JPS6313265B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus that performs recording or reproduction using a plurality of laser beams having different wavelengths.

For example, a recording area (pit) is formed by projecting an Ar laser beam onto a recording medium with a reflective metal layer provided on a glass substrate to evaporate the metal layer, and by following the recording beam, −
It is conceivable to project a Ne laser beam as a reproduction beam and perform monitoring at the same time as recording. In order to simplify such a recording device capable of simultaneous monitoring, it is desirable that most of the optical system be shared by the recording beam and the reproduction beam. However, even if they are simply shared, it becomes difficult to separate the two beams, and, for example, the reflected light of the recording beam, that is, the return beam, returns to the recording laser light source, making it difficult to perform good recording. Although the relationship between the recording beam and the reproduction beam has been described above, a similar problem occurs when the wavelength of the main reproduction beam and the wavelength of the control beam for tracking or the like differ during reproduction.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical recording or reproducing apparatus that can perform recording or reproducing well using a plurality of laser beams having different wavelengths.

To achieve the above object, the present invention includes a first laser beam sending device for projecting a first recording or reproducing laser beam of a first wavelength onto a recording medium; a second laser beam sending device for projecting a second recording or reproducing laser beam of two wavelengths onto the recording medium; , a polarizing prism type beam splitter configured to allow the second laser beam incident at an angle of 90 degrees with respect to the first laser beam to pass therethrough; the beam splitter and the recording medium; The beam splitter is disposed in the optical path of the first and second laser beams between the recording medium and the recording medium, and the reflected light of the first laser beam on the recording medium is reflected by the beam splitter to form the first laser beam. approximately the first wavelength in order to limit the return of the second laser beam to the beam delivery device and to allow the reflected light of the second laser beam on the recording medium to substantially pass through the beam splitter. An optical recording or reproducing device characterized by comprising a quarter-wave plate having a thickness determined based on a wavelength that is approximately the least common multiple of the second wavelength. It is.

According to the above invention, the thickness of the 1/4 wavelength plate is
Since the wavelength was determined based on the least common multiple of the wavelength of
It is now possible to circularly polarize the light with a quarter-wave plate to limit the return to the laser beam delivery device.
In addition, it becomes possible to circularly polarize the reflected light of the second laser beam on the recording medium by the quarter-wave plate so that it passes through the beam splitter. Therefore, it is possible to prevent the reflected light of the first laser beam from returning to the first laser beam sending device and destabilizing the sending of the first laser beam. Furthermore, since a polarizing prism type beam splitter is used to integrate and separate a plurality of light beams, it becomes possible to share the optical system and simplify the apparatus. Moreover, it becomes easy to maintain a constant positional relationship between the first laser beam and the second laser beam on the recording medium.

Next, embodiments of the present invention will be described with reference to FIGS. 1 to 4.

The optical disk recording and reproducing apparatus shown in FIG.
As a recording medium, it has a disk 3 consisting of a transparent glass substrate 1 and a reflective metal layer 2 such as chrome. Furthermore, a first laser beam sending device 5 comprising an Ar laser light source and an optical modulator that sends out a recording beam 4 with a first wavelength λ ₁ as a first laser beam, and a second laser beam sending device 5 as a second laser beam. a second He-Ne laser light source that emits a reproduction beam 6 of wavelength λ ₂ ;
It has a laser beam sending device 7. Between the first laser beam sending device 5 and the disk 3,
a convex lens 8 for making point _F1 a virtual light source, a fixed mirror 9, a first beam splitter 10,
A quarter-wave plate 11, a rotating mirror 12, and a converging objective lens 13 are provided between the second laser beam sending device 7 and the disk 3, with point _F2 serving as a virtual light source. and a diffraction grating 17 to obtain tracking beams 15 and 16.
, a reproduction beam position adjustment mirror 18 , a second beam splitter 19 , a first beam splitter 10 , a quarter wavelength plate 11 , a rotating mirror 12 ,
An objective lens 13 is arranged.

In order to perform reproduction and beam position detection using a reflection method, reflected lights 6a and 15 of beams 6, 15, and 16 are used.
A photodetecting device 20 consisting of a photodiode is provided in the optical path of a and 16a. This photodetecting device 20 has a reproducing photodetector 21 and a pair of beam position detecting photodetectors 22 and 23.

Reference numeral 24 denotes a mirror drive device for driving the rotary mirror 12, which is a mirror having a known galvanometer configuration, which is mainly used during main reproduction other than simultaneous monitoring. Reference numeral 25 denotes a drive device that changes the beam position adjustment mirror 18, which changes the mirror 1 in response to a control signal.
This is to adjust the angular position of 8.

Scanning for creating a relative scanning movement between the beams 4, 6, 15, 16 sent out from the recording/reproducing head 26 shown surrounded by dotted lines and the disk 3 to perform scanning in the form of a spiral or concentric track. As driving devices, a disk rotation drive device 27 and a feed drive device 28 for feeding the head 26 in the radial direction of the disk 3 are provided. The disk rotation drive device 27 includes a disk motor 29 and a turntable 3.
0 and a clamper 31, the feed drive device 28
are the feed motor 32, the feed screw 33, and the feed screw 33.
It consists of a screw hole (not shown) on the head side that is screwed into the head 26, and a guide member (not shown) that stops the head 26 from rotating and guides it in the radial direction.

A reproducing circuit 34 is connected to the reproducing photodetector 21, and is composed of an amplifier, a demodulating circuit, etc., and sends a reproduced signal to a monitor device (not shown). 35 is a differential amplifier for forming a beam position control signal, the positive input terminal of which is coupled with the first beam position detection photodetector 22, and the negative input terminal of which is coupled with the second beam position detection light detector 22; A detector 23 is coupled. 36 is a low pass filter;
The high frequency component corresponding to the recording pit is removed from the signal obtained from the differential amplifier 35, and only the component corresponding to the track shift is extracted. Reference numeral 37 denotes a changeover switch, which is connected to contact a for simultaneous monitoring in recording mode, and to contact b for playback mode. Reference numeral 38 is a drive amplifier, which forms a signal for driving the mirror displacement drive device 25 based on the output of the low-pass filter 36.

The 1/4 wavelength plate 11 is the disk 3 of the recording beam 4.
The reflected light 6a of the reproduction beam 6 and the tracking beams 15 and 16 is circularly polarized so as to prevent the reflected light from passing through the beam splitter 10 and reaching the first laser beam sending device 5 again. , 15a, 16a, the beam splitter 10
The thickness is set to allow circularly polarized light to pass through. That is, the thickness of the quarter-wave plate 11 is determined based on the least common multiple of the wavelength λ ₁ (4880 Å) of the recording beam 4 and the wavelength λ ₂ (6328 Å) of the reproduction beam 6.
In this example a crystal of approximately 0.5 mm thickness is used. By the way, the least common multiple of λ ₁ and λ ₂ is found to be 0.386 mm, and even if this is substituted into the following formula for determining the thickness d of the quarter-wave plate 11, d is 0.5 mm.
It doesn't become mm.

d ₍ n _X − n _Y ) = λ _/ 4 d = λ _/ 4 (n is the refractive index of approximately 1.553, n _Y is the refractive index of the crystal plate in the Y-axis direction of approximately 1.544, and λ is the wavelength (mm).

This is because the least common multiple was determined in a simplified manner in this embodiment. That is, in this example, λ ₁
is 5000Å, λ ₂ is 6000Å, and the least common multiple wavelength λ is 18000Å, and this 18000Å is (1)
Substituting into the formula, d becomes 0.5 mm. 1/4 wavelength plate 1
1 is set as described above, the reflected light from the disk 3 of the recording beam 4, that is, the return beam, is incident on the polarizing prism type beam splitter 10 consisting of a pair of prism blocks 10a and 10b and a dielectric multilayer film 10c. Even if the laser beam is not reflected in the direction of the first laser beam transmitting device 5, it is substantially no longer reflected. Further, it becomes possible to pass the reflected lights 6a, 15a, 16a of the reproduction beam 6 and the tracking beams 15, 16.

As shown in FIG.
The mirror 18 is supported by a fixing part 52 via the fixing part 52, and the angle a of the mirror 18 with respect to the fixing part 52 can be changed. More specifically, a screw hole 54 is provided in an arm 53 that is integral with the mirror mounting portion 50 and extends horizontally, and a screw 55 screwed into the hole presses the fixing portion 52 through a split groove 56. are doing. Therefore, when the screw 55 is moved forward and backward by the motor 57, the arm 53 rotates around the portion 51,
The angle a of the mirror 18 with respect to the fixed part 52 changes.

The geometrical positional relationship of the recording beam 4, the reproducing beam 6, and the tracking beams 15 and 16 is such that in a normal tracking state, the spot of each beam on the disk 3 is as shown by diagonal lines in FIG. It has been decided. That is, in the track 48, the recording beam 4 is placed first, followed by the first tracking beam 15, the reproduction beam 6, and so on.
The second tracking beams 16 are arranged in sequence. Note that when the reproduction beam 6 is located at the center of the track 48 consisting of pits 49, the first tracking beam 15 is projected toward the outer circumference of the track, and the second position detection beam 16 is projected toward the inner circumference of the track 48. It is projected off to the side.

When performing recording and simultaneous monitoring with the apparatus shown in FIG. ,1
5 and 16 onto the disk 3, and the metal layer 2 is evaporated by the modulated recording beam 4 with high energy to form pits 49 shown in FIG. 3, which serve as recording areas. Since the unmodulated reproduction beam 6 with low energy follows the recording beam 4, the recording pit 4
9 can be read sequentially, and an output corresponding to the pit 49 can be obtained from the reproduction photodetector 21. By the way, even if the positional relationship between the recording beam 4 and the reproduction beam 6 is fixed in advance, temperature changes,
There is a risk that the positional relationship between the two may shift due to changes over time. However, in this device, the tracking beam 1
5 and 16, the deviation is detected and corrected. That is, since the tracking beams 15 and 16 have a fixed positional relationship with respect to the reproduction beam 6, if the center of the spot of the reproduction beam 6 coincides with the center of the track, the pair of tracking beams 1
5 and 16 protrude from the pit 49 by the same amount, and a pair of beam position detection photodetectors 22 and 23
The outputs of the differential amplifier 35 become equal, and the output obtained from the differential amplifier 35 is zero. On the other hand, if the spot of the reproduced beam 6 deviates to the outer circumferential side of the track 48 in the state shown in FIG. The output of the photodetector 23 is larger than that of the differential amplifier 3.
5 produces a positive output. On the other hand, if the spot of the reproducing beam 6 shifts toward the inner circumferential side of the track 48 in the state shown in FIG. 3, a negative output is generated from the differential amplifier 35. Therefore, a signal corresponding to the track deviation can be obtained at the output stage of the low-pass filter 36 as shown in FIG. Since the contact a of the switch 37 is on during simultaneous monitoring, the output of the low-pass filter 36 is supplied to the motor 47 of the drive device 25 via the drive amplifier 38, and the mirror is connected so that the output of the filter 36 becomes zero. 18 is displaced. That is, when the motor 47 rotates forward, the screw 45 advances, the arm 43 is displaced counterclockwise with respect to the fixed part 42, and the angle a of the mirror 18 becomes smaller. If the motor 47 rotates in the opposite direction, the operation will be opposite to the above. If the beam position adjustment mirror 18 is displaced in this way, the recording beam 4
beam 6 of the reproduction system without changing the spot position of
It becomes possible to change only spots 15 and 16, and it becomes possible to accurately reproduce the track formed by the recording beam 4.

When the apparatus shown in FIG. 1 is used as a reproducing machine, the projection of the recording beam 4 is stopped and the switch 3
7 is inserted into contact b, and the reproduction beam 6 and tracking beams 15 and 16 are projected. This results in
As in the case of simultaneous monitoring, a reproduced output is obtained, and a beam position detection signal is also obtained. In this case, the beam position detection signal is applied to the drive coil of the rotating mirror drive device 24 by the switch 37, and the rotating mirror 12 is rotated at a rotation angle in response to the control signal, so that the spot of the reproduced beam 6 is positioned on the track. Controlled to match the center.

As is clear from the above, according to this example,
It becomes possible to perform recording and reproduction simultaneously using a common optical system, which not only simplifies the configuration but also enables monitoring with good simultaneity.

In addition, since the thickness of the quarter-wave plate 11 was determined based on the thickness of the least common multiple of λ ₁ and λ ₂ , the wavelength λ ₁ ,
It becomes possible to rotate the plane of polarization almost optimally for the beam of λ ₂ .

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, 1/4 with substances other than crystal
A wavelength plate 11 may also be formed. Alternatively, the optical path of the recording beam 4 and the optical path of the reproducing beam 6 may be reversed. A mirror 18 is placed in the optical path of the recording beam 4.
By moving the recording beam 4 and adjusting the spot position of the recording beam 4, the positional relationship between the recording beam 4 and the reproduction beam 6 may be set to a reproducible state. Alternatively, the radial feeding may be accomplished by feeding the disk 3 with the head 26 fixed. Furthermore, since fluctuations in the positional relationship between the reproduction beam 6 and the recording beam 4 do not occur frequently, the output of the filter 36 may be temporarily stored in a capacitor or the like, and the drive device 25 may be controlled by this storage. good. It is also applicable to a reproduction-only machine. In this case, for example, beam 4 is used as a tracking or focus control beam.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a disk recording and reproducing apparatus according to an embodiment of the present invention, FIG. 2 is a front view showing a mirror displacement drive device, and FIG. 3 is a plan view showing the relationship between a disk track and a beam. FIG. 4 is a characteristic diagram showing the relationship between track deviation and filter output. In addition, in the symbols used in the drawings, 3
is a disk, 4 is a recording beam, 5 is an Ar laser light source, 6 is a reproduction beam, 7 is a He-Ne laser beam,
10 is a first beam splitter, 11 is a 1/4 wavelength plate, 12 is a rotating mirror, 13 is an objective lens, 1
5 and 16 are tracking beams, 18 is a beam position adjustment mirror, 21 is a reproduction photodetector, 22,
23 is a photodetector for beam position detection, 24 is a rotating mirror drive device, 25 is a mirror displacement drive device, 26
27 is a disk rotation drive device, and 28 is a feed drive device.

Claims (1)

[Claims] 1. A first laser beam transmitting device for projecting a first recording or reproducing laser beam of a first wavelength onto a recording medium, and a second laser beam of a second wavelength different from the first wavelength. a second laser beam sending device for projecting a second laser beam for recording or reproduction onto the recording medium; a polarizing prism type beam splitter configured to allow the second laser beam incident at an angle of 90 degrees with respect to the laser beam to pass therethrough; is arranged in the optical path of the first and second laser beams, and the reflected light of the first laser beam on the recording medium is reflected by the beam splitter and sent to the first laser beam sending device. approximately the first wavelength and approximately the second wavelength to limit the return of the second laser beam and to allow reflected light of the second laser beam on the recording medium to substantially pass through the beam splitter. An optical recording or reproducing device, comprising: a quarter-wave plate having a thickness determined based on a wavelength that is the least common multiple of the wavelength. 2. The optical recording or reproducing apparatus according to claim 1, wherein the first laser beam is a recording laser beam, and the second laser beam is a reproducing laser beam. 3 The first laser beam has a wavelength of approximately 4880 Å.
Claim 1, wherein the second laser beam is an Ar laser beam, the second laser beam is a He-Ne laser beam with a wavelength of about 6328 Å, and the quarter-wave plate is a quartz plate with a thickness of about 0.5 mm. optical recording or reproducing device.