JP2720491B2 - Optical head device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device used for an information input / output device for recording and reproducing information using light.

(Prior Art) Currently, an information input / output device for recording and reproducing information by using light is provided with concentric or spiral tracks on a disk-shaped recording medium, and a laser light source is provided on the track. A recording pit is generated by condensing the emitted light as a minute spot, the presence or absence of the pit is recorded as information, and further, a small spot is irradiated on this track, and the presence or absence of a pit on the track is detected from the reflected light, There is a method of reading information.

With a demand for an increase in storage capacity, it is necessary to increase the recording density in such an apparatus. In order to increase the density, it is indispensable to reduce the spot of the light irradiated on the medium. In FIG. 1, the size of the minute spot irradiated on the medium depends on the wavelength λ of the laser 1 and the numerical aperture NA of the condenser lens 4, and is proportional to λ / NA. Therefore, in order to reduce the size of the minute spot, it is necessary to increase the NA for reducing λ. For this reason, developments are being made in the direction of shortening the oscillation wavelength of the semiconductor laser for optical disks, and the aperture of the condenser lens 4 is as large as possible.

(Problems to be Solved by the Invention) In the method described above, the size of the minute spot irradiated on the medium may be smaller than the value determined by the wavelength of the light source and the numerical aperture of the condenser lens. Can not. Accordingly, there is a disadvantage that the recording density cannot be increased beyond the value determined by this value.

An object of the present invention is to provide an optical head that generates a small spot smaller than the value determined by the wavelength of the light source and the numerical aperture of the condenser lens, and as a result, enables high-density recording at or above the limit value. It is in.

(Means for Solving the Problems) An optical head device according to the present invention includes a laser light source, a condensing lens that condenses light emitted from the laser light source as a minute spot on a recording medium, An optical system for guiding the reflected light to a photodetector, wherein the laser light source includes means for reducing the transmittance of cross-shaped light that intersects near the center of the cross section of the light beam emitted from the laser light source. A direction in which the transmittance of the light is reduced is set to coincide with a circumferential direction of the track and a direction perpendicular to the circumferential direction of the track between the light-collecting lens and the condenser lens.

(Operation) As shown in FIG. 2 (a), the intensity of light near the center is reduced by a light-shielding band 21 in a cross section of a circular or elliptical outgoing light beam 22 from a laser light source, and FIG. The intensity distribution on the medium surface of the beam irradiated on the condensing lens recording medium is represented by a solid line 24 in FIG.
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 condenser lens as compared with the case where the light-shielding band shown by the dotted line 23 is not used. This is conventionally known as a super-resolution technique (for example, see H. Osterberg and JEWilkins. Jr., J.
Opt. Soc. Am, 39, 553 (1949)) The present inventors have thus obtained a reduction of the condensed spot by the super-resolution effect only in one direction using the light-shielding band, and An invention is being filed in which an optical head that is aligned in the circumferential direction can be configured to improve the recording linear density. In the present invention, this is further developed to form a cross in the cross section of the light beam 22 equivalent to the case where two light-shielding bands 25 intersecting near the center as shown in FIG. By reducing the light, a condensed spot reduced in both the x and y directions as shown in FIG. 2E is obtained. by this,
It is possible to increase not only the recording linear density but also the track density in the radial direction of the disk.

(Example) In the following, means for changing the intensity distribution of light will be described.
In particular, the light intensity distribution modulator is generally referred to as a light intensity distribution modulator without being designated as a light shielding plate.

FIG. 1 shows one optical system of an embodiment of the optical head of the present invention. A light beam emitted from a semiconductor laser 1 which is a light source is collimated by a collimating lens 2 and shaped by a beam shaping prism 3 so that the light intensity within the beam cross section as shown in FIG. After passing through the light intensity modulator 4 to be reduced, the light passes through the beam splitter 5 and is condensed by the condenser lens 6 into the recording medium 7.
Is irradiated as a minute spot. At the time of signal reproduction, the light reflected from the disk is guided to the reproduction signal detection system 8 by the beam splitter 5.

FIG. 3 shows a configuration example of a transmission type light intensity distribution modulator used in the embodiment shown in FIG. FIG. 3 (a) shows a cross-shaped light-shielding plate 25 whose surface is finished to prevent light reflection, which is fixed by a jig 31. FIG. FIG. 3B shows two light-shielding bands 33 arranged so as to intersect with each other in a cross shape so as to shield the collimated light 32. FIG. 3 (c) shows A of the beam splitter 5 in FIG.
On the surface, a light-shielding portion is provided in a cross shape. FIG. 3E shows an example of a configuration using a light beam splitting prism. Third
When a prism as shown in FIG. 1D is used, the light beam is split as indicated by the arrow in the same figure, and the vicinity of the center can be in a state without light. FIG. 3 (e) shows an example in which two prisms are used and arranged so that the direction of division of the light beam is vertical.

FIG. 4 (a) shows an embodiment in which the intensity distribution modulator is a reflection type. The intensity distribution modulator can be realized by forming a portion 41 having extremely low reflectance on the mirror surface 42 as shown in FIG. 4 (b). By the reflecting mirror 43 shown in FIG. 4 (c), a light intensity distribution equivalent to the case of FIG. 3 (d) can be obtained. By using two of these reflectors and arranging them so that the light beam splitting directions are perpendicular to each other, it is possible to obtain a light height distribution equivalent to that shown in FIG. 3 (e).

(Effects of the Invention) According to the present invention, the diameter of a condensed spot in an optical head is reduced in two directions below the diffraction limit of the optical system, and both the recording density in the circumferential direction of the track and the track density in the radial direction are increased. Recording density can be increased.

[Brief description of the drawings]

1, 3, and 4 are diagrams showing an optical system according to an embodiment of the present invention, and FIG. 2 is a diagram showing the operation of an intensity distribution modulator used in the present invention. In the figure, 1 ... semiconductor laser, 2 ... collimating lens, 3 ...
Beam shaping prism, 4 ... light intensity distribution modulator, 5 ...
Beam splitter, 6: condenser lens, 7: recording medium, 8: reproduction signal detection system, 21: light-shielding band, 22: beam cross section, 23: light on the medium surface when no light-shielding band is used Intensity distribution, 24: light intensity distribution on the medium surface when a light-shielding band is used, 24 ': condensed spot pattern when the present invention is used, 25: cross-shaped light-shielding plate, 31: jig 32, collimated light, 33, a light intensity distribution modulator arranged in a direction where light-shielding bands intersect vertically, 34, a light beam splitting prism, 41, a region with extremely low reflectivity, 42, a mirror surface, reflection Type light beam splitter.

Claims (1)

(57) [Claims] An optical system includes: a laser light source; a condenser lens for condensing light emitted from the laser light source as a minute spot on a recording medium; and an optical system for guiding reflected light from the focal point to a photodetector. In the optical head device, means for reducing the transmittance of cross-shaped light that intersects near the center in the cross section of the light beam emitted from the laser light source includes a light transmittance between the laser light source and the condenser lens. An optical head device characterized in that the direction in which is reduced is made coincident with the circumferential direction of the track and the direction orthogonal thereto.