JPS62141651A - Optical head device - Google Patents

Abstract

PURPOSE:To simplify an optical adjustment and to reduce the influences of fluctuation of wavelength of a light source by dividing a diffraction grating structure into plural areas that diffract a luminous flux to different directions. CONSTITUTION:Reflected light rotated by the polarizing surface is led to a photodetector 9 through an photodetecting element 8, and control signals for automatic focusing and automatic tracking and signals of information recorded on a recording face 6 are detected. In the photodetector 9, four light receiving faces 9a, 9b, 9c, 9d are arranged in series in the direction of paper face. Focus error signals are detected by a diffraction grating 10a and light receiving faces 9a, 9b of the photodetector 9, and automatic focusing is made possible by moving an objective lens 5 or whole light head to a disk along the optical axis of incident light through an actuator. Track error signals are detected by diffraction gratings 10c, 10d and light receiving faces 9c, 9d of the photodetector, and automatic tracking is made possible by driving an tracking actuator and moving an objective lens 7 perpendicular to the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an optical head device for optically recording or reproducing information by irradiating light onto an information carrier.

[Prior art]

In recent years, compact discs, which record digitized audio using uneven surfaces, and video discs, which record TV images, have become extremely popular.

In particular, it is highly anticipated that compact disc players will expand from desktop and compact discs to portable portable players and car-mounted players.

These optical information recording/reproducing devices are required to be thin, small, and inexpensive as requirements from the user side. Similar demands are also growing for

Conventionally, in the original head device as described above, a cylindrical lens or the like is disposed in the optical path toward the photodetector, and the focus lens No. 16 is detected using astigmatism. However, special optical components such as a cylindrical lens do not increase the cost of the device, and optical adjustment between valley components is complicated during assembly. Therefore, an optical head device that solved these drawbacks was developed in Japanese Patent Application Laid-Open No. 60-542.
It is proposed in No. 5, etc. This example will be explained using the 15th bad.

FIG. 15 is a schematic diagram showing the configuration of a conventional optical head device. Here, the light beam 46 from the semiconductor laser light source 41 becomes a parallel light beam by the collimator lens 42, passes through the polarizing beam splitter 44, passes through the % wavelength plate 15'5, and then passes through the objective lens 45 with the ↑R signal. Record carrier side 1
The light is focused on 7. The light beam reflected on the information recording carrier surface and containing information is reflected by the beam splitter 44 and then enters the place type diffraction grating 20. This diffraction grating is designed to diffract an incident light beam in a direction that is approximately at a critical angle with respect to the plane of incidence. When the information recording carrier is far away from its normal position or close to it, the light beam incident on the diffraction grating becomes convergent light or emitted light.

As a result, an imbalance in the light amount distribution on the photodetector 51 occurs, and seven orcus error detection is performed.

However, the above-mentioned optical head device has a drawback that correct autofocus operation cannot be performed if the wavelength of the light source changes due to changes in environmental temperature, fluctuations in drive current, etc. during use.

For example - by way of example, a semiconductor laser with a wavelength of λ=830 nm experiences a wavelength shift of about 0.5 nm for a temperature increase of 1 DEG C., resulting in a wavelength shift of as much as 6 nm for a temperature increase of 20 DEG C. When such a wavelength change occurs, the diffracted light is totally reflected, and a focus shift of about ±1 μm causes a state in which the light intensity distribution on the photodetector 51 does not change at all, resulting in an automatic failure. Focus operation becomes impossible.

[Summary of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an original head device in which optical V8 adjustment is simple and is less affected by wavelength fluctuations of a light source.

The above object of the present invention is to provide a light source that irradiates light onto an information carrier;
disposed between the light source and the information carrier.

An optical head device 1 comprising a light splitter that separates the light beam reflected by the information carrier from the irradiation light beam, and a photodetector that detects the reflected light beam separated by the light splitter,
An optical element t having a diffraction grating structure that diffracts at least a part of the reflected light beam and guides it to the photodetector is provided between the light splitter and the photodetector, and the diffraction grating structure is used to guide the light beam to the photodetector. This is achieved by dividing the beam into a plurality of regions, each of which diffracts in a different direction.

〔Example〕

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a schematic diagram showing an embodiment of an optical head device of the present invention. Here, the S-polarized light emitted from the semi-integrated laser 1 passes through the collimator lens 2 and the beam-shaping prism 3 to become a parallel beam of light, and the S-polarized light passes through the collimator lens 2 and the beam-shaping prism 3 to become a parallel beam of light, and has an appropriate polarization time (for example, if the reflectance of P-polarized light is 70, the transmittance is 30, or S Reflectance of polarized light is better than 100)
The light beam passes through the polarized beam sinter 4 and is focused on the information recording surface 6 by the objective lens 5. Then, the reflected light whose polarization plane has been rotated according to the upward and downward magnetization information on the recording surface 46 on which information is magnetically recorded passes through the objective lens 5 again, and is combined with the incident light beam by the polarizing beam splitter 4. The light is separated and incident on an optical element 7 consisting of a parallel flat plate having a relief type diffraction grating formed on its -plane. The light diffracted by the diffraction grating passes through the analyzer 8 and is detected by the photodetector 9.
, and control signals for autofocus (hereinafter referred to as F) and autotracking (hereinafter referred to as AT) and signals of information recorded on the recording surface 6 are detected.

The optical element 7 shown in FIG.
It is shown in FIG. 1r and FIG. 2 as viewed from the side. The relief type diffraction grating of this embodiment has three parts 10a.

It is divided into 10b and 10c, each of which has a conical grating, and diffracted light beams 11a, 11b, 11c.
It has a lens action that focuses the light. Further, the photodetector 9 has four receivers and optical surfaces 9a, 9b, 9c, and 9d arranged in series in the direction of the paper. This light intensity distribution on the photodetector is
It changes depending on the focusing state of the spot on the recording surface 6 in FIG. First, the principle of autofocus will be explained in detail below.

The focus error signal is transmitted by the diffraction grating 10a and the photodetector 9.
It is detected by the light receiving surfaces 9a and 9b. Figure 3 (A).

(B) and (C) are light receiving surfaces 9a and 9b of the photodetector 9.
f, A diagram seen from the light incidence side, where the shaded area shows the shape of the beam, (B) shows the focused state, and (A) and (0) show the out-of-focus state. If the outputs from the light-receiving surface are respectively I and * Ibe, then in the electrical system shown in Figure 4 μ), Ia-
By performing the operation Ib in the differential multiplier 12,
At the output terminal 13, a focus error signal as shown in Figure 4 is obtained. error), and the vertical axis indicates the signal output.According to the obtained focus error signal, the objective lens 5 or the entire optical head is moved relative to the disk along the optical axis of the incident light via a 7-cut unit (not shown). This enables autofocus.

Next, the principle of auto-tracking in the embodiment shown in FIG. 1 will be explained. The track error signal is the diffraction grating 10c.
, 10b and the light receiving surface 9c of the photodetector.

Detected with 9d. Figure 5 (A), (B), (
Assuming that a cage 18a is formed on the substrate 18 of the information recording carrier as shown in C), the incident light beam is focused near this @18a by the objective lens 5. Here (b) is.

A state where a spot is formed on the target yeast 18a, (A
), ((') indicates that the spot is shifted to the right or left with respect to fermentation.The recording surface 1 on this cover plate 18
The light beam reflected at the groove 18a includes tracking information due to diffraction or scattering at the groove 18a.

When the reflected light is received by the light receiving surfaces 9c and 9d of the photodetector Or9 shown in FIG. 2, the light waves are
Figure 6 (
A) t (B) * ((J) Therefore, in an electric system other than that shown in FIG.
By performing the calculation c in the differential amplifier 14, a tracking error No. 18 as shown in FIG. 7 is obtained at the output terminal 16. In FIG. The axis indicates the No. 1 output.Auto tracking is possible by driving a tracking actuator (not shown) according to the obtained tracking error signal and moving the objective lens 7 perpendicular to the optical axis.

The influence of the wavelength fluctuation of the semiconductor laser in the detection method of the focus error signal and the track error signal explained above will be explained. The possible effects of wavelength variation are:
The original diffraction direction diffracted from the diffraction grating changes, “k,
@The position on the light output device changes, and the energy is not concentrated in one order of light, but multiple beams arrive on the light output device. In the present invention, the beam position on the optical oblique device changes only in the direction parallel to the dividing line of the photodetector and does not change in the perpendicular direction, so it is due to the wavelength fluctuation. There is no effect due to changes in beam position. In addition, when the mantissa beam goes around the photodetector, the energy of one beam is dispersed into multiple parts and is incident on the dividing line and a position that has moved parallel to it, so the total light intensity detects the source of one beam. Therefore, there is no effect due to multiple beams falling on the photodetector.

As described above, by making the light-receiving surface of the photodetector relatively large in the direction in which the light flux moves due to wavelength fluctuations, and by making the boundaries of each light-receiving surface parallel to this direction, the wavelength fluctuation of the light source can be Even if this occurs, the output of the six-light detection section is hardly affected, and correct autofocus and autotracking can be performed.

Next, an example of mold creation for manufacturing the diffraction grating structure of the optical element used in the present invention will be described.

In making the mold, as shown in FIG. 8, the mold is made by rotating the mold material 2° and moving the cutter 21 of the diamond temple in a direction perpendicular to the plane of the paper.

The apex angle of the cutting edge of the cutter 21 is determined by angles α and β, and in the above example, it has an angle of 65'. The mold material 20 may be made of metal such as phosphorus FW4 or X-brass N1.

You can also purchase polymeric materials such as wax discs and glass materials. However, in the case of a metal mold material, it has the advantage that it can be used directly as a stub bar, and there is no need for a step of creating a stub bar by electroforming or the like. When cut using the method shown in Figure 8, the relief structure is shaped like concentric circles as shown in Figure 9 (CB). J-7m construction is obtained. FIG. 9(6) is an enlarged view of a part of the diagram, with α-35°, β~80°, and pitch ~20 μm.

Next, as shown in FIG. 10, compression transfer is performed on a plastic material 23 such as acrylic. At this time, by applying appropriate temperature and pressure to the mold 22 and the acrylic material 25, it is possible to faithfully transfer the relief structure of the mold m22 to the acrylic material 25.

As shown in FIG. 11, a reflective layer 24 is provided on the transferred relief structure of the acrylic material by, for example, vapor deposition. Reflective layer 24
may have a multilayer structure or a single layer structure. Also, MfF
2. The optical element used in the present invention is fabricated by any of the above methods, which may be a dielectric dt film such as Tie□, ZrO7, 8102, etc., or a metal film such as Au, At, A4'', etc.

Optical head commonly used in single-source magnetic recording and reproducing devices! In the device, one reflected light has its polarization direction rotated on the recording surface, and the time it reaches the analyzer.

Depending on the polarization characteristics of the recording surface and the optical elements therebetween, a phase difference may occur between the P-polarized light component and the 8-polarized light component, resulting in a decrease in the Sρ value of the Rf signal.

Therefore, FIGS. 12(A), 12(B), and 12(C) show the structure of another embodiment of the present invention in which means for correcting the phase difference is provided.

FIG. 12 (lower side is a configuration diagram when the phase difference caused by the recording surface 6, objective lens 5, and polarizing beam splitter 4 is large and the phase difference caused by the optical element 7 is small. By inserting a phase correction plate 25 such as Pavine Soley 2 in between, the phase is corrected and the s-output is improved. FIG. 3 is a configuration diagram when the phase difference is small and the phase difference caused by the optical element 7 is large. By positioning the polarizer 26 between the polarization beam sinter 4 and the optical element 7, there is no effect of phase difference caused by the optical element 7, and the S/N ratio is improved.

FIG. 12 (q is a configuration diagram when the phase difference becomes large in each of the recording surface 6, objective lens 5, polarizing beam splitter 4, and optical element 7).

between the polarizing beam splitter 4 and the optical element 7.

Phase correction plate 25 gold case, analyzer 27 position 1R to position 4tl
By interposing it between the correction plate 25 and the optical cable 7, the phase difference is corrected and the value of sA is improved.

FIG. 13 is a diagram showing a preferred embodiment when there is a large amount of mutual leakage between the track error signal, the focus error signal, and the information signal.

The reflected light from the recording surface 6 passes through the objective lens 5 and the polarizing beam sinter 4 and enters the optical element 7 . The light r-wavelength element 7 diffracts a suitable light f out of the reflected light beam and sends it to a photodetector 9.
When the track error number 1 is detected, a focus error signal is generated. The rest of the reflected light passes through the optical element 7, passes through the analyzer 28 and the condensing lens 29, and then reaches another photodetector 3.
0 and the information signal recorded on the information carrier is compared. This reduces the mutual leakage between the error, trunk error signal, focus error signal, and f#N signal.

FIG. 14 is a configuration diagram of an optical head device applied to an optical disk device. In this case, the linearly polarized light emitted from the semi-24-body laser 1t'' passes through the collimator lens 2 and the beam shaping prism 3 to become a parallel beam of light, and is further transmitted by a polarizing beam splitter such as 8 polarized lights, 98 long reflections, and 98 P polarized lights. ) 34, becomes circularly polarized light by the wavelength plate 31, and is focused on the recording surface 56 by the objective lens 5. The reflected light is reflected by the bits formed on the recording surface 36.

The light passes through the objective lens 5 and the % wavelength plate 31 again, and becomes P-polarized linearly polarized light. This P-polarized linear 1fiil light passes through the polarizing beam splitter 64f and reaches the optical fiber 7.
A track error signal, a focus error signal, and an information signal are obtained by the photodetector 9.

〔Effect of the invention〕

As described above, according to the optical head device of the present invention, even if the wavelength of the light source varies due to K such as temperature change, it is possible to detect all signals without causing drift.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical head device of the present invention;
! @Figure 2 is W, Figure 1 is a diagram showing the optical element shown in Figure 1, Figures 3 and 4 are diagrams each showing the principle of autofocus in the present invention, Figures 5, 6, and 7 are diagrams showing the optical element shown in Figure 1, respectively. Figures 8, 9, 10 and 11 are diagrams showing the method of manufacturing the optical element used in the present invention, Figures 12, 13 and 1A14, respectively.
The figures are block diagrams showing other embodiments of the optical head device of the present invention, and FIG. 15 is a block diagram showing a conventional optical head device. 1... Semiconductor laser 2... Collimator lens 3... Beam shaping prism 4... Polarizing beam splitter 5... Objective lens 6... Recording surface 7... Optical element 8... Saving element Child 9...Photodetector

Claims (1)

[Claims] (1) a light source that irradiates light onto an information carrier; a light splitter that is disposed between the light source and the information carrier and separates the light flux reflected by the information carrier from the irradiation light flux; and a photodetector that detects the separated reflected light beam, the optical head device comprising: a diffraction grating that diffracts at least a portion of the reflected light beam and guides it to the photodetector between the light splitter and the photodetector. An optical head device comprising an optical element having a structure, the diffraction grating structure being divided into a plurality of regions each diffracting a light beam in a different direction.