JP2009288429A - Hologram recording/reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To record information with a laser beam at optimal wavelength even if the optimal wavelength of the laser beam varies with the change of dimension. <P>SOLUTION: A hologram information recording/reproducing apparatus records the information on a hologram medium 16 by making an information light interfere with a reference light, both light being emitted from the same light source 1, and reproduces the information by irradiating the hologram medium 16 with the reference light. In the hologram information recording/reproducing apparatus, the light source 1 can change an oscillating wavelength. The hologram information recording/reproducing apparatus includes a wavelength controlling circuit for determining the oscillating wavelength of the light source 1 when recording based on reproduction information from the hologram medium 16. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hologram recording / reproducing apparatus that multiplex-records information on a hologram disc as a hologram.

  In recent years, holographic memory has attracted attention in the field of practical use as next-generation ultra-high-density data storage.

  The digital hologram memory records a diffraction grating (holography) on a recording medium by causing interference between information light having two-dimensional digital pattern information and reference light.

  Information is reproduced as Bragg diffracted light from the diffraction grating recorded on the recording medium. In order for the reproduction signal light to be reproduced with a sufficient amount of light, it is necessary to satisfy the Bragg condition.

  Since the hologram medium has a high linear expansion coefficient due to the properties of the medium, when the medium temperature changes, the recorded material expands and contracts, and the refractive index also changes. The change in the dimension of the medium due to these temperature changes causes a change in the angle and grating interval of the diffraction grating recorded during recording.

  If a dimension change occurs between the previous and next recordings, even if recording is performed with the same wavelength of the laser beam, the angle of the recorded diffraction grating and the interval of the diffraction gratings change before and after the dimension change. That is, the wavelength of the laser beam optimum for reproduction differs for each recorded area, and reproduction cannot be performed with a constant wavelength of laser light.

As a method for improving the deterioration of the recording state due to the dimensional change, a method of detecting a temperature change with a temperature sensor and determining the wavelength of the laser beam from a memory table according to the temperature change has been proposed (Patent Document 1).
JP 2007-178780 A

  However, when a method of adjusting the wavelength of reference light during recording using a conventional temperature sensor is used, it is necessary to provide a separate temperature sensor, which increases costs and increases the size of the apparatus.

  Furthermore, when there is a sudden temperature change, it takes time for the temperature of the hologram medium to be the same as the surrounding temperature.

  For this reason, the actual dimension change may differ from the dimension change assumed from the temperature detected by the temperature sensor. In other words, the conventional method using a temperature sensor and a memory table cannot determine the optimum wavelength of laser light during recording.

  Therefore, the present invention provides a hologram information recording / reproducing apparatus and a hologram medium recording method capable of recording with the optimum laser light wavelength even when the optimum laser light wavelength changes with the dimension change. Objective. In addition, by recording with the optimum wavelength of the laser beam according to the change in dimension of the hologram medium, the entire surface of the hologram medium can be reproduced with a constant wavelength during reproduction.

  According to the present invention, as means for solving the above-mentioned problems, information light having the same light source interferes with reference light to record information on the hologram medium, and the hologram medium is irradiated with the reference light to receive information. In a hologram information recording / reproducing apparatus for reproducing information, a wavelength control circuit that can change an oscillation wavelength of the light source and determines an oscillation wavelength of the light source at the time of recording based on reproduction information from the hologram medium It is characterized by providing.

  According to the present invention, the area already recorded in the hologram medium is reproduced, and the optimum wavelength of the laser beam at the time of recording is determined based on the reproduced signal reproduced. Then, recording is performed using the determined wavelength of the laser beam. Therefore, even when a dimension change occurs between the previous recording and the current recording, it is possible to determine the optimum wavelength of the laser beam during recording without providing a separate temperature sensor or having a memory table. . Further, by recording at an optimum wavelength according to the change in dimension of the hologram medium, the entire hologram medium can be reproduced at a constant wavelength of reference light during reproduction.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a block diagram showing a collinear optical information recording / reproducing apparatus as an embodiment of the present invention.

  In FIG. 1, the spindle motor 15 rotates the hologram medium 16.

  The optical pickup 100 serves as a light source for information light and reference light irradiated onto the hologram medium 16.

  Further, the reproduction light from the hologram medium 16 is received in the optical pickup 100 and converted into a reproduction signal which is an electric signal.

  The reproduction signal processing circuit 26 stores the reproduction signal from the optical pickup 100 as two-dimensional data in a memory and outputs it as reproduction information.

  Further, the luminance evaluation value detection circuit 28 obtains the luminance evaluation value based on the reproduction signal from the optical pickup 100.

  Next, the controller 30 generates a wavelength change amount based on the luminance evaluation value from the luminance evaluation value calculation means 28.

  Further, the controller 30 generates a sled motor drive value so as to control the positional relationship between the hologram medium 16 and the optical pickup 100.

  In addition, the controller 30 gives the generated wavelength change amount to the wavelength control circuit 29 and controls the oscillation wavelength of the laser light source to be the target wavelength.

  Further, the controller 30 controls the position of the optical pickup 100 in the radial direction of the hologram medium 16 by supplying the generated thread motor drive value to the thread motor drive circuit 27 and driving the thread motor.

  Next, the case of recording with the optical information recording / reproducing apparatus according to the present invention will be described.

  FIG. 2 is a block diagram showing a configuration of the optical pickup 100 of FIG.

  First, as shown in FIG. 2, a light beam emitted from the first laser light source 1 is converted into a parallel light beam by a collimator 2 and illuminates a spatial light modulator (SLM) 4 via a mirror 3. To do.

  The light reflected by the pixel representing the information “1” on the SLM 4 is reflected in the direction of the hologram medium 16, and the light reflected by the pixel representing the information “0” is not reflected in the direction of the hologram medium 16. . On the collinear SLM 4, a portion for modulating the information light 6 and a portion for modulating the reference light 5 surrounding the information light 6 are provided.

  The reference light 5 and the information light 6 reflected by the pixel representing the information “1” by the SLM 4 pass through the polarization beam splitter (PBS) 7.

  Then, it is directed to the hologram medium (hologram recording medium) 16 side via the relay lens 8, the mirror 9, the relay lens 10, and the dichroic beam splitter (dichroic BS) 11. Then, the reference light 5 and the information light 6 that are transmitted through the quarter-wave plate (QWP) 12 and converted into circularly polarized light are reflected by the mirror 3 and enter the objective lens 14.

  The hologram medium 16 has a disk shape and is rotatably held on the spindle motor 15. By the objective lens 14, the reference light 5 and the information light 6 are condensed on a recording layer (not shown) provided on the hologram medium 16, and interfere to form interference fringes. In the polymer material in the recording layer, the interference fringe pattern at the time of recording is recorded as a refractive index distribution, and a digital volume hologram is formed.

  Further, a reflection film (not shown) is provided in the recording medium constituting the hologram medium 16.

  Here, the optical pickup 100 is fixed by a slider (not shown). Further, the slider can be slid parallel to the radial direction of the hologram medium 16.

  The thread motor 25 is driven by the thread motor drive circuit 27 of FIG. The sled motor 25 is driven to move the slider and change the recording position.

  In addition to the laser light source 1 that records and reproduces holograms, the above optical system is provided with a second laser light source 20 that emits light having a wavelength that is not photosensitive to the recording medium. The light emitted from the laser 20 can detect the displacement of the hologram medium 16 with high accuracy using the reflective film as a reference plane.

  As a result, even if surface blurring or eccentricity occurs in the hologram medium 16, the recording spot can dynamically follow the recording medium surface using the optical servo technology. As a result, the interference fringe pattern can be recorded with high accuracy.

  Briefly described below.

  First, the linearly polarized light beam emitted from the laser light source 20 passes through the beam splitter (BS) 21, is converted into a parallel light beam by the lens 22, is reflected by the mirror 23 and the dichroic BS 11, and is directed to the hologram medium 16.

  The light beam that has been transmitted through the quarter-wave plate (QWP) 12 and converted into circularly polarized light is reflected by the mirror 13 and incident on the objective lens 14 to be condensed as a small light spot on the reflection surface on the hologram medium 16. Is done.

  The reflected light beam becomes reversely circularly polarized light, re-enters the objective lens 14 to become a parallel light beam, is reflected by the mirror 13, passes through the quarter-wave plate (QWP) 12, and is perpendicular to the forward path. It is converted into a linearly polarized light beam. The light beam reflected by the dichroic BS 11 is reflected by the beam splitter (BS) 21 through the mirror 23 and the lens 22 in the same way as the forward path, and is guided to the light receiving unit 24.

  The light receiving unit 24 has a plurality of light receiving surfaces (not shown), detects position information of the reflecting surface by a known method based on a signal detected on each light receiving surface, and based on that, the focus of the objective lens 14 is detected. And tracking.

  Next, a case where recorded information is reproduced from the hologram medium 16 as a recording medium using the optical pickup will be described.

  The light beam emitted from the laser light source 1 of the light source illuminates the spatial light modulator (SLM) 4 in the same manner as in recording.

  At the time of reproduction, only the portion that modulates the reference light 5 on the SLM 4 displays “1” information, and all the portions that modulate the information light 6 display “0” information.

  Therefore, only the light reflected by the pixels of the reference light portion is reflected in the direction of the hologram medium 16, and the information light is not reflected in the direction of the hologram medium 16.

  As in the recording, the reference light 5 is circularly polarized and condensed on a recording layer (not shown) in the hologram medium 16 to reproduce information light from the recorded interference fringes. The information light reflected by the reflection film in the recording medium constituting the hologram medium 16 becomes reverse circularly polarized light and re-enters the objective lens 14 to be a parallel light beam.

  Then, the light is reflected by the mirror 13 and transmitted through the quarter-wave plate (QWP) 12 to be converted into a linearly polarized light beam perpendicular to the forward path. At this time, an intermediate image of the display pattern of the SLM 4 reproduced at a distance f from the objective lens 14 is formed.

  The light beam that has passed through the dichroic BS 11 is directed to the polarization beam splitter (PBS) 7 via the relay lens 10, the mirror 209, and the relay lens 8.

  The light beam reflected by the PBS 7 is re-imaged by the relay lens 10 and the relay lens 8 as an intermediate image of the display pattern of the SLM 4 at a position conjugate with the spatial light modulation element (SLM) 4. In this position, an opening 17 is placed in advance, and thereby unnecessary reference light in the periphery of the information light is shielded.

  Then, the intermediate image re-imaged by the lens 18 forms a display pattern of the SLM 4 on the light receiving portion 19 only for the information light portion.

  Thereby, since unnecessary reference light does not enter the light receiving unit 19, a reproduction signal with good S / N can be obtained. Here, the light receiving unit 19 includes a two-dimensional CCD, a CMOS sensor, and the like, and outputs a reproduction signal obtained by converting the received light intensity into an electric signal to the reproduction signal processing circuit 26.

  Next, a procedure for generating a reproduction signal by converting the light intensity received by the light receiving unit 19 into an electric signal will be described.

  FIG. 3 is a block diagram of the reproduction signal processing circuit 26. FIG. 4 is a schematic plan view showing the light receiving unit 19.

In FIG. 4, i _max indicates the number of pixels in the horizontal direction in the light receiving unit 19, and j _max indicates the number of pixels in the vertical direction.

In this case, it is assumed that i _max = j _max = 200. An arbitrary pixel position arranged in the light receiving unit 19 is assumed to be (i, j).

  First, scanning is performed from the pixel position (1, 1) of the light receiving unit 19 in the horizontal direction, and an electric signal is output to the AD converter 31 in the reproduction signal processing circuit 26. Similarly, an electrical signal is output to the AD converter 31 up to the pixel position (200, 1).

  Next, similarly, an electric signal is output to the AD converter 31 from the pixel position (1, 2) to the pixel position (200, 2). Then, scanning is repeated up to the pixel position (200, 200), and an electric signal is output to the AD converter 31.

  The AD converter 31 converts the electrical signal from the light receiving unit 19 into a digital signal and outputs it as a reproduction signal.

  Next, the reproduction signal from the AD converter 31 is recorded in the memory 32. Here, an address is assigned and recorded in the memory 32 so that the position of the reproduction signal in the light receiving unit 19 can be known. Based on the output, the luminance evaluation value calculation means 28 calculates the luminance evaluation value F.

  In the luminance evaluation value calculating means 28, when one screen of the light receiving unit 19 is recorded in the memory 32, the reproduction signal in the B1 region from the pixel position (1, j) to the pixel position (100, j) in the light receiving unit 19 is recorded. Calculate the sum of

  Similarly, the sum of the reproduction signals in the B2 region from the pixel position (101, j) to the pixel position (200, j) is calculated. In the present embodiment, it is assumed that the number of pixels included in the B1 area is the same as the number of pixels included in the B2 area.

  Next, the absolute value of the difference between the sum of the reproduction signals in the B1 region and the sum of the reproduction signals in the B2 region is calculated, and this is output to the controller 50 as the luminance evaluation value F. Note that j = 1 to 200.

  Next, a specific control operation of the controller 30 that adjusts the wavelength of laser light during recording according to the embodiment will be described. FIG. 5 is a flowchart showing the wavelength adjustment control operation of this embodiment.

  The controller 30 starts wavelength adjustment of the laser beam based on the recording request. Wavelength adjustment is performed by reproducing an already recorded area.

  Here, the wavelength adjustment region is determined by the collinear standard for the wavelength of the laser beam. Assume that recording was performed at 532.0 nm. Therefore, the wavelength of the laser light is set to λc = 532.0 nm.

  The wavelength control circuit 26 controls the wavelength of the laser light source 1 in the optical pickup 100 so that the wavelength of the laser light becomes λc (S100).

  Then, the reproduction light that has been transmitted through the hologram medium 16 is received by the light receiving unit 19.

  A reproduction signal obtained by converting the light intensity received by the light receiving unit 19 into an electric signal is input to the reproduction signal processing circuit 26.

Is AD converted by the AD converter 31 by the reproducing signal processing circuit 26, stored in the memory 32 as a two-dimensional image data, the luminance evaluation value computing unit 28 outputs the result of the luminance evaluation value F ₀ to the controller (S101) .

  Next, the wavelength control circuit 29 controls the wavelength of the laser light source 1 in the optical pickup 100 so that the deviation Δλ = 0.01 nm for a minute amount and the wavelength of the laser light becomes λc + Δλ (S102).

Then, it calculates the luminance evaluation value in the same manner as S101, to the result with _{F 1} (S103).

  Next, the wavelength control circuit 29 controls the wavelength of the laser light source 1 in the optical pickup 100 so that the wavelength of the laser light becomes λc−Δλ (S104).

Then, it calculates the luminance evaluation value in the same manner as S101, to the result with _{F 2} (S105).

  By performing the above procedure, luminance evaluation values at three types of wavelengths centering on λc are obtained.

Next, the obtained luminance evaluation values F ₁ and F ₂ are compared. As a result, it is determined whether the optimum wavelength of the laser beam is shorter or longer than λc (S106).

Here, when F ₁ falls below F ₂ , it is possible to determine that the optimum wavelength of the laser beam is λc or less.

Next, the obtained luminance evaluation values F ₀ and F ₁ are compared (S107).

Here, if F ₀ is less than F ₁ , the luminance evaluation value is the lowest at λc, and the wavelength λc of the laser light at this time becomes the optimum wavelength of the laser light. Then, the wavelength control circuit 26 controls the laser light source 1 in the optical pickup 100 with the wavelength λc as the optimum laser light wavelength, and recording is started.

On the other hand, when F ₁ falls below F ₀ , the optimum wavelength of the laser beam is longer than λ c, so λ c is updated to λ c + Δλ (S108).

  By repeating these procedures, the optimum wavelength of the laser beam can be obtained.

  The step size of the minute amount deviation is not limited to 0.1 nm in the present embodiment.

  The area already recorded in S100 is, for example, a management information area. The management information area is an area provided separately from the user data area in which address information, read-only information, and recording / playback conditions for recording / playback information are recorded in advance under certain conditions when the medium is manufactured. It is. By using this management information area in wavelength adjustment, stable wavelength control can be performed regardless of the recording state.

  In addition, the place where the wavelength adjustment of the laser beam at the time of recording is performed may be performed by using the data recorded by trial recording for the wavelength adjustment in the already recorded user data area or the vacant user data area. Good. Furthermore, the latest recorded data or recorded data at a position closest to the address to be recorded may be used.

  In the wavelength control, by using the user data area, the wavelength control can be performed in accordance with the recording data recorded by the other company's drive.

  Therefore, even when additional recording is performed on a hologram medium that has already been recorded by another company's drive, recording can be performed in accordance with the recording conditions, and reproduction can be performed over the entire surface of the hologram medium with a constant wavelength of reference light. it can.

  Another example of the method for calculating the luminance evaluation value F will be described. This method is calculated using a reproduction signal for one screen of the light receiving unit 19 recorded in the memory 32 in the same manner as described above. First, an average value of reproduction signals brighter than a certain threshold value is calculated. Similarly, an average value of reproduction signals darker than a certain threshold value is calculated. Then, the difference between the average value of the bright reproduction signal and the average value of the dark reproduction signal is calculated and output to the controller 30 as the luminance evaluation value F, and the wavelength of the reference light is adjusted so that this value becomes large. .

  As described above, according to the present embodiment, the wavelength of the reference light is deviated by a minute amount with respect to the predetermined wavelength, and the optimum wavelength of the reference light calculated from the luminance evaluation value of the reproduction signal is recorded. This is used as the wavelength of the laser beam. As a result, user data can be recorded with a certain recording quality even when the optimum wavelength of the laser beam changes due to a change in dimension during recording. In addition, reproduction can be performed over the entire surface of the hologram medium with a constant wavelength of reference light during reproduction.

(Second Embodiment)
In the second embodiment, an embodiment in which the angle of the reference light during recording is adjusted using the error rate of the reproduction signal as an index will be described.

  FIG. 6 is a block diagram showing a hologram information recording / reproducing apparatus in the second embodiment of the present invention. The description of the blocks having the same numbering as in FIG. 1 and the same operations as those in the first embodiment will not be repeated.

  In FIG. 6, an error rate calculation circuit 40 decodes reproduction information based on the reproduction information from the reproduction signal processing circuit 26, measures the number of error corrections of the reproduction information, and calculates an error rate.

  Next, the controller 50 generates a wavelength change amount based on the error rate information from the error rate calculation circuit 40.

  Further, the controller 30 generates a drive value for the sled motor so as to control the positional relationship between the hologram medium 16 and the optical pickup 100.

  Next, the operation of the controller 30 in the second embodiment of the present invention will be described. FIG. 7 is a flowchart showing the wavelength adjustment control operation of this embodiment.

  The controller 30 starts wavelength adjustment of the laser beam based on the recording request. Wavelength adjustment is performed by reproducing an already recorded area. Here, the wavelength adjustment region is determined by the collinear standard for the wavelength of the laser beam. Assume that recording was performed at 532.0 nm. Therefore, the wavelength of the laser light is set to λc = 532.0 nm.

  The wavelength control circuit 26 controls the wavelength of the laser light source 1 of the optical pickup 100 so that the wavelength of the laser light becomes λc (S200).

Then, the reproduction light that has been transmitted through the hologram medium 16 is received by the light receiving unit 19. A reproduction signal obtained by converting the light intensity received by the light receiving unit 19 into an electric signal is input to the reproduction signal processing circuit 26. Based on the reproduction information subjected to waveform equalization processing by the reproduction signal processing circuit 26, the error rate calculation circuit 40 performs error correction, calculates the error rate, calculates the error rate E ₀ , and sends the result to the controller 30. Is output (S201).

  Next, the wavelength control circuit 29 controls the wavelength of the laser light source 1 in the optical pickup 100 so that the deviation Δλ = 0.01 nm for a minute amount and the wavelength of the laser light becomes λc + Δλ (S202).

Then, calculated in the same manner as in the error rate and S101, to the result with _{E 1} (S203).

  Next, the wavelength control circuit 29 controls the wavelength of the laser light source 1 in the optical pickup 100 so that the wavelength of the laser light becomes λc−Δλ (S204).

Then, calculated in the same manner as in the error rate and S101, to the result with _{E 2} (S205).

  By performing the above procedure, error rates at three types of wavelengths centering on λc are obtained.

Next, the obtained error rates E ₁ and E ₂ are compared. As a result, it is determined whether the optimum wavelength of the laser beam is shorter or longer than λc (S206).

Here when E ₁ is below the E ₂ may be the wavelength of the optimum laser light is determined below [lambda] c.

Next, the obtained error rates E ₀ and E ₁ are compared (S207).

Here, if E ₀ is less than E ₁ , the error rate is minimized at λc, and the wavelength λc of the laser light at this time becomes the optimum wavelength of the laser light. Then, the wavelength control circuit 26 controls the laser light source 1 in the optical pickup 100 with the wavelength λc as the optimum laser light wavelength, and recording is started.

On the other hand, when E ₁ is less than E ₀ , the optimum wavelength of the laser light is longer than λc, so λc is updated to λc + Δλ (S208).

  By repeating these procedures, the optimum wavelength of the laser beam can be obtained.

  The step size of the minute amount deviation is not limited to 0.1 nm in the present embodiment.

  The area already recorded in S200 is, for example, a management information area.

  The management information area is an area provided separately from the user data area in which address information, read-only information, and recording / playback conditions for recording / playback information are recorded in advance under certain conditions when the medium is manufactured. It is. The management information area is located at a predetermined address of the hologram medium.

  By using this management information area in wavelength adjustment, stable wavelength control can be performed regardless of the recording state.

  In addition, the place where the wavelength adjustment of the laser beam at the time of recording is performed may be performed by using the data recorded by trial recording for the wavelength adjustment in the already recorded user data area or the vacant user data area. Good.

  Furthermore, the latest recorded data or recorded data at a position closest to the address to be recorded may be used.

  In the wavelength control, by using the user data area, the wavelength control can be performed in accordance with the recording data recorded by the other company's drive. Therefore, even when additional recording is performed on a hologram medium that has already been recorded by another company's drive, recording can be performed in accordance with the recording conditions, and reproduction can be performed over the entire surface of the hologram medium with a constant wavelength of reference light. it can.

  As described above, according to the present embodiment, the wavelength of the reference light is deviated by a minute amount with respect to the predetermined wavelength, and the optimum wavelength of the reference light obtained from the error rate of the reproduction signal is determined at the time of recording. Used as the wavelength of laser light.

  As a result, user data can be recorded with a certain recording quality even when the optimum wavelength of the laser beam changes due to a change in dimension during recording. In addition, reproduction can be performed over the entire surface of the hologram medium with a constant wavelength of reference light during reproduction.

  INDUSTRIAL APPLICABILITY The present invention can be used for a hologram recording / reproducing apparatus that multiplex-records information on a hologram recording medium as a hologram.

1 is a block diagram showing a collinear optical information recording / reproducing apparatus as a first embodiment of the present invention. FIG. FIG. 2 is a block diagram illustrating a configuration of the optical pickup 100 in FIG. 1. 3 is a block diagram of a reproduction signal processing circuit 26. FIG. 3 is a schematic plan view showing a light receiving unit 19. FIG. It is a flowchart which shows the control operation | movement of the wavelength adjustment of the 1st Embodiment of this invention. It is a block diagram which shows the hologram information recording / reproducing apparatus in the 2nd Embodiment of this invention. It is a flowchart which shows the control operation | movement of the wavelength adjustment of the 2nd Embodiment of this invention.

Explanation of symbols

1 Laser light source 2 Collimator 3 Mirror 4 SLM (DMD)
5 Reference light 6 Information light 7 PBS
8 Relay lens 9 Mirror 10 Relay lens 11 Dichro BS
12 QWP
DESCRIPTION OF SYMBOLS 13 Mirror 14 Objective lens 15 Spindle motor 16 Hologram medium 17 Aperture 18 Lens 19 Light-receiving part 20 Laser light source 21 BS
DESCRIPTION OF SYMBOLS 22 Lens 23 Mirror 24 Light-receiving part 25 Thread motor 26 Reproduction | regeneration signal processing circuit 27 Thread motor drive circuit 28 Luminance evaluation value calculation means 29 Wavelength control circuit 30 Controller 31 AD converter 32 Memory 40 Error rate calculation means

Claims (7)

In a hologram information recording / reproducing apparatus that causes information light and reference light having the same light source to interfere, records information on a hologram medium, and reproduces information by irradiating the hologram medium with the reference light,
The light source can change the wavelength of oscillation,
A hologram recording / reproducing apparatus comprising: a wavelength control circuit that determines an oscillation wavelength of the light source at the time of recording based on reproduction information from the hologram medium. The wavelength control circuit controls the wavelength of the reference light based on reproduction information from the hologram medium, and determines the oscillation wavelength of the light source during recording according to the wavelength of the reference light. The hologram recording / reproducing apparatus according to claim 1. The reproduction information is two-dimensional image data, and the two-dimensional image data is divided into two regions including the same number of pixels,
From the reproduction information, the sum of the reproduction information for each of the two areas is calculated,
The absolute value of the sum difference is calculated as a luminance evaluation value,
2. The hologram recording / reproducing apparatus according to claim 1, wherein the oscillation wavelength of the reference light is controlled so that the luminance evaluation value is close to zero. An error rate calculation circuit for decoding the reproduction information, measuring an error correction count of the reproduction information, and calculating an error rate;
2. The hologram recording / reproducing apparatus according to claim 1, wherein the wavelength control circuit controls the oscillation wavelength of the reference light so that the error rate is minimized. The reproduction information is two-dimensional image data,
An average value of the reproduction information in an area brighter than a certain threshold value and an average value of the reproduction information in an area darker than the certain threshold value are calculated,
The difference between the average value of the bright reproduction information and the average value of the dark reproduction information is calculated as a luminance evaluation value, and the wavelength of the reference light is adjusted so that the difference becomes large. 1. The hologram recording / reproducing apparatus according to 1. 2. The hologram recording / reproducing apparatus according to claim 1, wherein the reproduction information is information recorded in a management information area located at a predetermined address of the hologram medium. 2. The hologram recording / reproducing apparatus according to claim 1, wherein the reproduction information is latest recorded data on the hologram medium or data at a position close to a recording position.

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