JPS6227455B2 - - 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 further focused to form a light spot. Afterwards, it enters the photodetector 8. A pinhole 7 having approximately the same diameter as the optical spot is provided at the focal point of the condenser lens 6, and is vibrated in the optical axis direction at a frequency f by an oscillator 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, a signal with a frequency of 2f is obtained from the photodetector 8, and the phase detector The output of 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 has a frequency difference. A component of 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 actuator 13 is activated by the output of the phase detector 12 which phase-detects the output of the photodetector 8.
By driving the table 10 in the direction of the arrow A shown in the figure, the objective lens 3 can be automatically focused on the surface of the object 4.

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 diameter of this pinhole is approximately several microns, and it is very 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 light source such as a semiconductor laser device or a light emitting diode as a light source, stable automatic operation can be achieved without using pinholes as in conventional devices. It is an object of the present invention to provide a focusing device.

FIG. 2 is a configuration diagram showing an embodiment of this invention.
In the figure, 14 is a semiconductor light source such as a semiconductor laser device or a light emitting diode, and 15 is a light emitting section consisting of a pn junction thereof. Here, as object 4,
It is intended for video discs on which video signals are recorded optically. 16 is a processing circuit for signals read out from the video disk; 17 is an oscillator 11;
This is a mixer circuit for the output of the phase detector 12 and the output of the phase detector 12.

Laser light 2 emitted from semiconductor light source 14 is focused onto the surface of video disk 4 by objective lens 3 . The light reflected from the surface of the video disk 4 is again focused by the objective lens 3 and travels backward along the optical path to a light emitting section 15 made of a pn junction of a semiconductor light source 14.
incident on the This incident light causes the semiconductor light source 14 to
output changes. Then, this change in output is detected by a photodetector 8 placed behind the semiconductor light source 14, and processed by a signal processing circuit 16 for video reproduction.

By the way, when the light-emitting sections 15 are positioned so that an image is formed on the surface of the disk 4, almost all of the reflected light from the surface of the disk 4 enters the light-emitting section 15, but the surface of the disk 4 is located near the objective lens. 3, the size of the reflected image formed on the light emitting section 15 becomes large and extends beyond the light emitting section 15, reducing the amount of effective incident light. That is,
When the objective lens 3 is vibrated in the optical axis direction via the actuator 13 by the output of the oscillator 11 having the frequency f, an effect equivalent to that of the vibrating pinhole in the conventional device can be expected. 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, but when it deviates from the focal position, it has a frequency f component; The phase of is reversed depending on the direction of deviation from the above-mentioned focal point position. This is phase-detected by a phase detector 12 using the output of the oscillator 11 as a reference, and the detected output is mixed by a mixer circuit 17 and applied to the actuator 13 to adjust the average position of the objective lens 3 in the direction of arrow A in the figure. Thus, the focus can be automatically set on the surface of the video disk 4, which is the object.

In the embodiments described above, the backward radiated light of the semiconductor light source is detected, but the forward radiated light may be detected using a beam splitter.

As detailed above, in the automatic focusing device according to the present invention, a semiconductor light source such as a semiconductor laser device or a light emitting diode is used as a light source, and the output light changes as the reflected light from the object returns to the light emitting part. By using this technology to vibrate the objective lens of the optical system that projects the light from the light source onto the surface of the target object in the direction of the optical axis, it is possible to achieve the same functionality as the conventional device without the need for a pinhole. Therefore, there is no need for fine adjustment of the pinhole.
Adjustment of the optical system is extremely easy.

[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 light source, 15 is a light emitting unit, 2 is a laser beam, 3 is an objective lens, 4 is an object, 8 is a photodetector, 11 is an oscillator, 12 is a phase detector, 13 is an actuator, and 17 is It is a mixer circuit. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A semiconductor laser device, and an optical system that is arranged separately from the semiconductor laser device and that focuses the emitted light from the semiconductor laser device onto an object and focuses the reflected light onto the light emitting section of the semiconductor laser device. , an exciter that vibrates the optical system at a predetermined frequency and slightly vibrates the light converging position on the object in the optical axis direction at the predetermined frequency; an oscillator that excites the exciter;
The reflected light is re-injected into the semiconductor laser device by the optical system, and a shift between the object and the condensing position is detected from a change in the output of the light emitted from the semiconductor laser device based on a change in the intensity of the re-incoming light. a phase detector that detects the phase of the output of the photodetector using the output of the oscillator as a reference; and a phase detector that displaces only the optical system in the optical axis direction according to the output of the phase detector, an actuator that controls the position of the light to match the surface of the object.