JP2001357557A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head capable of reproducing information recording media different in recording density and realizing highly precise recording/ reproducing characteristics. SOLUTION: This optical head is provided with a semiconductor laser 1, an objective lens 5 which condenses a luminous flux from the semiconductor laser 1 on the information recording medium 6, a liquid crystal filter 26 which is positioned between the semiconductor laser 1 and the objective lens 5, makes variable transmissibity within a plane and controls a numerical aperture of the objective lens 5, a light spot shape on the information recording medium 6 or the distribution of light spot intensity, and a liquid crystal filter driving device 27 which applies a control voltage to the liquid crystal filter 26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head of a disk playing apparatus which optically records and reproduces information by projecting a light spot on a disk-shaped recording medium.

[0002]

2. Description of the Related Art In recent years, the use of disc players, such as MD players, CD players, and multi-laser players for high-definition televisions, has been diversified year by year, and the density has been increasing.
High performance, high quality and high added value. Particularly in a disk playing device using a recordable magneto-optical medium, the demand for a portable and on-vehicle use has been on a tremendous increase, and a further reduction in size, thickness, and performance has been demanded. The present invention relates to an optical head of a disk playing device for an optical disk.

Conventionally, there have been many reports on techniques relating to optical heads for magneto-optical disks.

Hereinafter, a conventional optical head for a magneto-optical disk will be described with reference to the drawings.

FIG. 10 is a schematic diagram showing a configuration of a conventional optical head, and FIG. 11 is a schematic diagram showing a configuration of a photodetector of the conventional optical head. In FIGS. 10 and 11,
Reference numeral 1 denotes a semiconductor laser, 2 denotes a collimating lens, 3 denotes a diffraction grating, 4 denotes a composite element composed of a beam splitter, a polarization splitting element and a folding mirror, 5 denotes an objective lens, 6 denotes an information recording medium having a magneto-optical effect, 7 Is a half-wave plate,
8 is a point lens, 9 is a substantially cylindrical lens, a cylindrical lens, 10 is a polarization beam splitter, 11
Is a six-segment photodetector, 12 is a four-segment photodetector, 13 and 14 are focal points of light spots, 15 is a main beam (P polarization) formed on the six-segment photodetector 11, and 16 is a four-segment photodetector Beam (S-polarized light) formed on the vessel 12, 1
7a and 17b are light spots of the preceding beam among the sub beams, and 18a and 18b are light spots of the following beam of the sub beams. 19a and 19b are two-divided light receiving regions, 20a, 20b, 20c and 20d are four-divided light receiving regions, 21a and 21b are light receiving regions of the preceding beam, 22a and
22b is a light receiving area of the following beam, 23 is a subtractor, 24 is an adder, and 25 is a monitoring photodetector.

The operation of the conventional optical head configured as described above will be described below.

The light emitted from the semiconductor laser 1 is converted into parallel light by a collimating lens 2 and separated into a plurality of different parallel light beams by a diffraction grating 3. A plurality of different parallel light beams pass through a beam splitter in the composite element 4 and are converted into a main beam having a diameter of about 1 micron on an information recording medium 6 by an objective lens 5 incorporated in an objective lens driving device (not shown). At the same time as the light beam is condensed, a leading beam and a trailing beam are formed at predetermined intervals as sub-beams before and after the main beam on the same track as the main beam by a so-called three-beam method. The parallel light beam reflected by the beam splitter in the composite device 4 enters the monitoring photodetector 25 and controls the drive current of the semiconductor laser 1.

[0008] The reflected light from the information recording medium 6 follows the reverse path, is reflected and separated by the beam splitter in the composite element 4, and enters the half-wave plate 7. The semiconductor laser 1 is installed so as to have a polarization direction parallel to the paper surface.
It is set to rotate by degrees. The reflected light that has passed through the half-wave plate 7 is converged by the convex lens 8,
The light enters the cylindrical lens 9. Here, in the conventional example, the cylindrical lens 9 has a lens effect in a direction of approximately 45 degrees with respect to the image of the recording track of the information recording medium 6 existing in the direction of W1 in a plane parallel to the paper surface. It is provided as follows. The light transmitted through the cylindrical lens 9 is split into two polarization components orthogonal to each other by a polarization beam splitter 10, one of which is transmitted and incident on a six-split photodetector 11, and the other is reflected and detected by a four-split photodetector. Incident on the vessel 12. The light transmitted through the polarization beam splitter 10 generates astigmatism by a cylindrical lens 9 which is a focus error signal detecting means. In the plane of the cylindrical lens 9 that does not have a lens surface, it becomes a solid line optical path and converges on the focal point 13, and in the plane having a lens effect, it becomes an optical path shown by a broken line.
Converge at focal point 14. The six-segment photodetector 11 has a light-receiving surface located substantially in the middle between the focal points 13 and 14, and the sum of the diagonals of the electric signals generated in the central four-segment light-receiving regions 20a, 20b, 20c, and 20d. Then, by subtracting them, a focus error signal is detected by a so-called astigmatism method.

Light spots 17a and 17 of the preceding beam
By taking the difference between b and the light spots 18a and 18b by the following beam, a tracking error detection signal by a so-called three-beam method is detected.

Also, based on the sum of the amounts of light received by the four divided light receiving regions 20a, 20b, 20c, and 20d at the center of the six-divided photodetector 11, the two divided light receiving regions 19a and 19b at the center of the four divided photodetector 12 are obtained. By taking the difference between the sums of the received light amounts, it is possible to detect the magneto-optical disk information signal by the differential detection method. Further, by taking all of these sums, a pre-pit signal (a signal corresponding to the presence or absence of a pit) can be detected.

[0011]

However, in the above-mentioned conventional configuration, since the intensity distribution of the light beam incident on the objective lens 5 is constant, the aperture ratio or the light spot shape is fixed, and the information recording density is reduced. When recording or reproducing on or from different information recording media, there is a limit in the recording / reproducing ability, and there has been a problem that information recording media with different recording densities are not compatible.

An object of the present invention is to solve the above-mentioned conventional problems, and to provide an optical head having a variable intensity distribution of a light beam incident on an objective lens, and to realize high-precision recording / reproducing characteristics. It was done.

[0013]

In order to achieve this object, an optical head according to the present invention comprises an information recording medium, a light source such as a semiconductor laser, and an object for condensing a light beam from the light source on the information recording medium. A light collecting means such as a lens, a light beam separating means such as a half mirror which is located between the light source and the light collecting means and separates a light beam from the light source and a reflected light from the information recording medium, and a light source and a light collecting means And an intensity distribution for changing the intensity distribution of a light beam incident on the light condensing means in order to control the aperture ratio of the light condensing means or the light spot shape or light spot intensity distribution on the information recording medium. Converting means, detecting means for detecting an information recording signal of the information recording medium when reflected light from the information recording medium separated by the light beam separating means is incident, and a multi-segmented photodetector for receiving a light beam passing through the detecting means. ,
A calculation circuit for calculating an electric signal generated by the multi-segment photodetector, wherein the intensity distribution converting means is constituted by an optical filter whose transmittance in a plane changes nonlinearly with respect to a change in the intensity of the incident light beam. I have.

[0014]

According to the present invention, the intensity distribution of a light beam incident on an objective lens can be changed by an intensity distribution conversion means such as an optical filter by the above-described structure, and accurate recording / reproducing of information recording media having different recording densities can be performed. It is possible to realize a high-performance optical head and a disk playing device. Also,
By making the intensity distribution of the light beam incident on the objective lens variable, recording with a small light spot diameter during recording, and reproducing with a normal light spot diameter during reproduction, it is possible to further improve the reproduction performance Becomes

[0015]

An embodiment of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a schematic view of an optical head according to a first embodiment of the present invention, and FIG. 2 is a diagram showing light detection of the optical head according to the first embodiment of the present invention. FIG. 3 is a schematic view of an optical head, and FIG. 3 is a schematic view of an intensity distribution converting means of an optical head according to a first embodiment of the present invention. 1, 2 and 3, 1 is a semiconductor laser, 2 is a collimating lens, 3 is a diffraction grating,
Reference numeral 4 denotes a composite element including a beam splitter, a polarization splitting element, and a folding mirror; 5, an objective lens; 6, an information recording medium having a magneto-optical effect; 7, a half-wave plate;
Is a conical lens, 9 is a substantially cylindrical lens, a cylindrical lens, 10 is a polarization beam splitter, 11 is a 6-split photodetector, 12 is a 4-split photodetector, and 13 and 1.
4 is a focal point of the light spot, 15 is a main beam (P-polarized) formed on the six-split photodetector 11, 16 is a main beam (S-polarized) formed on the four-split photodetector 12, 17
Reference numerals a and 17b denote light spots of the preceding beam among the sub beams, and reference numerals 18a and 18b denote light spots of the subsequent beam of the sub beams. 19a and 19b are two-divided light receiving regions, 20a, 20b, 20c and 20d are four-divided light receiving regions, 21a and 21b are light receiving regions of the preceding beam, 22a and
22b is a light receiving area of the following beam, 23 is a subtractor, 24 is an adder, 25 is a monitor photodetector, 26 is a liquid crystal filter, and 27 is a liquid crystal filter driving device.

The operation of the optical head of the present embodiment configured as described above will be described below.

The light emitted from the semiconductor laser 1 is converted into parallel light by a collimator lens 2 and separated into a plurality of different parallel light beams by a diffraction grating 3. The plurality of different parallel light beams pass through the beam splitter in the composite element 4 and
The light enters a liquid crystal filter 26 incorporated in an objective lens driving device (not shown). The liquid crystal filter 26 has a variable transmittance distribution in a plane according to the voltage applied by the liquid crystal filter driving device 27, and can change the intensity distribution of the light beam incident on the objective lens 5. Accordingly, the aperture of the objective lens 5 is limited by the voltage applied by the liquid crystal filter driving device 27 so that the parallel light flux incident on the liquid crystal filter 26 has an aperture ratio corresponding to the recording density of the information recording medium 6. The parallel light beam whose aperture is limited by the liquid crystal filter 26 is condensed by the objective lens 5 on the information recording medium 6 as a main beam having a diameter of about 1 μm, and at the same time, the main beam is focused on the same track as the main beam by a so-called three-beam method. A leading beam and a trailing beam are formed at regular intervals as sub-beams before and after the beam. The parallel light beam reflected by the beam splitter in the composite device 4 enters the monitoring photodetector 25 and controls the drive current of the semiconductor laser 1.

The reflected light from the information recording medium 6 follows the reverse path, is reflected and separated by the beam splitter in the composite element 4, and enters the half-wave plate 7. The semiconductor laser 1 is installed so as to have a polarization direction parallel to the paper surface.
It is set to rotate by degrees. The reflected light that has passed through the half-wave plate 7 is converged by the convex lens 8,
The light enters the cylindrical lens 9. In this embodiment, the cylindrical lens 9 has a lens effect in a direction of approximately 45 degrees with respect to the image of the recording track of the information recording medium 6 existing in the direction of W1 in a plane parallel to the paper in this embodiment. It is provided to have. The light transmitted through the cylindrical lens 9 is split into two polarization components orthogonal to each other by a polarization beam splitter 10, one of which is transmitted and incident on a six-split photodetector 11, and the other is reflected and detected by a four-split photodetector. Incident on the vessel 12. The light transmitted through the polarization beam splitter 10 generates astigmatism by a cylindrical lens 9 which is a focus error signal detecting means. In the plane of the cylindrical lens 9 that does not have a lens surface, it becomes a solid line optical path and converges on the focal point 13, and in the plane having a lens effect, it becomes an optical path shown by a broken line.
Converge at focal point 14. The six-segment photodetector 11 has a light-receiving surface located substantially in the middle between the focal points 13 and 14, and the sum of the diagonals of the electric signals generated in the central four-segment light-receiving regions 20a, 20b, 20c, and 20d. Then, by subtracting them, a focus error signal is detected by a so-called astigmatism method.

Light spots 17a and 17 of the preceding beam
By taking the difference between b and the light spots 18a and 18b by the following beam, a tracking error detection signal by a so-called three-beam method is detected.

Also, based on the sum of the amounts of light received by the four divided light receiving regions 20a, 20b, 20c and 20d at the center of the six-divided photodetector 11, the two divided light receiving regions 19a and 19b at the center of the four divided photodetector 12 are obtained. By taking the difference between the sums of the received light amounts, it is possible to detect the magneto-optical disk information signal by the differential detection method. Furthermore, the pre-pit signal can be detected by taking the sum of all of them.

As described above, according to the present embodiment, the transmittance distribution of the liquid crystal filter 26 is changed by the liquid crystal filter driving device 27.
, The aperture ratio of the parallel light beam incident on the objective lens 5 can be changed, and the shape of the light spot formed on the information recording medium 6 can be changed. This makes it possible to record and reproduce information on and from a plurality of information recording media 6 having different recording densities, thereby realizing a high-performance and high-quality optical head and a disk playing device.

Further, the aperture ratio of the light beam incident on the objective lens 5 is made variable, and recording is performed with a large aperture ratio at a small light spot diameter during recording, and reproduction is performed at a normal light spot diameter during reproduction. Thereby, the deterioration of the reproduction signal due to the deviation (off-track) of the reproduction light spot is reduced, so that the reproduction capability can be further improved.

In the first embodiment, the condensing system is a so-called infinite system using the collimating lens 2, but may be a finite system.

Further, the position of the liquid crystal filter 26 is set between the beam splitter and the objective lens 5 in the composite element 4, but may be anywhere between the semiconductor laser 1 and the objective lens 5.

(Second Reference Example) Next, a second reference example will be described with reference to FIG. FIG. 4 is a schematic view of an intensity distribution conversion means of an optical head according to a second reference example of the present invention. The difference from the first reference example is that the liquid crystal filter 3
In the transmittance distribution in the plane 6, the transmittance of only the substantially central portion is reduced or only the substantially central portion is shielded, and the intensity distribution of the parallel light beam incident on the objective lens 5 is reduced only in the substantially central portion. is there.

As described above, according to the present embodiment, the so-called super-resolution phenomenon caused by the transmittance distribution of the liquid crystal filter 36 can reduce the light spot diameter on the information recording medium 6, and The diameter of the light spot formed on the information recording medium 6 can be changed. As a result, recording / reproducing of the information recording medium 6 having a higher recording density becomes possible, and a higher performance optical head and disk playing device can be realized.

In the second embodiment, the position of the liquid crystal filter 36 is set between the beam splitter in the composite device 4 and the objective lens 5, but the semiconductor laser 1 and the objective lens 5
Anywhere.

(Third Reference Example) Next, a third reference example will be described with reference to FIG. FIG. 5 is a schematic view of an intensity distribution converting means of the optical head according to the third embodiment of the present invention. The difference from the first reference example is that the liquid crystal filter 4
In the transmittance distribution of No. 6, as a substantially elliptical transmittance,
The point is that the intensity distribution of the parallel luminous flux incident on the objective lens 5 is made elliptical, and an elliptical shape is formed in which the jitter value and crosstalk of the reproduction signal are in an optimum state according to the recording state of the information recording medium 6.

Generally, the light spot is radial (radius)
In the case of an elliptical shape having a major axis in the direction, jitter (fluctuation of the reproduction signal) is improved (reduced), but crosstalk (leakage of a signal from a track other than the reproduction target track) is increased. When the light spot has an elliptical shape whose major axis is in the tangential (tangential to the track row) direction, jitter (fluctuation of the reproduction signal) becomes worse (increases), but crosstalk (other than the reproduction target track) occurs. Signal leakage from the track).

As described above, according to the present embodiment, the intensity distribution incident on the objective lens 5 is controlled by the liquid crystal filter 46 so that jitter and crosstalk have an optimum light spot shape according to the recording state of the information recording medium. By making it elliptical (having a major axis in the radial or tangential direction), an elliptical light spot (having a major axis in the radial or tangential direction) can be formed on the information recording medium, It is possible to set the jitter value and the crosstalk of the reproduction signal at the time of reproduction of the information recording medium 6 to an optimum state, and it is possible to accurately record and reproduce the information recording medium 6, and to provide a high-performance optical head and a disk playing device. It can be realized.

(First Embodiment) Next, a first embodiment will be described with reference to FIGS. 6 and 7. FIG. FIG. 6 is a characteristic diagram showing the light intensity dependence of the transmittance of the nonlinear optical filter 28 of the optical head according to the first embodiment of the present invention. FIG. 7 is a diagram showing the nonlinearity of the optical head according to the first embodiment of the present invention. FIG. 4 is a characteristic diagram showing the light intensity dependence of the transmittance distribution in the plane of the optical filter 28. In FIG. 7, the solid line shows the transmittance at the light intensity at the time of recording, and the broken line shows the transmittance at the light intensity at the time of reproduction. The difference from the first embodiment is that, instead of the liquid crystal filter 26 and the liquid crystal filter driving device 27, a non-linear optical filter 28 whose transmittance in a plane changes non-linearly according to the light intensity of the incident light beam.
Is inserted between the semiconductor laser 1 and the objective lens 5 to change the aperture ratio of the objective lens 5 during recording and during reproduction.

As described above, according to the present embodiment, the aperture ratio of the parallel light beam incident on the objective lens 5 is high during recording by the nonlinear optical filter 28 whose transmittance changes nonlinearly according to the light intensity of the incident light beam. Further, the size can be reduced during reproduction, and the diameter of a light spot formed on the information recording medium 6 can be changed during recording and reproduction.
As a result, the information recording medium 6 can be reproduced with high precision, and a high-performance and high-quality optical head and a disk playing device can be realized.

(Second Embodiment) Next, a second embodiment will be described with reference to FIGS. FIG. 8 is a characteristic diagram showing the light intensity dependence of the transmittance of the nonlinear optical filter 29 of the optical head according to the second embodiment of the present invention, and FIG. 9 is a diagram showing the nonlinearity of the optical head according to the second embodiment of the present invention. FIG. 4 is a characteristic diagram showing the light intensity dependence of the transmittance distribution in the plane of the optical filter 29. In FIG. 9, the solid line shows the transmittance at the light intensity at the time of recording, and the broken line shows the transmittance at the light intensity at the time of reproduction. The difference from the first embodiment is that a non-linear optical filter 29 whose transmittance in a plane changes non-linearly according to the light intensity of the incident light beam is used. Is to be shut off.

As described above, according to the present embodiment, the intensity distribution of the low-intensity light beam at the time of reproduction or the like is incident on the objective lens 5 without change, and the high-intensity light beam at the time of recording or the like is blocked only at a substantially central portion. The light flux having the obtained intensity distribution is incident on the objective lens 5,
A spot diameter smaller than the diffraction limit can be formed on the information recording medium 6 by a so-called super-resolution phenomenon. As the light intensity of the luminous flux is increased, the information recording medium 6 having a higher recording density can be reproduced. -A high-quality optical head and a disk playing device can be realized.

[0036]

As described above, according to the present invention, by changing the intensity distribution of the light beam incident on the objective lens by the intensity distribution converting means, it is possible to accurately record / reproduce information on / from information recording media having different recording densities. It is possible to form a light spot shape optimal for the reproduction state of the recording medium, and it is possible to realize a high-performance optical head and a disk playing device.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical head according to a first reference example of the present invention.

FIG. 2 is a schematic diagram of a photodetector of the optical head according to the first embodiment of the present invention.

FIG. 3 is a schematic diagram of an intensity distribution conversion unit of the optical head according to the first embodiment of the present invention;

FIG. 4 is a schematic diagram of an intensity distribution converting means of an optical head according to a second reference example of the present invention.

FIG. 5 is a schematic diagram of an intensity distribution conversion unit of an optical head according to a third reference example of the present invention.

FIG. 6 is a characteristic diagram showing the light intensity dependence of the transmittance of the nonlinear optical filter of the optical head according to the first embodiment of the present invention.

FIG. 7 is a characteristic diagram showing the light intensity dependence of the transmittance distribution of the nonlinear optical filter of the optical head according to the first embodiment of the present invention.

FIG. 8 is a characteristic diagram showing the light intensity dependence of the transmittance of the nonlinear optical filter of the optical head according to the second embodiment of the present invention.

FIG. 9 is a characteristic diagram showing the light intensity dependence of the transmittance distribution of the nonlinear optical filter of the optical head according to the second embodiment of the present invention.

FIG. 10 is a schematic view of a conventional optical head.

FIG. 11 is a schematic view of a photodetector of a conventional optical head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Collimating lens 3 Diffraction grating 4 Composite element 5 Objective lens 6 Information recording medium 7 1/2 wavelength plate 8 Lens 9 Cylindrical lens 10 Polarization beam splitter 11 Six-segment photodetector 12 Four-segment photodetector 15 Main beam (P-polarized light) 16 Main beam (S-polarized light) 17a, 17b Light spot 19a, 19b Two-part light receiving area 20a to 20b Four-part light receiving area 23 Subtractor 24 Adder 26 Liquid crystal filter 27 Liquid crystal filter driver 28 Nonlinear optical filter

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor ▲ Makoto Shima 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. Company F term (reference) 5D075 CD03 CD18 CD19 5D119 AA01 AA11 AA22 AA41 BA01 BB01 BB05 DA01 DA05 EB02 EB05 EB09 EC37 JA62 JA63 JB02

Claims (3)

[Claims] An information recording medium, a light source such as a semiconductor laser, a light condensing means such as an objective lens for condensing a light beam from the light source on the information recording medium, and a light source and the light condensing means. A light beam separating unit such as a half mirror that separates a light beam from the light source and a reflected light from the information recording medium, and a light beam separating unit that is located between the light source and the light collecting unit. An intensity distribution converting means for changing an intensity distribution of a light beam incident on the condensing means for controlling an aperture ratio of the light beam or a light spot shape or a light spot intensity distribution on the information recording medium; and the light beam separating means. Detecting means for detecting an information recording signal of the information recording medium by receiving reflected light from the information recording medium separated by the above, a multi-segment photodetector for receiving a light beam having passed through the detecting means, With photodetector A calculating circuit for calculating the generated electric signal, wherein the intensity distribution converting means is an intensity distribution converting means comprising an optical filter whose transmittance in a plane changes nonlinearly with respect to a change in the intensity of the incident light beam. An optical head, comprising: 2. The intensity distribution conversion means, wherein the transmittance in the plane changes nonlinearly with respect to the change in the intensity of the incident light beam, and the aperture ratio of the light condensing means is variable. The optical head according to claim 1, wherein: 3. The intensity distribution converting means is an intensity distribution converting means in which a transmittance in a plane changes nonlinearly with respect to a change in the intensity of the incident light beam, and shields substantially only a central portion of the incident light beam. The optical head according to claim 1, wherein