JPH01315040A - Optical head device and information recording and reproducing system - Google Patents

Abstract

PURPOSE:To increase the number of recording bits and to improve the recording density by diminishing the light intensity in the vicinity of a center of a cross section of an outgoing beam when reflected light from a converging point as a microspot formed from the outgoing light from a laser light source is led to a photodetector. CONSTITUTION:When the outgoing light from a semiconductor laser 1 is condensed by a condenser lens 4 to be converged on a recording medium 5, a part of the outgoing light is reflected by a beam splitter 2 located usually between the laser 1 and a lens 3, and the intensity of the beam is detected by a regenerative signal detector 6. In this constitution, a light intensity distribution modulator 3 is newly inserted between the splitter 2 and the lens 4, so as to diminish the light in the vicinity of the center of a circular or ellipsoidal beam cross section. That is, the modulator 3 is specified as a transmission type, and in the vicinity of its middle part, an aluminum metal 62 finished with black dye for lowering the reflection intensity is provided to reduce the light intensity in the center part of the beam. By this method, the effect of the reflected light from the medium 5 is reduced to promote the recording density.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical head device used in an information input/output device that records and reproduces information using light.

(Prior Art) Currently, in information input/output devices that record and reproduce information using light, concentric or spiral tracks are provided on a disk-shaped recording medium, and light from a laser light source is placed on these tracks. A recording pit is generated by focusing the emitted light as a minute spot, the presence or absence of the pit is recorded as information, the minute spot is irradiated onto the track, and the presence or absence of the pit on the track is detected from the reflected light, There is a method for reading information.

In recent years, with the demand for increased storage capacity, it has become necessary to increase the recording density in such devices. Since storage capacity depends on the number of recording pits that can be generated on a recording medium, making the recording pits smaller, that is, reducing the spot of light irradiated onto the medium, is the key to higher density. It is essential. The size of the minute spot irradiated onto the medium depends on the wavelength λ of the laser and the numerical aperture NA of the condensing lens, and is proportional to λ/NA. Therefore, to reduce the size of the minute spot,
It is necessary to reduce λ and increase NA. For this reason, development is progressing in the direction of shortening the oscillation wavelength of semiconductor lasers for optical disks, and the aperture of the condenser lens is being used as large as possible.

(Problems to be Solved by the Invention) In the method described above, the size of the minute spot irradiated onto the medium is smaller than the value determined by the wavelength of the light source and the numerical aperture of the condensing lens. Therefore, there was a drawback that the recording density could not be increased beyond the value determined by this value.

An object of the present invention is to provide an optical head device and information system that generate a minute spot smaller than the value determined by the wavelength of the light source and the numerical aperture of the condensing lens, and as a result, enable high-density recording exceeding the above-mentioned limit value. The objective is to provide a recording and reproducing method.

(Means for Solving the Problems) The optical head device of the present invention focuses light emitted from a laser light source into a minute spot, and guides reflected light from this focused point to a photodetector (having an optical system). The optical head device is characterized by having means for reducing the intensity of light near the center within the cross section of the light beam emitted from the laser light source on the optical axis between the light source and the recording medium.

The second invention of the present application is an information recording/reproducing method in which light emitted from a laser light source is focused on a recording medium as a minute spot, information is recorded, and reflected light from the recording medium is detected during information reproduction. This is an information recording and reproducing method characterized by reducing the intensity of light near the center of a light beam emitted from a laser light source within a cross section of the light beam.

(Function) As shown in Fig. 2(a), the light intensity near the center is reduced by the light shielding band 21 within the circular or elliptical cross-section of the emitted light beam from the laser light source, and as shown in Fig. 2(b). By setting the light intensity distribution as shown, the intensity distribution on the medium surface of the beam irradiated onto the recording medium by the condenser lens becomes as shown by the solid line 24 in FIG.
Compared to the case shown in No. 3 in which the light-shielding band is not used, the size of the beam spot on the medium surface can be made smaller than the limit value determined by the wavelength of the light source and the numerical aperture of the condensing lens. This is conventionally known as super-resolution technology.

(For example, see the references Osterbarb and Wilkins, Journal of the Optical Society of
America (■, Osterberg and J, E,
Wilkins, Jr., +J, Opt.

(See Soc, Am. 39, 553 (1959))
However, as the area that reduces the intensity of light near the center of the cross-section of the light beam emitted from the light source (hereinafter referred to as the shading area) becomes larger, the diameter of the central beam spot on the medium surface becomes smaller. Correspondingly, the intensity of the central beam decreases, and the intensity of the peripheral portion (the height of the side lobe indicated by 25 in FIG. 2(c)) increases. If the intensity of the central beam is lower than the intensity required to form recording pits on the medium, the writing operation will not be performed correctly. Furthermore, if the increase in strength in the peripheral portion extends to adjacent tracks or pits, it will adversely affect the read operation. Therefore,
In order to apply this technology to an optical head, it is necessary to have a configuration in which this adverse effect does not affect recording and reproducing operations. In the present invention, in order to prevent the decrease in light intensity near the center of the beam on the medium surface from falling below the minimum value required for writing, a light-shielding area is set in the light intensity distribution modulator, and this area is formed into a strip. In the case shown in FIG. 2(a), the increase in the light intensity on the medium surface at the peripheral portion is in one direction, so this is taken as the linear direction of the track to prevent the light from going around to the adjacent track during reading. Further, in the case as shown in FIG. 2(d) in which the light-shielding region is not made into a band-like shape but only in the central portion, the light-shielding region is set to such an extent that the increase in intensity in the peripheral portion does not extend to adjacent tracks or pits. Furthermore, when recording information, the light-shielding band is controlled to be in a solid state to generate super-resolution operation, and during reproduction, the light-shielding band is controlled to be in a blank state.
By using a recording and reproducing method that stops super-resolution operation, it is possible to prevent the sidelobes that occur due to the super-resolution effect during recording from occurring during playback, thereby eliminating sidelobe light from entering the playback signal. becomes possible. This makes it possible to construct an optical head that utilizes super-resolution technology and guarantees normal recording and reproducing operations.

Therefore, the size of the recording pits generated on the medium can be reduced to about 80% of the conventional size.
Recording information at a higher density than the value determined by the limit value,
And it becomes possible to play.

(Embodiment) FIG. 1 shows an optical system of an embodiment of the optical head of the present invention. When writing information, a light beam emitted from a semiconductor laser 1 serving as a light source passes through a beam splitter 2, and then passes through a light intensity distribution modulator 3 that reduces the intensity of light near the center within the beam cross section. rear,
The condensing lens 4 irradiates the recording medium 5 as a minute spot. On the other hand, when reading information from a recording medium, a reading light beam is irradiated onto the medium surface using the same optical system as used for writing, and the reflected light from the medium surface is sent to the reproduction signal detection system 6 by the beam splitter 2. lead.

FIG. 2(e) shows the result of actually measuring the relationship between the light-shielding band width and the main beam diameter when the light intensity distribution modulator shown in FIG. 2(a) is used as a transmission type configuration.

The light-shielding band is made of metal aluminum with a black-dyed finish, and the condensing lens has a focal length of f = 3.9.
am and a numerical aperture of NA': 0.55 was used. The values indicated by d1 and d2 in the figure indicate the beam diameters at the position where the light intensity becomes 1/e2 of the maximum value and at the position where the light intensity becomes 1/2 of the maximum value at the condensing spot, y, respectively. In addition, FIG. 6(f) shows the relationship between the shading band width and the ratio of side lobe intensity to main lobe intensity measured with the same configuration as FIG. 4(e). The smaller the main lobe diameter, the better;
c) If the height of the side lobe indicated by 25 is larger than about 1/3 of the main lobe height, the influence of the side lobe becomes large during recording and reproduction, and performance deteriorates. From this, if the light-shielding band width is approximately 1 m111, the beam diameter will be approximately 80% compared to when this modulator is not used, and the performance necessary for practical use with less sidelobe effects during recording and reproduction can be obtained. I can do it. In addition, in FIG. 3(d), the light-shielding region is not set in a strip shape but only in the center of the beam cross section. In this case, the light intensity distribution in a cross section including the optical axis of the condensed spot will be such that the X-axis direction in FIG. 2C is an arbitrary radial direction of the beam.

FIG. 3 shows an embodiment in which the light intensity distribution modulator is placed closer to the light source than the beam splitter. The operations during writing and reading are the same as in the case of FIG.

In the case of the configurations shown in Figures 1 and 3, the light intensity distribution modulator is provided with a means for switching between the presence and absence of a light-shielding band during recording and playback, thereby preventing side lobes from wrapping around adjacent tracks or pits. It is possible to prevent false detection due to One of the embodiments is shown in FIG. 6(C). LCD 6
Electrodes 64 and 65 are provided on both end surfaces of 3, and polarizers ee and 67 are further provided on both sides thereof. By switching the direction of the electric field applied between these electrodes during writing and reading, if the incident light is linearly polarized and this polarization direction is constant, it is possible to control the presence or absence of transmitted light, and the above function can be achieved. .

FIG. 4 shows one embodiment in which a reading light source is provided separately from a writing light source. When writing,
After the light emitted from the writing light source 1a passes through the intensity distribution modulator 3 and the beam splitter 2a%2b, it is irradiated onto the recording medium 5. On the other hand, at the time of reading, the operation of the light source 1a is stopped, the light source 1b is operated, and the light emitted from this light source is guided to the optical system by the beam splitter 2b, thereby irradiating the medium as a read beam. By adopting such a configuration, the present invention can be realized even if the intensity distribution modulator 3 itself does not have a function of switching operations. In this case, the intensity distribution modulator may be a jig having a structure that simply has a light-shielding band near the center of the beam, as shown in FIG. 6(a).

FIG. 5 shows an embodiment in which the intensity distribution modulator is of a reflective type. The intensity distribution modulator can be realized by forming a portion 82 with extremely low reflectance on the mirror surface A, as shown in FIG. 6(b). During writing, the light emitted from the light source 1, after being reflected by the intensity distribution modulator 3, has the same intensity distribution as that after passing through the transmission type intensity distribution modulator.

FIGS. 6(a) to 6(d) show various embodiments of the light intensity distribution modulator. FIG. 5A shows a jig-like structure that is a transmission type and has a light-shielding band near the center of the transmitted beam. FIG. 6(b) shows an example of a reflective type. FIG. 2C shows an example of a transmissive modulator that uses liquid crystal and can control an electric field. In addition, in the same figure (d), the light-shielding band 22 is held by a suitable support arm 68, and this is attached to a drive device 69 movable in the X1Y directions in the figure.
This method switches the light blocking operation for the beam by changing the position of the light blocking band during recording and during playback.

(Effects of the Invention) According to the present invention, the number of pits that can be recorded on a medium is increased compared to the conventional method, and the recording density can be increased.

In addition, by limiting the presence or absence of a light-shielding area in the optical modulator when recording and reproducing information, the influence of the write operation will not affect the reflected light from the medium in the reproduced signal detection optical system ( Reading becomes possible.

[Brief explanation of the drawing]

Figures 1, 3, 4, and 5 are diagrams showing an optical system according to an embodiment of the present invention, and Figures 2 (a) to (f) are diagrams showing a light intensity distribution modulator used in the present invention. Figures showing embodiments and effects, No. 6
Figures (a) to (d) are diagrams showing examples of this optical intensity distribution modulator. In the figure, 1.1a11b...semiconductor laser, 2.
2ax 2b... Beam splitter, 3... Light intensity distribution modulator, 4... Condensing lens, 5... Recording medium, 6... Reproduction signal detection system, 21... Light shielding band, 22・
...Beam cross section, 23...Light intensity distribution on the medium surface when the present invention is not used, 24...Light intensity distribution on the medium surface when the present invention is used, 25...When the present invention is used Intensity-increasing portion in the peripheral portion, 26...shading area, 61.
... Reflective light intensity distribution modulator, 62... Area with extremely low reflectance, 63... Liquid crystal, 64.65... Electrode plate, 66.67... Polarizing plate, 68... Support Arm, 6
9... Drive device.

Claims (2)

[Claims] (1) In an optical head device that has an optical system that focuses the emitted light from a laser light source as a minute spot and guides the reflected light from this focused point to a photodetector, within the cross section of the emitted light beam from the laser light source, An optical head device comprising means for reducing the intensity of light near the center on an optical axis between a light source and a recording medium. (2) In an information recording/reproducing method in which the light emitted from a laser light source is focused as a minute spot onto a recording medium to record information, and the reflected light from the recording medium is detected during information reproduction, the light emitted from the laser light source is An information recording and reproducing method characterized in that the intensity of light near the center of an emitted light beam is reduced within a cross section of the light beam.