JP2005044448A - Optical information reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce reproduction errors in an optical information reproducing device using holographic recording. <P>SOLUTION: This optical information reproducing device reproduces optical information recorded as interference fringes on the recording layer of a disk D. The device comprises laser device 21 for emitting a laser beam B1 used for reproducing the optical information, a mirror M2 and a lens L3 for converging the laser beam B1 on the interference fringes on the disk D, a photodetector 31 for irradiating the disk D with a laser beam, and receiving and converting a generated diffractive light B6 into an electric signal, a signal processing circuit 40 for decoding information based on the electric signal output from the photodetector 31, and a controller 50 which is a wavelength adjusting circuit for adjusting the wavelength of the laser beam B1 emitted from the laser device 21 based on the electric signal emitted from the photodetector 31. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical information reproducing apparatus that records information on an optical information recording medium using holography.

  In recent years, an information recording apparatus (optical information reproducing apparatus) using holography has been developed as a technique for recording information with high density. Holographic recording is generally performed by superimposing light having image information and reference light inside a recording medium and recording interference fringes formed at that time on the recording medium. When reproducing the recorded information, the recording medium is irradiated with reference light, and the light is diffracted by the interference fringes to reproduce the image information.

  As a conventional holographic recording method, a method using a recording medium in which an optical information recording layer for recording optical information is interposed between two transparent substrates is known. In this method, reference light and information light carrying information on a recording medium are irradiated at a predetermined angle, and interference fringes are generated in the optical information recording layer due to interference between the reference light and the information light. The interference fringes are recorded as a physical or chemical change in the constituent components of the optical information recording layer. The information recorded on the optical information recording layer is reproduced by irradiating the recording medium with reference light, diffracting and interfering the reference light with the interference fringes of the optical information recording layer, and reproducing the reproduction light having the same information as at the time of recording. This is done by creating and reading this.

  In addition, an optical information recording layer for recording optical information is interposed between two transparent substrates, such as CD (Compact Disc) and DVD (Digital Video Disk), and reflected on the outer side of one transparent substrate. A method using a recording medium provided with a layer has also been used. In this method, reference light and information light carrying information are irradiated from the opposite side of the reflective layer, and interference fringes are generated in the optical information recording layer due to interference between the reference light and the information light. Information reproduction is performed by the same method as described above, but reproduction light is also read on the opposite side of the reflective layer.

  By the way, in the holographic recording, the output of the laser beam used is shifted between the time of recording and the time of reproduction, so that the reproduction output is rapidly deteriorated. FIG. 13 is a graph showing changes in reproduction output due to wavelength shift, where the horizontal axis indicates the wavelength shift logarithmically, and the vertical axis indicates the signal level by relative intensity. As shown in FIG. 13, in the reflection type, the signal level rapidly deteriorates when the wavelength shift is near 0.1 nm, and even in the transmission type, the signal level rapidly deteriorates when the wavelength shift is near 1 nm. To do.

On the other hand, the wavelength of the laser beam is not necessarily constant depending on the temperature of the transmitter. For this reason, even with one optical information reproducing apparatus, there is a possibility that the wavelength of the laser beam is shifted between recording and reproduction. Further, when the optical information reproducing apparatus at the time of recording is different from the apparatus at the time of reproducing, the possibility that the wavelength is shifted further increases.
Therefore, in the conventional optical information reproducing apparatus, there is a possibility that a signal level (output) is lowered due to a difference in wavelength between recording and reproduction, and an information reproduction error is likely to occur.

For this reason, a method for stabilizing the temperature and injection current of a semiconductor laser in a hologram recording / reproducing apparatus has been invented (see, for example, Patent Document 1).
JP-A-8-202246

However, the above-described control of the semiconductor laser does not take into account the wavelength difference between recording and reproduction, so that there remains a problem that the signal level (output) is lowered and an information reproduction error may occur. It had been.
From such a background, the present invention has been made, and an object of the present invention is to provide an optical information reproducing apparatus capable of reducing information reproduction errors.

  In order to solve the above-described problems, the present invention provides an optical information reproducing apparatus for reproducing optical information recorded as interference fringes on a recording layer of an optical information recording medium, and a laser that emits a laser beam used for reproducing optical information Device, condensing optical system for condensing the laser beam on interference fringes on the optical information recording medium, and receiving the diffracted light generated by irradiating the optical information recording medium with the laser beam and converting it into an electrical signal And a signal processing circuit for decoding information based on the electrical signal output from the photodetector, and adjusting the wavelength of the laser beam emitted by the laser device based on the electrical signal output from the photodetector And a wavelength adjusting circuit for performing the above operation.

  According to such an optical information reproducing apparatus, the wavelength of the laser beam emitted from the laser apparatus is adjusted based on the electrical signal output from the photodetector. That is, since the recorded information is reproduced and the wavelength is adjusted according to the signal of the reproduced information, it is possible to reproduce the information under favorable conditions that match the wavelength when recorded on the optical information recording medium.

  During recording, it is not necessary to adjust the wavelength of the laser beam, and the laser wavelength of the laser device may be controlled to be constant. For example, a temperature sensor that measures the temperature of the transmitter of the laser device and a temperature control device that heats and cools the transmitter according to the temperature measured by the temperature sensor can be provided.

  The wavelength adjusting circuit is preferably configured to adjust the wavelength of the laser beam based on the intensity of the light detected by the photodetector so that the intensity is increased.

  In holographic recording, if there is a difference in wavelength between recording and reproduction, the amount of light received by the light receiver decreases. However, in the optical information reproducing apparatus of the present invention, the wavelength of the laser beam is controlled so that the amount of light detected by the photodetector is increased. As a result, the signal reproduction error rate can be reduced as a result of the improved SN ratio.

  Alternatively, the wavelength adjustment circuit has an error rate calculation unit that calculates an error rate from the information decoded by the signal processing circuit, and the laser beam is reduced so that the error rate calculated by the error rate calculation unit is small. It can also be configured to adjust the wavelength.

  In such an optical information reproducing apparatus, the final error rate is monitored and the wavelength is adjusted so as to reduce the error rate. Therefore, the reliability of the optical information reproducing apparatus can be further improved.

  In the optical information reproducing apparatus described above, the laser device has a semiconductor laser element as a transmitter, the semiconductor laser element is provided with temperature control means, and the wavelength adjustment circuit is provided with the temperature control means. The wavelength of the laser beam is adjusted by applying a heating or cooling signal to the laser beam.

  Thus, when a semiconductor laser element is used as the transmitter of the laser device, the wavelength of the laser beam changes depending on the temperature of the transmitter, so by adjusting the temperature of the semiconductor laser element with the temperature control device, The wavelength of the laser beam can be adjusted.

  In the measuring instrument, the laser device includes a wavelength conversion device that converts the wavelength of the laser beam, and a temperature control unit provided in the wavelength conversion device, and the wavelength adjustment circuit includes the temperature control unit. The wavelength of the laser beam is adjusted by applying a heating or cooling signal to the laser beam.

  Thus, the wavelength of the laser beam output from the wavelength conversion device can be adjusted by adjusting the temperature of the wavelength conversion device with the temperature control means.

Furthermore, the laser apparatus includes a wavelength conversion device that converts the wavelength of the laser beam, and a pressure control unit that changes a pressure applied to the wavelength conversion device,
The wavelength adjusting circuit is configured to adjust the wavelength of the laser beam by giving a pressure signal to the pressure control unit.

  Further, a Peltier element can be used as the temperature control means, and a piezo element can be used as the pressure control means.

  According to the present invention, data reproduction errors can be reduced.

Next, embodiments of the present invention will be described with reference to the drawings as appropriate.
[First Embodiment]
FIG. 1 is a perspective view of a transmission type holographic information recording / reproducing apparatus as an example of the optical information reproducing apparatus of the present invention, and FIG. 2 is a schematic diagram of the transmission type holographic information recording / reproducing apparatus. It is.
As shown in FIG. 1, a transmission-type holographic information recording / reproducing apparatus (hereinafter simply referred to as “information recording / reproducing apparatus”) 1 includes an optical information recording disk (optical information recording medium) D (hereinafter simply referred to as “disc D”). A motor 10 that rotates and drives the disk D, an irradiation unit 20 that irradiates the disk D with a laser beam, a light receiving unit 30 that receives light transmitted through the disk D, a signal processing circuit 40, and a controller 50. It is configured.

  The disc D is configured by interposing an optical information recording layer (hereinafter simply referred to as “recording layer”) for recording hologram information between two transparent substrates (not shown).

  The motor 10 has a rotating spindle 11, and a chuck 12 that locks the disk D through a hole D <b> 1 formed in the center of the disk D is provided at the tip of the spindle 11.

The irradiation unit 20 mainly includes a laser device 21, a beam splitter 22, and a spatial light modulator 23.
In FIG. 1, the laser device 21 is disposed below the disk D and offset a predetermined distance from the central axis of the spindle 11 (the center of the disk D) so as to emit a laser beam parallel to the radial direction of the disk D. ing. The laser device 21 has a semiconductor laser 210 as shown in FIG. The semiconductor laser 210 has a semiconductor laser element 211 as a transmitter. The semiconductor laser element 211 is provided with a Peltier element 212 as temperature control means in close contact with the semiconductor laser element 211. The semiconductor laser 210 is provided with a temperature sensor 213 in close contact therewith. The temperature sensor 213 is connected to the controller 50 and outputs a detected temperature signal to the controller 50.

A collimator lens L1, a wave plate 24, and a mirror M1 are installed on the optical path of a laser beam (hereinafter, also simply referred to as “light beam”) B1 emitted from the laser device 21. ing.
The mirror M1 is disposed so as to reflect the light beam B1 in parallel and perpendicularly to the disk D and to emit the light beam B2.

  The beam splitter 22 is installed on the optical path of the light beam B2, and, as shown in FIG. Divide. The beam splitter 22 is configured by, for example, two prisms facing each other at a slight interval.

As shown in FIG. 4, the spatial light modulator (SLM) 23 is an element that displays input digital data as a two-dimensional lattice pattern. For example, a lattice point 23a that allows light to pass through. ON / OFF information such as “1” and “0” for the grid point 23b through which light passes is arranged in a grid pattern. The spatial light modulator 23 is disposed on the optical path of the information light B4 separated by the beam splitter 22, and expresses information as a pattern on the cross section of the information light B4 by the lattice pattern described above.
Further, on the optical path of the information light B4, a lens L2 for condensing the information light B4 on the recording layer of the disk D is disposed next to the spatial light modulator 23.

In order to collect the reference light B3 (B5) at the same position where the information light B4 is collected on the recording layer of the disk D, a mirror M2 and a lens L3 are disposed on the optical path of the reference light B3. ing. The lens L3 is provided on the optical path of the reference light B5 after the reference light B3 is reflected by the mirror M2.
The signal light B4 and the reference light B5 interfere with each other on the recording layer of the disk D, and optical information is recorded as spot-like interference fringes S.
The mirror M2 and the lens L3 correspond to a condensing optical system referred to in the claims.

  The mirror M1, the beam splitter 22, the mirror M2, the spatial light modulator 23, and the lenses L2 and L3 are fixed to the slider 25. The slider 25 is slidably engaged with a slider rail 26 parallel to the radial direction of the disk D. The irradiation unit 20 is provided with an actuator 27 (see FIG. 2) for moving the slider 25. By moving the slider 25 along the slide rail 26 by the actuator 27, recording of the interference fringes S in the radial direction of the disk D is performed. The position can be changed. The actuator 27 is controlled by the controller 50.

The light receiving unit 30 includes a lens L4 disposed on the optical path of the diffracted light B6 that has passed through the disk D and a photodetector 31 disposed thereafter.
The lens L4 is a collimator lens that collimates the diffracted light B6 transmitted through the disk D.
The photodetector 31 is configured by, for example, a CCD (Charge-Coupled Device) having a grid-shaped light receiving pixel. The photodetector 31 converts the intensity of light received by each light receiving pixel into an electrical signal and outputs the electrical signal to the signal processing circuit 40. As shown in FIG. 2, the light receiving unit 30 is provided with an actuator 32 that moves the photodetector 31 and the lens L4. The actuator 32 is controlled by the controller 50 similarly to the actuator 27. The slider 25 and the light receiving unit 30 are moved together by the actuators 27 and 32 so that the photodetector 31 can reliably receive the diffracted light B6.

The signal processing circuit 40 is a circuit that decodes output data detected by the photodetector 31 and reproduces information recorded in the interference fringes S of the disk D.
The signal processing circuit 40 is connected to the controller 50 for outputting the reproduced information, and is connected to an external device (not shown) for outputting the information.

FIG. 5 is a block diagram of the controller 50.
As shown in FIG. 5, the controller 50 includes an actuator driver 51, a laser device driver 52, an error rate calculator 53, and an injection current controller 54. The controller 50 corresponds to a wavelength adjustment circuit as defined in the claims.

  The actuator driving unit 51 is a part that outputs a signal for driving the actuators 27 and 32 in accordance with recording and reproduction addresses on the disk D.

  The laser device driving unit 52 is a portion that generates a pulse signal at a predetermined timing in order to irradiate the laser beam B1 from the laser device 52 in synchronization with the operation of the actuator driving unit 51.

  The error rate calculation unit 53 is a part that calculates an error rate in the reproduction signal based on the data signal input from the signal processing circuit 40 by a known method and outputs the error rate to the injection current control unit 54.

The injection current control unit 54 is a part that injects a current into the Peltier element 212 so that the error rate is reduced based on the error rate input from the error rate calculation unit 53. In order to reduce the error rate, the injection current control unit 54 stores the relationship between the past injection current and the error rate, and determines the next injection current with reference to this history.
The injection current control unit 54 controls the current injected into the Peltier element 212 so that the temperature of the semiconductor laser element 211 is constant in order to keep the wavelength of the laser beam emitted from the laser device 21 constant during information recording. That is, the injection current control unit 54 receives the temperature signal detected by the temperature sensor 213, and absorbs heat if the temperature is higher than a predetermined temperature, and generates heat if the temperature is low. The current value to be injected is determined.

The information recording / reproducing apparatus 1 configured as described above operates as follows.
First, when information is recorded on the disk D, data (information) is input to the spatial light modulator 23 and the data modulated into a two-dimensional pattern is displayed on the spatial light modulator 23. At the same time, the actuator driving unit 51 drives the actuators 27 and 32 according to the address to be written on the disk D to control the positions of the irradiation unit 20 and the light receiving unit 30. Then, a pulse for emitting a laser beam from the laser device 21 is generated by the laser device driving unit 52, and the laser beam B1 is emitted from the laser device 21.
The laser beam B1 is reflected by the mirror M1 (beam B2), and then divided into information light B4 and reference light B3 by the beam splitter 22. The information light B4 passes through the spatial light modulator 23, becomes a light beam having a cross section corresponding to the above-described two-dimensional pattern, is converged by the lens L2, and is condensed at almost one point on the recording layer of the disk D.

On the other hand, the reference light B3 is reflected by the mirror M2 (reference light B5), then converged by the lens L3, and condensed at one point on the recording layer of the disk D.
As shown in FIG. 6, the information light B4 and the reference light (B5) interfere with each other on the recording layer of the disk D to form interference fringes, and the interference fringes are recorded in the recording layer.

At this time, the temperature sensor 213 measures the temperature of the semiconductor laser element 211 and outputs it to the injection current control unit 54 of the controller 50. Then, the injected current control unit 54 determines and flows the current value to be injected into the Peltier element 212 so that the constant temperature is set in advance.
Therefore, the temperature of the semiconductor laser element 211 is always maintained at a predetermined constant temperature, and the laser beam B1 emitted from the semiconductor laser element 211 is maintained at a constant wavelength.
Therefore, interference fringes can be accurately recorded on the recording layer of the disk D under the prescribed conditions.

Next, a case where information recorded on the disk D is reproduced will be described.
In the case of reproducing information, the spatial light modulator 23 is inputted with a signal for blocking light to block the information light B4. Alternatively, the information light B4 may be blocked by a mechanical shutter.

  Then, as in the case of recording information, the actuators 27 and 32 are driven to align the irradiation unit 20 and the light receiving unit 30 with the address of the reproduction position on the disk D, and the laser beam B1 is emitted from the laser device 21. Irradiate. The laser beam B1 is reflected by the mirror M1 (ray B2), passes through the beam splitter 22 (reference light B3), is further reflected by the mirror M2 (reference light B5), is focused by the lens L3, and interferes. The light is condensed at almost one point by the stripe S.

When the reference light B5 is irradiated onto the interference fringes S, the reference light B5 is diffracted by the interference fringes S as shown in FIG. 7, and is opposite to the disk D (upper side in FIG. 1) in the same state as during recording. (Diffracted light B6). That is, the diffracted light B6 has the same cross-sectional pattern as the information light B4 at the time of recording. The transmitted diffracted light B6 becomes parallel light by the lens L4 and then enters the photodetector 31.
The photodetector 31 receives the cross-sectional pattern of the diffracted light B6 and outputs the light intensity of each pixel of the pattern to the signal processing circuit 40 as an electrical signal.
In the signal processing circuit 40, the electric signal input from the photodetector 31 is decoded and output as a reproduced signal to an external device, and at the same time, the error rate calculation unit 53 of the controller 50 is used for controlling the laser device 21. Output as a signal.

The error rate calculation unit 53 calculates the error rate from the signal input from the signal processing circuit 40 by a known method and outputs the error rate to the injection current control unit 54.
The injection current control unit 54 determines the next injection current value so that the error rate becomes smaller from the error rate input from the error rate calculation unit 53 and the relationship between the accumulated past error rate and the injection current. In addition, a current is supplied to the Peltier element with the current value.
The Peltier element 212 generates heat or absorbs heat according to the injected current and controls the temperature of the semiconductor laser element 211.

  In this way, the information recording / reproducing apparatus 1 of the present embodiment controls the temperature of the semiconductor laser element 211 so that the error rate is reduced according to the error rate when reproducing the information recorded on the disk D. . Therefore, regardless of the wavelength of the laser beam when recorded on the disk D, information can be reproduced under the optimum wavelength condition. For example, when information is recorded on the disk D by another information recording / reproducing apparatus, there is a possibility that information may be recorded with a laser beam having a slightly different wavelength. However, information is reproduced by the information recording / reproducing apparatus 1 of this embodiment. By doing so, reproduction errors can be reduced.

[Second Embodiment]
Next, a second embodiment of the present invention will be described.
In the present embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
Unlike the first embodiment, the information recording / reproducing apparatus 1A shown in FIG. 8 does not control the temperature of the semiconductor laser element 211 during reproduction, but controls the wavelength of the laser beam B1 by controlling the pressure. In addition, the wavelength is controlled so as to increase the intensity of the signal detected by the photodetector 31, instead of controlling the error rate to be small when reproducing information.

  As shown in FIG. 9, the semiconductor laser 210 </ b> A includes a semiconductor laser element 211, a Peltier element 212, a temperature sensor 213, and a piezo element 215, similarly to the semiconductor laser 210. The piezo element 215 is an element whose thickness changes according to the applied voltage. The piezo element 215 is provided in a state in which the semiconductor laser element 211 is sandwiched between the frame 217 of the semiconductor laser 210A and pressure can be applied.

  Further, as shown in FIG. 10, the controller 50 </ b> A has an applied voltage control unit 55 instead of the error rate calculation unit 53. The injection current control unit 54A only controls the temperature of the semiconductor laser element 211 to be constant during information recording, and does not perform temperature control during reproduction.

  The signal processing circuit 40A generates decoded data from the received light intensity at each pixel input from the light detector 31 and outputs the decoded data to an external device. The signal processing circuit 40A receives light from the light intensity distribution detected by the pixel of the light receiver. A state evaluation signal (light reception evaluation signal) is output to the applied voltage control unit 55. The light reception evaluation signal can be, for example, a signal in which the intensity of light received by each pixel of the photodetector 31 is arranged in order.

  The applied voltage control unit 55 receives a light reception evaluation signal from the signal processing circuit 40A. Then, the voltage applied to the piezo element 215 is determined so that the difference between the strengths of the signals becomes large, and the voltage is applied to the piezo element 215. For determining the applied voltage, the applied voltage control unit 55 stores the relationship between the past applied voltage and the light reception evaluation signal.

Such an information recording / reproducing apparatus 1A operates as follows.
First, when recording data, the laser beam B1 is emitted from the laser device 21 while controlling the semiconductor laser element 211 to a constant temperature while measuring the temperature with the temperature sensor 213, as in the information recording / reproducing apparatus 1. Data is recorded on disk D.

When reproducing the data recorded on the disk D, the signal processing circuit 40A applies the light reception evaluation signal to the controller 50A by arranging the received light intensity in order from the light intensity distribution received by the light receiving pixels of the photodetector 31. Output to the voltage controller 55.
Based on the received light reception evaluation signal, the applied voltage control unit 55 refers to the relationship between the stored past light reception evaluation signal and the applied voltage so that the difference in intensity of the received light intensity increases. In other words, the next applied voltage is determined so that the intensity of the light reception evaluation signal is increased, and the voltage is applied to the piezo element 215.
The thickness of the piezo element 215 changes based on the applied voltage, and the pressure applied to the semiconductor laser element 211 is increased or decreased.
In the semiconductor laser element 211, the transmission wavelength changes according to a change in pressure.
When the wavelength of the laser beam B1 when the interference fringe S is recorded on the disk D is different from the wavelength of the laser beam B1 during reproduction, diffraction due to the interference fringe S occurs in a state different from that during recording and cannot be reproduced accurately. However, by controlling the pressure applied to the semiconductor laser element 211 in this way, the laser beam B1 is irradiated at an appropriate wavelength according to the recorded interference fringes, and data reproduction errors can be reduced.

[Third Embodiment]
Next, a third embodiment of the present invention will be described.
FIG. 11 is a schematic diagram of an information recording / reproducing apparatus 1B according to the third embodiment. FIG. 12 is a cutaway perspective view of a semiconductor laser used in the laser apparatus of the third embodiment. In the present embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
As shown in FIG. 11, the information recording / reproducing apparatus 1B of the third embodiment is different from the information recording / reproducing apparatus 1 of the first embodiment in that a laser apparatus 21 is replaced with a laser apparatus 21B.

  The laser device 21B has a semiconductor laser 210B as shown in FIG. The semiconductor laser 210B includes a semiconductor laser element 211 and a wavelength conversion device 216 provided on an optical path emitted from the semiconductor laser element 211.

The wavelength conversion device 216 is an element that shortens the wavelength of the laser beam B1 emitted from the semiconductor laser element 211. The wavelength conversion device 216 performs second harmonic generation (SHG) and third harmonic generation (THG: Third Harmonic Generation). The resulting device can be used. Examples of the material having the second-order nonlinear optical effect (SHG) include LiNbO ₃ , KNbO ₃ , KTiOPO ₄ , Ba ₂ NaNb ₅ O ₁₅ , KH ₂ PO ₄ , and KD ₂ PO ₄ .

  The wavelength conversion device 216 is provided with a temperature sensor 213 and a Peltier element 212 in close contact with each other. The controller 50 and the temperature sensor 213 are connected so that the temperature detected by the temperature sensor 213 is output to the controller 50. The controller 50 is the same as that in the first embodiment. The Peltier element 212 is controlled by the injection current control unit 54 of the controller 50.

  In the information recording / reproducing apparatus 1B having the above-described configuration, the current injected into the Peltier element 212 is injected into the injected current control unit 54 so that the temperature detected by the temperature sensor 213 is constant, as in the first embodiment. Controlled by Therefore, the interference fringes S are recorded while the wavelength conversion is performed at a constant rate.

When the recorded data is reproduced, the injection current control unit 54 determines the next injection current value so that the error rate becomes small based on the error rate calculated by the error rate calculation unit 53, and the Peltier Current is injected into the element 212.
The Peltier element 212 generates heat or absorbs heat according to the injected current to adjust the temperature of the wavelength conversion device 216. Then, by adjusting the temperature of the wavelength conversion device 216, the wavelength conversion ratio in the wavelength conversion device 216 changes, and the wavelength of the laser beam B1 is adjusted so that the error rate is reduced.

  Therefore, when the wavelength of the laser beam B1 when the interference fringe S is recorded on the disk D is different from the wavelength of the laser beam B1 at the time of reproduction, the diffraction due to the interference fringe S occurs in a state different from that during recording. Although not reproduced, as in this embodiment, the wavelength of the laser beam B1 is adjusted by controlling the temperature of the wavelength conversion device 216, and the laser beam B1 is irradiated with an appropriate wavelength according to the recorded interference fringes. Data reproduction errors can be reduced.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, It can change and implement suitably. For example, in the embodiment, the transmission type holographic recording method has been described as an example, but the reflection type holographic recording method can be similarly applied. Further, although the laser device 21 using the semiconductor laser 210 is taken as an example, a laser beam is provided by controlling the temperature of the wavelength converter 216 by providing the wavelength converter 216 in another type of laser instead of the semiconductor laser. You may comprise so that the wavelength of B1 may be adjusted.

  Further, in the embodiment, the case where the wavelength is always adjusted has been described. However, this is not always necessary. For example, it is performed every time the recording medium (disk D) is replaced or a writing block on the recording medium is renewed. It can also be configured as follows. Further, the wavelength adjustment can be performed only when the amount of diffracted light or the error rate is deteriorated from a predetermined value. As described above, by appropriately reducing the number of times of performing the wavelength adjustment control, the processing speed can be increased and the data access speed can be increased.

  Furthermore, in the embodiment, a disk-type recording medium is taken as an example, but a tape-type optical information recording medium can also be used.

It is a perspective view of a transmission type holographic information recording / reproducing apparatus. It is a schematic diagram of a transmission type holographic information recording / reproducing apparatus. It is a fractured perspective view of a semiconductor laser. It is a figure which shows an example of the data displayed on the spatial light modulator. It is a block diagram of a controller. It is an enlarged view near the disk D for explaining data recording. It is an enlarged view of the vicinity of the disk D for explaining data reproduction. It is a schematic diagram of the information recording / reproducing apparatus which concerns on 2nd Embodiment. It is a fractured perspective view of the semiconductor laser concerning a 2nd embodiment. It is a block diagram of a controller concerning a 2nd embodiment. It is a schematic diagram of the information recording / reproducing apparatus which concerns on 3rd Embodiment. It is a fractured perspective view of the semiconductor laser concerning a 3rd embodiment. It is a graph which shows the relationship between the shift | offset | difference of a wavelength, and a signal level.

Explanation of symbols

1. Transmission type holographic information recording / reproducing device (optical information reproducing device)
DESCRIPTION OF SYMBOLS 21 Laser apparatus 22 Beam splitter 23 Spatial light modulator 31 Photo detector 40 Signal processing circuit 50 Controller (wavelength adjustment circuit)
L1, L2, L3, L4 lens

Claims (8)

An optical information reproducing apparatus for reproducing optical information recorded as interference fringes on a recording layer of an optical information recording medium,
A laser device that emits a laser beam used for reproducing optical information;
A condensing optical system for condensing the laser beam on interference fringes on an optical information recording medium;
A photodetector that receives the diffracted light generated by irradiating the optical information recording medium with the laser beam and converts it into an electrical signal;
A signal processing circuit that decodes information based on the electrical signal output by the photodetector;
An optical information reproducing apparatus comprising: a wavelength adjustment circuit that adjusts a wavelength of a laser beam emitted from the laser device based on an electrical signal output from the photodetector.   2. The light according to claim 1, wherein the wavelength adjustment circuit is configured to adjust the wavelength of the laser beam based on the intensity of the light detected by the photodetector so that the intensity of the light is increased. Information playback device.   The wavelength adjustment circuit has an error rate calculation unit that calculates an error rate from information decoded by the signal processing circuit, and sets the wavelength of the laser beam so that the error rate calculated by the error rate calculation unit is small. The optical information reproducing apparatus according to claim 1, wherein the optical information reproducing apparatus is configured to adjust. The laser device has a semiconductor laser element as a transmitter,
This semiconductor laser element is provided with temperature control means,
4. The optical information reproduction according to claim 2, wherein the wavelength adjusting circuit is configured to adjust the wavelength of the laser beam by applying a heating or cooling signal to the temperature control means. apparatus. The laser apparatus has a wavelength conversion device that converts the wavelength of the laser beam, and a temperature control means provided in the wavelength conversion device,
4. The optical information reproduction according to claim 2, wherein the wavelength adjusting circuit is configured to adjust the wavelength of the laser beam by applying a heating or cooling signal to the temperature control means. apparatus. The laser apparatus includes a wavelength conversion device that converts a wavelength of a laser beam, and a pressure control unit that changes a pressure applied to the wavelength conversion device,
4. The optical information according to claim 2, wherein the wavelength adjusting circuit is configured to adjust a wavelength of a laser beam by applying a pressure signal or a pressure signal to the pressure control unit. Playback device.   6. The optical information reproducing apparatus according to claim 4, wherein the temperature control means is a Peltier element.   The optical information reproducing apparatus according to claim 6, wherein the pressure control means is a piezo element.

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