JP2009288428A - Hologram information recording and reproducing device - Google Patents

Abstract

An object of the present invention is to provide a hologram information recording / reproducing apparatus capable of recording with the optimum reference light angle even when the optimum reference light angle changes with the dimension change.
In a hologram information recording / reproducing apparatus that records information on a hologram medium 1 by causing information light and reference light to interfere with each other, and reproduces information by irradiating the hologram medium 1 with the reference light, the reference light is applied to the hologram medium 1. Is read by the mirror 9 that irradiates the mirror 9, the mirror angle driving circuit 60 that adjusts the angle of the reference light incident on the hologram medium 1 by driving the mirror 9, and the reference light that is applied to the hologram medium 1. A reproduction signal processing circuit 20 for reproducing the information recorded on the hologram medium 1 based on the signal, and the angle of the reference light at the time of recording based on the reproduction information output from the reproduction signal processing circuit 20 It is characterized by determining.
[Selection] Figure 1

Description

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

  In recent years, development of hologram recording systems for recording information by irradiating a hologram medium with information light and reference light to generate an interference pattern in the hologram medium has progressed.

  As one of the methods, a two-beam interference method in which information light and reference light are interfered by different optical paths has been proposed (for example, see Patent Document 1).

  In this two-beam interference method, the recorded information can be reproduced by irradiating the information recorded on the hologram medium with the reference light at the time of reproduction so as to have the same angle as the reference light at the time of recording. It is a method.

  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 of the recorded diffraction grating and a change in the grating spacing.

  FIG. 14 is a diagram showing a change in the angle of the diffraction grating and a change in the grating interval due to the change in dimension of the hologram medium.

  As shown in FIG. 14, as a result of the hologram medium contracting, the angle between the diffraction grating and the hologram medium changes from φ to φ + Δφ. As a result, the diffraction grating interval changes.

  Here, if a dimension change occurs between the previous recording and the current recording, even if recording is performed at the same reference beam angle, the recorded diffraction grating interval changes before and after the dimension change. . That is, the optimum angle of the reference light differs for each recorded area, and reproduction cannot be performed at a constant reference light angle.

As a method for improving the deterioration of the recording state due to the dimensional change, a method has been proposed in which a temperature change is detected by a temperature sensor and the angle of reference light at the time of recording is determined from a memory table according to the temperature change (Patent Literature). 2).
JP 2004-177958 A JP 2007-178780 A

  However, when the method of adjusting the angle of the reference light at the time of recording using the conventional temperature sensor is used, it is necessary to provide a separate temperature sensor, which increases the cost and enlarges 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 the temperature sensor and the memory table cannot determine the optimum reference light angle at the time of recording.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a hologram information recording / reproducing apparatus capable of recording with the optimum reference light angle even when the optimum reference light angle changes with the dimension change. It is another object of the present invention to record the entire hologram medium at a constant reference light angle during reproduction by recording at an optimum reference light angle according to the change in dimension of the hologram medium.

  As a means for solving the above-mentioned problem, the present invention records information on a hologram medium by causing information light and reference light to interfere with each other, and irradiates the hologram medium with the reference light to reproduce information. In the reproducing apparatus, a mirror that irradiates the hologram medium with the reference light, a mirror angle driving circuit that adjusts an angle of the reference light that is incident on the hologram medium by driving the mirror, and irradiation of the hologram medium A reproduction signal processing circuit for reproducing the information recorded on the hologram medium based on the signal read by the reference light, and based on the reproduction information output from the reproduction signal processing circuit The angle of the reference light at the time of recording is determined.

  According to the present invention, an area already recorded in a hologram medium is reproduced, and an optimum angle of reference light at the time of recording is determined based on the reproduced signal reproduced. The determined reference light angle is recorded as the reference light angle at the time of recording. Therefore, even when a dimension change occurs between the previous recording and the current recording, it is possible to determine the optimum reference light angle during recording without providing a separate temperature sensor or having a memory table. .

  Further, by recording with the optimum reference light angle according to the change in dimension of the hologram medium, the entire surface of the hologram medium can be reproduced with a constant reference light angle 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 schematic configuration of a two-beam interference method hologram information recording / reproducing apparatus as a first embodiment of the present invention. The two-beam interference method hologram information recording / reproducing apparatus is hereinafter simply referred to as “hologram information recording / reproducing apparatus”.

  In FIG. 1, a spindle motor 2 rotates a hologram medium 1.

  The optical pickup 100 serves as a light source for information light and reference light irradiated onto the hologram medium 1. In addition, the reproduction light from the hologram medium 1 is received in the optical pickup 100 and converted into a reproduction signal which is an electric signal.

  Then, the reproduction signal processing circuit 20 performs waveform equalization processing on the reproduction signal from the optical pickup 100 and outputs it as reproduction data.

  Further, the luminance evaluation value detection circuit 30 obtains the luminance evaluation value based on the reproduction signal from the optical pickup 100.

  Next, the controller 50 generates an angle drive value based on the luminance evaluation value from the luminance evaluation value detection circuit 30. Further, the controller 50 generates a stepping motor drive value so as to control the positional relationship between the hologram medium 1 and the optical pickup 100.

  In addition, the controller 50 gives the generated angle drive value to the mirror angle drive circuit 60 and controls the angle of the reference light by driving the angle of the mirror. Further, the controller 50 gives the generated stepping motor driving value to the stepping motor driving circuit 70 and drives the stepping motor to control the position of the optical pickup 100 in the radial direction of the hologram medium 1.

  Next, the case of recording in the hologram information recording / reproducing apparatus of this embodiment will be described.

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

  In FIG. 2, a light beam emitted from a laser 3 as a light source is converted into a parallel light beam by a collimator 4 and enters a beam splitter (BS) 5. This incident light beam is branched into a transmitted light beam and a reflected light beam by a beam splitter (BS) 5.

  The light beam transmitted through the beam splitter (BS) 5 illuminates the spatial light modulation element (SLM), and is narrowed down to an optimum light beam by the third relay lens 10 and the fourth relay lens 11. Then, the light enters the objective lens 12 and is irradiated onto the hologram medium 1 as information light.

  On the other hand, the light beam reflected by the beam splitter (BS) 5 is focused by the first relay lens 7 and the second relay lens 8 to the optimum light beam to be incident on the hologram medium 1 and reflected by the mirror 9. Is done. The light beam reflected by the mirror 9 is directed to the hologram medium 1 and enters the hologram medium 1 as reference light.

  As a result, the irradiated information light and reference light are mixed in the hologram medium 1 to form light interference fringes.

  Here, the laser 3, the collimator 4, the beam splitter (BS) 5, the SLM 6, the mirror 9, and the objective lens 12 are fixed by a slider (not shown). The first relay lens 7, the second relay lens 8, the third relay lens 10, the fourth relay lens 11, the lens 13, and the light receiving element 14 are also fixed by the same slider.

  This slider enables parallel sliding in the radial direction of the hologram medium 1.

  The stepping motor 15 is driven by the stepping motor drive circuit 70 of FIG. The stepping motor 15 is driven to move the slider and change the recording position.

  Further, the mirror 9 is driven by the mirror angle driving circuit 60 of FIG. 1, the angle of the reference light incident on the hologram medium 1 is adjusted, and the same recording position is irradiated, so that recording can be performed by the angle multiplexing method. .

  Next, the case of reproducing will be described.

  FIG. 3 is a block diagram showing a configuration of the optical pickup 100 in FIG.

  In FIG. 3, the light beam emitted from the laser 3 of the light source is converted into a parallel light beam by the collimator 4 in the same manner as at the time of recording, and enters the beam splitter (BS) 5.

  This incident light beam is reflected by the beam splitter (BS) 5, and is focused by the first relay lens 7 and the second relay lens 8 to the optimum light beam to be incident on the hologram medium 1 and reflected by the mirror 9. The The light beam reflected by the mirror 9 is directed to the hologram medium 1 and enters the hologram medium 1 as reference light.

  During reproduction, the spatial modulation element (SLM) 6 is put in a light-shielding state so that the light beam that has passed through the beam splitter (BS) 5 does not enter the hologram medium 1 through the objective lens 12.

  Then, by irradiating the reference light, the reproduction light transmitted through the hologram medium 1 is made parallel by the lens 13 and received by the light receiving element 14.

  The light receiving element 14 is constituted by a two-dimensional CCD, a CMOS sensor, or the like, and outputs a reproduction signal obtained by converting received light intensity into an electric signal to the reproduction signal processing circuit 20.

  Next, a procedure for generating a reproduction signal by converting the light intensity received by the light receiving element 14 into an electric signal will be described.

  FIG. 4 is a block diagram of the reproduction signal processing circuit 20. FIG. 5 is a schematic diagram of the light receiving element 14.

Note that i _max in FIG. 5 represents the number of pixels in the horizontal direction in the light receiving element 14, and j _max represents the number of pixels in the vertical direction. In the present embodiment, it is assumed that i _max = j _max = 200. Further, the pixel position arranged in the light receiving element 14 is assumed to be (i, j).

  First, the pixel position (1, 1) of the light receiving element 14 is scanned in the horizontal direction, and an electric signal is output to the AD converter 200 in the reproduction signal processing circuit 20. Similarly, an electric signal is output to the AD converter 200 up to the pixel position (200, 1).

  Next, similarly, an electric signal is output to the AD converter 200 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 200.

  The AD converter 200 converts the electrical signal from the light receiving element 14 into a digital signal and outputs it as a reproduction signal.

  Next, the reproduction data processing circuit 201 outputs the reproduction signal from the AD converter 200 as reproduction information. On the other hand, the reproduction signal converted into a digital signal by the AD converter 200 is also output to the luminance evaluation value detection circuit 30.

  Next, an example of a method for calculating the luminance evaluation value F will be described.

  FIG. 6 is a block diagram of the luminance evaluation value detection circuit 30.

  The reproduction signal from the AD converter 200 is once recorded in the memory 300 of the luminance evaluation value detection circuit 30. Here, an address is assigned and recorded in the memory 300 so that the position of the reproduction signal in the light receiving element 14 can be known.

  In the luminance evaluation value calculation circuit 301, when one screen of the light receiving element 14 is recorded in the memory 300, the pixel position (1, j) in the light receiving element 14 to the pixel position (100, j) in the B1 region. Calculate the sum of the playback signals. 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 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 50 that adjusts the angle of the reference light during recording will be described. FIG. 7 is a flowchart showing the control operation of the controller 50.

  Note that i in θ + Δθi in FIG. 7 indicates the i-th of a predetermined number of times. Here, since the predetermined number of times is set to five, i = 1 to 5.

  The controller 50 starts angle adjustment of the reference light based on the recording request. The angle adjustment is performed by reproducing an already recorded area. Here, it is assumed that the angle adjustment region is recorded with the angle of the reference light being 40.00 (deg).

  Therefore, the predetermined angle of the reference light is set to θ = 40.00 (deg). Further, the mirror angle driving circuit 60 sets the optical pickup so that the deviation Δθ1 = −0.02 (deg) by a minute amount and the angle of the reference light is 39.98 (deg) as the first angle (θ + Δθ1). The mirror 9 in 100 is controlled (S100).

  Then, the reproduction light that has passed through the hologram medium 1 is made parallel by the lens 13 and received by the light receiving element 14. The electric signal received by the light receiving element 14 is converted into a reproduction signal by the AD converter 200 in the reproduction signal processing circuit 20 and output to the luminance evaluation value detection circuit 30.

  Next, the luminance evaluation value detection circuit 30 calculates a luminance evaluation value based on the reproduction signal using the method described above (S101).

  And the result of the obtained luminance evaluation value F is held in the controller 50 as D1 (S102).

  Next, it is determined whether the angle has been set a predetermined number of times (S103). Here, the number of times of angle setting is the first time, and since the predetermined number of times 5 has not been reached, i is set to 2 and similarly the angle setting from S100 to S103 is performed (S104).

  Here, the optical pickup is performed by the mirror angle driving circuit 60 such that the deviation Δθ2 = −0.01 (deg) by a minute amount and the angle of the reference light is 39.99 (deg) as the second angle (θ + Δθ2). The mirror 9 in 100 is controlled (S100).

  Next, the luminance evaluation value F is calculated in the same manner as D1 (S101). Then, the obtained luminance evaluation value F is held in the controller 50 as D2 (S102).

  Next, it is determined whether or not the angle has been set a predetermined number of times (S103), and i is set to 3, 4, and 5 similarly until the predetermined number of times 5 is reached (S104).

  Next, Δθ3 = ± 0.00 (deg), Δθ4 = + 0.01 (deg), Δθ5 = + 0.02 (deg), and the third angle 40.00 (deg) and the fourth angle 40.01. (Deg), the fifth angle 40.02 (deg) and the angle of the reference light are set (S100).

  Next, the luminance evaluation value F is calculated similarly to D1 and D2 (S101). Then, the obtained luminance evaluation value F is held in the controller 50 as D3, D4, and D5, respectively (S102).

  When the luminance evaluation value F of the reproduction signal at the five reference light angles is held in the controller 50, it is determined that the predetermined number of times has been reached because the angle setting has been performed five times. Then, it is determined whether or not an optimum value is obtained among the five luminance evaluation values (S105). Here, the value with the brightness evaluation value closest to zero is set as the optimum value.

  For example, as shown in FIG. 8, the results of five different brightness evaluation values F are D1 = −0.01, D2 = 0.00, D3 = 0.01, D4 = 0.02, D5 = 0.03. Suppose that. In this case, since D2 can be determined to be the optimum value, 39.99 (deg) corresponding to D2 is set as the optimum reference light angle (S106).

  Then, the mirror 9 in the optical pickup 100 is controlled by the mirror angle driving circuit 60 so that the optimum reference light angle is 39.99 (deg) (S107). Then, the light beam reflected by the mirror 9 enters the hologram medium 1.

  As a result, the irradiated information light and reference light are mixed in the hologram medium 1 to form interference fringes of the light, whereby user data is recorded.

  However, when D1 = 0.04, D2 = 0.03, D3 = 0.02, D4 = 0.01, D5 = 0.005, it cannot be said that the optimum value is obtained (S105).

  Then, i + 1 is set to i as in the case of less than the predetermined number of times, and the angle is set from S100 to S103 (S104).

  Here, similarly to the above, the mirror angle drive circuit 60 uses the mirror angle driving circuit 60 to set the mirror in the optical pickup 100 so that the deviation Δθ6 = + 0.03 (deg) by a minute amount and the angle of the reference light becomes 40.03 (deg). 9 is controlled (S100).

  Next, a luminance evaluation value is calculated in the same manner as D1 (S101). Then, the obtained luminance evaluation value F is held in the controller 50 as D6 (S102).

  If the luminance evaluation value F at that time is D6 = −0.01 as shown by the white circle in FIG. 9, it can be determined that D5 is the optimum value closest to zero, and therefore 40. 02 (deg) is the optimum angle of the reference light (S106).

  Then, the mirror 9 in the optical pickup 100 is controlled by the mirror angle driving circuit 60 so that the optimum reference light angle is 39.99 (deg) (S107). Then, the light beam reflected by the mirror 9 enters the hologram medium 1.

  As a result, the irradiated information light and reference light are mixed in the hologram medium 1 to form interference fringes of the light, whereby user data is recorded.

  When the optimum value of the luminance evaluation value F is obtained, the angle of the reference light at that time is controlled as the optimum angle of the reference light, and recording of user data on the hologram medium 1 is started (S107).

  Further, other than the predetermined angle θ = 40.00 (deg), for example, reference light of another page that is angle-multiplexed and recorded at an angle θ = 40.10 (deg) or θ = 40.20 (deg) of the reference light. The angle is also adjusted in the same way for the angle.

  Note that the predetermined number of times of angle setting is not limited to five in the present embodiment. Further, the step size of the minute amount deviation is not limited to 0.01 (deg) 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 angle adjustment, stable angle control can be performed regardless of the recording state.

  It should be noted that the reference light angle adjustment at the time of recording may also be performed by using data recorded by trial recording for angle adjustment in other already recorded user data areas or vacant user data areas. Good. In the angle control, by using the user data area, the angle 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 reference light angle condition. Can do.

  Furthermore, the latest recorded data or recorded data that is closest to the next recording address may be used. In the angle control, it is possible to make the recording conditions in the hologram medium uniform by using data with relatively similar recording conditions.

  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 element 14 recorded in the memory 300 in the same manner as described above.

  First, an average value of reproduction signals in an area brighter than a certain threshold value is calculated. Similarly, an average value of reproduction signals in an area 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 50 as the luminance evaluation value F, and the angle of the reference light is adjusted so that this value becomes large. .

  As described above, according to this embodiment, the angle of the reference light is deviated by a minute amount with respect to the predetermined angle, and the optimum angle of the reference light obtained from the luminance evaluation value of the reproduction signal is recorded. Used as the angle of the reference light.

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

(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. 10 is a block diagram showing a schematic configuration of 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. 10, the error rate calculation circuit 40 calculates the error rate based on the reproduction information from the reproduction signal processing circuit 20.

  Next, the controller 50 generates an angle drive value based on the error rate information from the error rate calculation circuit 40. Further, the controller 50 generates a stepping motor drive value so as to control the positional relationship between the hologram medium 1 and the optical pickup 100.

  Next, the operation of the controller 50 in the second embodiment will be described along the flowchart of angle adjustment in FIG.

  FIG. 11 is a flowchart showing the control operation of the controller 50 of the present embodiment.

Note that _i in θ + Δθ _i in FIG. 11 indicates the i-th number of times. Here, since the predetermined number of times is set to five, i = 1 to 5.

  The controller 50 starts angle adjustment of the reference light based on the recording request. Here, it is assumed that the angle adjustment region is recorded with the angle of the reference light being 40.00 (deg). Therefore, the predetermined angle of the reference light is set to θ = 40.00 (deg).

  Further, the mirror angle driving circuit 60 sets the optical pickup so that the deviation Δθ1 = −0.02 (deg) by a minute amount and the angle of the reference light is 39.98 (deg) as the first angle (θ + Δθ1). The mirror 9 in 100 is controlled (S200).

  Then, the reproduction light that has passed through the hologram medium 1 is made parallel by the lens 13 and received by the light receiving element 14. A reproduction signal obtained by converting the light intensity received by the light receiving element 14 into an electric signal is output to the reproduction signal processing circuit 20.

  Next, in the reproduction signal processing circuit 20, the error rate calculation circuit 40 performs error correction based on the reproduction information subjected to waveform equalization processing, and calculates the error rate (S201).

  Then, the obtained error rate result is held in the controller 50 as E1 (S202).

  Next, it is determined whether or not the angle has been set a predetermined number of times (S203). Here, the number of times of angle setting is the first time, and since the predetermined number of times 5 has not been reached, i is set to 2 and similarly the angle setting from S100 to S103 is performed (S204).

  Here, the optical pickup is performed by the mirror angle driving circuit 60 such that the deviation Δθ2 = −0.01 (deg) by a minute amount and the angle of the reference light is 39.99 (deg) as the second angle (θ + Δθ2). The mirror 9 in 100 is controlled (S200).

  Next, the error rate is calculated in the same manner as E1 (S201). The obtained error rate result is held in the controller 50 as E2 (S202).

  Next, it is determined whether or not the angle has been set a predetermined number of times (S203), and i is set to 3, 4, and 5 similarly until the predetermined number of times 5 is reached (S204).

  Next, Δθ3 = ± 0.00 (deg), Δθ4 = + 0.01 (deg), Δθ5 = + 0.02 (deg), and the third angle 40.00 (deg) and the fourth angle 40.01. (Deg), the fifth angle 40.02 (deg) and the angle of the reference light are set (S200).

  Next, an error rate is calculated in the same manner as E1 and E2 (S201). The obtained error rate results are held in the controller 50 as E3, E4, and E5, respectively (S202).

  When the error rate result of the reproduction signal at the above five reference light angles is held in the controller 50, it is determined that the angle has been set a predetermined number of times. Then, it is determined whether or not the minimum value is obtained among the five error rates (S205).

  For example, assume that the five error rate results are E1 = 5e-6, E2 = 1e-6, E3 = 3e-6, E4 = 7e-6, and E5 = 1e-5, as shown in FIG. In this case, since E2 can be determined to be a minimum value, 39.99 (deg) corresponding to E2 is set as the optimum reference light angle (S206).

  Then, the mirror 9 in the optical pickup 100 is controlled by the mirror angle driving circuit 60 so that the optimum reference light angle is 39.99 (deg) (S207). Then, the light beam reflected by the mirror 9 enters the hologram medium 1. As a result, the irradiated information light and reference light are mixed in the hologram medium 1 to form interference fringes of the light, whereby user data is recorded.

  However, when E1 = 4e-5, E2 = 1e-5, E3 = 7e-6, E4 = 5e-6, E5 = 3e-6, it is monotonically decreasing as shown by the black circles in FIG. It can be judged that the minimum value is not obtained. Then, i + 1 is set to i in the same manner as in the case of less than the predetermined number of times, and the angle setting from S200 to S203 is similarly performed (S204).

  Here, similarly to the above, the mirror angle drive circuit 60 uses the mirror angle driving circuit 60 to set the mirror in the optical pickup 100 so that the deviation Δθ6 = + 0.03 (deg) by a minute amount and the angle of the reference light becomes 40.03 (deg). 9 is controlled (S200). Next, error rate information is calculated as in E1 (S201). Then, the obtained error rate result is held in the controller 50 as E6 (S202).

  If the error rate result at that time is E6 = 6e−6 as indicated by the white circle in FIG. 13, it can be determined that E5 is not a monotonous decrease and that E5 is a minimum value, and therefore 40.02 ( deg) is set to the optimum angle of the reference light (S206).

  Then, the mirror 9 in the optical pickup 100 is controlled by the mirror angle driving circuit 60 so that the optimum reference light angle is 39.99 (deg) (S207). Then, the light beam reflected by the mirror 9 enters the hologram medium 1. As a result, the irradiated information light and reference light are mixed in the hologram medium 1 to form interference fringes of the light, whereby user data is recorded.

Meanwhile, although not shown, as E6 = 1e-6, if it was monotonously decreased, can not determine the minimum value is obtained in the same manner as described above, it sets the i + 1 to i, a minute amount deviation [Delta] [theta] _i The process is changed in increments of 0.01 (deg) until the minimum value of the error rate is obtained. If the minimum value of the error rate is obtained, the reference light angle at that time is controlled as the optimum reference light angle (S207).

  Then, the light beam reflected by the mirror 9 enters the hologram medium 1. As a result, the irradiated information light and reference light are mixed in the hologram medium 1 to form interference fringes of the light, whereby user data is recorded.

  Although not shown, the minimum value can be obtained even when monotonically increasing, such as E1 = 3e-6, E2 = 5e-6, E3 = 7e-6, E4 = 1e-5, E5 = 4e-5. Cannot be judged.

  Therefore, similarly to the above, the mirror angle driving circuit is set so that i + 1 is set to i, the minute amount deviation Δθ6 = −0.03 (deg), and the angle of the reference light is 39.97 (deg). 60 controls the mirror 9 in the optical pickup 100.

  Therefore, if E6 = 6e−6, it can be determined that the minimum value has been obtained, so 39.98 (deg) corresponding to E1 is set as the optimum angle of the reference light.

  Then, the mirror 9 in the optical pickup 100 is controlled by the mirror angle driving circuit 60 so that the optimum reference light angle is 39.98 (deg). Then, the light beam reflected by the mirror 9 enters the hologram medium 1.

  As a result, the irradiated information light and reference light are mixed in the hologram medium 1 to form interference fringes of the light, whereby user data is recorded.

On the other hand, although not shown, if E6 = 1e-6, it cannot be determined that the minimum value has been obtained. Therefore, as described above, i + 1 is set to _i, and the deviation Δθ _i corresponding to the minute amount is set to −0.01 (deg.). ) Change in increments until the minimum error rate is obtained.

  Further, other than the predetermined angle θ = 40.00 (deg), for example, the reference beam of another page that is angle-multiplexed and recorded at an angle θ = 40.10 (deg) or θ = 40.20 (deg) of the reference beam. Regarding the angle, the angle is adjusted in the same manner.

  Note that the predetermined number of times of angle setting is not limited to five in the present embodiment. Further, the step size of the minute amount deviation is not limited to 0.01 (deg) in the present embodiment.

  Similarly to the first embodiment, the angle control of the reference light at the time of recording is performed in the management information area, the user data area that has already been recorded, and the vacant user data area. Therefore, data obtained by trial recording may be used.

  As described above, according to the present embodiment, the angle of the reference light is deviated by a minute amount with respect to the predetermined angle, the angle of the reference light that minimizes the error rate of the reproduction signal is obtained, and recording is performed. Used as the angle of the reference beam.

  As a result, not only when the angle of the optimum reference light changes due to a change in dimensions during recording, but also with the noise characteristics of the hologram medium 1 / light receiving element 14, etc. Data can be recorded. In addition, even during reproduction, reproduction can be performed over the entire surface of the hologram medium under a certain reference light angle condition.

  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 schematic configuration of a two-beam interference method hologram information recording / reproducing apparatus as a first embodiment of the present invention. FIG. It is a block diagram which shows the structure of the optical pick-up 100 in FIG. It is a block diagram which shows the structure of the optical pick-up 100 in FIG. FIG. 2 is a block diagram of a reproduction signal processing circuit 20 in FIG. 1. It is a schematic diagram of the light receiving element 14 in FIG. FIG. 2 is a block diagram of a luminance evaluation value detection circuit 30 in FIG. 1. It is a flowchart which shows the control operation of the controller 50 in the 1st Embodiment of this invention. It is a graph which shows an example of the brightness | luminance evaluation value result in the 1st Embodiment of this invention. It is a graph which shows another example of the brightness | luminance evaluation value result in the 1st Embodiment of this invention. It is a block diagram which shows schematic structure of the hologram information recording / reproducing apparatus in the 2nd Embodiment of this invention. It is a flowchart which shows the control operation of the controller 50 in the 2nd Embodiment of this invention. It is a graph which shows an example of the brightness | luminance evaluation value result in the 2nd Embodiment of this invention. It is a graph which shows another example of the brightness | luminance evaluation value result in the 1st Embodiment of this invention. It is a figure which shows the mode of the angle change of a diffraction grating by the dimension change of a hologram medium, and the change of a grating | lattice space | interval.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hologram medium 2 Spindle motor 3 Laser 4 Collimator 5 Beam splitter (BS)
6 Spatial light modulator (SLM)
7 First relay lens 8 Second relay lens 9 Mirror 10 Third relay lens 11 Fourth relay lens 12 Objective lens 13 Lens 14 Light receiving element 15 Stepping motor 20 Reproduction signal processing circuit 30 Luminance evaluation value detection circuit 40 Error Rate calculation circuit 50 Controller 60 Mirror angle drive circuit 70 Stepping motor drive circuit 100 Optical pickup 200 AD converter 201 Reproduction data processing circuit 300 Memory 301 Brightness evaluation value calculation circuit

Claims (7)

In a hologram information recording / reproducing apparatus for causing information light and reference light to interfere, recording information on a hologram medium, and reproducing information by irradiating the hologram medium with the reference light,
A mirror for irradiating the hologram medium with the reference light;
A mirror angle driving circuit that adjusts an angle of the reference light incident on the hologram medium by driving the mirror;
A reproduction signal processing circuit for reproducing information recorded on the hologram medium based on a reproduction signal read by the reference light applied to the hologram medium;
A hologram information recording / reproducing apparatus, wherein an angle of the reference light at the time of recording is determined based on reproduction information output from the reproduction signal processing circuit. The mirror angle driving circuit determines the angle of the reference light for each page on which information is recorded,
2. The hologram information recording / reproducing apparatus according to claim 1, wherein the information is recorded by irradiating the reference light to the same position as the page on which the information is recorded. The hologram medium has an area for recording management information of information recorded on the hologram medium,
2. The hologram information recording / reproducing apparatus according to claim 1, wherein the reproduction signal is reproduced based on light from which the management information is read. The reproduction signal processing circuit reproduces the reproduction signal based on light from which the latest recorded data in the hologram medium or recorded data at a position closest to an address to be recorded next is read out. The hologram information recording / reproducing apparatus according to claim 1. The light receiving element that receives the reproduction light is divided into two regions including the same number of pixels,
From the reproduction signal, the sum of the reproduction signal for each of the two regions is calculated,
The difference of the sum is calculated as a luminance evaluation value,
2. The hologram information recording / reproducing apparatus according to claim 1, wherein an angle of the reference light is determined so that the luminance evaluation value is close to 0, and an angle of the reference light is adjusted based on the angle. In the light receiving element that receives the reproduction light, the average value of the reproduction signal in a region brighter than a certain threshold and the average value of the reproduction signal in a region darker than a certain threshold are calculated,
2. The hologram information recording / reproducing apparatus according to claim 1, wherein an angle of the reference light that increases a difference between the calculated average values is determined, and the angle of the reference light is adjusted based on the angle. An error rate calculation circuit for calculating an error rate based on the reproduction information;
2. The hologram information recording / reproducing apparatus according to claim 1, wherein an angle of the reference light that minimizes the error rate is determined, and an angle of the reference light is adjusted based on the angle.

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