JPS6243254B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focusing device that automatically focuses light on an object.

FIG. 1 is a configuration diagram showing an example of a conventional automatic focusing device. In the figure, 1 is a laser light source such as a helium/neon gas laser, 2 is a laser beam,
3 is an objective lens, 4 is an object on which the beam 2 is to be focused, 5 is a beam splitter, 6 is a focusing lens, 7 is a pinhole, 8 is a photodetector, 9 is the optical axis of the pinhole 7 A vibrator that vibrates in the direction, 10
11 is an oscillator that excites the vibrator 9; 12 is a phase detector that detects the phase of the output of the photodetector 8 with reference to the output of the oscillator 11; and 13 is a phase detector. This is an actuator that drives the table 10 with 12 outputs.

In this device, a laser beam 2 emitted from a laser light source 1 is focused onto the surface of an object 4 by an objective lens 3. The light reflected from the surface of the object 4 is again focused by the objective lens 3, separated from the incident optical path by the beam splitter 5, directed to the focusing lens 6, and then further focused to form a light spot. , enters the photodetector 8. A pinhole 7 having approximately the same diameter as the optical spot is provided at the focal point of the focusing lens 6, and is vibrated in the optical axis direction at a frequency f by a vibrator 9 excited by an oscillator 11. The output of the photodetector 8 that receives the light that has passed through the pinhole 7 is phase-detected by the phase detector 12 using the output of the oscillator 11 as a reference, and this detected output is supplied to the actuator 13 and the table 1
0 in the direction of arrow A in the figure. That is, when the surface of the object 4 is at the focus of the objective lens 3, the focus of the condenser lens 6 is at the vibration center of the pinhole 7, and a signal with a frequency of 2f is obtained from the photodetector 8.
The output of phase detector 12 is zero. However, when the surface of the object 4 deviates from the focal position of the objective lens 3, the position of the light spot formed by the condenser lens 6 also deviates from the vibration center of the pinhole 7, and accordingly, the output from the photodetector 8 changes. A component of frequency f appears. The phase corresponds to the direction of deviation of the surface of the object 4 from the focal position of the objective lens 3. Therefore, the table 10 is driven in the direction of arrow A in the figure by the output of the phase detector 12 which phase-detects the output of the photodetector 8, and the focus of the objective lens 3 is focused on the surface of the object 4. can be automatically adjusted.

By the way, in the conventional device as described above, it is not necessarily necessary to vibrate the pinhole 7 itself, and the objective lens 3 or the condensing lens 6 may be vibrated, but in any case, the pinhole 7 is necessary. The appropriate diameter of this pinhole is approximately several tens of microns, and it is extremely difficult to place it in the center of the light spot. Furthermore, there is a risk that the settings may change over time due to external vibrations, etc., causing errors in the operation of the device. In particular, it is difficult to apply this method to devices such as video disc playback devices, which require low cost and whose usage environment is not constant.

This invention was made in view of the above points, and by using a semiconductor laser device as a laser light source, it is possible to provide a stable automatic focusing device without using a pinhole as in conventional devices. That is.

FIG. 2 is a configuration diagram showing an embodiment of this invention.
In the figure, 14 is a semiconductor laser device such as a laser diode, and 15 is a light emitting section consisting of a pn junction thereof. Here, the object 4 is a video disk on which video signals and the like are optically recorded. 16 is a processing circuit for signals read out from the video disk.

Laser light 2 emitted from semiconductor laser device 14 is focused onto the surface of video disk 4 by objective lens 3 . Then, the light reflected from the surface of the video disk 4 is again focused by the objective lens 3, travels the optical path backwards, and enters the light emitting path 15 consisting of a pn junction of the semiconductor laser device 14. The output of the semiconductor laser device 14 changes depending on this incident light. and,
This change in output is detected by a photodetector 8 placed at the rear of the semiconductor laser device 14, and processed by a signal processing circuit 16 for video reproduction.

Now, the oscillator 11 excites the vibrator 9 to vibrate the semiconductor laser device 14 at a constant frequency f in the optical axis direction. Now, the light emitting section 15 is placed on the surface of the disk 4.
When the position is such that an image is formed, almost all of the light emitted from the surface of the disk 4 enters the light emitting section 15, but when the surface of the disk 4 is out of focus by the objective lens 3, no light is emitted. The size of the reflected image formed on the light emitting portion 15 becomes larger.
The effective incident light is reduced. By this means, when the semiconductor laser device 14 is vibrated in the optical axis direction, an effect equivalent to that of a vibrating pinhole in a conventional device can be expected. That is, the output of the photodetector 8 has a frequency 2f component when the surface of the disk 4 is at the focal position of the objective lens 3, and has a frequency f component when it deviates from the focal position. The phase of this frequency f component is reversed depending on the direction of deviation from the focal point position. The phase detector 1 uses the output of the oscillator 11 as a reference.
2 performs phase detection, and the detected output moves the objective lens 3 via the actuator 13 in the direction indicated by the arrow A.
The focus can be automatically adjusted to the surface of the disk 4, which is the object.

In the above embodiment, the backward radiated light of the semiconductor laser device is detected, but the forward radiated light may be detected using a beam splitter.

As described in detail above, the automatic focusing device according to the present invention uses a semiconductor laser device as a light source, and utilizes the fact that the output light changes due to the return of the reflected light from the object to the light emitting part. By vibrating this semiconductor laser device in the optical axis direction, there is no need for a pinhole in conventional devices.
It can perform the same function as this, and therefore,
There is no need for fine adjustment of the pinhole, and the adjustment of the optical system is extremely easy.

Furthermore, if forward radiation light is detected,
Compared to those that detect backward radiation, when the reflected light from the object enters the semiconductor laser device again,
The reflected light is not rejected by the semiconductor laser chip and directly enters the photodetector, and only changes in the output power of the semiconductor laser device can be detected, allowing for more accurate automatic detection than when using backward emitted light. This has the unique effect of enabling focusing.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional automatic focusing device, and FIG. 2 is a block diagram showing an embodiment of the present invention. In the figure, 14 is a semiconductor laser device, 15 is a light emitting unit, 2 is a laser beam, 3 is an objective lens, 4 is an object, 8 is a photodetector, 9 is an oscillator, 11 is an oscillator, 12 is a phase detector, 13 is an actuator. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A semiconductor laser device, an optical system that focuses emitted light from the semiconductor laser device onto a disk and returns the reflected light to a light emitting section of the semiconductor laser device, and a direction of the optical axis of the optical system that directs the semiconductor laser device. a vibrator that vibrates at a predetermined frequency; an oscillator that excites the vibrator; a photodetector that detects the output intensity of the disk-side emitted light of the semiconductor laser device that changes based on changes in the intensity of the reflected light; A phase detector that detects the phase of the output of the detector with reference to the output of the oscillator, and an actuator that adjusts the optical system according to the output of the phase detector so that the focal position matches the surface of the disk. Focusing device.