JPH01269238A - Focus detecting device for optical recording/reproducing device - Google Patents

Abstract

PURPOSE:To exactly execute the focusing of an optical beam to be just scanned by forming an optical detector with a slender three-dividing detector and detecting dislocation from a focusing position with an astigmatism method. CONSTITUTION:When a reflected light RP of a laser beam irradiating an optical recording medium, is made incident on a cylindrical lens 18, the reflected light PR is converged only in a Y-axis direction. When the light passes a focus X1, the light is diffused again and a light in an X-axis direction is converged at a second focus position X2. Accordingly, when an optical detector 19 divided into three parts in a slender shape is provided between the two focus positions X1 and X2, an astigmatic spot is formed on the photo-detecting surface of the detector 19. This astigmatic spot shows a circular shape when a distance between an objective lens and the optical recording medium is a suitable focus distance. An electric signal outputted from photo-detecting surfaces A and B is added by an adder 19A and inputted to one terminal of a comparator 19B. Then, when the circular astigmatic spot is formed in the detector 19, the comparator 19B goes to almost zero. Thus, the focusing can be exactly executed.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is directed to recording information on an optical recording medium by irradiating the optical recording medium with a laser beam, or recording information recorded on the optical recording medium. The present invention relates to a focus detection device for an optical recording/reproducing device that can read data.

[Summary of the invention]

The optical recording/reproducing device of the present invention employs an astigmatism method as a focus servo device that controls the laser beam irradiated onto the optical recording medium to be in focus, and the optical recording medium is swept. As a photodetection device for receiving reflected light from It is designed to detect the focal point position of the laser beam being scanned.

[Conventional technology]

Optical players, which read information by irradiating laser beams onto optical recording disks, are widely used as playback devices for video signals and audio data. A scanning type optical recording/reproducing device has been developed in which a laser beam is deflected by a polygon mirror or an optical deflector and irradiated onto the recording medium. ing.

[Problem that the invention seeks to solve]

In the case of such scanning-type optical recording/reproducing devices, it is necessary to focus the laser beam on the recording medium at a focused point in order to improve the recording surface density and resolution, but the laser beam spot is constantly swept. Therefore, there was a problem in that it was extremely difficult to detect the focused state using a conventional fixed photodetector.

[Means for solving problems]

The present invention provides such a scanning type optical recording/reproducing device,
In order to detect the focal point position of the laser beam irradiating the recording medium, the scanning beam light is received by a three-part detector with an elongated light-receiving surface and a cylindrical lens, and the deviation from the focal point position is detected using the astigmatism method. It is designed to detect.

[Effect]

The light-receiving surface of the optical detector that receives the scanning beam light is divided into three parts so that it becomes longer in the direction of deflection of the scanning light, so even when the laser beam irradiating the recording surface is swept, The focus error signal can be detected by the astigmatism method.

〔Example〕

FIG. 1 shows an overview of the scanning type optical recording/reproducing device of the present invention, and
This is a perspective view of the focus detection device.
1 is a semiconductor laser light emitting device, and 11 is an optical system that shapes laser light emitted from the semiconductor laser light emitting device 10 into a predetermined beam light.

Reference numeral 12 denotes an acousto-optic deflection element, which includes a medium through which light can pass, a piezoelectric element 12A that generates an ultrasonic compression wave in this medium, and a sound absorbing material 12B.As will be described later, the optical system 11 It polarizes and manipulates the laser beam irradiated by the laser beam.

13 is a collimator that focuses the light polarized by the acousto-optic deflection element 12 into parallel light; 14 is a deflection beam splitter;
5 is a 1/4 wavelength plate, 16 is an objective lens, and 17 is an optical recording medium such as a tape or card having a recording surface sensitive to light.

Reference numerals 18 and 19 indicate a device for detecting the focal point position by receiving the reflected light from the optical recording medium 17, and 18 indicates a cylindrical lens (tubular lens) on which the return light reflected by the deflection beam splitter 14 is irradiated. 19 indicates an optical detector divided into three elongated parts as will be described later.

For example, the optical recording/reproducing device described above includes an optical recording medium 17.
When recording information, the output of the semiconductor laser light emitting device 10 is modulated based on the recorded information, and the optical system 11 makes a predetermined laser beam incident on the acousto-optic deflection device 12.

The piezoelectric element 12A of the acousto-optic deflection element 12 includes, for example, 1
A repetitive sweep signal whose frequency changes continuously from fl to f2 is supplied, and the ultrasonic compression waves formed by this sweep signal are applied to the laser beam passing through the medium of the acousto-optic deflection element. Due to the interference, the laser beam is deflected and scanned at a predetermined angle (Bragg angle).

Then, the swept laser beam is transmitted to a polarizing beam splitter 14, 174, a wavelength plate 15. By irradiating the optical recording medium 17 through the objective lens 16, scanning tracks 17A having angles with respect to the tape traveling direction are successively formed on the recording surface of the optical recording medium 17.

Further, unmodulated laser light is output from the semiconductor laser light emitting device 10, and information is recorded on the optical recording medium 17 by irradiating it along the scanning track 17A of the optical recording medium 17 on which information is recorded by a servo system (not shown). You can also read out the information that is displayed.

The reflected light of the laser beam irradiating the optical recording medium 17 returns to the polarizing beam splitter 14 via the objective lens l 6 and the 174-wave plate 15, where it is deflected by approximately 90 degrees and enters the cylindrical lens 18. . The laser beam focused by the single cylindrical lens 18 is received by the optical detector 19.

As is well known, the optical system consisting of the cylindrical lens 18 and the optical detector 19 detects the focal position of the beam of light irradiated onto the optical recording medium 17 using an astigmatism method.

That is, as shown in FIG.
4, the reflected light R converges at the rear of the objective lens 16.
When P is incident on the cylindrical lens 18, this cylindrical lens 1
The reflected light RP is focused only in the Y-axis direction by the convex surface on the exit side of the lens 8, and after passing the focal point XI, the light is diffused again. Then, the light in the X-axis direction is focused at the second focal position x2, which is set by the position of the objective lens 16. "Therefore, if a light detector 19 is provided between these two focal positions XI and X2, an astigmatic spot S will be formed on the light receiving surface of this light detector 19 in FIGS. 3(a), (b), (
It is formed as shown in c).

The solid line in FIG. 3(a) indicates the objective lens 16 and the optical recording medium 1.
Indicates the horizontally long astigmatic spora) Sn when the distance of 7 is close,
FIG. 3(C) shows a vertically long astigmatic spot Sr when the objective lens 16 and the optical recording medium 17 are too far apart.

When the objective lens 16 and the optical recording medium 17 have a proper focal length, the astigmatic spot Sj of the optical detector 19 has a circular shape as shown in FIG. 3(b).

In the case of the present invention, the optical detector 19 is provided with three light-receiving surfaces A, B, and C divided in the longitudinal direction.

The amount of light irradiated onto the light receiving surfaces A and B, that is, the electrical signals output from the light receiving surfaces A and B is calculated by the adder 19A.
and is input to one terminal of the comparator 19B.

In addition, the amount of light irradiated onto the light receiving surface C, that is, the light receiving surface C
The electrical signal output from the comparator 19B is input to the other terminal of the comparator 19B.

The width dimensions of each of the light-receiving surfaces A, B, and C are the same when the objective lens 16 is at the focused position, that is, when the circular astigmatism spora) Sj in FIG. 3(b) is formed on the optical detector 19. is set so that the output of the comparator 19B is approximately O.

As a result, when the objective lens 16 is close to the optical recording surface, that is, when the astigmatism (Sn) in FIG. 3(a) occurs, the - signal from the comparator 19B is In other words, when the astigmatism Sr in FIG. 3(C) is exceeded, a signal of 10 is output from the comparator 19B.

The output of the comparator 19B is supplied to the focus actuator as a focus error signal, so that the objective lens 16 is always controlled to the in-focus position.

By the way, in the scanning type optical recording/reproducing apparatus of the present invention, since the laser beam is scanned, the reflected light also moves up and down in the Y-axis direction of the cylindrical lens 18.

Therefore, on the optical detector 19, the astigmatic spot S
As shown by the dashed line, the images sU and s move up and down together, but since the light detector 19 is formed of a long and narrow three-part light receiving surface, the signal indicating the focus error of the comparator 19B does not change. Become.

Further, the reflected light RP is scanned in the Y-axis direction of the cylindrical lens 18, and since the convex surface on the exit side of the cylindrical lens 18 is formed to have a curved surface in the Y-axis direction, one reflected light RP is scanned in the Y-axis direction. Even when the light beam moves, the distance it moves is compressed by the convex surface of the cylindrical lens 18, and the light is irradiated onto the light detector 19.

Therefore, the long side of the optical detector can be made shorter than the actual scanning distance of the spot, which has the advantage that the focus detection device can be made smaller.

In the above embodiments, an acousto-optic device is used as a laser beam deflector, but the focus detection device of the present invention is applicable to a scanning optical recording/reproducing device in which the deflector is a rotating mirror. Needless to say, it can also be applied.

〔Effect of the invention〕

As explained above, in the focus detection device of the optical recording/reproducing apparatus of the present invention, since the optical detector is formed of an elongated three-part detector, information is recorded by sweeping the laser beam over the optical recording medium. , or even in the case of a reproducing scanning type, it is possible to constantly detect the focal point position of the objective lens, and by applying focus servo based on this detection signal, it is possible to accurately focus the light beam during scanning. There is an effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an optical recording/reproducing apparatus of the present invention, FIG. 2 is a perspective view showing an embodiment of the present invention that detects a focal position using astigmatism, and FIG. 3(a). (b) and (C) are plan views for explaining spots of beam light projected onto a light detector. In the figure, 10 is a semiconductor laser light emitting device, 11 is an optical system, 1
2 is an acousto-optic deflection element, 13 is a collimator, 14 is a deflection beam splitter, 16 is an objective lens, 17 is an optical recording medium, 18 is a cylindrical lens, and 19 is an optical detector.

Claims (1)

[Claims] In an optical recording/reproducing apparatus that scans an optical recording medium with a light beam deflected by a deflection optical element, records information on the optical recording medium, or reads recorded information, the optical recording medium is irradiated with As an optical detector that detects the focal position of a light spot using astigmatism,
A focus detection device for an optical recording/reproducing device, characterized in that it has an elongated light-receiving surface divided into three parts in the direction in which a light beam is scanned.