JP2605469B2 - Optical head device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical head device used for an information input / output device for recording and reproducing information for light. More specifically, the present invention relates to an improvement of an optical head device which has improved recording density by using a super-resolution effect.

(Prior Art) To improve the recording density of an optical disk, it is effective to reduce the diameter of a light spot on a recording medium. Means for reducing the beam diameter include a main lobe 61 having a small diameter as shown by the solid line in FIG. 6 due to the effect of super-resolution by reducing the intensity near the center of the light incident on the condenser lens.
(JP-A-1-315040, JP-A-2-315040).
-91829). The broken line in FIG. 6 shows the light intensity distribution of the light spot when the super-resolution effect is not used, and the solid line shows the light intensity distribution of the light spot in the field using the super-resolution effect. However, as the intensity decreases near the center, the diameter of the main lobe 61 becomes smaller, but the side lobe 62 becomes larger.

FIG. 5 shows an example of an optical head device using super-resolution. The light emitted from the semiconductor laser 1 becomes parallel light by the collimating lens 2, and the light intensity near the center is reduced by the light shielding band 3. The light is condensed as a super-resolution spot on a recording medium 7 by a condensing lens 6 via a polarizing beam splitter 4 and a 波長 wavelength plate 5. The reflected light from the recording medium is reflected by the polarizing beam splitter 4 and split into two by the beam splitter 30. One is condensed again by the converging lens 9 and only the main lobe component is extracted by the slit 31 placed at the condensing point. The light is received by the photodetector 11. By using such a detection system, it is possible to obtain a reproduced signal that is less affected by side lobes. The separated reflected light is subjected to a focus error signal detection by a knife edge method by a converging lens 9, a knife edge 12, and a two-segment type photodetector 13.

(Problem to be Solved by the Invention) Even in such a conventional optical head device, high-density recording can be realized. However, in an optical system that detects reflected light, there is an amount of light kicked by the slit,
Light utilization is not enough. In particular, in a recording medium requiring a sufficient S / N, it is indispensable to improve the utilization rate of the medium reflected light.

An object of the present invention is to solve the above-described problems and to provide an optical head device using super-resolution using reflected light from a medium with high efficiency.

(Means for Solving the Problems) An optical head device according to the present invention includes means for reducing the intensity of light near the center in a cross section of a light beam emitted from a light source, and a lens for condensing light on the light source and the surface of a recording medium. An optical system having an optical system for focusing light emitted from the light source as a minute spot on a recording medium, and guiding reflected light from the focal point to a photodetector. An optical system for condensing the reflected light from again, and an optical system for separating a main lobe component and a side lobe component at the refocus point,
An optical system for obtaining a focus error signal from the side lobe component is provided.

Further, the above-mentioned optical head device is characterized in that it has an optical system that shields only one half of the separated side lobe component and guides the remaining side lobe component to a two-part photodetector.

(Function) The present invention is characterized in that an information signal is detected from a main lobe component and a focus error signal is detected from a side lobe component when the recording medium reflected light is collected again. By performing such detection, components that have been conventionally shielded by the slit can be effectively used, and the reflected light of the recording medium can be used without waste.

Further, in the second invention, even if a slit necessary for detecting an information signal is devised to reflect only a side lobe component on one side, a focus error detection can be performed without newly configuring an error detection optical system. Is made possible. This is because the slit at the focal plane acts as a knife edge. According to the present invention, the optical system is further simplified.

(Embodiment) FIG. 1 shows a first embodiment of the present invention.

The light emitted from the semiconductor laser 1 becomes parallel light by the collimating lens 2, and the light intensity near the center is reduced by the light shielding band 3. The light is condensed as a super-resolution spot on a recording medium 7 by a condensing lens 6 via a polarizing beam splitter A4 and a quarter-wave plate 5. The reflected light from the recording medium is 1/4 of the polarization beam splitter B8 separated by the polarization beam splitter A4.
Are condensed again by the converging lens 9 via the wave plate. The polarization directions of the transmitted and reflected polarization beams of the polarization beam splitters A and B are reversed, and the light reflected at A is transmitted at B. Only the main lobe component is extracted by the mirror 10 having the slit at the focal point and received by the photodetector 11. The side lobe component is reflected by the mirror portion of the mirror 10 having the slit and passes through the quarter-wave plate 5 again, so that the polarization direction changes by 90 degrees and is reflected by the polarization beam splitter B8. Further, a focus error is detected by the converging lens 9, the knife edge 12, and the two-divided photodetector 13.

According to the present optical system, sufficient utilization efficiency can be obtained. The track error signal can be detected by the principle of the push-pull method if the photodetector 11 is of a two-part type. The focus error detection may be performed by an astigmatism method using a cylindrical lens. Further, in the present embodiment, the light-shielding band on the stripe is used. However, a configuration in which only the vicinity of the center of the collimated beam is shielded by a circular light-shielding plate, and the main lobe component is detected by a circular holed mirror instead of the slit. Good.

 FIG. 2 shows a second embodiment.

A semiconductor laser 1, a collimating lens 2, a light-shielding band 3, a polarizing beam splitter A4, a quarter-wave plate 5, a condenser lens 6,
The recording medium 7, the polarizing beam splitter B8, the quarter-wave plate, the converging lens 9, and the mirror 10 with the slit 10 and the photodetector 11 are the same as in the first embodiment. At the converging point of the converging lens 9, the side lobe component on one side is shielded by the knife edge 12, and only the side lobe component on the other side is reflected by the slit mirror and reflected by the polarization beam splitter B8 to be divided into two parts. The light is detected by the photodetector 13. In such a configuration, the focus error signal is detected as follows. FIG. 3 shows a change in the beam shape 15 on the two-segment detector 13. In the focused state, since the mirror 10 with the slit is located at the focal position, the beam shape becomes substantially symmetric on the photodetector on the four-field surface. If the mirror position deviates from the focal position, the mirror position becomes the far field surface, and the beam shape on the photodetector changes asymmetrically. Therefore, a focus error signal can be obtained as in the knife edge method. The track error signal can be obtained by the push-pull method by making the photodetector 11 into a two-part type as in the first embodiment. The mirror and the knife edge can be integrated.

As shown in FIG. 4, a wedge prism 20 may be used instead of the slit mirror 10 and the knife edge 12. In this case, the side lobe kicked by the prism is
The split photodetector 13 may be provided.

(Effects of the Invention) According to the present invention, it is possible to obtain an optical head device for high-density recording with a high utilization of reflected light from an optical disk.

[Brief description of the drawings]

1, 2 and 4 are views showing an embodiment of the present invention, FIG. 3 is a view showing the operation of the present invention, and FIGS. 5 and 6 are views showing a conventional technique. 1 ... Semiconductor laser, 2 ... Collimate lens, 3 ...
Shielding band, 4 ... Polarizing beam splitter A, 5 ... 1/4 wavelength plate, 6 ... Condensing lens, 7 ... Recording medium, 8 ... Polarizing beam splitter B, 9 ... Converging lens, 10 ... Mirror with slit, 11 ... Photodetector, 12 ... Knife edge, 13
... A two-segment photodetector, 15 a beam shape, 20 a wedge prism, 30 a beam splitter, 31 a slit.

Claims (2)

(57) [Claims] A means for reducing the intensity of light near the center in the cross section of the light beam emitted from the light source, between the light source and a lens for condensing the light on the surface of a recording medium; In an optical head device having an optical system that condenses the emitted light as a minute spot on a recording medium and guides the reflected light from the focal point to a photodetector, an optical system that condenses the reflected light from the recording surface again And an optical system for separating a main lobe component and a side lobe component at the refocusing point, and an optical system for obtaining a focus error signal from the side lobe component. And a means for reducing the intensity of light near the center in the cross section of the light beam emitted from the light source, between the light source and a lens for condensing light on the surface of the recording medium, and In an optical head device having an optical system that condenses the emitted light as a minute spot on a recording medium and guides the reflected light from the focal point to a photodetector, an optical system that condenses the reflected light from the recording surface again An optical system for separating a main lobe component and a side lobe component at the refocusing point, and shielding only one half of the side lobe component at the focusing point and guiding the remaining side lobe component to a two-split photodetector. An optical head device having an optical system.