JPS599976B2 - information reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a light source and a photodetector for converting the light beam emitted from the light beam and modulated by an information storage medium into an electrical signal, the invention comprises The present invention relates to an apparatus for reading information from an information recording medium recorded on at least one track having an information recording medium.

In the above device, a light spot is imaged on the recording medium in order to ensure that the photodetector, which converts the video information of the recording medium into an electronic signal, always receives light from only one track. Continuously detects the soil position, 1
It is necessary to adjust the light spot so that it is always located in the center of one track.

(This operation is hereinafter referred to as tracking.) Furthermore, in order to read the aforementioned optical structure, the light spot imaged onto the photodetector must be of a size approximately equal to the smallest detail of the optical structure. For this purpose, it is necessary to detect the amount of defocus and adjust the optical system so that the focal plane of the optical system that images the light source always coincides with the information recording medium. (Hereinafter, this operation will be referred to as automatic focusing.) The purpose of the present invention is to eliminate the drawbacks of conventional optical video disc playback devices, and to provide a compact, low-cost playback device with high light utilization efficiency. There is a particular thing. In order to achieve the above object, the present invention uses a semiconductor laser having at least three or more light emitting regions arranged substantially linearly as a light source, and records information by recording the arrangement of three or more laser beams from the semiconductor laser. Three or more photodetectors are arranged on the medium at a slight inclination with respect to the information track and converge to detect reflected light or transmitted light from the information recording medium. One photodetector is positioned in an imaging relationship with the light-emitting area, and the other photodetector is placed at a slight angle to the photodetection surface so that the optical path length is approximately equal to the imaging relationship and is shifted in opposite directions. , extracts the information signal from the photodetector in the imaging relationship, separates and extracts the tracking signal and the defocus detection signal from the remaining photodetectors,
Automatic focusing and tracking are performed using each signal to reproduce the video signal.

Alternatively, a semiconductor laser having at least three light emitting points as a light source may be tilted with respect to the recording medium surface, and a plurality of photodetectors may be arranged on the photodetection surface. The present invention will be described in detail below with reference to Examples.

FIG. 1 shows a first embodiment of the invention.

A laser beam (only the optical axis is shown in FIG. 1) from a semiconductor laser having light emitting regions 2, 2', and 2'' arranged on a substrate 1 passes through a lens 3, and then enters a galvano mirror 4 and a converging lens 5. Therefore, the information tracker of the video disk 6 is guided.The laser beam irradiated onto the video disk is modulated by the information, and the reflected beam is sent by the beam splitter 8 to the photodetectors 9, 9', 9''. Each will be guided.
The detector 9' detects the information signal, and the information signal processing circuit 1
0 and reproduces the image on the television 11. The differential outputs of the photodetectors 9 and 9I go to the drive circuit 13;
The output drives the galvanometer mirror 4 to cause the laser beam to follow the information track that changes in the direction of the arrow, thereby performing tracking.The principle of tracking in the present invention is described in Japanese Patent Laid-Open No. 49-50954 " Since the details of the flat record carrier reading device are well known, the explanation will be omitted here. Next, the outputs of the photodetectors 9 and 9'' are input to low-pass filters 12 and 12', respectively, to take out only the respective DC components, and the respective outputs are sent to the lens drive circuit 1.
4, the differential output drives the converging lens 5, and automatic focusing is performed by keeping the distance between the lens and the disk constant against vertical vibration of the disk that fluctuates in the direction of the arrow. The principle of automatic focusing in the present invention will be explained with reference to FIGS. 2 and 3.

Figure 2 shows the geometrical arrangement of the three photodetectors. The photodetector 9' is precisely positioned at the back focal plane 15 (also called the photodetecting plane) of the converging lens 5. The photodetector 9 is set on the opposite side of the lens from the accurate back focal plane 15, that is, on the positive side, and the photodetector 9'' is set on the lens side from the accurate rear focal plane 15, that is, on the positive side. 0, which is set on the negative side, and the photodetectors 9 and 92 are set equivalently on the optical axis 16 and symmetrical about 9'.In FIG. It shows the change in the output of the photodetector 9' when the disk 6 moves away from the front focus of the lens 5.

Curves B and c show the output changes with respect to the amount of defocus of the photodetectors 9 and 9'', respectively. In FIG.
9" will be the same, and the difference in output will be zero.Next, when the disk 6 slightly shifts from the focal point of the lens 5 to the lens side, that is, to the negative side, the output signal of the photodetector 9 increases and the output of 9″ decreases. Therefore, the difference between the output signals from 92 and 9 has a negative sign. Similarly, when the disk 6 slightly moves from the focal point of the lens 5 to the opposite side of the lens, that is, to the positive side, the output of 9 decreases and the output of 9'' increases.Therefore, the output from 9'' and 9 The signal difference has a positive sign. In order to automatically adjust the focus, the lens 5 may be moved using a voice coil or the like depending on the magnitude and sign of the difference between the outputs of 9/' and 9.

As mentioned earlier, if you take the difference between the signals from the low-pass filters 12 and 12', you will get a signal that represents the focus shift, which is how far the disk 6 is shifted from the lens 5 and in which direction. If this is input to a drive system that changes the relative position of the lens 5 and the disk 6, the focus will be automatically adjusted. As a result, the lens 5 moves with respect to the ground shaking of the disk 6, the distance between the lens and the disk is always kept constant, and the focus is maintained on the disk surface.The first embodiment of the present invention as described above In this example, tracking and automatic focusing can be achieved simultaneously and easily using one optical system by using three semiconductor lasers without reducing light utilization efficiency. In order to obtain a defocus detection signal, the photodetector was placed at an angle with respect to the photodetection surface 15, but instead of this, three semiconductor lasers serving as light sources could also be arranged in the geometrical arrangement shown in FIG. 4) as described above. However, in this case, the photodetectors are arranged on the photodetection surface 15. For automatic focusing, the imaging positions of the two light sources used for tracking and the photodetector are slightly different from the imaging positions of the light source and photodetector used for the video signal for tracking signal detection. to the extent that it does not affect.

This deviation may be about 1 to 2 μm in terms of the amount of deviation from the focus. However, this value depends on the magnification of the converging lens 5 and the third
It changes depending on the tendency of curve a in the figure, and there is nothing to be concerned about. In addition, in this example, to simplify the explanation, the light emitting area of the semiconductor laser is set to three points, but it is not limited to this and there may be more. In that case, tracking accuracy and Automatic focusing accuracy can be improved.

Further, although FIGS. 1 and 4 show an optical system using two lenses, the present invention is not limited to this, and for example, an imaging system using one lens may be used. Note that as the above laser, JOunalOfApplledphysics (
GaAs-Gal-XA! on pages 4899-4906 of VOlume 45, NOvember 974, ll. XA
sbarried one Heter Ostnusturein
It is convenient to use three injectiOnlasers formed in parallel on the same substrate. As for semiconductor lasers, it is easy to construct a plurality of light emitting regions on the same substrate using current diode growth technology.

Furthermore, although only the reflective type has been described so far, it goes without saying that the same explanation holds true for the transmissive type as well.
As explained above, by using the light source and imaging optical system of the present invention, tracking and automatic focusing required for optical video discs can be simultaneously realized.

The advantage is that the optical system is not complicated, so the number of parts can be reduced, and costs can be reduced and compactness can be achieved. Greatly improves conventional optical video disc playback equipment,
Practical soil can be very effective.

[Brief explanation of the drawing]

Claims (1)

[Claims] 1 comprises a light source, an optical system that focuses the light beam from the light source onto information recorded in a track shape on a recording medium, and a photodetector that receives the light beam modulated by the information, and the light source includes: A semiconductor laser is used that has three or more light emitting regions arranged on the same substrate at a distance apart from each other in a substantially straight line, and the direction in which the light beams from the three or more light emitting regions are arranged is slightly tilted with respect to the track. The semiconductor laser is arranged such that at least one photodetector is used for each of the light beams from the three or more light emitting regions, and one of these photodetectors is configured to The semiconductor laser and the photodetector are arranged at a position in an imaging relationship with the light emitting region, and the other photodetector is shifted in opposite directions by an approximately equal optical path length with respect to the imaging relationship, An information reproducing device characterized in that an information signal is extracted from one photodetector, and a tracking signal and a defocus signal are extracted from another photodetector.