JPH05217186A - Optical head device - Google Patents

Abstract

PURPOSE:To stably obtain a track error signal even if an effective depth of a pit of an optical disk is near to lambda/4. CONSTITUTION:A diffraction grating 2, light screen band 3 and a polarization beam splitter 4 are disposed in a divergent luminous flux from a semiconductor laser 1. It is converted into a parallel luminous flux by a collimator lens 5, and condensed at a plurality of super-resolution spots on a recording surface of an optical disk 8 by an objective lens 7. A light reflected on the surface of the disk 8 is reflected by the splitter 4 and condensed on a slit 11. A transmitting part, a reflecting part and an absorption part are provided on the slit 11. Only a main lobe of a zero-order luminous flux and + or - primary luminous flux are transmitted to a photodetector 12, and a track error signal and a reproduced signal are detected. Only one side of a side lobe of the zero-order luminous flux is reflected, and a focus error signal is detected by a photodetector 13.

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, and more particularly to an optical head device applied to an optical signal recording / reproducing device using a laser light source.

[0002]

2. Description of the Related Art When data is recorded on an optical disk, pits having the same size as a laser beam narrowed down to the diffraction limit are formed and recorded on the optical disk. Therefore,
Since the recording density is inversely proportional to the square of the laser wavelength, it is required to shorten the wavelength of the laser light source in order to increase the recording density. However, the semiconductor laser that can be used in the optical disk device is considered to have a limit of about 650 nm.

For this reason, a super-resolution method has been introduced in order to realize a spot below the diffraction limit, and a video disk reproduction experiment has been conducted. About this experiment, Proceedings of 38th Joint Lecture Meeting on Applied Physics, Spring 1991,
Reported by lecture number 29p-C-1.

According to this experimental report, an optical system as shown in FIG. 3 is constructed. Here, the emitted light from the semiconductor laser 1 is made into a parallel light flux by the collimator lens 5, and is shaped into a circle by the shaping prism 10. Next, the intensity near the center of the beam is attenuated by the light-shielding band 3, and the super-resolution spot is formed on the optical disk 8 by the objective lens 7. Further, the reflected light from the optical disk 8 has a wavelength of λ / 4.
After being converted into S-polarized light by the plate 6, it is guided by the polarization beam splitter 4 to the polarization beam splitter 14 of the detection system. Then, all the reflected light from the optical disk is reflected by the polarization beam splitter 14, and is focused on the slit 17 by the plano-convex lens 16.

The slit 17 is constructed as shown in FIG. 4, and is used to separate the main lobe and the side lobe of the optical disk reflected light. The main lobe passes through the transmission part of the slit 17 and is incident on the photodetector 12. The side lobe has slit 1 on only one side.
The light is reflected by the reflection part 7 and converted into P-polarized light by the λ / 4 plate 15, and then passes through the polarization beam splitter 14 and enters the photodetector 13. The other side of the side lobe is absorbed by the absorbing portion of the slit 17.

The photodetector 12 detects a reproduction signal and a track error signal from the incident main lobe, and
The photodetector 13 detects the focus error signal from one side of the incident side lobe.

[0007]

However, in the above-mentioned optical system, the focus error signal detection method is the knife edge method, and the track error signal detection method is the far field method. Therefore, in the detection of the track error signal, when the effective depth of the pits formed on the optical disc is close to λ / 4, the phase difference of the reflected and diffracted light becomes π, so that they interfere with each other and cancel out. However, there is a problem in that the detection sensitivity decreases and the detection of the track error signal becomes unstable.

It is an object of the present invention to provide an optical head device capable of stably detecting a track error signal even when the effective depth of pits on an optical disk is close to λ / 4.

[0009]

An optical head device of the present invention generates a laser light source for emitting a laser beam, and a zero-order light beam and a ± first-order light beam in a light beam cross section with respect to a divergent light beam from the laser light source. A diffraction grating, a light-shielding band that reduces the light intensity near the center of light passing through the diffraction grating to generate a main lobe and a side lobe in the 0th-order light beam and the ± 1st-order light beams, respectively, and a light-shielding band that passes through this light-shielding band. First condensing means for condensing the generated light on the recording medium surface as a plurality of super-resolution spots, second condensing means for condensing the reflected light from the recording medium surface, and the second condensing means. And a slit for transmitting only the main beam of the 0th-order luminous flux and the ± 1st-order luminous fluxes and reflecting one side of the side lobes of the 0th-order luminous flux. Receive the transmitted light Second detecting a first light detection means for detecting a reproduction signal and a track error signal, a focus error signal by receiving the light reflected by the slit
And a light detecting means.

[0010]

The present invention will be described below with reference to the drawings.

FIG. 1 is a layout view of an optical system showing an embodiment of the present invention. The divergent light beam emitted from the semiconductor laser 1 passes through the diffraction grating 2, so that the 0th-order light beam and the + 1st-order light beam having a certain diffraction angle, -1 in the cross section of the emitted light beam.
It is separated into the next luminous flux. Next, the intensity of light near the center of the divergent light flux is reduced by the light-shielding band 3 to reduce the 0th-order light flux and ± 1.
A main lobe and a side lobe are generated in the next light flux. Further, the light is transmitted through the polarization beam splitter 4, and is made into a parallel light flux by the collimator lens 5. The P-polarized parallel light beam is converted into circularly polarized light by the λ / 4 plate 6 and is condensed on the recording surface of the optical disc 8 by the objective lens 7 to form a plurality of super-resolution spots.

The laser light from which information has been read from the recording surface of the optical disk 8 is reflected, enters the objective lens 7 again, becomes a parallel light flux, passes through the λ / 4 plate 6, and is converted from circularly polarized light to S polarized light. Since the polarization beam splitter 4 reflects S-polarized light, all the reflected light from the optical disk 8 is projected by the plano-concave lens 9.
Reflect on. The reflected light whose focal length has been extended by the plano-concave lens 9 is converted into circularly polarized light by the λ / 4 plate 15 and condensed on the slit 11.

The slit 11 has a structure as shown in FIG. 2, and has a main lobe of the 0th-order luminous flux and ± 1.
It has the function of separating the next luminous flux. That is, the main lobe of the 0th-order light beam, the + 1st-order light beam and the -1st-order light beam are respectively transmitted, one side lobe of the 0th-order light beam is reflected, and the other sidelobe of the 0th-order light beam is absorbed.
Therefore, the main lobes of the ± first-order light flux and the zero-order light flux enter the photodetector 12, respectively.

The photodetector 12 has a photodetection surface divided into three parts, detects a reproduction signal from the main lobe of the 0th-order luminous flux, and tracks by the differential output of the light amounts of the + 1st-order luminous flux and the -1st-order luminous flux. Detect an error signal.

In this case, +1 regardless of the phase of the reflected light.
Since the difference in light amount between the secondary light beam and the −1st light beam is detected as a track error signal, the detection sensitivity does not decrease even when the effective depth of the pits on the optical disk is close to λ / 4.
Therefore, the track error signal can be detected stably.

On the other hand, one side lobe of the reflected 0th-order light beam is converted into P-polarized light by the λ / 4 plate 15, passes through the polarization beam splitter 4, and enters the photodetector 13 located on the opposite side. Incident. The photodetector 13 has a photodetection surface divided into two, and detects a focus error signal according to the knife-edge principle.

[0017]

As described above, according to the present invention, the emitted light from the semiconductor laser is passed through the diffraction grating, the light-shielding band, and the polarization beam splitter as it is as a divergent light beam, and after reaching the collimating lens, it is converted into a parallel light beam. Then, by converging on the recording surface of the optical disc with the objective lens, multiple super-resolution spots diffracted by the diffraction grating can be formed, and the converged light reflected on the recording surface of the optical disc is converted by the polarization beam splitter. The light is reflected and condensed on the slit, and the slit is provided with a transmitting portion, a reflecting portion, and an absorbing portion, and only the main lobe of the 0th-order luminous flux and the ± 1st-order luminous flux are transmitted and made incident on the photodetector. By detecting the error signal and the reproduced signal respectively,
The three-beam method of the main lobe of the first-order light flux, the −1st-order light flux, and the 0th-order light flux can be used, and the light amount difference between the + 1st-order light flux and the −1st-order light flux is detected as a track error signal. Even if the target depth is close to λ / 4, the track error signal can be stably detected without affecting the detection sensitivity. Furthermore, the focus error signal can be detected by reflecting only one side lobe of the 0th-order light beam at the reflecting portion of the slit and making it enter the photodetector.

[Brief description of drawings]

FIG. 1 is a layout view of an optical system showing an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a slit 11 shown in FIG.

FIG. 3 is a layout diagram of an optical system showing an example of a conventional optical head device.

FIG. 4 is a diagram showing a configuration of a slit 17 shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Diffraction grating 3 Light-shielding band 4 Polarization beam splitter 6 λ / 4 plate 8 Optical disk 11 Slit 12, 13 Photodetector

Claims (1)

[Claims] 1. A laser light source that emits laser light, a diffraction grating that generates a 0th-order light flux and a ± 1st-order light flux within a light beam cross section for a divergent light flux from the laser light source, and light that has passed through this diffraction grating. A light-shielding band that reduces the light intensity near the center of the beam to generate a main lobe and a side lobe in the 0th-order light flux and the ± 1st-order light fluxes, respectively, and the light passing through the light-shielding band is superposed on a recording medium surface. First condensing means for condensing as an image spot, second condensing means for condensing reflected light from the surface of the recording medium, and a condensing point of the second condensing means are provided. A slit that transmits only the main beam of the 0th-order beam and the ± 1st-order beams, and reflects one side lobe of the 0th-order beam.
First light detecting means for receiving the light transmitted through the slit to detect the reproduction signal and the track error signal, and second light detecting means for receiving the light reflected by the slit and detecting the focus error signal are provided. An optical head device characterized by the above.