JPS6130326B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical reproducing device that projects a light beam onto a recording medium and optically reads a recorded signal, and more specifically, a tracking beam is created using a diffraction grating. The present invention relates to a playback device configured as described above.

For example, in a Flippus-MCA video disc player, invisible or visible laser light emitted from a laser light source is guided to a diffraction grating, where 0th-order diffracted light and ±1st-order diffracted light are obtained. The 0th order diffracted light is used as a light beam for reading information,
The ±1st-order diffracted light is projected onto a disk, that is, a recording medium, as a tracking light beam. Then, the two tracking light beams are projected onto one side and the other side of the track on the disk, and tracking detection is performed based on the difference in the amount of reflected light between the two tracking light beams. However, in conventional disk players, the incident positions of the two tracking light beams in the entrance pupil of the objective lens do not match, so when the two tracking light beams are swung greatly by the tracking mirror, , the amounts of protrusion of the two tracking light beams from the entrance pupil of the objective lens are not the same. That is, even if one of the two tracking light beams protrudes from the entrance pupil, a situation may occur in which the other does not protrude from the entrance pupil. If such a situation occurs, the spots of the pair of tracking light beams on the disk will not be the same, and the amount of reflected light of the tracking light beam will change due to factors other than track deviation, making it difficult to perform accurate tracking control. becomes impossible. If the entrance pupil of the objective lens is made larger, the above-mentioned problem will not occur, but the apparatus will inevitably become larger.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical reproducing device that can accurately perform tracking control even when the entrance pupil of an objective lens is small.

To achieve the above object, the present invention will be described with reference to the reference numerals in the drawings showing the embodiments. and a diffraction grating 9 for obtaining the third light beams 4, 5, 6;
A convex lens 7 that converges the light beams 5 and 6 and then widens them, a tracking mirror 11, an objective lens 12, first, second and third photodetectors 13, 14 and 15, and a differential amplifier. 20 and a mirror driver 24, the second and third light beams 5, 6 are incident on the same location of the entrance pupil 28 of the objective lens 12. Therefore, the distance between the diffraction grating 9 and the convex lens 7 is x, the focal length of the convex lens 7 is f, and the distance between the focal position on the exit side of the convex lens 7 and the entrance pupil 28 of the objective lens is When L, the diffraction grating 9, the convex lens 7, and the entrance pupil 2 of the objective lens are located at positions where the relationship 1/x+1/L+f=1/f holds.
8 are arranged respectively.

With the above configuration, when the first, second, and third beams 4, 5, and 6 are swung by the tracking mirror 11, the second and third tracking light beams 5, 6 are directed to the objective lens. 12 entrance pupils 2
8, move to the same position. If the movement positions of the second and third light beams 5 and 6 are the same in this way, when the second and third light beams 5 and 6 protrude from the entrance pupil 28, the amount of protrusion will be the same, Disk 1 despite the protrusion
The shapes of the spots of the second and third light beams 5, 6 on the top remain substantially the same. Therefore,
Accurate tracking control can be performed by suppressing changes in the difference in the amount of reflected or transmitted light between the second and third light beams 5 and 6 due to factors other than track deviation. Furthermore, even if the entrance pupil is small enough to cause the second and third light beams 5 and 6 to protrude, track deviation can be detected accurately, making it possible to downsize the device. Become.

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 to 3.

The optical disk player shown in FIG. 1 rotates a disk 1 at a constant speed of, for example, 1800 rpm by a disk drive motor 2 serving as a main scanning drive device, as in the Philips-MCA system, and also uses an optical pick-up, i.e. A first light beam 4 for reading information and second and third light beams 5 and 6 for tracking are projected onto the disk 1 from the information reading head 3, and the head 3 is further used as a feeding device as a sub-scanning drive device. 27 in the radial direction of the disk to pass beams 4, 5, 6 over the disk 1.
It is configured to read recorded information while scanning in a spiral manner. More specifically, the laser beam emitted from the light beam generation source 8 of the head 3 passes through the diffraction grating 9, thereby forming a first beam 4 of 0th-order diffracted light and a second beam of +1st-order diffracted light. They become a light beam 5 and a third light beam 6 of -1st order diffracted light.
The first, second, and third light beams 4, 5, and 6 are transmitted through a convex lens 7 and a beam spiriter 1.
0 and a tracking rotating mirror 11 to reach a beam converging objective lens 12, where it is converged and projected onto the disk 1. By scanning the track of the disk 1 with the first light beam 4 for information reading, a modulated reflected beam 4a corresponding to the presence or absence of a recording signal is obtained, and this reflected beam 4a is transmitted to the objective lens 12, the rotary mirror 11, and enters the first photodetector 13 through the beam splitter 10,
Here it is converted into an electrical signal. The second and third light beams 5 and 6 for tracking are also projected onto the disk 1 in a predetermined positional relationship with the first light beam 4, and based on this, reflected beams 5a and 6a are generated, and the objective The second and third photodetectors 1 pass through the lens 12, the rotating mirror 11, and the beam splitter 10.
4 and 15, where it is converted into an electrical signal.

In FIG. 1, for convenience of illustration, the first, second, and third light beams 4, 5, and 6 are arranged in the radial direction of the disk 1, but in reality, the tracks are arranged as shown in FIG. When the first light beam 4 for information reading is located at the center of the track consisting of the array of pits 16, the second light beam 5 is arranged at a predetermined interval in the scanning direction. (inner circumferential side), and the third light beam 6
are located on the upper side (outer circumferential side) of the track. Therefore, in the optimum tracking state, the detection output of the reflected beam 5a of the second light beam 5 and the detection output of the third light beam 6 are equal.

The output of the second photodetector 14 is inputted to a differential amplifier 20 via an amplifier 17, a bandpass filter 18, and an AM detector 19, and the output is inputted to a differential amplifier 20.
The output of 5 is sent to the differential amplifier 2 via an amplifier 21, a bandpass filter 22, and an AM detector 23.
0, and both inputs are compared and amplified by a differential amplifier 20. Note that the AM detectors 19 and 23 perform envelope detection of the high frequency signal corresponding to the pit 16, and detect the high frequency signal corresponding to the pit 16.
This excludes the effects of Therefore, differential amplifier 2
0, signals corresponding to the positions of the second and third light beams 5 and 6 are input. The difference comparison output, that is, the error signal obtained from the differential amplifier 20 is transmitted to the rotating mirror 1.
1, the rotating mirror 11 is controlled so that the output of the differential amplifier 20 becomes zero, and the first beam 4 for information reading is directed to the center of the track. is maintained.
The mirror driver 24 has a drive coil and is configured to rotate the mirror 11 on the same principle as a galvanometer. Since a low-pass filter 25 and an amplifier 26 are provided between the differential amplifier 20 and the feed device 27, the feed device 27 is controlled by a signal obtained by smoothing the output of the differential amplifier 20, and the head 3 is controlled by a signal obtained by smoothing the output of the differential amplifier 20. As it progresses, it moves in the radial direction of the disk 1. As a result, disk 1 and light beams 4, 5,
6, a relative scanning movement occurs in which a spiral scanning track is formed, making it possible to read the recorded signal.

By the way, in this apparatus, the diffraction grating 9, the convex lens 7 for obtaining beam spread, and the entrance pupil 28 of the objective lens 12 are arranged in a specified positional relationship. FIG. 3 is an explanatory diagram of this positional relationship, where x is the distance between the diffraction grating 9 and the convex lens 7, f is the focal length of the convex lens 7, and is the focal plane on the exit side of the convex lens 7, which serves as a virtual light source. When the distance between the position P and the entrance pupil 28 of the objective lens 12 is L, the diffraction grating 9, the convex lens 7, and the entrance pupil 28 are arranged so that the relationship 1/x+1/L+f=1/f holds. are placed respectively.
Note that if the distance between the convex lens 7 and the entrance pupil 28 is determined in advance, the diffraction grating 9 is arranged at the position of x=f(L+f)/L.

With this arrangement, the first light beam 4 of the 0th order diffracted light is at the focal plane position P of the convex lens 7 _.
After converging to a point, the beam diverges and reaches the entrance pupil 28, where it becomes a beam with an appropriate spread. Further, the second light beam 5 of the +1st order diffracted light converges at a point P ₂ on the focal plane and then reaches the entrance pupil 28 in a diverging form. Similarly, the third light beam 6 of the −1st order diffracted light converges at point P ₃ on the focal plane, and then reaches the entrance pupil 28 in a diverging form. Since the settings are as shown in the above equation, the first, second, and third light beams 4,
5 and 6 have substantially the same width in the entrance pupil 28. Note that the mutual spacing between the _P1 point, _P2 point, and _P3 point is the distance between the first, second, and third photodetectors 1.
It is set to correspond to intervals of 3, 14, and 15. A third lens is placed in the entrance pupil 28 of the objective lens 12.
The first, second, and third light beams 4, 5, and 6 incident as shown in the figure are converged by the objective lens 12 and projected onto the disk 1 as shown in FIG.
The reflected light passes through the objective lens 12 again and is transmitted to the first, second, and third photodetectors 13, 14, 15.
leading to. first, second, and third photodetectors 13,
14 and 15 are P ₁ point, P ₂ point, and P ₃ point as mentioned above.
Since they are arranged corresponding to the points, the first, second,
It becomes possible to independently detect the third reflected beams 4a, 5a, and 6a.

As is clear from the above, in the reproducing apparatus of this embodiment, since the second and third optical beams 5 and 6 for tracking are incident on the same location of the entrance pupil 28 of the objective lens 12, the rotating mirror 11 When the first, second and third light beams 4, 5 and 6 are swung,
Second and third light beams 5, 6 for tracking
Even if it protrudes from the entrance pupil 28, the amount of protrusion remains the same. As a result, despite the protrusion, the second and third
The shapes of the spots of the light beams 5, 6 can be kept substantially the same. Therefore, changes in the difference in the amount of reflected or transmitted light between the second and third light beams 5 and 6 due to factors other than track deviation can be suppressed, and accurate tracking control can be performed. Also,
Even if the entrance pupil is so small that the second and third light beams 5 and 6 protrude, track deviation can be detected accurately, making it possible to downsize the apparatus.

Although the embodiments of the present invention have been described above, the present invention is not limited thereto and can be further modified. For example, in the case of a disk in which tracks are arranged at equal intervals in the radial direction of the disk, the second and third light beams 5, 6 may be projected onto adjacent tracks. That is, the first
The second and third light beams 4, 5, 6 may be arranged in the radial direction of the disk 1. Furthermore, when forming a track exclusively for tracking, the second and third light beams 5 and 6 may be projected onto the track. Further, the light beams 4, 5, and 6 may be either visible light beams or non-visible light beams. Further, the objective lens 12 may be configured by a combination of a plurality of lenses. Alternatively, the scanning drive device may be constructed so that the head 3 is fixed, the disk 1 is rotated by the motor 2, and the disk 1 is sent in the radial direction to perform spiral or concentric scanning.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical disc player according to an embodiment of the present invention, FIG. 2 is a plan view illustrating a part of a first disc, and FIG.
FIG. 3 is an optical path diagram showing the optical system shown in the figure. In the symbols used in the drawings, 1 is a disk, 2 is a motor, 3 is a head, 4, 5, and 6 are light beams, 7 is a convex lens, 8 is a beam source, and 9
1 is a diffraction grating, 11 is a rotary mirror, 12 is an objective lens, 13, 14, 15 are photodetectors, 27 is a feeding device, and 28 is an entrance pupil.

Claims (1)

[Scope of Claims] 1. A light beam generation source that generates a light beam for projecting onto a recording medium disk on which information is recorded by arranging optically readable recording areas in a predetermined track form; a scanning drive device for producing a relative scanning motion between the disk and the light beam; and a first light beam based on 0th-order diffracted light and a first light beam based on positive first-order diffracted light from the light beam generated from the light beam generation source. A second light beam and a third light beam formed by negative first-order diffracted light are obtained, and when the first light beam is projected onto the center of the track on the disk, the second light beam is projected onto the center of the track on the disk. the first; such that the beam is projected offset to one side of the track; and the third light beam is projected offset to the other side of the track.
a diffraction grating for transmitting second and third light beams; a convex lens for converging the first, second, and third light beams and then making them spread out; disposed in the path of the first, second, and third light beams on the beam exit side of the convex lens for changing the radial positions of the first, second, and third light beams of the disk; a tracking mirror; and an objective disposed between the tracking mirror and the disk to converge the first, second, and third light beams incident in a spread form and project them onto the disk. a lens; first, second, and third photodetectors that detect reflected or transmitted light of the first, second, and third light beams on the disk; and the second photodetector. a comparison circuit for obtaining a difference output between the output of the second photodetector and the output of the third photodetector, and driving the mirror so as to make the difference output zero in response to the difference output of the comparison circuit. an optical reproducing device comprising: a mirror driver; the diffraction grating and the convex lens; x, the focal length of the convex lens is f, and the distance between the focal position on the exit side of the convex lens and the entrance pupil of the objective lens is L, then 1/x+1/L+f=1/ An optical reproducing device characterized in that the diffraction grating, the convex lens, and the entrance pupil of the objective lens are respectively arranged at positions where a relationship of f is established.