JPH0528524A - Optical head device - Google Patents

Abstract

PURPOSE:To improve the optical availability of an ultra resolution optical head limiting a converged beam spot on a disk face to a diffraction limit or below while detecting a track by a three beam method. CONSTITUTION:The 1st-order diffracted light beams of a light beam transmitting through a diffraction grating 3 inserted to an optical path along to the radial direction of an optical disk 7 form sub-beams 10a, 10b on the optical disk 7 face and are reflected from the optical disk 7 as a track detecting light. On the other hand, though the light beam passing through the outside of the diffraction grating 3 generates side robes 9a, 9b on the optical disk 7 face to the linear velocity direction of the disk, a main robe 8 can be converged to the diffraction limit or below at a beam diameter. When the reflected return light beam is converged by a detecting lens 11, only the side robes 17a, 17b of the main beam are intercepted by arranging a slit 12 in the vicinity of a focus, thus, recorded information picked up by the main robe 8 below the diffraction limit is read and the improvement of the recording and reproducing density of the disk and the improvement of a C/N are expected. Further. the track detection is performed from the sub-beams 10a, 10b generated by the 1storder diffracted light beams transmitting the diffraction grating and the optical availability of the optical head is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION An optical head device used in an information input / output device for recording / reproducing information by using light, particularly a track by a three-beam method using a diffraction grating in a super-resolution optical system using a light shielding element. The present invention relates to an optical head device that is combined with an optical system that detects an error.

[0002]

2. Description of the Related Art An optical system of a conventional super-resolution optical head will be described in detail with reference to the drawings. FIG. 4 is a diagram showing a configuration of a conventional super-resolution optical system. This optical head device includes a semiconductor laser 1 as a light emitting device, a collimator lens 2 for converting the emitted light into parallel light, a light blocking band 27 for blocking a part of the parallel light beam, and a polarization beam splitter 4b for guiding the light to a two-divided detector 29a. , A polarization beam splitter 4b for guiding light to the two-divided detector 29b, a quarter-wave plate 5 for producing a 90-degree phase difference between a wave oscillating in the optical axis direction of the crystal and a wave oscillating perpendicularly thereto. An objective lens 6, a detection lens 11 for once narrowing the luminous flux of return light from the optical disk 7, a slit 28 for taking out a main lobe,
The re-detection lens 14 for collecting the light flux into the two-split detector 29b, the detection lens 30 for narrowing the return light from the polarization beam splitter 4a, the knife edge 31 for splitting the return light flux into two, the two-split detector for detecting the focus error. 29a, a two-divided detector 29b for detecting a signal and a track error.

The semiconductor laser 1 emits light of a single wavelength in a radial direction, and collimates the light on the optical disc 7 by a collimator lens 2 to collimate the light. The objective lens 6 forms a condensing spot on the optical disc surface. Is becoming The collimated light that has passed through the collimator lens 2 is blocked by the light-shielding band 27.
To enter the polarization beam splitter 4a. Shading zone 2
The parallel light that has passed through 7 has two polarization beam splitters 4
After passing through a, 4b, and the quarter-wave plate 5, it is focused by the objective lens 6 to form a focused spot on the surface of the optical disk 7. The 1/4 wavelength plate is set by inclining the optical axis of the crystal by 45 degrees with respect to the plane of polarization of the incident light, and the linearly polarized light that has passed through the polarization beam splitter 4b becomes circularly polarized light and enters the objective lens 6.

FIG. 5 shows how the collimated light 22 is blocked by a light-shielding band 27 inserted in the disk radial direction.

FIG. 6 shows the intensity distribution 32 in the cross section of the light beam blocked by the light-shielding band.

FIG. 7 shows the intensity distribution at the focused spot point on the surface of the optical disk 7 which is focused by the objective lens 6. The beam shape 34 before the light-shielding band is inserted is narrowed in the direction of linear velocity and the main lobe 33 is shown. And side lobes 35 are generated.

In FIG. 4, the light beam reflected by the optical disk 7 travels backward through the going optical system, and the circularly polarized light becomes linearly polarized light which oscillates perpendicularly to the polarization plane of the going collimated light at the quarter-wave plate 5. A part of the light is reflected by the polarization beam splitter 4b on the objective lens side to the detection lens 11, and the rest is transmitted, and the whole is reflected on the polarization beam splitter 4a on the collimator lens side to reach the detection lens 30. The light beam that has entered the detection lens 11 is narrowed and the side lobes are blocked by a slit 28 provided near the focal point. Then, it is converged by the re-detection lens 14 and is received by the two-divided detector 29b in the far field. Track errors due to the push-pull method are detected. On the other hand, the light flux incident on the detection lens 30 is condensed and half is blocked by the knife edge 31, and the focus error is detected by the two-divided detector 29a at the focus.

As described above, in the conventional optical system, the light beam partially shielded by the light-shielding band is narrowed to the diffraction limit or less on the disc surface by the objective lens, whereby the disc recording density and the C / N are improved. It was possible.

FIG. 8 is a block diagram for explaining an optical system of a conventional method of detecting a track error by a three-beam method using a diffraction grating. Laser light emitted from the semiconductor laser 1 passes through the collimator lens 2, the diffraction grating 36, and the polarization beam splitter 4a, becomes circularly polarized by the quarter-wave plate 5, is condensed by the objective lens 6, and is a condensed spot on the optical disk 7. Is formed. The laser light reflected by the optical disk 7 travels backward in the optical system going forward, and changes from circularly polarized light to linearly polarized light that oscillates perpendicularly to the polarization plane of the incident light at the quarter-wave plate, and is reflected by the polarization beam splitter 4a. Cylinder lens 1
After having a non-heavenly aberration at 3, it is narrowed down by the detection lens 14, and the detector 15 detects a focus error, a track error, and a signal.

[0010]

In the detection of the track error using the push-pull method, the track offset is generated by the movement of the lens, and the track servo characteristic is not good as compared with the three-beam method. On the other hand, when a light-shielding band is used in the three-beam method shown in FIG. 8 and a light-shielding band is inserted between the diffraction grating 36 and the polarization beam splitter 4a to realize super-resolution, there is a light amount kicked by the light-shielding band, and the light is used. The rate has dropped. Therefore, in order to obtain good reproduction signal characteristics in the optical system, it is necessary to prepare a light source having a higher output than that of an optical system that does not include a light-shielding band. The present invention is to perform stable track detection by the three-beam method, and to control the reduction in the high utilization rate of the optical head while superfocusing the focused beam spot on the disk surface to the diffraction limit or less by super-resolution. The purpose is to make up for the disadvantages of the super-resolution optical head while drawing out its advantages.

[0011]

In order to achieve the above object, the present invention condenses the emitted light from the light source as a minute spot on the surface of the optical disc by a converging optical system, and reflects the reflected light from this condensing point. In an optical head device for guiding information to a photodetector to reproduce information, a diffraction grating is provided in the optical path of the emitted light from the light source to block the emitted light in a band shape in the radial direction of the optical disc. A lens that re-receives the light beam reflected by the optical disk after passing through the grating and the outside thereof, and ± 1 next time caused by the light beam passing through the diffraction grating in the vicinity of the condensing point of the light beam by the lens A slit is provided which allows the folding light to pass therethrough and shields the 0th-order light from the outside through the central portion in the track direction. Ra has a configuration for detecting a reproduced signal.

[0012]

In the optical head device of the present invention, a diffraction grating is inserted in the central portion of the light flux of the light source in the radial direction of the disk, diffracts the light flux, and the ± first-order light diffracted by the diffraction grating is on the optical disk surface. Due to the effect of super-resolution, the light beam that passes through the outside of the diffraction grating and reaches the objective lens after detecting the track error has a focused beam spot that is below the diffraction limit on the disk surface. Therefore, track detection by the 3-beam method and reproduction by super-resolution using a light-shielding band are possible.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1A is a configuration diagram of an optical system according to an embodiment of the present invention. In the optical head device of this embodiment, a semiconductor laser 1 as a light emitting device, a collimator lens 2 for converting the emitted light into parallel light, a diffraction grating 3 for diffracting a part of the parallel light beam, and a signal detection detector 15 for guiding light. A polarization beam splitter 4a, a quarter-wave plate 5 for producing a 90-degree phase difference between a wave oscillating in the optical axis direction of the crystal and a wave oscillating perpendicularly thereto, an objective lens 6 for focusing a light beam on an optical disk 7, Detection lens 1 for narrowing the return light flux
1, a slit 12 for taking out the main lobe and ± 1st order diffracted light, a cylindrical lens 13 for generating astigmatism for focus detection, a re-detection lens 14 for narrowing down to a signal detection detector 15 of a light beam, and a signal detection detector 15. Composed.

The semiconductor laser 1 radially emits light of a single wavelength, and in order to focus the light on the optical disk 7, it is collimated by the collimator lens 2 in this embodiment, and then is converged by the objective lens 6 on the disk surface of the optical disk. It is configured to connect. The parallel light that has passed through the collimator lens 2 passes through the diffraction grating 3 and enters the polarization beam splitter 4a.

FIG. 2 shows how the parallel beam 22 is blocked by the diffraction grating 3. The diffraction grating 3 is inserted in the disc radial direction, diffracts about 40% of the incident light flux as ± first-order diffracted light, and the grating direction is designed to be slightly angled with respect to the disc radial direction.

The parallel light that has passed through the polarization beam splitter 4a passes from the linearly polarized state to the circularly polarized state after passing through the quarter-wave plate 5 which is set by tilting the optical axis of the crystal by 45 degrees with respect to the polarization plane of the incident light. Then, the focused spot is focused by the objective lens 6, and the focused spot on the surface of the optical disk 7 is constituted by the sub-beams 10a and 10b, the main lobe 8 and the side lobes 9a and 9b on the surface of the optical disk 7. Since the diffraction grating 3 is designed at a slight angle with respect to the disk radial direction, the sub-beams 10a and 10b hit the land and the group boundary line and the track error signal can be detected. In the main beam, side lobes 9a and 9b are also included.
However, the diameter of the main lobe 8 used for signal reading is reduced in the direction of the disk linear velocity.

FIG. 3 shows the intensity distribution in the focused spot, the parallel light transmitted outside the diffraction grating 3 shows the intensity distribution in the spot, and the parallel light transmitted outside the diffraction grating 3 is shown. The beam is focused below the diffraction limit by obtaining the super-resolution effect. That is, the main lobe 24 has a diameter smaller than that of the intensity distribution 25 when the diffraction grating 3 is not inserted, and the side lobe 26 is generated. Diffraction grating 3 Diffraction ± 1st order light is sub beam 23
a and 23b.

In FIG. 1 (A), after the laser light is reflected by the optical disk, it travels backward through the going optical system and is changed from circularly polarized light to linearly polarized light by the quarter-wave plate, which is perpendicular to the vibration in the going optical system. Vibrate. As a result, the light is totally reflected by the polarization beam splitter 4a and reaches the detection lens 11. The light flux is once stopped by the detection lens 11, and the side lobes are blocked by the slit 12. Section A-A (Fig. 1
As shown in (B), the side lobes 17a and 17B are blocked by the slit 12, the main lobe 16 and the sub-beams 18a and 18b pass through the slit 12, and the cylindrical lens 13 has astigmatism and reaches the re-detection lens 14. Reach The light beam is narrowed down by the re-detection lens 14 and focused on the detection detector 15. A cross section BB (FIG. 1C) shows the arrangement of the focused spots on the detection detector 15. The sub-beams are arranged on the detectors 20 and 21, and the main lobe is arranged on the quadrant detector 19. The track error is detected by the detectors 20 and 21 at ef, and the focus error is detected by the detector 19 at (a + c)-.
It is detected by (b + d).

[0019]

As described above, in the super-resolution optical head using the diffraction grating of the present invention, compared with the case of using the conventional track detection by the three-beam method and the super-resolution means by the light-shielding band, Since the amount of light that has been kicked is used, it is possible to narrow the focused beam spot on the disk surface below the diffraction limit as in the conventional super-resolution optical head, but it is possible to increase the light utilization efficiency. Therefore, when the 3-beam method, which is a stable track detection method, and the super-resolution method are used, the load of the power of the light source required for the optical head can be reduced, and the reproduction signal light amount can be reduced by using the conventional 3-beam method. Since it is larger than the resolution optical head, the reproduction signal characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a schematic view of an embodiment using an optical system of a super resolution optical head of the present invention.

FIG. 2 is a diagram showing super-resolution realizing means of the super-resolution optical head of the present invention.

FIG. 3 is a diagram showing an intensity distribution in a focused beam spot of the super-resolution optical head of the present invention.

FIG. 4 is a structural explanatory view of an optical system of a normal super-resolution optical head.

FIG. 5 is a diagram showing a super-resolution realizing unit of a normal super-resolution optical head.

FIG. 6 is a diagram showing an intensity distribution of a light beam incident on an objective lens of a normal super-resolution optical head.

FIG. 7 is a diagram showing an intensity distribution in a focused beam spot of a normal super-resolution optical head.

FIG. 8 is a structural explanatory view of an optical system of an optical head using a normal three-beam method.

[Explanation of symbols]

 1 Semiconductor Laser 2 Collimating Lens 3 Diffraction Grating 4a Polarizing Beam Splitter 4b Polarizing Beam Splitter 5 1/4 Wave Plate 6 Objective Lens 7 Optical Disc 8 Mainlobe 9a Sidelobe 9b Sidelobe 10a Sub-beam 10b Sub-beam 11 Detection Lens 12 Slit 13 Cylindrical Lens 14 Re-detection lens 15 Signal detection detector 16 Main lobe 17a Side lobe 17b Side lobe 18a Sub-beam 18b Sub-beam 19 4-division detector 20 Detector 21 Detector 22 Luminous flux 23a Sub-beam 23b Sub-beam 24 Main lobe 25 Normal beam shape 26 Side lobe 27 Light-shielding band 28 Detection Slit 29a Two-divided detector 29b Two-divided detector 30 Detection lens 31 Knife edge 32 pairs The intensity distribution of the lens before entering the collimated light 33 main lobe 34 normal beam shape 35 side lobe 36 diffraction grating

Claims (1)

Claims: 1. Light emitted from a light source is condensed as a minute spot on an optical disk disk surface by a converging optical system, and reflected light from this condensing point is guided to a photodetector to reproduce information. In the optical head device for performing, in the optical path of the emitted light from the light source, a diffraction grating that blocks the emitted light in a band shape in the radial direction of the optical disc is provided, and after passing through the diffraction grating and the outside thereof, A lens that re-receives the light flux reflected by the optical disc, and a ± 1st-order diffracted light generated by the light flux passing through the diffraction grating pass near the condensing point of the light flux by the lens, and a 0th-order light Is provided with a slit that shields the outside through the central portion in the track direction, and the focus error, the track error, and the reproduction signal can be detected by the light passing through the slit. Characteristic optical head device.