JPH0393049A - Multibeam optical reproducing device - Google Patents

Abstract

PURPOSE:To improve multibeam reproducing speed by storing information by N tracks between light beam spots on an optical disk and reading the information at every optical beam. CONSTITUTION:Five laser beams formed by a diffraction grating are incident upon their respective corresponding detectors 28A-28E in a photo detector 28, and are converted into voltage signals by I-V converting circuits 50-58 and moreover calculated by calculating circuits 60 and 62. Off-track correction is performed by a tracking servo circuit 36, a focus servo circuit 38, a phase compensation circuit 34, a driving circuit 40 and a rotary actuator 42, and each laser beam irradiates an information track. The voltage signals converted by the circuits 50-58 are inputted to amplifying decoder circuits 64-72, where the signals are amplified and demodulated respectively and stored in storage circuits 74-82. Thus, since the storage circuits are provided by corresponding to plural light beams respectively, the optical disk can be read out at high speed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a multi-beam optical reproducing device that reproduces an optical disc using multiple beams, and particularly relates to a multi-beam optical reproducing device that reproduces an optical disc using a multi-beam. This paper concerns improvements to multi-beam optical regenerators. [Prior art] Recording on an optical disc by irradiating an information bit string with a single light beam. Playback requires low data transfer speeds, and playback cannot be performed immediately after recording. Therefore, we recorded using multiple light beams. A multi-beam method for reproduction has been proposed. FIG. 6 schematically shows a first conventional example of an optical disk device using the multi-beam method. This is disclosed in Japanese Patent Application Laid-Open No. 117744/1983. In the figure, a large number of laser beams are output from a laser array 100. These laser beams are collimated by a collimator lens. Polarizing beam splitter. l/4 wavelength plate. The light is incident on an optical disk 104 through an optical head optical system 102 that includes an objective lens and the like. and,
Each laser beam reflected by the optical disk 104 passes through the optical head optical system 102 to the detector array 10.
6, where it is converted into an electrical signal. According to this first conventional example, compared to the case where one light beam is used, the laser array l (number of light sources of IQ.
In other words, the recording and reproducing speed increases by the number of beams. Next, FIG. 7 shows an outline of a second conventional example. This is rOPTIcAL ENGINEER)NG
J. July/ August 1983/ V
ol. 22 No. 4, P464-472
This is disclosed in . In the figure, first, during writing, a single laser beam output from a writing laser 110 is irradiated onto an optical disk 114 by an optical head optical system 112, and writing is performed using an l beam. On the other hand, during reading, the laser beam output from the reading laser 116 is converted into a multi-beam by the diffraction grating 118 provided in the optical head optical system 112, and a plurality of laser beams are sent to the optical disk 112.
is irradiated. In either case, the reflected beam from optical disk 114 is converted into an electrical signal by detector array 120. According to this second conventional example, recording is performed using one beam, but
Since reproduction is performed using multiple beams, the speed increases by the number of beams used for reproduction. Next, FIG. 9 shows an outline of a third conventional example. This is the 1988 Spring Applied Physics Association Lecture. It was announced as 28a-ZQ-2. In the figure, the laser array 13
The plurality of laser beams outputted from the optical head optical system 132 are irradiated onto the optical disk 134 . Each laser beam reflected from the optical disk 134 passes through the optical head optical system 132 to the detector array 13.
6, where it is converted into an electrical signal. In this case, in order to simultaneously irradiate a plurality of light spots onto desired tracks, the roof prism 138 provided in the optical head optical system 132 is rotated around the optical axis. According to this third conventional example, it becomes possible to perform parallel tracking for multiple spots, which could not be performed sufficiently by tracking only by lens shift. [Problems to be Solved by the Invention] However, the above-mentioned conventional techniques have the following disadvantages. First, in the first conventional example shown in FIG. The spacing between the spots is approximately 25 μm. On the other hand, the field of view with little distortion in the objective lens of the optical head optical system 102 is ±100 μm (
200μmΦ) is the limit. Therefore, in this method,
The limit is 8 beams, which also limits the data transfer rate. In contrast, in the second conventional example shown in FIG. 7, a diffraction grating is used, so data can be read by irradiating, for example, 3 to 21 light beams onto the information bit string of the optical disk 114. ．． However, in this conventional example, as shown in Fig. 8, the spot of the light beam away from the central light beam deviates from the information bit string due to mechanical accuracy errors in the kick-up feed mechanism, eccentricity of the optical disk, etc. There is an inconvenience. In the figure, focus on a light spot 152 that is a distance d away from the central beam spot 150, and assume that the kick-up feed deviates from the ideal standard 1jill54 by ΔL. At this time, the light spot 152 is an optical disc! The off-track amount Δr that deviates from the information bit string on l4 is . It is calculated by [arm length]×[deviation angle], and becomes Δr:dXtan instep=d×(ΔL/R) (1). In addition, as a standard value, d=50um (
=O, 05mm). If R=30 mm and ΔL=0.1 mm are substituted, the off-track amount Δr becomes about 0.17 μm. It is said that it is preferable that the amount of off-track is about 0.05 um or less, and sufficient reproduction cannot be performed if this state is maintained. Next, in the third conventional example shown in FIG. 9, although the off-track of the light spot is reduced, the roof prism 13
There is a disadvantage that the image rotation actuator constituted by 8 is large as a component, and the entire optical surprise is also large. The present invention has been made in view of these points, and its purpose is to satisfactorily reduce the track deviation of multi-beams generated by a diffraction grating with a small and simple configuration. Another object of the present invention is to improve the playback speed by multi-peam and obtain even better data transfer speed. [Means for Solving the Problems] One aspect of the present invention is a multi-beam optical reproducing device that reads information from a large number of tracks on an optical disc using a large number of light beams generated by a diffraction grating. The present invention is characterized in that, when there is an interval of N tracks between light beam spots, a storage means capable of storing N tracks of information is provided for each light beam from which information is to be read. Another invention provides an off-track amount detecting means for detecting an off-track amount using a beam reflected from an optical disk of a light beam other than the central beam; a rotating means for rotating the diffraction grating around a predetermined axis; The present invention is characterized by comprising a drive means for driving the rotation means in accordance with the off-track amount detected by the off-track amount detection means. According to one embodiment, the diffraction grating has a diffraction pattern in two directions. According to another aspect, a multi-beam light source that outputs a large number of light beams is used as the light source that makes the light beams enter the diffraction grating. [Function] According to the present invention, a storage means having a capacity equivalent to the number of tracks between spots on a multi-beam optical disk is provided for each light beam for signal reading. and data read out by the other beams during readout by either beam is stored in those storage means,
It is read at an appropriate timing and at a high transfer rate.
Furthermore, according to the present invention, the amount of deviation between the track and the beam at a position deviated from the center beam among the many beams generated using the diffraction grating. That is, the off-track amount is detected using a beam other than the center beam, and based on this, the diffraction grating is rotated to correct the off-track amount. Embodiments] Hereinafter, examples of a practical gallery according to the present invention will be described with reference to the accompanying drawings. First Embodiment> First, a first embodiment of the present invention will be described with reference to FIGS. 1 to 3. First, the overall configuration of the first embodiment will be explained with reference to FIG. In the figure, a diffraction grating 14 is connected to the laser beam output side of the laser diode 10 via a collimator lens l2.
A polarizing beam splitter l6 is arranged on the multi-beam output side of this diffraction grating l4. In this example, five laser beams are connected to the grating 14.
It is designed to be formed by On one beam output side of the polarizing beam brick 16, a quarter wavelength plate 18. Objective lenses or condensing lenses 20 are arranged one after the other, and a laser beam output from the objective lenses 20 is directed onto an optical disc 22 . Further, on the other beam output side of the polarizing beam splitter 16, a concave lens 24. Cylindrical drill lenses 26 are arranged one after the other, and a photodetector 28 is arranged on the beam output side of the cylindrical drill lenses 26. A laser beam is designed to form an image on each detector element of this photodetector 28. The electrical signal output side of the photodetector 28 is connected to the input side of a signal conversion processing circuit 30, and the output side of the signal conversion processing circuit 30 is connected to a readout circuit 32. Phase compensation circuit 34. Tracking servo circuit 36. They are connected to each input side of the focus servo circuit 38. Further, the output side of the phase compensation circuit 34 is connected to the input side of the rotary actuator 42 of the diffraction grating 14 via a drive circuit 40. Next, details of the signal processing portion of each of the above sections will be explained with reference to FIG. In the figure, the photodetector 28 includes detectors 28A. 28B.
28C. 28D. 28E are provided for each. Among these, the detector 28 corresponding to the central laser beam
C is 4 for tracking servo and focus servo.
The detector arm 28E is divided into two parts for controlling the rotation of the diffraction grating l4. These detectors 28A. 28B. 28C. 28D.
Each output side of 28E is connected to the input side of a current-to-voltage (hereinafter referred to as rI-VJ) conversion circuit 50, 52, 54, 56, and 58, respectively. Of these, the IV conversion circuit 54 outputs the divided outputs a, b of the detector 28C. c. t6I-V conversion circuits 54A. 54B. 54C.
54D, and the IV conversion circuit 58 receives the divided output e. IV conversion circuits 58A. Each has 58B. Then, the IV conversion circuit 54A. 54B. 54C. 54
Each output side of I-V58A.D is connected to the input side of the arithmetic circuit 60. Each output side of 58B is connected to the input side of an arithmetic circuit 62. In the six arithmetic circuits 60, the divided human power a. b, c. For d, a+b+c+
d. (a+b)-(c+d). (a+c)−(b+
The calculation d) is now performed. In addition, in the arithmetic circuit 62, the divided human power e. For f, e+f. The calculation ef is now performed. Next, each output side of the I-V conversion circuit 50, 52, 56 is as follows.
It is connected to the input side of the amplification and decoder circuits 64, 66, and 70. Also, the calculation result a+b+c+d of the calculation circuit 60
The output side of . This causes the detectors 28A, 28B. 28C28D. 2
The r-v conversion signal of 8E is sent to the amplification decoder circuit 64.66
．． 68, 70, and 72, respectively, and the signals are decoded. Next, the output sides of the memory circuits 74, 76, 78, 80, 82 are connected to the input side of the read circuit 32. Further, the output side of the calculation result (a+b)-(c+d) of the calculation circuit 60 is connected to the input side of the tracking servo circuit 36, and the output side of the calculation result (a+c)-(b+d) is connected to the focus It is connected to the input side of the servo circuit 38. Further, the output side of the calculation result ef of the calculation circuit 62 is connected to the input side of the phase compensation circuit 34. Among the above-mentioned components, the installation angle of the diffraction grating l4 is adjusted so that the five laser beam rows formed thereby are lined up on the information track of the optical disc 22. Note that the intervals between the plurality of light spots irradiated onto the optical disc 22 are 5 um or more. l○0μm
It is preferable that it is about the following. First of all, r5um or more.”
This restriction is based on the restriction of reducing the diffraction angle of the diffraction grating l4 and the restriction on the arrangement interval of each detector in the photodetector 28. The diffraction angle θ of the diffraction grating 14 is approximately the wavelength of light. For the period P of the grating, θ= sin-' (L/P) ---・=(2
It is represented by 1. For this θ, on the optical disk 22
Distance from which the +1st order light spot separates from the secondary light spot.
That is, the spot interval d is d = f o t a n θ, where f0 is the focal length of the objective lens 20.
・・・・・・−・・・・・・・・・・・・(3)
Here, as a standard value, n=0.78 μm. P=
200μm. Substituting fo=4mm, d=15.6
It becomes μm. In design, it is easy to increase the grating period P in response to decreasing the spot spacing d. However, in this case, the number of spots of the diffraction grating l4 included in the laser beam spot and irradiated with it is reduced. For this reason, the width of the diffraction angle θ becomes wider, and the beam spot diameter on the optical disk 22 becomes larger. Due to this restriction, it is preferable that the spot interval d is approximately 5 μm or more. On the other hand, when the spot interval d is widened to about 100 am, the objective lens 2 for the beam tilted from the central optical axis
0 aberration has a negative effect. Therefore, the spot spacing d
is preferably 100 μm or less. Next, the I-V conversion circuits 50 to 5 of the signal conversion processing circuit 30
8 is configured to have a wide band so that it can detect and convert up to the frequency band of the information signal. In addition, the amplification decoder circuit 64
~72 is a known signal amplification. This is a signal demodulation circuit in which the I-V converted signal is demodulated into digital data format. Furthermore, memory circuits 74 to 82
are each configured to be able to store data for approximately one revolution of the optical disc 22. Next, the tracking servo and focus servo as an optical head are
Using the central laser beam, the detection is performed using a well-known four-division method using a detector 28C. That is, the calculation result of the calculation circuit 60 (a+ne)−(c+d)
Tracking servo is performed by the tracking servo circuit 36 based on the calculation result (a+C) - (b+d)
Focus servo is performed by the focus servo circuit 38 based on this. Next, the above-mentioned diffraction grating 14 is attached to the rotary actuator 4.
2, so that the above-mentioned off-track correction of the beam spot can be performed. FIG. 3 shows the effect of such off-track correction. In the figure, a rotary actuator 42 has a magnetic circuit and an electromagnetic coil similar to, for example, a known moving coil ammeter, and is designed to produce minute angular motion. The diffraction grating 14 is configured to be slightly rotated or oscillated by the rotary actuator 42 about a suitable rotation axis 84 in the direction of the arrow Fl. Note that, as illustrated, the rotation center of the diffraction grating 14 does not have to be the center of the diffraction grating l4. When such rotation is performed, the O-order light beam spot 86 traveling straight is not affected at all, and the diffracted light beam spot 8
8.90 is arrow F2. As shown by F3, the diffraction grating 14 rotates by the rotation angle. By this, the first (1st
The off-track correction shown in Equation 1 is now performed. Next, the off-track amount of the beam spot is detected using a laser beam other than the center beam. That is, the dividing direction of the two-divided detector 28H that receives the fifth laser beam is set to be orthogonal to the direction in which the information bit moves when it goes off-track. Therefore, the difference e-f between the detection outputs represents the amount of off-track, and the negative feedback servo circuit is configured so that this becomes small. Next, the overall operation of the above embodiment will be explained. Laser die talent
The laser beam output from the dot l○ is collimated by the collimator lens l2, and further enters the diffraction grating 14. In the diffraction grating 14, a plurality of beams are formed by diffraction of the incident beam, and these beams are passed through a polarizing beam splitter 16, a quarter-wave plate 18, and a polarizing beam splitter 16. Objective lens 20
are irradiated onto the information tracks of the optical disc 22 through the respective channels. The plurality of laser beams reflected from the information track are transmitted through an objective lens 20.a quarter wave plate 18. Polarizing beam splitter 16. The detectors 28A to 28 of the photodetector 28 are
28H respectively. These detectors 28A-2
The outputs of 8H are each converted into a voltage signal by IV conversion circuits 50 to 58, and further the above-mentioned calculations are performed in calculation circuits 60 and 62. Then, using the calculation output from the calculation circuit 60, the tracking servo circuit 36. A focus servo circuit 38 performs tracking of the optical head and control of focus. Further, the calculation output from the calculation circuit 62 is manually inputted to the drive circuit 40 after phase compensation by the phase compensation circuit 34, and the diffraction grating l4 is driven by the rotary actuator 42 based on the drive output. by this,
The above-described off-track correction is performed, and each laser beam is properly irradiated onto the information track of the optical disc 22. On the other hand, the signals read out by these laser beams are first converted into voltage signals by IV conversion circuits 50 to 58, and then input to amplification and decoder circuits 64 to 72, where they are amplified and amplified. Demodulation is performed for each. The demodulated data is then stored in the recording circuits 74 to 82, respectively, and read out and output as appropriate by the readout circuit 32. For example, assume that five beams are irradiated to the first to fifth tracks, respectively. At this time, the data of the first track to be read is outputted via the readout circuit 32 at the same time as the data is read by the first beam. On the other hand, the data of the second to fifth tracks read by the second to fifth beams are stored in the storage circuits 76 to 824, respectively. The data of these second to fifth tracks are outputted from the reading circuit 32 at a high transfer rate after the optical disc 22 rotates once and the reading of the l-th track is completed. Note that on commonly used spiral optical discs, track jumps are not required when reading up to the 6th track in succession, but when reading tracks 7 to 9, jumps from tracks 1 to 4 are required. Let's do it. The same goes for the subsequent tracks. As described above, according to the first embodiment, since the memory circuit is provided corresponding to each of the plurality of light beams, the data is normally arranged sequentially to match the reading using one light beam. read optical discs,
It can be done at high speed. Furthermore, if the data is arranged on the optical disk in accordance with the arrangement of the reading beam, 1
Even for data whose length is within one revolution of the track, the reading speed is increased by the number of reading beams. <Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. In this practical example, as the diffraction grating l4, 2
This uses a material that has a diffraction pattern in the direction.
The beam spots SA on the optical disc 22 are arranged as shown by circles in the figure. Note that a line 92 in the figure represents an information track. According to this second embodiment, a large number of beam spots can be generated, and the reading speed can be improved accordingly. Note that there are restrictions on beam spacing and... Off-track correction by rotation of the diffraction grating is the same as in the first embodiment described above. However, in this embodiment, the distance of the light spot away from the central spot. That is, the spot interval d (see equation (3)) can be reduced, and as a result, the off-track amount can be reduced. Furthermore, in the illustrated example, each light beam is separated by three tracks. Therefore, as a recording circuit (see FIG. 2) for storing demodulated data, one having a capacity of three tracks is used. A standard optical disc has approximately 17KBytes.
The capacity is approximately X 3 (trucks). this is,
The standard memo +7 I'C is equivalent to 100 units, so it is fully achievable. Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, in addition to using the diffraction grating having a diffraction pattern in two directions as used in the second embodiment, a laser diode array having three light emitting sources is used in place of the laser diode IO. That is, in FIG. 5, beam spot SB is a diffracted light spot generated based on the first laser beam, and beam spot SC is a diffracted light spot generated based on the second laser beam. , the beam spot SD is a diffracted light spot generated based on the third laser beam. Also, beam spot SBC. S.C.
C. SDC is the central light spot. If an attempt is made to further increase the number of optical spots using the second embodiment described above, the optical power distributed to each spot will become smaller. However, in this third embodiment, since the number of light emitting sources is increased, such inconvenience does not occur. As described above, according to the embodiments of the present invention, the off-track correction that occurs in the multiple beams generated by the diffraction grating is well compensated for by the small and simple rotary actuator, and the data read by the multiple beams is Since the information is temporarily stored in the memory circuit and read out at appropriate timing at a high transfer rate, the playback speed of optical discs can be greatly improved. Other Embodiments> The present invention is not limited to the above-described embodiments; for example, in the first embodiment, a case was shown in which five laser beams are generated by the diffraction grating; The number of beams can be set as necessary. Also, instead of using all the beams generated by the diffraction grating, you can select and use any of the 6 beams. Furthermore, it can be used as a photodetector for tracking servo. Various design changes are possible within the scope of the present invention, such as providing a separate focus servo. [Effects of the Invention] As explained above, according to the present invention, since the read data is stored in the storage means, the reproduction speed by the multi-beam is improved and an even better data transfer speed can be obtained. In addition, since the diffraction grating is rotated around a predetermined axis using a rotation means, it is possible to effectively reduce the track deviation of the multi-beams generated by the diffraction grating with a small and simple configuration. effective.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention, FIG. 2 is a circuit block diagram showing a signal processing portion of the first embodiment, and FIG. 3 is a state of off-track correction in the first embodiment. FIG. 4 is an explanatory diagram showing the spot arrangement on the optical disc in the second embodiment of the present invention. FIG. 5 is an explanatory diagram showing the spot arrangement on the optical disc in the third embodiment of the invention. Figure 6 is an explanatory diagram showing the first conventional example, and Figure 7 is an explanatory diagram showing the first conventional example.
The figure is an explanatory diagram showing the second conventional example, FIG. 8 is an explanatory diagram showing off-track in the second conventional example, and FIG. 9 is an explanatory diagram showing the off-track in the second conventional example.
FIG. 2 is an explanatory diagram showing a conventional example. IO...Laser diode, l2...Collimator lens, l4...Diffraction grating, l6...Polarizing beam splitter, 18-1/4 wavelength plate, 2o...Objective lens, 22... Optical disc, 24...Concave lens, 2
6... Cylindrical canor lens, 28... Photodetector, 30... Signal conversion processing circuit, 32... Readout circuit, 36... Tracking servo circuit, 38
... Focus servo circuit, 40... Drive circuit (drive means), 42... Rotation actuator (rotation means)
, 74.76.7B. 80.82...Memory circuit (memory means).t Figure 3 Figure μ Figure 6

Claims (4)

[Claims] (1) In a multi-beam optical reproducing device that reads information from many tracks on an optical disk using many light beams generated by a diffraction grating, when there is an interval of N tracks between the light beam spots on the optical disk. A multi-beam optical reproducing device characterized in that a storage means capable of storing N tracks of information is provided for each light beam from which information is read. (2) In a multi-beam optical reproducing device that uses a large number of light beams generated by a diffraction grating to read out information on a large number of tracks on an optical disk, the light beams other than the central beam are read out using reflected beams from the optical disk. an off-track amount detection means for detecting an off-track amount; a rotation means for rotating the diffraction grating around a predetermined axis; and a drive for driving the rotation means in response to the off-track amount detected by the off-track amount detection means. A multi-beam optical reproducing device characterized by comprising: a driving means for. (3) A multi-beam optical reproducing device according to claim 1 or 2, characterized in that a diffraction grating having diffraction patterns in two directions is used as the diffraction grating of the multi-beam optical reproducing device. (4) A multi-beam light reproducing device according to any one of claims 1 to 3, characterized in that a multi-beam light source that outputs a large number of light beams is used as the light source that makes the light beam incident on the diffraction grating. Beam light regenerator.