JP2578589B2 - Optical head device - Google Patents

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 for irradiating an information carrier with light and optically recording or reproducing information.

[0002]

2. Description of the Related Art In recent years, compact discs on which digitized audio is recorded with unevenness on the surface and video discs on which TV images are recorded have become remarkably popular.

[0003] In particular, there is a great expectation for compact disc players to be portable or portable players that can be freely carried, or to be mounted on vehicles.

These optical information recording / reproducing devices are required to be thin, small, and inexpensive as demands from the user side. Therefore, the same applies to an optical head device for recording or reproducing information on an information carrier as described above. Demands are growing.

Conventionally, in the above-described optical head device, a cylindrical lens or the like is usually arranged in an optical path toward a photodetector, and a focus error signal is detected using astigmatism. However, special optical components such as a cylindrical lens cause an increase in the cost of the apparatus, and optical adjustment between components during assembly is complicated.
Therefore, an optical head device that solves such a defect has been proposed in Japanese Patent Application Laid-Open No. Sho 60-5425. This example will be described with reference to FIG.

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 is converted into a parallel light beam by the collimator lens 42, passes through the polarizing beam splitter 44, passes through the 波長 wavelength plate 15, and then is passed through the objective lens 45 by the objective lens 45. The light is condensed at 17. The light beam reflected by the information recording carrier surface and containing information is reflected by the beam splitter 44 and then enters the blazed diffraction grating 20. This diffraction grating has a direction in which the critical angle is almost
It is designed to diffract incident light. If the information record carrier is farther or closer than the regular position,
The light beam incident on the diffraction grating becomes convergent light or divergent light. As a result, the light amount distribution on the photodetector 51 becomes unbalanced, and the focus error is detected.

However, the optical head device as described above has a drawback that a correct autofocus operation cannot be performed when the wavelength of the light source changes due to a change in environmental temperature during use, a change in drive current, or the like.

For example, as an example, a semiconductor laser having a wavelength of λ = 830 nm has a temperature rise of about 1.degree.
A wavelength shift of nm results in a wavelength variation of as much as 6 nm at a temperature rise of 20 ° C. When such a wavelength change occurs, the diffracted light is completely totally reflected,
With a focus shift of about ± 1 μm, a state occurs in which the light amount distribution on the photodetector 51 does not change at all, and the autofocus operation becomes impossible.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to further improve an optical head device using the above-mentioned diffraction, and to reduce mutual leakage between a control signal and an information signal for auto focus and auto tracking. An optical head device is provided.

Another object of the present invention is to provide an optical head device which can simplify the arithmetic processing of signals after the photodetector.

[0011]

In order to achieve the above object, an optical head device according to the present invention comprises: a light source for irradiating a light beam to an information carrier; and a light source disposed between the light source and the information carrier. A light splitter that separates the light beam reflected by the light beam emitted from the light source, and the reflected light beam separated by the light splitter enters, an optical element having a diffraction grating,
A first photodetector for detecting a light beam diffracted by the optical element, and a second photodetector for detecting a light beam transmitted through the optical element; A control signal for focusing and auto-tracking is detected, and an information signal recorded on the information carrier is detected by the second photodetector.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic view showing a reference example of an optical head device according to the present invention. Here, the S-polarized light emitted from the semiconductor laser 1 passes through the collimator lens 2 and the beam shaping prism 3 to become a parallel light beam, and has an appropriate polarization characteristic (for example, the reflectance of P-polarized light is 70%, the transmittance is 30%, and the S-polarized light is Reflectance is 1
(00%) through the polarizing beam splitter 4 and is focused on the information recording surface 6 by the objective lens 5. The reflected light whose polarization has been rotated according to the upward and downward magnetization information on the magnetically recorded information on the recording surface 46 passes through the objective lens 5 again and passes through the polarization beam splitter 4.
Is separated from the incident light beam, and is incident on an optical element 7 composed of a parallel flat plate having a relief type diffraction grating formed on one surface. The light diffracted by the diffraction grating is guided to a photodetector 9 via an analyzer 8, and a control signal for auto-focusing (hereinafter, referred to as AF) and auto-tracking (hereinafter, referred to as AT), and An information signal recorded on the recording surface 6 is detected.

FIG. 2 shows the optical element 7 shown in FIG. 1 as viewed from the polarization beam splitter 4 side. The relief type diffraction grating of this embodiment is divided into three portions 10a, 10b, and 10c, each of which is formed in a conical shape, and has a lens function of converging the diffracted light beams 11a, 11b, and 11c. The light detector 9 has four light receiving surfaces 9.
a, 9b, 9c, and 9d are arranged in series in the paper surface direction. The light quantity distribution on the photodetector changes according to the focus state of the spot on the recording surface 6 in FIG. First, the principle of autofocus will be described in detail below.

The focus error signal is the diffraction grating 10a.
Is detected by the light receiving surfaces 9a and 9b of the photodetector 9. FIG.
(A), (B), (C) are light receiving surfaces 9a, 9 of the photodetector 9.
b is a diagram viewed from the light incident side, where the hatched portions indicate the beam shape, (B) indicates a focused state, and (A) and (C) indicate out-of-focus states. Assuming that outputs from the light receiving surface are Ia and Ib, respectively, in an electric system as shown in FIG.
By performing the operation b by the differential amplifier 12, a focus error signal as shown in FIG. 4B is obtained at the output terminal 13. In FIG. 4B, the horizontal axis represents the distance (focus error) between the objective lens and the recording surface when the focus position is set to zero, and the vertical axis represents the signal output. By moving the objective lens 5 or the entire optical head with respect to the disk along the optical axis of the incident light via an actuator (not shown) in accordance with the obtained focus error signal, auto-focusing becomes possible.

Next, the principle of the auto tracking in the reference example shown in FIG. 1 will be described. The tracking error signal is transmitted to the diffraction gratings 10c and 10b and the light receiving surface 9c of the photodetector.
Detect at 9d. Assuming that a groove 18a is formed in the substrate 18 of the information recording carrier as shown in FIGS. 5A, 5B and 5C, the incident light beam is
The light is focused near a. Here, (B) shows the target groove 18.
(A) and (C) show a state where the spot is shifted to the right or left with respect to the groove, respectively. The light beam reflected by the recording surface 19 on the substrate 18 includes tracking information by diffraction or scattering at the groove 18a.

The light receiving surfaces 9c, 9 of the photodetector 9 shown in FIG.
When the reflected light is received at d, the amount of the reflected light is
According to the states of (A), (B) and (C), FIG.
(A), (B), and (C). Therefore, FIG.
In the electric system shown in FIG. 1A, the operation of Ic-Id is performed by the differential amplifier 14, so that the output terminal 16
A tracking error signal as shown in FIG. 7B is obtained. In FIG. 7B, the horizontal axis represents the tracking error,
The vertical axis indicates the signal output. According to the obtained tracking error signal, a tracking actuator (not shown) is driven to move the objective lens 7 perpendicularly to the optical axis, thereby enabling auto tracking.

The influence of the wavelength fluctuation of the semiconductor laser in the above-described method of detecting the focus error signal and the tracking error signal will be described. Possible effects due to wavelength fluctuations are that the diffraction direction of the light diffracted from the diffraction grating changes, the position on the photodetector changes, and that multiple beams do not concentrate energy in one order of light. Coming over the photodetector. The change of the beam position on the photodetector is, in the present invention, relative to the division line of the photodetector.
Since there is no change in the vertical direction only in the parallel direction, there is no influence from the change in the beam position due to the wavelength change. In the state where a plurality of beams come on the photodetector, the energy of one beam is dispersed into a plurality of beams, and the beam is incident on the position shifted in parallel along the dividing line. Since there is no difference from the light amount detection, there is no influence due to a plurality of beams coming on the photodetector.

As described above, the light-receiving surface of the photodetector is made relatively large in the direction in which the light beam moves due to wavelength fluctuation, and the boundary of each light-receiving surface is made parallel to this direction. Even if the wavelength variation occurs, the output of each photodetector is hardly affected, and correct autofocusing and autotracking can be performed.

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

In forming the mold, as shown in FIG.
The mold is created by rotating the cutter 0 and moving the cutter 21 such as diamond in the direction perpendicular to the paper surface. The vertex angle of the cutting edge of the cutter 21 is determined by the angles α and β.
Have an angle of 5 °. The shape material 20 is phosphor bronze, brass Ni
Or a high-molecular material such as a brazing board or a plastic material. However, in the case of a metal mold, there is an advantage that a step of forming a stamper by electroforming or the like is not required, because it can be directly used as a stamper. When the relief structure is cut by the method shown in FIG. 8, a concentric relief structure is obtained as shown in FIG. 9B. FIG.
(A) is an enlarged view of a part of (B) in FIG.
β to 80 °, pitch to 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 23, it is possible to faithfully transfer the relief structure of the mold 22 to the acrylic material 23.

As shown in FIG. 11, a reflection layer 24 is provided on the relief structure of the transferred acrylic material 23, for example, by vapor deposition. The reflection layer 24 may have a multilayer structure or a single-layer structure. Further, a dielectric film such as MgF ₂ , TiO ₂ , ZrO ₂ , SiO ₂ or a metal film such as Au, Ag, Al, Cu may be used. The optical element used in the present invention is produced by the above method.

In general, in an optical head device using a magneto-optical recording / reproducing apparatus, the reflected light is reflected on the recording surface and the polarization characteristics of the optical element between the recording surface and the analyzer while the polarization plane is rotated on the recording surface. As a result, a phase difference occurs between the P-polarized component and the S-polarized component, so that the S / N value of the Rf signal may decrease. Therefore, FIGS. 12 (A), (B),
(C) shows a configuration of another reference example of the present invention in which means for correcting the phase difference is provided.

FIG. 12A is a configuration diagram when the phase difference due to the recording surface 6, the objective lens 5, and the polarization beam splitter 4 is large and the phase difference due to the optical element 7 is small. By inserting a phase correction plate 25 such as Babinet Soleil between the polarization beam splitter 4 and the optical element 7, the phase is corrected and the S / N is improved. FIG. 12B shows the recording surface 6,
FIG. 4 is a configuration diagram when the phase difference due to the objective lens 5 and the polarization beam splitter 4 is small and the phase difference due to the optical element 7 is large. By setting the position of the polarizer 26 between the polarization beam splitter 4 and the optical element 7, the S / N is improved without the influence of the phase difference due to the optical element 7.

FIG. 12C is a configuration diagram when the recording surface 6, the objective lens 5, the polarizing beam splitter 4, and the optical element 7 each have a large phase difference. A phase correction plate 25 is inserted between the polarization beam splitter 4 and the optical element 7, and the position of the analyzer 27 is adjusted by the phase correction plate 25 and the optical element 7.
By doing so, the phase difference is corrected, and the value of S / N is improved.

FIG. 13 is a diagram showing an embodiment of the optical head device according to the present invention which is suitable for a case where mutual leakage between the tracking error signal, the focus error signal and the information signal is large.

The reflected light from the recording surface 6 enters the optical element 7 via the objective lens and the polarizing beam splitter 4. The optical element 7 diffracts an appropriate amount of the reflected light beam, guides the diffracted light amount to the photodetector 9, and detects a tracking error signal and a focus error signal. The rest of the reflected light passes through the optical element 7 and passes through the analyzer 28 and the condenser lens 29 to another photodetector 30, where the information signal recorded on the information carrier is detected. As a result, mutual leakage between the tracking error signal, the focus error signal, and the information signal is reduced.

In this embodiment, since the photodetector for detecting the tracking error signal and the focus error signal and the photodetector for detecting the information signal are configured independently,
The arithmetic processing of the detected signal is facilitated.

FIG. 14 is a configuration diagram of an optical head device of another reference example applied to an optical disk device. In this case, the linearly polarized S-polarized light that has exited the semiconductor laser 1 passes through the collimator lens 2 and the beam shaping prism 3 to become a parallel light flux. Further, a polarization beam splitter, for example, S-polarized light, 98% reflection, P-polarization, 98% transmission 34 Reflected by 、 wavelength plate 3
The light becomes circularly polarized light at 1 and is condensed on the recording surface 36 by the objective lens 5. The light reflected by the pits formed on the recording surface 36 passes through the objective lens 5 and the quarter-wave plate 31 again,
It becomes direct polarized light of P polarized light. The direct polarization of the P-polarized light passes through the polarization beam splitter 34 and reaches the optical element 7.
The light is guided to the photodetector 9 to obtain a tracking error signal, a focus error signal, and an information signal.

[0031]

As described above, the optical head device of the present invention comprises a light source for irradiating a light beam to an information carrier, and a light beam disposed between the light source and the information carrier and reflected by the information carrier. And a reflected light beam separated by the light splitter are incident on the light beam splitter. An optical element having a diffraction grating, a first photodetector for detecting a light beam diffracted by the optical element, and a second photodetector for detecting a light beam transmitted through the optical element; The control signal for auto-focusing and auto-tracking is detected by the first photodetector, and the information signal recorded on the information carrier is detected by the second photodetector. ) Mutual leakage between the control signal and the information signal for autofocus and autotracking is reduced.

(2) The signal processing after the photodetector can be simplified.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a reference example serving as a basis of an embodiment of an optical head device according to the present invention.

FIG. 2 is a diagram illustrating the optical element of FIG. 1;

FIG. 3 is a diagram illustrating the principle of autofocus in the present invention.

FIG. 4 is a diagram illustrating the principle of autofocus in the present invention.

FIG. 5 is a diagram illustrating the principle of auto tracking according to the present invention.

FIG. 6 is a diagram showing the principle of auto tracking according to the present invention.

FIG. 7 is a diagram illustrating the principle of auto tracking according to the present invention.

FIG. 8 is a diagram illustrating a method for manufacturing an optical element used in the present invention.

FIG. 9 is a view illustrating a method of manufacturing an optical element used in the present invention.

FIG. 10 is a diagram illustrating a method for manufacturing an optical element used in the present invention.

FIG. 11 is a diagram illustrating a method of manufacturing an optical element used in the present invention.

FIG. 12 is a configuration diagram showing a reference example serving as a basis for an embodiment of the optical head device of the present invention.

FIG. 13 is a configuration diagram showing an embodiment of the optical head device of the present invention.

FIG. 14 is a configuration diagram showing another reference example serving as a basis for an optical head device according to an embodiment of the present invention.

FIG. 15 is a configuration diagram showing a conventional optical head device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 4 Polarization beam splitter 5 Objective lens 6 Information recording surface 7 Optical element 9, 30 Photodetector 28 Analyzer

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-151844 (JP, A) JP-A-61-162839 (JP, A) JP-A-61-178740 (JP, A) JP-A-61-178740 230634 (JP, A) Actually open sho 61-203427 (JP, U)

Claims (1)

(57) [Claims] 1. A light source for irradiating a light beam to an information carrier, and a light splitter disposed between the light source and the information carrier for separating a light beam reflected by the information carrier from a light beam emitted from the light source An optical element having a diffraction grating on which the reflected light beam split by the light splitter is incident; a first photodetector for detecting the light beam diffracted by the optical element; and a light beam transmitted through the optical element And a control signal for auto-focusing and auto-tracking is detected by the first photo-detector.
An optical head device wherein an information signal recorded on the information carrier is detected by the photodetector.