JPS649657B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for focusing in an optical head device that reads information from an information recording medium such as an optical video disk or a digital audio disk, and writes information to the information recording medium. The present invention relates to a defocus detection device.

A conventional device of this type is shown in FIG. FIG. 1 is a schematic diagram showing a conventional defocus detection device for an optical head device, in which 1 is a semiconductor laser light source;
2 is the light emitted from this light source, 3 is a beam splitter, 4 is an objective lens, 5 is an optical disk that is an information recording medium, 6 is a motor that rotates this optical disk, and 7 is information recorded on the optical disk 5. A spiral information track, 8 is a photodetector, and has three light receiving parts 8a, 8b, 8c divided by two parallel lines.
It is made up of 9 is a differential amplifier, and 10 is a focus drive device that drives the objective lens 4 in the optical axis direction.

To explain its effect, the emitted light 2 from the light source 1
is bent by 90° by the beam splitter 3, and the information track 7 of the optical disk 5 is bent by the objective lens 4.
The light is irradiated upward and focused on a minute spot. The reflected light 2' from this minute spot is focused by the objective lens 4, transmitted through the beam splitter 3, and sent to the photodetector 8.
The difference between the light reception signals of the light receiving sections 8a, 8b and 8c is extracted by the differential amplifier 9 as a signal corresponding to the focal shift of the light focusing spot on the information track 7 of the optical disk 5, and this signal is After appropriate processing and amplification, the focus drive device 10 is energized to move the objective lens 4 in the optical axis direction, thereby automatically compensating for the focal shift caused by the displacement of the optical disk. This defocus detection operation will be explained in more detail with reference to FIGS. 2 and 3. FIG. 2 is an optical path diagram explaining the operation of the optical system shown in FIG. 1, and FIG. 3 is a diagram showing changes in the spot on the photodetector shown in FIG. 1. In the figure, A, B, and C correspond to the displacement of the optical disk 5 in the optical axis direction. C indicates a state where the object is far from the focal point. Corresponding to such disk displacement, the reflected light 2' changes as shown by three types of lines in the figure: a solid line, a dashed line, and a broken line, and the focal point F in front of the detector 8 is A, b,
It is displaced as F ₁ , F ₂ , F ₃ with respect to C. The photodetector 8 has an inner light receiving section 8a as shown in FIG.
It is divided into three outer light receiving parts 8b and 8c, and is electrically insulated from each other. The three circles in the figure S ₁ , S ₂ ,
_S3 is a light spot connected on the photodetector for disk displacements A, B, and C. That is, disk 5
When is in position A, the condensing point of the reflected light 2' is F ₁ , the spot is S ₁ , the amount of light received at the light receiving section 8a is equal to the sum of the amounts of light received at 8b and 8c, and the differential amplifier The signal corresponding to the difference in the amount of light received from 9 becomes the minimum, and when the disk 5 shifts to the side A, the amount of light received at the light receiving section 8a becomes larger, and when it shifts to the side C, the amount of light received at the light receiving sections 8b and 8c increases. The sum of the quantities becomes larger, and an electric signal whose positive and negative polarities are determined by the amount of deviation is obtained depending on the direction of deviation from the differential amplifier 9. In this way, defocus is detected.

In the conventional apparatus as described above, a defocus signal is obtained by comparing the intensity near the center of the reflected light beam from the recording medium with the intensity near the periphery.
There were problems such as zero point offset occurring when the emission intensity distribution of the light source changed. In particular, when a semiconductor laser is used as a light source, there are many variations in the emission intensity distribution, which poses practical problems.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and by making the distribution of reflected light on the photodetector uniform, it is an optical system that eliminates the offset of the zero point in defocus detection. It is an object of the present invention to provide a defocus detection device for a head device.

An embodiment of the present invention will be described below with reference to FIGS. 4 and 5. FIG. 4 is a schematic diagram for explaining one embodiment of the present invention, and FIG. 5 is a diagram showing emission intensity distribution characteristics of a semiconductor laser light source.

In the figure, 1 to 8 indicate the same or corresponding parts as the same reference numerals in FIG. 1, and the defocus detection operation is the same as that in FIG. 1. In this invention, a semiconductor laser is used as the light emitting source 1, and the direction of the PN junction 11 in the plane orthogonal to the emitted light is y, and the direction perpendicular to it is x, and the coordinates x, y of the semiconductor laser light source 1 are , optically, x' at the objective lens 4,
y′, x″, y″ at the photodetector 8, and x″, y″ on the optical disk 9. The photodetector 8 is arranged so that the direction of the dividing line coincides with y'', and the direction of the cutting line of the information track on the disk 5 coincides with x''.

Semiconductor lasers generally have emission intensity distribution characteristics in which the light intensity distribution in a plane perpendicular to the emitted light is wide in the x direction and narrow in the y direction;
It has a divergence angle that is 2 to 3 times the direction. Therefore,
By arranging the semiconductor laser 1 so that the direction y'' that optically matches the PN junction direction y of the semiconductor laser 1 is the parallel dividing line direction of the detector 8, the semiconductor laser 1 is placed in the direction x'' perpendicular to the dividing line direction. A wide-angle distribution of the emission characteristics of the laser light source can be located. It will be explained with reference to FIG. 5 that by doing this, the offset of the focusing position that depends on fluctuations in the emission distribution of the semiconductor laser is reduced. The horizontal axis in Figure 5 is x
and the emission angle in the y direction, the vertical axis is the emission intensity, I _x is the emission intensity distribution in the x direction, I _y is the emission intensity distribution in the y direction, and θ is the lens aperture angle. As shown in the figure, when looking at the emission intensity distribution in the x and y directions within the lens aperture angle θ, the y direction distribution, which is a narrow-angle distribution, shows a non-uniform distribution with strong intensity at the center, but the x-direction distribution, which is a wide-angle distribution, shows a non-uniform distribution with strong intensity at the center. shows a fairly uniform distribution within the aperture angle θ.
When the emission intensity distribution of the semiconductor laser fluctuates as shown by the dotted line, the y-direction distribution is greatly affected by the fluctuation because most of the emitted light flux of the semiconductor laser is taken into the lens aperture angle. On the other hand, in the x direction, only the central portion of the light beam emitted from the semiconductor laser is used because it is eclipsed by the lens aperture. Therefore, even if the luminous flux distribution changes, the variation in the distribution within the lens aperture angle is extremely small. Therefore, by locating the direction x of such wide-angle distribution in the direction x'' perpendicular to the dividing line of the photodetector 8, the central light receiving section 8
The influence of the emission intensity distribution of the semiconductor laser on the balance between the output of a and the sum of the outputs of the peripheral light receiving sections 8b and 8c can be minimized. Even if the light intensity distribution fluctuates in the y-direction (y'' direction on the photodetector), it is along the dividing line of the photodetector, so there is no effect on the defocus detection signal output.This division of the external light detector By aligning the wide-angle distribution direction of the semiconductor laser emission characteristics with the direction perpendicular to the line, there is an advantage that the mounting adjustment of the photodetector in the x'' direction becomes easy and the detection sensitivity increases. Furthermore, if the direction of the information track 7 of the optical disk, that is, the direction of its cutting line is set perpendicular to x'', that is, the radial direction of the optical disk is set as y'', and the direction of the dividing line of the photodetector is set as y'', the objective When controlling the light spot in the y'' direction by driving the lens 4 in the y' direction, so-called radial tracking control, the movement of the reflected light flux on the photodetector also moves in the dividing line direction.
y'', and errors in the defocus detection signal due to this can be prevented.

In the above embodiments, an information reproducing head device has been described, but an information recording head device may also be used, and the same effects as in the above embodiments can be obtained. In this case, the optical disc 5 is an unrecorded optical disc,
It is sufficient to modulate the semiconductor laser 1 with the information to be recorded.

Since the present invention is configured as described above, it has the excellent effect of being less affected by the light intensity distribution of the semiconductor laser light source, and having a uniform distribution, resulting in high sensitivity and highly accurate defocus detection. have.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing a defocus detection device of a conventional optical head device, Fig. 2 is an optical path diagram explaining the operation of the optical system shown in Fig. 1, and Fig. 3 is a schematic diagram showing the defocus detection device of a conventional optical head device. FIG. 4 is a diagram showing changes in spots, FIG. 4 is a schematic diagram illustrating an embodiment of the present invention, and FIG. 5 is a diagram showing emission intensity distribution characteristics of a semiconductor laser light source. In the figure, 1 is a laser light source, 3 is a beam splitter, 4 is an objective lens, 5 is an optical disk which is an information recording medium, 7 is an information track, 8 is a photodetector, 8
a, 8b, and 8c are the divided light receiving parts. The same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A laser light source, an information recording medium on which information is recorded in the form of a track, an optical system that irradiates and focuses a light beam from the laser light source onto the information track on the information recording medium, and this optical system. and a photodetector that receives the reflected light flux from the information track guided by the information track, and this photodetector is composed of three light receiving sections divided by at least two parallel lines, and the light receiving signal to these light receiving sections is In the defocus detection device for an optical head device, which obtains a signal corresponding to the defocus of the irradiated light beam on the information track based on the difference in A semiconductor laser with emission intensity distribution characteristics of a wide-angle distribution and a narrow-angle distribution in the direction perpendicular to this is used, and the direction of this wide-angle distribution is optically aligned with the direction orthogonal to the parallel dividing line of the photodetector. A defocus detection device for an optical head device, characterized in that: 2. A defocus detecting device for an optical head device according to claim 1, wherein the direction of the parallel dividing line of the photodetector and the direction perpendicular to the information track are optically matched.