JPH0146927B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical information reproducing device that includes a focusing sensor that requires few additional optical components and requires almost no adjustment.

Optical information reproducing devices such as video discs have extremely high recording densities, and the diameter of the reading light spot is 1 to 2 μm. Therefore, the depth of focus is 2~
Considering that it is only 3 μm and the surface runout during disk rotation reaches 200 to 300 μm, some kind of automatic focusing device is required.

Conventionally, there has been a device of this type as shown in FIG. In the figure, 1 is a semiconductor laser, 2 is a collimating lens, 3 is an objective lens, 4 is an information disk, 5 is a photodetector, 6 is a prism, 7 is a two-split photodetector, and 8 is a differential amplifier.

Next, the operation will be explained. Semiconductor laser 1
The light emitted from the collimating lens 2 becomes parallel light, and is projected onto the information disk 4 by the objective lens 3 as a light spot with a diameter of 1 to 2 μm.
Since information such as images and sounds is recorded on the information disk 4 in an optically readable form such as a row of depressions or a row of black and white patterns, the light reflected from the information disk 4 is modulated. When the reflected light is received again by the objective lens 3 and returned to the semiconductor laser 1, the output of the semiconductor laser 1 changes depending on the intensity of the returned light, so the change is detected by the photodetector 5, and the demodulation circuit (not shown) detects the change. The original information is reproduced by processing.

At this time, the focusing signal is obtained by extracting a part of the reflected light using a prism 6 and making it incident on a two-split photodetector 7. A beam of light extracted by a prism 6 is transferred from an objective lens 3 to an information disk 4
The optical path when the light enters the lens is a partial beam that is largely tilted with respect to the information disk 4 as shown by the dotted line 9. Therefore, when the information disk 4 is displaced in the optical axis direction 10 with respect to the objective lens 3, two-split light detection is performed. The light spot of the reflected light on the vessel 7 moves across the dividing line in response to the displacement. For example, when the disk 4 approaches the objective lens 3, the light spot will move to the lower side 1 in FIG.
1, and as it moves away, it moves upward to 12. Therefore, by differentially processing the output of the two-split photodetector 7 with the differential amplifier 8, a displacement signal proportional to the amount of deviation in the optical axis direction between the disk 4 and the focal point of the objective lens 3, that is, focusing I had a signal.

Although the above-mentioned conventional device has a small number of additional parts and seems simple at first glance, it has the following drawbacks.

That is, the collimating lens 2 is used to form an image of the light from the prism 6 on the two-split photodetector 7 to form a small light spot (detection sensitivity is low unless the light spot is made small). In this case, the reflected light beam must pass through the collimating lens 2, and its imaging position will be near the semiconductor laser. It is necessary to set the two-split photodetector 7 at that location, but the heat sink of the semiconductor laser 1 protrudes around the semiconductor laser 1, and the tip of the metal frame of the collimating lens 2 and the semiconductor laser 1 In reality, this was extremely difficult, as the distance between the window and the window was only 2 to 3 mm. In an attempt to solve this problem, the light from the prism 6 is extracted into a relatively wide space between the collimating lens 2 and the objective lens 3, as shown by the dashed line 13, but in that case, the light does not form an image. Since the particles remain spread out without being detected, high detection sensitivity could not be obtained.

Another drawback is that the collimating lens 2 requires back and forth adjustment in the optical axis direction 10 in order to convert the light from the semiconductor laser 1 into parallel light; Even the position of the light beam for focusing is affected,
It was also difficult to set up the two-split photodetector 7.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and it is possible to image a part of the reflected light from the information disk on a two-split photodetector without passing it through a collimating lens. It is an object of the present invention to provide an optical information reproducing device equipped with an automatic focusing device that can perform automatic focusing.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 2, the same reference numerals as in FIG. 1 indicate the same parts. The reading light 20 emitted from the semiconductor laser 1, which is a light source, has its diffusion angle suppressed by the collimating lens 2, and enters the objective lens 3 as parallel light 20a. The incident light is focused by the objective lens 3 onto an information disk 4, which is an information recording carrier, and then becomes a reflected light 21. The objective lens 3 again turns the incident light into parallel light 21a, which then travels in the direction of the collimating lens 2.

In order to extract a part 22 of this reflected light 21 as displacement detection light 23, an extraction lens 25 is disposed between the collimating lens 2 and the objective lens 3, facing the outer periphery of the objective lens 3 away from the optical axis. There is. The extraction lens 25 is an off-axis lens made of a fragment of the lens 24 having a focal length f and having an optical axis 26 outside the parallel light 21a, and the off-axis distance is H. The extracted displacement detection light 23 is focused on the two-split photodetector 7 placed at the focus of the extraction lens 25. The output of the two-split photodetector 7 is input to the differential amplifier 8 as a displacement detection signal 27, the difference is taken and amplified by the servo amplifier 28, and the output is sent to the objective lens 3.
is applied to an actuator 29 that moves the light in the optical axis direction 10.

Next, the operation will be explained. The extraction lens 25 is
A part (peripheral light) 22 of the parallel reflected light 21a formed by the collimating lens 2 and the objective lens 3 is focused onto the two-split photodetector 7. Therefore, when the information disk 4 moves in the optical axis direction 10 and is removed from the focus of the objective lens 3, the light spot on the two-split photodetector 7 moves in the direction 30 across the dividing line. The output of the two-split photodetector 7 is transferred to a differential amplifier 8.
The defocus signal of the information disk 4 can be obtained by differentially amplifying the information disk 4. By amplifying this with the servo amplifier 28 and controlling the movement of the objective lens 3 in the optical axis direction 10 with the actuator 29, the amount of deviation between the focal position of the objective lens 3 and the information disk 4 can always be made zero.

In the above configuration, the displacement detection light 23 is directly extracted from the extraction lens 2 without passing through the collimating lens 2.
5 to focus the light on the two-split photodetector 7,
There is no movement of the image due to adjustment of the collimating lens 2, and the two-split photodetector 7 can be placed in a space with sufficient space between the collimating lens 2 and the objective lens 3, so placement is easy. .

The off-axis distance H of the off-axis lens 25 is set so that the two-split photodetector 7, its holder, etc. do not touch the outer edge of the collimating lens 2 or the outer edge of the parallel light 21a. This can be achieved freely by appropriately selecting the extraction lens 25. This point has also been considered difficult in the past.

This invention further has the following advantages in terms of assembly and adjustment. Since the reflected light passing through the extracting lens 25 forms an image at the focal point of the extracting lens 25, 2
The split photodetector 7 is extracted from the optical axis 26 with a lens 25.
It is only necessary to arrange it at a distance of f from . In other words, the positional relationship between the extraction lens 25 and the two-split photodetector 7 is constant. Therefore, the extraction lens 25
By integrating the holding of the two-split photodetector 7 and achieving mechanical precision, adjustment of the two-split photodetector 7 can be made almost unnecessary. This is a problem that has been difficult with conventional devices in which the prism 6 for extracting reflected light and the two-split photodetector 7 are separated on both sides of the collimating lens 2.

The dimensions of the extraction lens 25 are such that the number of parallel lights 21a is
In the case of a diameter of 1 mm x 1 mm, sufficient detection sensitivity can be obtained. Even if the extraction lens 25 having such a size ratio is placed at a position facing the outer circumferential portion of the objective lens 3, the light spot on the information disk 4 is hardly deformed and a good image can be obtained. Further, the reflected light entering the outer peripheral part of the objective lens 3 from the information recording carrier 4 is reflected from the information recording carrier 4.
Therefore, the amount of displacement of the objective lens 3 in the optical axis direction, and the amount of displacement in which the light extracted from the outer circumference moves in the direction crossing the dividing line of the two-split photodetector 7, In other words, since the output of the two-split photodetector 7 is linearly proportional, focusing control using the output signal of the two-split photodetector 7 can be performed accurately. The extraction lens 25 may be a circular lens, or it may be a cylindrical lens since it is not necessary to form an image in the direction along the dividing line of the two-split photodetector, that is, in the direction perpendicular to the plane of the paper in FIG. Good too. Furthermore, any lens that has an imaging function such as a spherical lens, a Fresnel lens, or a hologram lens may be used.

3 and 4 show other configuration examples of the extraction lens 25. FIG. That is, the off-axis lens 25 is formed on the outer periphery of the disc 31 made of a transparent material. The disk 31 and the lens are actually made integrally by pressing plastic or the like. A semiconductor laser 1, a collimating lens 2, and an objective lens 3 are housed in a cylindrical case, and the disk 3 is
1 into the cylindrical case between both lenses 2 and 3, the extraction lens 25 can be easily attached.
The extraction lens 25 may be a spherical lens, a Fresnel lens, or a hologram lens, and can be similarly manufactured integrally with the disk 31 by press working.

In the present invention, when the light source 1 is a semiconductor laser having a striped light emitting pattern, the extraction lens 25 is located at a position facing the outer periphery of the objective lens 3, and the striped light emitting pattern By placing it on top,
The optical power incident on the two-split photodetector 7 can be increased, and as a result, the sensitivity of defocus detection can be improved.

As described above, according to the present invention, the arrangement of the extraction lens and the 2-split photodetector is facilitated, and there is no need to adjust the position between the extraction lens and the 2-split photodetector due to movement adjustment of the collimating lens. It has the effect of Further, since the output of the two-split photodetector is linearly proportional to the amount of movement of the objective lens, focusing control can be performed accurately.

This invention is particularly effective when implemented in the optical self-feedback pickup (SCOOP) optical system shown in the embodiment. That is, the above-mentioned pick-up has a small number of parts in the optical system, and there is a demand for miniaturization by incorporating a semiconductor laser, a collimating lens, and an objective lens into one cylindrical case, and there is particularly no space available, so the pick-up lens according to the present invention is The effect of facilitating the arrangement of the two-split photodetector is significant.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a conventional optical information reproducing device, FIG. 2 is a schematic diagram showing an optical information reproducing device according to an embodiment of the present invention, and FIG. 3 is a modified example of an extraction lens. A front view and FIG. 4 are side views showing the same modification. DESCRIPTION OF SYMBOLS 1... Light source, 2... Collimating lens, 3... Objective lens, 4... Information recording carrier, 7... 2-split photodetector,
10...Optical axis direction, 20...Reading light, 21...Reflected light,
24...Lens, 25...Extraction lens, 26...Optical axis, 31...Disc. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1: a light source that emits reading light; a collimating lens that suppresses the diffusion angle of the reading light; an objective lens that focuses the reading light that has passed through the collimating lens onto an information recording carrier; an extraction lens integrally formed on the outer periphery of a disc made of a transparent material inserted between the collimating lens and the objective lens, which deflects a part of the reflected light from the information recording carrier and extracts it as displacement detection light; , a two-part photodetector that receives the displacement detection light and outputs a displacement detection signal corresponding to the amount of deviation between the focal point of the information recording carrier and the objective lens; and a two-part photodetector that receives the displacement detection signal and reduces the amount of deviation to zero. an actuator for moving the objective lens in the optical axis direction so that the extraction lens is a part of a lens having an optical axis outside the optical path of the reflected light, An optical information reproducing device configured to collect a portion of the reflected light. 2. The optical information reproducing device according to claim 1, wherein the light source is a semiconductor laser, and the extraction lens is located on the stripe of the striped light emitted from the semiconductor laser.