, and the spatial filter that selectively reflects or transmits only the main lobe component of the main spot of the converged spots and the spot position from the remaining light components An optical system for detecting an error signal is provided.

[0009]

The operation of the present invention will be described with reference to the drawings. As in the embodiment shown in FIG. 1, the diffraction grating 3 is inserted before or after the super-resolution spatial filter 2 to form side spots on the recording medium 7. Here, the super-resolution is generated only in one direction by the light-shielding band. The reflected light of the recording medium is condensed on the spatial filter 8. By devising the pattern of the filter in this space, it is possible to detect the track error by the 3-beam method.

FIG. 2 shows the pattern of the spatial filter. Three
Of the light intensity distribution 23 consisting of one super-resolution spot, the side lobe component of the main spot is removed and the rest is transmitted. The transmitted light is detected on the light receiving surface 20 of the three-divided photodetector 9. A reproduction signal is obtained from the central light receiving surface, and a track error signal is obtained from both light receiving surfaces. One of the side lobe components is reflected by the reflecting portion 21, and one of the side lobe components is absorbed by the absorbing portion 22. The reflected light is guided to the two-divided detector 10 and the focus error is detected by the knife edge method principle.

The absorbing portion 22 of the spatial filter 8 does not have to be 100% absorbing as long as there is a difference in reflectance between the absorbing portion and the reflecting portion. Further, it is also possible to obtain a focus error signal by configuring both as reflecting parts and configuring an optical system such as a knife edge system or an astigmatism system at the position of the two-divided detection part.

In the case of another invention shown in FIGS. 3 and 4, only the main lobe component of the main spot in the light intensity distribution 23 is selectively reflected by the reflecting portion 21 of the spatial filter 11. The reflected light is received by the photodetector 15 to detect a reproduction signal. The transmitted light is received by the 6-division photodetector 12 via an astigmatism optical system including a converging lens 13 and a cylindrical lens 14. A focus error signal is obtained on the four light receiving surfaces 20 at the center, and a track error signal is obtained from the light receiving surfaces 20 on both sides. It is also possible to obtain a focus error signal by dividing the side light receiving surface into four. In the present invention, the optical system is slightly complicated, but the spatial filter pattern is simple, so that the filter can be easily manufactured and installed. Even if the pattern of the spatial filter 11 is inverted and the positions of the photodetector 15 and the astigmatism optical system are exchanged, the same function can be realized.

In the above example, the super-resolution pattern is generated only in one direction, but it is also possible to generate the super-resolution pattern in two directions or concentrically, and the spatial filter may be a concentric pattern such as a pinhole.

As described above, it is possible to obtain a stable error signal by the three-beam method by appropriately setting the pattern of the spatial filter.

[0015]

FIG. 1 shows an embodiment of the present invention. The emitted light of the semiconductor laser 1 forms a spot on the recording medium 7 by the condenser lens 6 through the super-resolution spatial filter 2, the diffraction grating 3, the polarization beam splitter 4, and the quarter wavelength plate 5. The super-resolution spatial filter 2 may be a phase type instead of a light shield. In addition, the super-resolution spatial filter 2 and the diffraction grating 3
May change positions. The reflected light from the recording medium 7 is
It is reflected by the polarization beam splitter 4 and is focused on the spatial filter 8 via the quarter-wave plate 5. Except for the side lobe component of the main beam, it is transmitted and received by the three-division photodetector 9, and the reproduction signal and the track error signal are detected. A part of the side lobe component is reflected, transmitted through the polarization beam splitter 4 and received by the two-split photodetector 10, and a focus error signal is detected. The optical system may be an optical system that enters a condenser lens via a collimator lens.

Another embodiment of the present invention is shown in FIG. The emitted light of the semiconductor laser 1 passes through the super-resolution spatial filter 2, the diffraction grating 3, the polarization beam splitter 4, and the quarter wavelength plate 5,
A spot is formed on the recording medium 7 by the condenser lens 6. The reflected light from the recording medium 7 is reflected by the polarization beam splitter 4 and passes through the quarter wavelength plate 5 to the spatial filter 1
It is focused on 1. The main lobe component of the main beam is reflected, transmitted through the polarization beam splitter 4 and received by the two-split photodetector 10, and the reproduction signal is detected. The remaining components are received by the 6-division photodetector 12 via the converging lens 13 and the cylindrical lens 14. A track error signal is detected from the received side lobe component, and a focus error signal is detected from the main lobe component.

[0017]

According to the present invention, it is possible to detect a stable track error signal by the three-beam method with a super-resolution structure.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a detailed view of a spatial filter and a three-division photodetector according to an embodiment of the present invention.

FIG. 3 is a diagram showing an embodiment of the present invention.

FIG. 4 is a detailed view of a spatial filter and a 6-division photodetector according to an embodiment of the present invention.

FIG. 5 is a diagram showing a conventional technique.

FIG. 6 is a detailed view of a prior art spatial filter.

[Explanation of symbols]

1 Semiconductor laser 2 Super-resolution spatial filter 3 diffraction grating 4 Polarizing beam splitter 5 1/4 wave plate 6 Condensing lens 7 recording media 8 spatial filters 9 3-division photodetector 10 2 split photodetector 11 Spatial filter 12 6-segment photodetector 13 Converging lens 14 Cylindrical lens 15 Photodetector 16 spatial filters 20 Light receiving surface 21 Reflector 22 Absorber 23 Light intensity distribution

Claims (2)

[Claims] 1. An optical pickup device comprising a condensing optical system that condenses light emitted from a laser light source as a minute spot on a recording medium, and a detection optical system that separates and detects reflected light from the recording medium. In the detection optical system, the condensing optical system includes a diffraction grating that divides a spot on a recording medium into a main spot and two side spots, and a super-resolution spatial filter that reduces a condensing spot beam diameter. Then, an optical system that refocuses the reflected light from the recording medium and selectively transmits the remaining components except the side lobe component of the main spot in the converged spot and an optical system that detects the focus error from the side lobe component are provided. An optical pickup device characterized by being provided. 2. An optical pickup device comprising a condensing optical system that condenses light emitted from a laser light source as a minute spot on a recording medium, and a detection optics that separates and detects reflected light from the recording medium. In the condensing optical system, a spot on the recording medium is provided with a super-resolution spatial filter for reducing the main spot beam diameter, and the recording medium reflected light is refocused in the detection optical system, An optical pickup device, comprising: a spatial filter that selectively reflects or transmits only a main lobe component of a main spot inside the optical spot; and an optical system that detects a spot position error signal from the remaining optical components.