WO2015075827A1

WO2015075827A1 - Hologram reconstruction device and hologram reconstruction method

Info

Publication number: WO2015075827A1
Application number: PCT/JP2013/081579
Authority: WO
Inventors: 愼介尾上; 山田　健一郎; 岳緒方
Original assignee: 日立コンシューマエレクトロニクス株式会社
Priority date: 2013-11-25
Filing date: 2013-11-25
Publication date: 2015-05-28

Abstract

An objective of the present invention is to provide a hologram reconstruction device and hologram reconstruction method capable of appropriately reconstructing information recorded in a hologram recording medium. The hologram reconstruction device reconstructs information which is recorded in a hologram recording medium, and the hologram reconstruction method is used with the hologram reconstruction device. The hologram reconstruction device comprises: a light source which emits a reference light; an entry angle change unit which is capable of changing the entry angle of the reference light which enters the hologram recording medium; an angle error signal generating unit which generates an angle error signal; a target angle setting unit which sets a target angle of the entry angle of the reference light; and an entry angle control unit which controls the entry angle change unit, using as a control target the target angle set by the target angle setting unit. The target angle setting unit changes the target angle on the basis of the angle error signal in a period wherein the entry angle control unit controls the entry angle change unit to change the entry angle of the reference light.

Description

Hologram reproducing apparatus and hologram reproducing method

The present invention relates to a hologram reproducing apparatus and a hologram reproducing method for reproducing using holography.

While research on next-generation storage technology is underway, hologram recording technology that records digital information using holography is drawing attention.

Hologram recording technology is a method in which signal light having page data information two-dimensionally modulated by a spatial light modulator is superimposed on reference light inside the recording medium, and the interference fringe pattern generated at that time is placed in the recording medium. This is a technique for recording information on a recording medium by causing refractive index modulation.

However, in the hologram recording technique, it is a problem to control the relative angle between the signal light and the reference light with high accuracy. In order to solve such a problem, in Patent Document 1, signal light is detected by an image sensor in order to search for a relative angle between the signal light and the reference light, and an SNR that is a reproduction performance is calculated for each recording angle. The relative angle of the reference light with respect to the signal light is controlled by predicting the relative angle.

US2009 / 0207710A1

One major advantage of hologram recording technology is that it can record large amounts of data. However, when an increase in recording capacity is pursued, it is necessary to improve the accuracy of positioning control related to the position and angle at which the signal light and reference light are irradiated more than before.

Patent Document 1 can search for a relative angle between signal light and reference light, but has two major problems. The first is high-speed playback, and the second is playback performance.

In the case of the configuration of Patent Document 1, there is an effect that it is not necessary to add a detection unit. On the other hand, a control signal for a relative angle can be generated only after the reproduction signal is detected by the image sensor and the SNR is calculated. Is an issue.

Further, Patent Document 1 is characterized in that control is performed to an angle shifted by a minute amount from the relative angle at which the reproduction signal is best in order to generate a reference light angle control signal. For this reason, in principle, it is impossible to reproduce at the optimum angle, and it is obvious that the best reproduction signal cannot be obtained.

As described above, it is a problem to detect the angle error signal of the reference light that can realize high-speed reproduction and obtain the best reproduction signal.
Therefore, an object of the present invention is to provide a hologram reproducing apparatus and a hologram reproducing method capable of detecting an angle error signal of a reference light angle, which can realize high-speed reproduction and obtain the best reproduction signal.

The above problem is solved by, for example, the invention described in the scope of claims.

According to the present invention, information recorded on the hologram recording medium can be suitably reproduced.

1 is a block diagram showing a hologram recording / reproducing apparatus of Example 1. FIG. It is a figure explaining the recording principle of a hologram recording / reproducing apparatus. It is a figure explaining the reproduction | regeneration principle of a hologram recording / reproducing apparatus. It is a flowchart until the preparation of recording or reproduction | regeneration in a hologram recording / reproducing apparatus is completed. It is a flowchart of the recording process in a hologram recording / reproducing apparatus. It is a flowchart of the reproduction | regeneration processing in a hologram recording / reproducing apparatus. 6 is a flowchart of seek processing in the first embodiment. 3 is a flowchart of data reproduction processing according to the first embodiment. It is a figure explaining the signal S1 and the signal S2 in Example 1. FIG. It is a figure explaining the angle error signal AES in Example 1. FIG. FIG. 3 is a block diagram illustrating a first incident angle control circuit according to the first embodiment. FIG. 6 is a diagram illustrating a scanning direction of reference light in page seek in a book according to the first exemplary embodiment. FIG. 6 is a diagram illustrating a scanning direction of reference light in page seek in a book according to the first exemplary embodiment. In Example 1, it is a figure explaining the angle error signal (AES) when expansion | swelling of a medium generate | occur | produces. FIG. 4 is a schematic diagram of signal waveforms at various parts in the page seek according to the first embodiment. It is a figure explaining the influence by the speed of the incident angle of the reference light in the vicinity of the incident angle from which an angle error signal (AES) is obtained. It is a figure explaining the problem that the time which passes an angle error signal (AES) becomes short. FIG. 6 is a block diagram showing a hologram recording / reproducing apparatus of Example 2. It is a figure for demonstrating the effect of Example 2. FIG. It is a figure explaining the definition of the incident angle in this specification. It is a figure explaining the definition of the orthogonal incident angle in this specification. It is a figure explaining the definition of the orthogonal incident angle in this specification.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing a recording / reproducing apparatus for a holographic recording medium that records and / or reproduces digital information using holography.

The hologram recording / reproducing device 10 is connected to an external control device 91 via an input / output control circuit 90. When recording information on the hologram recording medium 1, the hologram recording / reproducing apparatus 10 receives an information signal to be recorded from the external control device 91 by the input / output control circuit 90. When reproducing information from the hologram recording medium 1, the hologram recording / reproducing device 10 transmits the reproduced information signal to the external control device 91 by the input / output control circuit 90.

The hologram recording medium 1 in this embodiment has a disk shape and has an angle detection mark for detecting the rotation angle of the hologram recording medium.

The hologram recording / reproducing apparatus 10 includes a pickup 11, a reproduction reference light optical system 12, a cure optical system 13, an angle error detection optical system 30, a rotation angle detection sensor 14, a radial position detection sensor 15, a spindle motor 50, and a radial direction conveyance unit. 51 is provided.

The spindle motor 50 has a medium attaching / detaching portion (not shown) that allows the hologram recording medium 1 to be attached to and detached from the rotation axis. The hologram recording medium 1 is configured to be rotatable by the spindle motor 50. At the same time, the hologram recording medium 1 is configured to be movable in the radial direction by the radial transport unit 51 with reference to the position of the pickup 11.

The position where the signal light and / or reference light is irradiated is determined by the position of the pickup 11 described later, and is a position fixed to the apparatus. In the present embodiment, the spindle motor 50 and the radial direction conveyance unit 51 function as means for changing the position on the hologram recording medium 1 irradiated with the signal light and / or the reference light.

The rotation angle detection sensor 14 detects the rotation angle of the hologram recording medium 1 using an angle detection mark provided on the hologram recording medium 1. The output signal of the rotation angle detection sensor 14 is input to the spindle control circuit 40. When changing the rotation angle irradiated with the signal light and the reference light, the spindle control circuit 40 generates a drive signal based on the output signal of the rotation angle detection sensor 14 and the command signal from the controller 80, and the spindle drive circuit The spindle motor 50 is driven via 41. Thereby, the rotation angle of the hologram recording medium 1 can be controlled. This control is called spindle control.

Further, a scale 16 having a predetermined pattern is fixed to the movable part of the radial direction transport part 51. The radial position detection sensor 15 detects the position of the movable part of the radial direction transport part 51 using the scale 16. When the radial position irradiated with the signal light and the reference light is changed, the radial direction transport control circuit 42 generates a drive signal based on the output signal of the radial position detection sensor 15 and the command signal from the controller 80, and the radial direction The radial conveyance unit 51 is driven via the conveyance drive circuit 43. Thereby, the hologram recording medium 1 is conveyed in the radial direction. Thereby, the radial position irradiated with the signal light and the reference light can be controlled. This control is called radial position control.

Further, the spindle control circuit 40 and the radial direction conveyance control circuit 42 return information to the controller 80 as to whether or not each drive is completed.

The pickup 11 is used when information is recorded on the hologram recording medium 1 and when information recorded on the hologram recording medium 1 is reproduced. When recording information on the hologram recording medium 1, the hologram recording medium 1 is irradiated with reference light and signal light, and digital information is recorded on the recording medium using holography. At this time, the information signal to be recorded is sent by the controller 80 to a spatial light modulator (described later) in the pickup 11 via the signal generation circuit 81, and the signal light is modulated by the spatial light modulator.

When reproducing the information recorded on the hologram recording medium 1, the reproduction reference light optical system 12 generates a light wave that causes the reference light emitted from the pickup 11 to enter the hologram recording medium 1 in the direction opposite to that during recording. To do. Diffracted light reproduced by the reproduction reference light is detected by a photodetector 226 described later in the pickup 11, and a signal is reproduced by a signal processing circuit 82.

Furthermore, the angle at which the reference light enters the hologram recording medium 1 is controlled by the first incident angle control circuit 21, the second incident angle control circuit 24, and the orthogonal incident angle control circuit 27. Here, “incident angle” and “orthogonal incident angle” are defined in this specification with respect to the angle at which the reference light is incident on the hologram recording medium 1. Hereinafter, a description will be given with reference to FIG.

FIG. 17A is a diagram showing the wave number vector Ks of the signal light, the wave number vector Kr of the reference light, and the medium surface of the hologram recording medium 1 during recording. The incident surface of the signal light is defined as a plane including the wave vector Ks of the signal light and the normal vector of the hologram recording medium 1. When the apparatus is in an ideal state, the wave number vector Kr of the reference light exists in the incident surface of the signal light, and FIG. 17 (a) shows the state. At this time, as shown in FIG. 17A, the angle of the wave number vector Kr of the reference light can be changed in the incident surface of the signal light. This change in the angle of the reference light on the incident surface is referred to as “change in the incident angle” in this specification.

Subsequently, “Changing the orthogonal incidence angle” will be described. FIG. 17B and FIG. 17C are diagrams for explaining it. FIG. 17B shows a state in which the orthogonal incident angle is changed from the state of FIG. Further, FIG. 17C shows a state when FIG. 17B is viewed from the side.

As can be seen from FIG. 17B, when the orthogonal incident angle of the reference light is changed, the wave number vector Kr of the reference light is not on the incident surface of the signal light but on the plane A of FIG. 17B. That is, “changing the orthogonal angle” means changing the angle at which the reference light is incident on the hologram recording medium 1 in a direction perpendicular to the incident surface of the signal light.

In the state where the orthogonal incident angle is changed as shown in FIG. 17B, “change of the incident angle” refers to change of the angle of the reference light in the plane A.

As is clear from FIG. 17C, the direction in which the incident angle is changed (that is, the direction included in the plane A) and the direction in which the orthogonal incident angle is changed (the direction of the arrow in FIG. 17C) are Must be orthogonal.

The angle error signal generation circuit 31 generates and outputs an angle error signal (AES) described later using output signals of the photodetector 234 and the photodetector 236 described later in the angle error detection optical system 30. The angle error signal (AES) is a signal indicating a deviation (error) from the optimum angle with respect to the incident angle.

The incident angle target value setting circuit 32 receives the instruction from the controller 80 and the angle error signal (AES) output from the angle error signal generation circuit 31, and sets the incident angle target value Tgtφ for use in control. Output as a signal. Further, the controller 80 outputs the target value Tgtρ of the orthogonal incident angle.

The first incident angle signal generation circuit 20 generates a signal used for controlling the incident angle of the reference light from the output signal of the pickup 11. The first incident angle control circuit 21 generates a drive signal using the output signal of the first incident angle signal generation circuit 20 and the output signal Tgtφ of the incident angle target value setting circuit 32. The first incident angle drive circuit 22 drives an actuator 221 described later in the pickup 11 using a drive signal from the first incident angle control circuit 21.

The second incident angle signal generation circuit 23 generates a signal used for controlling the incident angle of the reference light from the output signal of the reproduction reference light optical system 12. The second incident angle control circuit 24 generates a drive signal using the output signal of the second incident angle signal generation circuit 23 and the output signal Tgtφ of the incident angle target value setting circuit 32. The second incident angle drive circuit 25 drives an actuator 224 (described later) in the reproduction reference light optical system 12 using a drive signal from the second incident angle control circuit 24.

In this way, by driving the actuator 221 and the actuator 224, the incident angle of the reference light incident on the hologram recording medium 1 is controlled.

The orthogonal incident angle signal generation circuit 26 generates a signal to be used for controlling the orthogonal incident angle of the reference light from the output signal of the pickup 11. The orthogonal incident angle control circuit 27 generates a drive signal using the output signal of the orthogonal incident angle signal generation circuit 26 and the command value Tgtρ of the orthogonal incident angle from the controller 80. The orthogonal incident angle drive circuit 28 drives an actuator 219 (described later) in the pickup 11 using a drive signal from the orthogonal incident angle control circuit 27. By driving the actuator 219 in this way, the orthogonal incident angle of the reference light incident on the hologram recording medium 1 is controlled.

When the angle specified by the controller 80 to the orthogonal incident angle control circuit 27 is the reference position (orthogonal incident angle command value Tgtρ = 0), the reference light passes through the same plane as the signal light incident surface. It will be in the state shown by 17 (a). On the other hand, when the angle instructed by the controller 80 to the orthogonal incident angle control circuit 27 is other than the reference position, the reference light is inclined by a predetermined amount in the direction orthogonal to the incident surface of the signal light. The state shown in (b) is obtained.

Adjustment of the irradiation time of the reference light and the signal light with which the hologram recording medium 1 is irradiated is performed by the controller 80 transmitting a signal to the shutter control circuit 84, and the shutter control circuit 84 using the signal transmitted from the controller 80. Control is performed to open and close.

The cure optical system 13 plays a role of generating a light beam used for pre-cure and post-cure of the hologram recording medium 1. Pre-curing is a pre-process for irradiating a predetermined light beam in advance before irradiating the reference light and signal light to the desired position when recording information at the desired position in the hologram recording medium 1. Post-cure is a post-process for irradiating a predetermined light beam after recording information at a desired position in the hologram recording medium 1 so that additional recording cannot be performed at the desired position. The light beam used for pre-cure and post-cure is preferably incoherent light, that is, light with low coherence.

The light source drive circuit 83 supplies a predetermined light source drive current to the light sources in the pickup 11 and the cure optical system 13 in accordance with an instruction from the controller 80. The light source of the light source in the pickup 11 and the cure optical system 13 emits a light beam with a predetermined light amount.

Here, the pickup 11, the reproduction reference light optical system 12, the cure optical system 13, and the angle error detection optical system 30 may be simplified by combining some optical system configurations or all optical system configurations. .

FIG. 2 shows a recording principle in an example of a basic optical system configuration of the pickup 11, the reproducing reference light optical system 12 and the angle error detection optical system 30 in the hologram recording / reproducing apparatus 10. The reproduction reference light optical system 12 includes an actuator 224 and a galvanometer mirror 225.

The light beam emitted from the light source 201 passes through the collimator lens 202 and enters the shutter 203. When the shutter 203 is open, after the light beam passes through the shutter 203, the optical element 204 composed of, for example, a half-wave plate or the like, adjusts the light quantity ratio of p-polarized light and s-polarized light to a desired ratio. After the polarization direction is controlled, the light beam enters a PBS (Polarization Beam Splitter) prism 205.

The light beam that has passed through the PBS prism 205 functions as signal light 206, and after the light beam diameter is expanded by the beam expander 208, the light beam passes through the phase mask 209, the relay lens 210, and the PBS prism 211 and passes through the spatial light modulator 212. Is incident on.

The signal light 206 to which information is added by the spatial light modulator 212 is reflected by the PBS prism 211 and propagates through the relay lens 213 and the spatial filter 214. Thereafter, the signal light is condensed on the hologram recording medium 1 by the objective lens 215.

On the other hand, the light beam reflected from the PBS prism 205 is set to a predetermined polarization direction according to recording or reproduction by the polarization direction conversion element 216 and then enters the Wollaston prism 230.

The Wollaston prism 230 is an optical element that branches into two beams whose propagation directions differ by an angle φ according to the polarization of the incident light beam. However, at the time of recording by the hologram recording / reproducing apparatus of the present embodiment, the polarization direction conversion element 216 passes only s-polarized light. Thereby, the light beam at the time of recording goes straight without polarization state or branching of the light beam occurring in the polarization direction conversion element 216 and the Wollaston prism 230. The light beam that has traveled straight becomes reference light 207.

The light beam that has passed through the Wollaston prism 230 is incident on the galvanometer mirror 220 via the mirror 217 and the galvanometer mirror 218. The galvanometer mirror 220 can adjust the angle in the paper surface by the actuator 221, and the incident angle of the reference beam 207 incident on the hologram recording medium 1 after passing through the lens 222 and the lens 223 can be set to a desired angle. . In order to set the incident angle of the reference beam 207, an element that converts the wavefront of the reference beam 207 may be used instead of the galvanometer mirror.

Further, the galvanometer mirror 218 can adjust the angle in the direction perpendicular to the paper surface by the actuator 219, and sets the orthogonal incident angle of the reference light incident on the hologram recording medium 1 after passing through the lens 222 and the lens 223 to a desired angle. Can do.

Thus, the signal light 206 and the reference light 207 are incident on the hologram recording medium 1 so as to overlap each other, whereby an interference fringe pattern is formed in the hologram recording medium 1 and this pattern is written to the hologram recording medium 1. To record information. In addition, since the incident angle of the reference light incident on the hologram recording medium 1 can be changed by the galvanometer mirror 220, recording by angle multiplexing is possible.

Hereinafter, in holograms recorded in the same area with different incident angles of the reference light, holograms corresponding to each incident angle are called pages, and a set of pages angle-multiplexed in the same area is called a book. To do.

FIG. 3 shows a reproduction principle in an example of a basic optical system configuration of the pickup 11, the reproduction reference light optical system 12, and the angle error detection optical system 30 in the hologram recording / reproduction apparatus 10.

During reproduction, the polarization direction conversion element 216 converts the incident S-polarized light into a polarized light component composed of P-polarized light and S-polarized light. The Wollaston prism 230 is an optical element that branches into two beams whose propagation directions differ by an angle φ according to the polarization of the incident light beam. For this reason, the reference light 207 transmitted through the Wollaston prism 230 is a light beam in two propagation directions having different polarizations. Here, of the two beams, the S-polarized light beam is referred to as reference light, and the P-polarized light beam is referred to as a control light beam. The reference light travels straight through the Wollaston prism 230.

The two light beams transmitted through the Wollaston prism 230 are incident on the hologram recording medium 1 via the galvanometer mirror 218 and the galvanometer mirror 220 in the same manner as in recording.

At this time, since the reference light and the control light beam are incident on the recording area in the hologram recording medium 1, two diffracted lights corresponding to the incident angle are generated in the direction of the lens 231. These diffracted lights pass through the lens 231 and enter the PBS prism 232. Here, since the diffracted light generated in the hologram recording medium 1 is the same polarization as the incident polarized light, the diffracted light generated from the reference light reflects the PBS prism 232, and the diffracted light generated from the control light beam is the PBS prism. 232 is transmitted. Then, the respective diffracted lights enter the light receiving portions of the photodetector 234 and the photodetector 236 through the detection lens 233 and the detection lens 235.

The output signal of the photodetector 234 and the output signal of the photodetector 236 are input to the angle error signal generation circuit 31. Here, when the signal obtained by the photodetector 234 is S1, and the signal obtained by the photodetector 236 is S2, the angle error signal (AES) can be expressed as follows.

Signals S1 and S2 are sum signals obtained by detecting the total amount of each diffracted light. The angle error signal generation circuit 31 performs the calculation of (Equation 1) and outputs an angle error signal (AES).

Further, the reference beam 207 reflected from the galvanometer mirror 220 is incident on the hologram recording medium 1, and the light beam transmitted through the hologram recording medium 1 is reflected by the galvanometer mirror 225 whose angle can be adjusted by the actuator 224. A reference beam is generated.

The diffracted light reproduced by the reproduction reference light propagates through the objective lens 215, the relay lens 213, and the spatial filter 214. Thereafter, the reproduced diffracted light passes through the PBS prism 211 and enters the photodetector 226, and the signal recorded in the hologram recording medium 1 can be reproduced. For example, an image sensor such as a CMOS image sensor or a CCD image sensor can be used as the photodetector 226. However, any element may be used as long as page data can be reproduced.

In this embodiment, the first incident angle signal generation circuit 20 uses the output signal of the angle detection sensor (not shown) provided in the actuator 221 to finally generate the reference light 207 reflected from the galvanometer mirror 220. A signal AS1 indicating the incident angle when entering the medium is generated. Similarly, with respect to the reproduction reference light optical system 12, the second incident angle signal generation circuit 23 uses the output signal of the angle detection sensor (not shown) provided in the actuator 224 to reproduce the galvano mirror 225. A signal AS2 indicating an incident angle when the reference light for use finally enters the medium is generated.

The orthogonal incident angle signal generation circuit 26 generates a signal indicating the orthogonal incident angle of the reference light reflected from the galvanometer mirror 218 using an output signal of an angle detection sensor (not shown) provided in the actuator 219, and performs orthogonal incidence. Generated as a signal for use in angle control. For example, an optical encoder can be used as the angle detection sensor provided in the actuator 221, the actuator 224, and the actuator 219.

Here, a method of detecting the angle error signal (AES) will be described.
First, a method for detecting the angle error signal (AES) will be described. FIG. 7 shows a signal S1 obtained by the photodetector 234, a signal S2 obtained by the photodetector 236, and a reproduction signal when the incident angle of the reference beam 207 to the hologram recording medium 1 is changed by rotating the galvanometer mirror 220. The signal intensity is shown. Each signal intensity is normalized with the maximum value.

It can be seen that the signal S1 and the signal S2 are shifted by an angle Δφ with respect to the incident angle of the reference beam 207 with respect to the hologram recording medium 1. This is because two light beams having different angles are generated by the Wollaston prism 230 and separated and detected.

FIG. 8 shows the angular differential signal AES of the present invention calculated from the signals S1 and S2 of FIG. It can be seen from FIG. 8 that the angle P1 (or P2, P3) at which the reproduction signal is maximum is shifted from the angle Z1 (or Z2, Z3) (the angle at which zero crossing is performed) at which the angle error signal is zero. Note that the amount of angular deviation between P1 and Z1 (or P2 and Z2, P3 and Z3) is Δφ / 2 because the angular difference between the signals S1 and S2 shown in FIG. 7 is Δφ.

Here, when normal control is performed using the angle error signal (AES), it is difficult to control to the angle P1 at which the reproduction signal is maximized. For example, in the case of a conventional optical disk represented by BD (Blu-ray (registered trademark)) or the like, an offset is electrically provided for offset by control, but the angle error signal (AES) shown in FIG. Since the signal is at the bottom (or peak), there is a problem that the same control cannot be performed.

The configuration of the first incident angle control circuit 21 of the present embodiment will be described with reference to FIG. The first incident angle control circuit 21 includes a subtractor 2101, a servo compensator 2102, an output control switch 2103, and a static determination circuit 2104.

The first incident angle control circuit 21 receives the output signal AS1 of the first incident angle signal generation circuit 20 and the target value Tgtφ of the incident angle output from the incident angle target value setting circuit 32, and the reference beam 207 is a hologram. The angle of the galvanometer mirror 220 is controlled so that the incident angle when entering the recording medium 1 becomes Tgtφ. Hereinafter, this control is referred to as first incident angle control.

Here, the AS1 signal is a signal indicating an incident angle when the reference light 207 reflected by the galvano mirror 220 finally enters the medium.

The subtractor 2101 subtracts the AS1 signal and the Tgtφ signal and outputs a value of (AS1−Tgtφ). The servo compensator 2102 performs gain and phase compensation on the output signal of the subtractor 2101, and outputs a drive signal for controlling the angle of the galvanometer mirror 220. The subtractor 2101 and the servo compensator 2102 constitute a feedback control system for controlling the angle of the galvanometer mirror 220.

Further, the target value of the feedback control system is Tgtφ, and control is performed so that the angle of the galvano mirror 220 becomes Tgtφ. According to the configuration of the present embodiment, the position information fed back is the AS1 signal.

The output control switch 2103 receives the output signal of the servo compensator 2102 and switches whether to output the output signal of the servo compensator 2102 according to the control signal G1ON from the controller 80. When the G1ON signal is High, the output control switch 2103 selects the terminal a and outputs the output signal of the servo compensator 2102 as the GD1 signal. On the other hand, when the G1ON signal is Low, the output control switch 2103 selects the terminal b, outputs the reference potential as the GD1 signal, and does not output the servo compensator 2102 output signal. Thus, the G1ON signal is a signal for instructing on / off of the first incident angle control. Thus, the output control switch 2103 functions as a switch for switching on / off the first incident angle control. The GD1 signal output from the output control switch 2103 is amplified by the first incident angle drive circuit 22 and becomes a drive signal for controlling the actuator 221 that is driven integrally with the galvanometer mirror 220.

The static determination circuit 2104 receives the output signal of the subtractor 2101 and determines whether the incident angle when the reference light 207 reflected from the galvano mirror 220 is finally incident on the medium is a value near the target value Tgtφ. The determination result is output as a G1OK signal. It is assumed that the G1OK signal becomes High when the incident angle when the reference light 207 reflected by the galvanometer mirror 220 finally enters the medium is a value in the vicinity of the target value Tgtφ. The static determination circuit 2104 is, for example, a circuit that measures an elapsed time after the absolute value of the output signal of the subtractor 2101 becomes equal to or less than a predetermined threshold, and makes a determination when the measured time continues for a predetermined time or longer. This can be achieved. The G1OK signal that is the determination result is output to the controller 80. Therefore, the controller 80 can determine whether or not the incident angle when the reference light 207 reflected from the galvano mirror 220 is finally incident on the medium is a value in the vicinity of the target value Tgtφ by the G1OK signal. That is, the static determination circuit 2104 functions as a circuit that determines the convergence of the first incident angle control.

The configuration of the second incident angle control circuit 24 is the same as the configuration of the first incident angle control circuit 21. The AS1 signal, G1ON signal, GD1 signal, and G1OK signal in the first incident angle control circuit 21 are referred to as the AS2 signal, G2ON signal, GD2 signal, and G2OK signal in the second incident angle control circuit 24, respectively. The control by the control system configured by the second incident angle control circuit 24 is referred to as second incident angle control.

The configuration of the orthogonal incident angle control circuit 27 is the same as that of the first incident angle control circuit 21.

FIG. 4 shows a flowchart of recording and reproduction in the hologram recording / reproducing apparatus 10. Here, processing relating to recording / reproduction using holography in particular will be described. In the present specification, a process from when the hologram recording medium 1 is inserted into the hologram recording / reproducing apparatus 10 until preparation for recording or reproduction is completed is referred to as a setup process. The process of recording information on the hologram recording medium 1 from the ready state is called a recording process, and the process of reproducing information recorded on the hologram recording medium 1 from the ready state is called a playback process.

4 (a) shows a flowchart of the setup process, FIG. 4 (b) shows a flowchart of the recording process, and FIG. 4 (c) shows a flowchart of the reproduction process.

When the setup process is started as shown in FIG. 4A (step S401), the hologram recording / reproducing apparatus 10 determines whether the inserted medium is a medium for recording or reproducing digital information using holography, for example. The medium is determined (step S402).

If it is determined that the hologram recording medium 1 records or reproduces digital information using holography as a result of medium discrimination, the hologram recording / reproducing apparatus 10 reads control data provided on the hologram recording medium 1 (step S403). For example, information on the hologram recording medium 1 and information on various setting conditions at the time of recording and reproduction are obtained.

After reading the control data, the hologram recording / reproducing apparatus 10 performs various adjustments according to the control data and learning processing related to the pickup 11 (step S404). Thereby, the hologram recording / reproducing apparatus 10 completes preparation for recording or reproduction, and ends the setup process (step S405).

Next, processing from the ready state to recording of information will be described with reference to the flowchart of FIG. When the recording process is started (step S411), the hologram recording / reproducing device 10 receives the recording data from the external control device 91 (step S412), and the signal generation circuit 81 generates two-dimensional data corresponding to the data. The light is sent to the spatial light modulator 212 in the pickup 11.

Thereafter, the holographic recording / reproducing apparatus 10 learns for various recordings such as optimization of the power of the light source 201 and optimization of the exposure time by the shutter 203 so that high quality information can be recorded on the holographic recording medium 1. Processing is performed in advance (step S413).

Thereafter, in the seek process (step S414), the hologram recording / reproducing apparatus 10 controls the spindle motor 50 and the radial transport unit 51 using the spindle control circuit 40 and the radial transport control circuit 42. Thus, the hologram recording medium 1 is positioned so that the light beam irradiated from the pickup 11 and the cure optical system 13 is irradiated to a predetermined position of the hologram recording medium 1. When the hologram recording medium 1 has address information, the address information is reproduced, and it is confirmed whether the irradiation position of the light beam is positioned at a position corresponding to the address information. If the irradiation position of the light beam is not positioned at the position corresponding to the address information, a deviation amount from the position corresponding to the address information is calculated, and the spindle control circuit 40 and the radial direction conveyance control circuit 42 are used again to calculate the spindle. The operation of controlling and positioning the motor 50 and the radial conveyance unit 51 is repeated.

Thereafter, the hologram recording / reproducing apparatus 10 performs a data recording process for recording data to be recorded as a hologram on the hologram recording medium 1 (step S415). In the angle multiplexing method, a reference is made to the same area as the hologram stored in the hologram recording medium. The light irradiation angle is changed by a predetermined angle, and a hologram different from the already recorded hologram is stored to form a book. When the data recording process is completed, the recording process is terminated (step S416). Note that data recorded in the hologram storage medium 1 may be verified as necessary.

Next, processing from the ready state to playback of recorded information will be described with reference to the flowchart of FIG. When the reproduction process is started (step S421), the hologram recording / reproduction apparatus 10 first uses the spindle control circuit 40 and the radial direction conveyance control circuit 42 in the seek process (step S422), and uses the pickup 11 and the reproduction reference light optical system. The hologram recording medium 1 is positioned so that the light beam irradiated from 12 is irradiated to a predetermined position of the hologram recording medium 1. When the hologram recording medium 1 has address information, the address information is reproduced, and it is confirmed whether the irradiation position of the light beam is positioned at a position corresponding to the address information. If the irradiation position of the light beam is not positioned at the position corresponding to the address information, a deviation amount from the position corresponding to the address information is calculated, and the spindle control circuit 40 and the radial direction conveyance control circuit 42 are used again to calculate the spindle. The operation of controlling and positioning the motor 50 and the radial conveyance unit 51 is repeated.

Thereafter, the hologram recording / reproducing apparatus 10 emits the reference beam 207 from the pickup 11 to the hologram storage medium 1. The diffracted light reproduced by the reference light is detected as two-dimensional data by the photodetector 226, and the signal processing circuit 82 processes the two-dimensional data to read out the data recorded on the hologram recording medium 1 ( Step S423). The hologram recording / reproducing device 10 transmits the read data to the external control device 91 as reproduced data (step S424). When transmission of the reproduction data is completed, the reproduction process is terminated (step S425).

Subsequently, the seek process S414 in the present embodiment will be described with reference to the flowchart of FIG. Note that the same flowchart is applied to the seek process S422. Here, in the seek process when the hologram recording medium 1 has a disk shape as in this embodiment, the radius r and the rotation angle θ are parameters. Hereinafter, the drive shaft having the radius r is referred to as r-axis, and the drive shaft having the rotation angle θ is referred to as θ-axis. On the other hand, the positioning on each page in the book uses the incident angle φ of the reference light as a parameter. Hereinafter, the drive axis at the incident angle φ of the reference light is referred to as the φ axis. Further, the movement of the hologram recording medium 1 in the r-axis direction and the θ-axis direction is performed by the spindle 50 and the radial direction transporter 51.

When the seek process is started (step S501), the difference between the coordinates (r, θ) of the book where the hologram of the target address is located and the current irradiation position is calculated, and the movement amount is calculated for the r axis and the θ axis ( Step S502). Next, it is determined whether the amount of movement in the r-axis direction is other than zero (step S503). If the movement amount in the r-axis direction is other than zero (Yes in step S503), the movement in the r-axis direction is started (step S504). After step S504, the process proceeds to step S505 described later. If the amount of movement in the r-axis direction is zero (No in step S503), the process proceeds to step S505 without performing step S504.

In step S505, it is determined whether the amount of movement in the θ-axis direction is other than zero. If the movement amount in the θ-axis direction is other than zero (Yes in step S505), the movement in the θ-axis direction is started (step S506). After step S506, the process proceeds to step S507 described later. If the amount of movement in the θ-axis direction is zero (No in step S505), the process proceeds to step S507 without performing step S506.

In step S507, it is determined whether the movement in the r-axis direction and the θ-axis direction is completed. The completion of the movement is determined based on output signals from the spindle control circuit 40 and the radial direction conveyance control circuit 42.

If it is determined that the movement has not been completed (No in step S507), the process returns to step S507 again. That is, the operation waits until the movement is completed.

If it is determined that the movement has been completed (Yes in step S507), the movement is terminated (step S508).

Next, it is determined whether or not the seek process during reproduction is performed (step S509). If it is not the seek process at the time of reproduction (No in step S509), the process proceeds to step S516 described later, and the seek process is terminated. In the case of seek processing at the time of reproduction (Yes in step S509), the seek processing is not finished with this, and finally, the address information obtained by reproducing the recorded hologram is used to set the target address. Continue seeking until it is correctly positioned. This is because the seek process at the time of recording is a seek process to an unrecorded portion in the hologram recording medium 1, and address information cannot be obtained.

In the case of seek processing during reproduction (Yes in step S509), reproduction of the first page in the book recorded at the coordinates represented by the r-axis and θ-axis is performed (step S510). .

After step S510, it is determined whether the page can be reproduced (step S511). If reproduction is impossible (No in step S511), it means that the movement of the hologram recording medium 1 by the spindle 50 and the radial transporter 51 from step S502 to step S508 could not be performed accurately. To do. Therefore, based on the predetermined retry parameter, the r-axis and θ-axis retry values are calculated (step S512), and the process returns to step S502. As a result, seek processing for moving to the vicinity of the positioning is performed.

If the hologram can be reproduced (Yes in step S511), the address information included in the reproduced hologram is acquired (step S513). Subsequently, it is determined whether or not the acquired address is a target address (step S514). If the acquired address is not the target address (No in step S514), it means that positioning has not been performed correctly. Therefore, the difference between the coordinates (r, θ) of the acquired address and the coordinates (r, θ) of the target address is calculated (step S515), and the process returns to step S502. Thereby, a seek process based on the address information of the hologram is performed.

If the acquired address is the target address (Yes in step S514), the seek process is terminated (step S516).

Subsequently, the data reproduction process S423 in the present embodiment will be described with reference to the flowchart of FIG.

When the data reproduction process S423 is started (step S601), first, the variable j indicating the book number and the variable i indicating the page number in the book are initialized to zero (step S602).

Subsequently, seek processing is performed on the j-th book (referred to as Book [j]) (step S603). The seek process at this time is the same as the seek process shown in FIG.

After step S603, the controller 80 instructs the incident angle target value setting circuit 32 to set Tgtφ = φ0 [1] as the target value of the incident angle (step S604). Here, φ0 [i] is an incident angle corresponding to the i-th page. That is, step S604 sets an incident angle corresponding to the first page.

Subsequently, the controller 80 sets the G1ON signal and the G2ON signal to High, and starts control of the φ axis. That is, the control of the actuator 221 and the actuator 224 is started by the first incident angle control circuit 21 and the second incident angle control circuit 24 (step S605). Thereby, control is started about the angle of the galvanometer mirror 220 and the angle of the galvanometer mirror 225 so that the incident angle when the reference beam 207 enters the hologram recording medium 1 becomes Tgtφ.

After step S605, for the first page, the process proceeds to step S612 without controlling the reference beam 207 based on the angle error signal (AES).

In step S612, the controller 80 monitors the G1OK signal and the G2OK signal, and determines whether the movement is completed by determining whether both signals are high (step S612).

If either the G1OK signal or the G2OK signal is not High (No in Step S612), the process returns to Step S612 and waits until both the G1OK signal and the G2OK signal become High.

If both the G1OK signal and the G2OK signal are High (Yes in Step S612), it means that the actuator 221 and the actuator 224 have both moved. As a result, when both the G1OK signal and the G2OK signal become High, the page data is reproduced (step S613), and it is determined whether the reproduction is possible (step S614).

If the page data cannot be reproduced (No in step S614), a retry value is set based on a predetermined retry parameter (step S615), and the process returns to step S612. Here, in step S615, the target value Tgtφ of the incident angle of the reference beam 207 and the target value Tgtρ of the orthogonal incident angle are reset based on a predetermined retry parameter.

If the page data can be reproduced (Yes in step S614), 1 is added to the variable i (step S616). Subsequently, it is determined whether the variable i is larger than a predetermined value PageNum (step S617). The predetermined value PageNum is the number of pages in the book.

If the variable i is not larger than the predetermined value PageNum (No in step S617), since there is an unreproduced page in the book, the process proceeds to step S606, and the process proceeds to reproduction for the second and subsequent pages.

Subsequently, steps S606 to S611 performed in the reproduction from the second page onward will be described.

In step S606, the controller 80 instructs the incident angle target value setting circuit 32 to set Tgtφ = φ0 [i] as the target value of the incident angle (step S606). Thereby, since the target value of the incident angle is changed, the angle of the galvanometer mirror 220 and the angle of the galvanometer mirror 225 are set so that the incident angle when the reference light enters the hologram recording medium 1 becomes φ0 [i]. , Control is started.

Subsequently, the incident angle target value setting circuit 32 monitors the angle error signal (AES) and determines whether the voltage level of the angle error signal (AES) is greater than the threshold value Vth (step S607).

If the voltage level of the angle error signal (AES) is not greater than the threshold value Vth (No in step S607), the process returns to step S607 and waits until the voltage level of the angle error signal (AES) becomes greater than the threshold value Vth.

If the voltage level of the angle error signal (AES) is greater than the threshold value Vth (Yes in step S607), then the incident angle target value setting circuit 32 monitors the angle error signal (AES), and the angle error signal (AES). It is determined whether or not the voltage level crosses the reference potential Vref (step S608). As an example, this operation can be realized by sampling the angle error signal (AES) at a predetermined sampling period and comparing the value of the previous sample and the current value with the reference potential Vref.

When the voltage level of the angle error signal (AES) does not cross the reference potential Vref (No in step S608), the process returns to step S608 and waits until the voltage level of the angle error signal (AES) crosses the reference potential Vref. .

When the voltage level of the angle error signal (AES) crosses the reference potential Vref (Yes in step S608), the current AS1 signal is acquired, and the incident angle when the reference light is incident on the hologram recording medium 1 from the value. Conversion to φz is performed (step S609). That is, φz is the incident angle of the reference light at the timing when the angle error signal (AES) becomes the reference potential.

Subsequently, the incident angle target value setting circuit 32 calculates the following value as a new incident angle target value φ1 (step S610), and rewrites the incident angle target value Tgtφ with φ1 (step S611).

Thus, the control target value is corrected so that the incident angle when the reference light is incident on the hologram recording medium 1 is φ1 with respect to the angle of the galvanometer mirror 220 and the angle of the galvanometer mirror 225.

That is, according to the flowchart of this embodiment, in the data reproduction for the second and subsequent pages in the book, the angle of the galvano mirror 220 and the angle of the galvano mirror 225 are set to the incident angle φ [i] corresponding to the i-th page. After starting to move as an angle, the target angle is corrected to φ1 based on the angle error signal (AES).

It can be said that this is an operation of setting the provisional target angle φ [i] at the start of movement and starting the movement, and then correcting the target angle to φ1 based on the angle error signal (AES).

After step S611, the process proceeds to step S612. Steps S612 to S617 are as described above. Steps S606 to S617 are processes related to page data reproduction of one page. Among these, steps S606 to S612 can be regarded as a seek process between pages in which the galvano mirror 220 and the galvano mirror 225 are controlled to control the incident angle of the reference light in a stepwise manner. Hereinafter, this process is referred to as page seek.

When the page data reproduction is completed for all pages of the book, the variable i becomes larger than the predetermined value PageNum (in the case of Yes in step S617), and the process proceeds to step S618.

In Step S618, the controller 80 sets the G1ON signal and the G2ON signal to Low to stop the first incident angle control and the second incident angle control (Step S618), and adds 1 to the variable j (Step S619). Subsequently, it is determined whether the variable j is larger than a predetermined value BookNum (step S620). The predetermined value BookNum is the total number of books to be reproduced in the data reproduction process.

If the variable j is not larger than the predetermined value BookNum (No in step S620), since there is an unreproduced book, the process returns to step S603 to shift to the reproduction of the next book.

When page data reproduction is completed for all pages in all books to be reproduced in the data reproduction process, the variable j becomes larger than the predetermined value BookNum (in the case of Yes in step S620), and the data reproduction process is completed (step S621).

Here, the reproduction order of each page in the book in the present embodiment, that is, the scanning direction of the reference beam 207 in the page seek in the book will be described with reference to FIG.

FIG. 10A schematically shows a state in which the reference light 207 and the control light beam branched by the Wollaston prism 230 are incident on the hologram recording medium 1. A mirror that passes after passing through the Wollaston prism 230 is omitted. As described above, the two light beams are incident on the hologram recording medium 1 while being shifted by Δφ.

Here, as shown in FIG. 10B, the incident angle when entering the hologram recording medium 1 is considered. The incident angle is defined by the angle between the normal line of the hologram recording medium 1 and the light beam. In FIG. 10B, the incident angle of the reference beam 207 is α.

In this embodiment, it is assumed that the incident angle of the reference beam 207 is larger than that of the control beam as shown in FIG. In this embodiment, the scanning direction of the reference beam 207 in the page seek in the book is the direction indicated by the arrow D. This direction is a direction from the incident angle of the control light beam toward the incident angle of the reference light 207. In other words, in FIG. 10, since the incident angle of the reference light 207 is larger than the incident angle of the control light beam, the scanning direction of the reference light 207 is a direction in which the incident angle is increased.

The reference light 207 is light for generating diffracted light to the photodetector 226 for reproducing the recorded signal, whereas the control light beam is only for generating an angle error signal (AES). The light. Therefore, it is preferable that the light branching ratio in the Wollaston prism 230 is not 1: 1, and the intensity of the reference light 207 is larger than the intensity of the control light beam.

Therefore, the scanning direction of the reference beam 207 in the page seek in the book can be rephrased as the direction from the incident angle of the weak light beam toward the incident angle of the strong light beam.

Next, the effect of this embodiment will be described.

Consider a page seek that moves from the (i-1) th page to the i-th page.

FIG. 11 shows an angle error signal (AES) when the incident angle of the reference beam 207 is changed by rotating the galvanometer mirror 220. FIG. 11A shows an ideal state, for example, a case where there is no shrinkage of the medium before and after recording, and there is no temperature change during recording and during reproduction. In such an ideal state, each page at the time of reproduction is optimally reproduced at an angle at which the galvano mirror 220 is positioned at the time of recording. That is, the i-th page is optimally reproduced at φ0 [i] that is the incident angle corresponding to the i-th page.

However, the hologram recording medium 1 contracts before and after recording. Furthermore, expansion / contraction of the medium also occurs due to temperature changes. FIG. 11B shows a case where the medium is expanded as an example. As a result, the angle at which the i-th page can be optimally reproduced deviates from φ0 [i]. In the figure, the angle indicated by φ1 is an angle at which the i-th page can be optimally reproduced. Therefore, when the present invention is not used, the incident angle of the reference light is shifted by the amount indicated by A in the drawing, and the page cannot be reproduced properly.

On the other hand, in the present invention, in either the ideal state shown in FIG. 11A or the non-ideal state shown in FIG. Note that Δφ / 2. This is because the angle difference from the zero cross point of the angle error signal (AES) to the optimum angle depends only on the branch angle by the Wollaston prism 230 and does not depend on the expansion / contraction of the hologram recording medium 1 or the like.

FIG. 12 is a schematic diagram of the signal waveform of each part in the page seek based on the flowchart of the data reproduction process shown in FIG. 12A shows the angle error signal (AES), FIG. 12B shows the target value Tgtφ of the incident angle, FIG. 12C shows the incident angle φ of the reference beam 207, and FIG. This is the output signal GD1 of the angle control circuit 21. Note that FIG. 12C can also be regarded as an AS1 signal or an AS2 signal. In addition, FIG. 12D can be regarded as the output signal GD2 of the second incident angle control circuit 24.

If it demonstrates corresponding to the flowchart of a present Example, time t0 is the time which started the movement of the angle of the galvano mirror 220 and the angle of the galvano mirror 225 by step S606. The target value Tgtφ of the incident angle set at time t0 is φ0 [i] as shown in FIG. 12 (b), and is directed to the angle φ0 [i] until time t3 as shown in FIG. 12 (c). Control.

Time t1 is the time when the voltage level of the angle error signal (AES) becomes larger than the threshold value Vth, and corresponds to the condition that becomes Yes in step S607. Time t2 is the time when the angle error signal (AES) first crosses zero after time t1, and corresponds to the condition of Yes in step S608. As described above, the zero-cross point of the angle error signal (AES) of the i-th page can be detected by steps S607 and S608.

As shown in FIG. 12C, at time t2, a new incident angle target value φ1 is set in steps S609 to S611. This angle is a value determined based on (Expression 2), and is an angle advanced by Δφ / 2 with respect to the incident angle φz at time t2.

Since the target value of the incident angle is corrected at time t2, the angle of the galvanometer mirror 220 and the angle of the galvanometer mirror 225 are controlled toward the angle φ1. At this time, since the target value of the control system changes discretely, even in the angle of the galvano mirror 220 or the drive signal for driving the galvano mirror 225 as shown in FIG. The change appears at the time t2 after passing through.

Time t3 is a time when the movement of the angle of the galvano mirror 220 and the angle of the galvano mirror 225 is completed, and corresponds to the condition of Yes in step S612. As a result, the incident angle of the reference beam 207 is controlled to φ1 as shown in FIG. 12C, and the angle error signal (AES) at this time is the value at the bottom of the signal as shown in FIG. Become.

Also, as shown in FIG. 12 (c), most of the movement distance to the provisional target angle φ0 [i] has been completed before moving to the incident angle at which the angle error signal (AES) is obtained. . Therefore, the incident angle φ of the reference beam 207 is controlled to be low in the vicinity of the incident angle at which the angle error signal (AES) is obtained. Thereby, the zero cross timing of the angle error signal (AES) can be detected with high accuracy.

The influence of the speed of the incident angle φ of the reference light in the vicinity of the incident angle at which the angle error signal (AES) is obtained will be described with reference to FIG. FIG. 13A shows the angle error signal (AES) in this embodiment, and FIG. 13B shows the incident angle φ of the reference light in this embodiment. On the other hand, in FIG. 13C and FIG. 13D, the movement of the movement distance to the provisional target angle φ0 [i] is not completed before the movement to the incident angle at which the angle error signal (AES) is obtained. It is a figure explaining a case. FIG. 13C shows the angle error signal (AES), and FIG. 13D shows the incident angle φ of the reference beam 207.

In FIG. 13D, since the movement of the movement distance to the provisional target angle φ0 [i] is not completed before the movement to the incident angle at which the angle error signal (AES) is obtained, the angle error signal ( The speed of the incident angle φ of the reference light in the vicinity of the incident angle at which AES) is obtained is fast. Therefore, the time for passing through the range of the angle of the reference beam 207 from which the angle error signal (AES) is obtained is also shortened. As a result, as shown in FIG. 13C, the time for passing the angle error signal (AES) is shortened.

Next, the problem that the time for passing through the angle error signal (AES) is shortened will be described with reference to FIG. FIG. 14A shows a case where the velocity of the incident angle φ of the reference beam 207 is low in the vicinity of the incident angle at which the angle error signal (AES) is obtained. In this embodiment, whether or not the voltage level of the angle error signal (AES) crosses the reference potential Vref in step S608 is determined by acquiring a value every predetermined sampling time. This can be easily realized with a digital circuit. In FIG. 14, a vertical broken line indicates the sampling timing, and a black circle indicates a sampled value.

As shown in FIG. 14A, when the speed of the incident angle φ of the reference light in the vicinity of the incident angle at which the angle error signal (AES) is obtained, many samplings can be performed near the zero cross point. Therefore, the threshold value is crossed by the value indicated by A in FIG. 14A, and the zero cross timing tz can be detected with high accuracy.

On the other hand, FIG. 14B shows a case where the speed of the incident angle φ of the reference beam 207 is high in the vicinity of the incident angle at which the angle error signal (AES) is obtained. In this case, many samplings cannot be performed near the zero cross point. According to the flowchart FIG. 6 of the present embodiment, the zero cross timing tz is obtained by crossing the threshold value with the value indicated by B in FIG. However, the accurate zero-cross timing is point C in FIG. 14B, and the zero-cross timing tz cannot be accurately detected. As a result, the new incident angle target value φ1 set based on (Equation 2) also shifts. As a result, the incident angle of the reference beam 207 cannot be accurately controlled, and the reproduction performance is deteriorated.

As described above, when the time for passing the angle error signal (AES) is shortened, the accuracy of positioning of the incident angle of the reference beam 207 is deteriorated. Therefore, it is preferable to control the incident angle φ of the reference beam 207 at a low speed in the vicinity of the incident angle at which the angle error signal (AES) is obtained. This can be realized by completing most of the movement of the movement distance to the provisional target angle φ0 [i] before moving to the incident angle at which the angle error signal (AES) is obtained.

This implementation is characterized in that the galvanometer mirror 220 is driven at a speed slower than the average speed in the page seek in the range of the incident angle where the angle error signal (AES) is obtained during page seek in the book.

The first effect of the present invention is that the page data can be optimally reproduced because the incident angle of the reference light 207 is controlled based on the angle error signal (AES) generated based on the diffracted light. By controlling based on the angle error signal (AES) generated based on the diffracted light, the relative angle between the signal light 206 and the reference light 207 even when the medium described with reference to FIG. Can be controlled with high accuracy. Further, unlike Patent Document 1, it is possible to perform reproduction at an optimum angle.

The second effect is that the

dedicated photodetectors

234 and 236 are provided, and the angle error signal (AES) is generated by calculating the amount of received light, thereby having high speed. Compared with the method of calculating the SNR as in Patent Document 1, a signal indicating the amount of deviation with respect to the incident angle (the angle error signal (AES) in this embodiment) can be generated at high speed.

Furthermore, the third effect is that high-speed movement is possible by correcting the target value while driving the incident angle of the reference beam 207. For example, as control based on the angle error signal (AES), control based on the angle error signal (AES), pulling in the zero cross point φz, and then moving to the angle φ1 can be considered. However, once it is drawn into the zero cross point φz, it is necessary to decelerate after acceleration as control, so it decelerates and moves to φz, then accelerates again and then decelerates and moves to φ1 . In order to achieve this, the angle error signal (AES) as position feedback in the incident angle control circuit and the AS1 signal obtained from the angle detection sensor provided in the actuator 221 are switched halfway.

In contrast, in this embodiment, the angle error signal (AES) is not used as position feedback in the incident angle control circuit. As described with reference to FIG. 9, the AS1 signal is used as the position feedback in the first incident angle control circuit 21. The angle error signal (AES) is not used as an input signal in the control system, but is used only for the purpose of correcting the target value of the control system during driving.

As a result, the AS1 signal obtained from the angle detection sensor provided in the actuator 221 is used as position feedback in the incident angle control circuit to control when the reference light angle moves between pages. Further, while driving the incident angle of the reference beam 207, the target value is corrected based on the angle error signal (AES). By the above operation, high-speed positioning control to the optimum angle φ1 can be realized without decelerating at the zero cross point φz.

Furthermore, the fourth effect is that high-speed movement is possible by setting the scanning direction of the reference beam 207 that matches the characteristics of the angle error signal (AES). 11A, the angle error signal (AES) according to the present embodiment has an optimum angle obtained by increasing the angle of the reference beam 207 by Δφ / 2 with respect to the zero cross point. . In the case of this characteristic, the reference beam 207 should be scanned in the direction in which the incident angle of the reference beam 207 increases in the page seek at the time of reproduction as in this embodiment. This is because if the reference beam 207 is scanned in a direction in which the incident angle of the reference beam 207 decreases during page seek, it cannot be controlled to the optimum position unless the zero cross is detected. Accompanied by the returning action is not high speed because it must be decelerated until the speed becomes zero after the zero cross is detected.

As shown in FIG. 11, the angle obtained by increasing the angle of the reference beam 207 by Δφ / 2 with respect to the zero cross point of the angle error signal (AES) is the optimum angle. This means that the two beams branched by the Wollaston prism 230 are used. This means that the reference light 207 has a larger incident angle than the control light beam. That is, the state is as shown in FIG.

In FIG. 10, the reference light 207 has a larger incident angle than the control light beam. Conversely, when the control light beam has a larger incident angle than the reference light 207, the reference light 207 Should be scanned in a direction that decreases the angle of incidence. As described above, when the angle error signal (AES) of this embodiment is used, the scanning direction of the reference beam 207 in the page seek in the book at the time of reproduction is inevitably determined by the configuration of the optical system.

A preferable scanning direction of the reference light is a direction from the incident angle of the control light beam toward the incident angle of the reference light 207, thereby enabling high-speed movement.

The fifth effect is that the intensity of the reference light 207 is larger than the intensity of the control light beam, so that the amount of diffracted light can be secured and suitable reproduction is possible.

Furthermore, the sixth effect is that the movement of most of the moving distance is completed by the time it moves to the incident angle at which the angle error signal (AES) is obtained, so the zero cross timing of the angle error signal (AES) is highly accurate. This is a point that can be detected. As a result, the incident angle of the reference beam 207 can be controlled with high accuracy.

In addition, when the velocity of the incident angle φ of the reference beam 207 in the vicinity of the incident angle at which the angle error signal (AES) is obtained in FIG. 14B is high, a point B that is a timing at which the zero crossing is detected is an accurate zero crossing. The deviation from the point C, which is the timing, has been described. In order to prevent this deviation, the zero cross timing may be detected as follows.

The incident angle target value setting circuit 32 acquires the value of the angle error signal (AES) at every predetermined sampling time, and stores the previous value for one sampling time. When it is determined that the angle error signal (AES) crosses the reference potential Vref, the current value (the value of the AES signal at the point B) and the value stored at the immediately preceding sampling time (the value of the AES signal at the point D) ) To calculate the zero cross timing from the linear approximation. As a result, it is possible to detect a timing close to point C, which is an accurate zero cross timing. Based on this result, the new incident angle target value φ1 can be calculated more accurately by calculating the incident angle φz of the reference beam 207 at the timing when the angle error signal (AES) becomes the reference potential. As a result, the incident angle of the reference beam 207 can be controlled with high accuracy.

In the above description, the previous value for one sampling time is stored, and linear approximation is performed using two values before and after the reference potential Vref. However, a plurality of past sampling values are stored, and more than two values are stored. A linear approximation may be performed using the sampling value.

As described above, according to the present embodiment, it is possible to realize a hologram recording / reproducing apparatus capable of detecting an angular error signal (AES) capable of realizing high-speed reproduction and obtaining the best reproduction signal.

FIG. 15 is a block diagram showing a recording / reproducing apparatus for a holographic recording medium for recording and / or reproducing digital information using holography. In addition, the same number is attached | subjected about the same component as FIG. 1 which is a block diagram of Example 1, and description is abbreviate | omitted. The structural difference from the first embodiment is the temperature measurement sensor 17.

The temperature measurement sensor 17 is a sensor for measuring the temperature of the hologram recording medium 1, and the measurement result is sent to the controller 80. The temperature measurement sensor 17 measures the temperature of the hologram recording medium 1 with a non-contact type thermometer, for example. Alternatively, the controller 80 may be installed in the vicinity of the hologram recording medium 1, measure the ambient temperature of the hologram recording medium 1 by measuring the temperature of air around the sensor, and the controller 80 may estimate the temperature of the hologram recording medium 1.

The flowchart of the data reproduction process S423 in the present embodiment is the same as FIG. 6 which is the flowchart in the first embodiment. In the first embodiment, φ0 [i] is the incident angle corresponding to the i-th page, but in this embodiment, φ0 [i] is adjusted based on the measurement result of the temperature measurement sensor 17. That is, when the medium expands / contracts from the measurement result of the temperature measurement sensor 17, φ0 [i] is adjusted accordingly.

Next, the effect of this embodiment will be described.

FIG. 16 shows an angle error signal (AES) when the temperatures are different. In contrast to FIG. 16A, FIG. 16B shows a case where the medium expands due to a temperature difference. For the sake of explanation, in FIG. 16A and FIG. 16B, (i-1) The angle position of the second page is displayed in the same position. Φ1 [i] is the optimum angle of the i-th page.

In contrast to FIG. 16A, since the medium is expanded in FIG. 16B, the optimal angle φ1 [i] of the i-th page is equal to the optimal angle φ1 [i− of the (i-1) -th page. 1]. Therefore, in the case of FIG. 16B, φ0 [i] set as the temporary target value of the incident angle in step S606 should be set as a larger value than in the case of FIG.

If the same φ0 [i] as in FIG. 16A is set, as shown by A in FIG. 16, the zero cross point does not appear even if the target value φ0 [i] of the temporary incident angle is moved. High speed movement cannot be realized.

In view of the points described above and the fact that the expansion / contraction of the hologram recording medium 1 can be estimated from the temperature of the hologram recording medium 1, φ0 [i] is set based on the measurement result of the temperature measurement sensor 17 in this embodiment. adjust.

Thus, even when the hologram recording medium 1 is expanded or contracted due to temperature, it is possible to move between pages at high speed.

As described with reference to FIG. 9, the first incident angle control circuit 21, the second incident angle control circuit 24, and the orthogonal incident angle control circuit 27 in the embodiment described above are the control circuits that constitute the feedback control system. did. However, for example, it may be a control circuit that constitutes a two-degree-of-freedom control system having feed-forward control in addition to feedback control.

In the above embodiment, an apparatus for recording / reproducing with respect to the hologram recording medium 1 has been described as an example. However, the present invention can also be applied to a reproduction-only apparatus.

In the above embodiment, it has been described that the reproduction order of each page in the preferred book, that is, the preferred scanning direction of the reference light in the page seek in the book is uniquely determined by the configuration of the optical system. However, the preferred scanning direction of the reference beam in the page seek in the book is determined only during reproduction. That is, in the case of a device that performs recording and reproduction instead of a reproduction-only device, the page seek in the book at the time of recording is not limited to this.

Therefore, the order of reproducing the pages in the book at the time of reproduction may be different from the order of recording the pages in the book at the time of recording. For this reason, the recording order may be designed as a suitable order for recording the hologram, and in an order different from that during reproduction. As a result, high-speed reproduction according to the present invention can be realized while preferably recording a hologram.

In the above embodiment, as a mechanism for controlling the light beam irradiated from the pickup 11 and the cure optical system 13 to be irradiated to a predetermined position of the hologram recording medium, for example, the radial transport unit 51 in the first embodiment is used. As described above, the hologram recording medium 1 is transported. However, the mechanism for sharing the irradiation position of the light beam is not limited to this. For example, the hologram recording medium may be fixed, and the pickup 11 and the cure optical system 13 may be transported.

Note that the present invention is not limited to the above-described embodiments, and includes various modifications in addition to the above-described modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

In addition, each of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware by designing a part or all of them with, for example, an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by interpreting and executing a program that realizes each function by the processor. Information such as programs, tables, and files that realize each function can be stored in a memory, a hard disk, a recording device such as an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.

Also, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.

DESCRIPTION OF SYMBOLS 1 ... Hologram recording medium 10 ... Hologram recording / reproducing apparatus 11 ... Pickup 12 ... Reproduction reference light optical system 13 ... Cure optical system 17 ... Temperature measurement sensor 20 ... First incident angle signal generation circuit 21 ... First incident angle control Circuit 22 ... First incident angle drive circuit 30 ... Angle error detection optical system 31 ... Angle error signal generation circuit 32 ... Incident angle target value setting circuit 80 ... Controller

Claims

A hologram reproducing device for reproducing information recorded on a hologram recording medium,
A light source that emits reference light;
An incident angle changing unit capable of changing the incident angle of the reference light incident on the hologram recording medium;
An angle error signal generator for generating an angle error signal;
A target angle setting unit for setting a target angle of the incident angle of the reference light;
With the target angle set by the target angle setting unit as a control target, an incident angle control unit that controls the incident angle change unit,
The target angle setting unit changes the target angle based on the angle error signal during a period in which the incident angle control unit controls the incident angle changing unit to change the incident angle of the reference light. A hologram reproducing apparatus.
The hologram reproducing apparatus according to claim 1,
An optical axis branching section for branching the reference light into at least two light beams having different propagation directions;
A light detection unit that detects diffracted light generated when at least two light beams having different propagation directions are incident on the hologram recording medium, and
The hologram reproduction apparatus, wherein the angle error signal generation unit generates the angle error signal from an output signal of the light detection unit.
A hologram reproducing apparatus according to claim 1 or 2, wherein
An angle detection unit that detects an angle of the reference light changed by the incident angle change unit,
The hologram reproduction apparatus according to claim 1, wherein the incident angle control unit performs control based on an output signal of the angle detection unit.
A hologram reproducing apparatus according to claim 1 or 2, wherein
The target angle setting unit monitors a timing at which the angle error signal becomes a predetermined threshold, and changes the target angle based on the timing.
A hologram reproducing apparatus according to claim 1 or 2, wherein
The target angle setting unit monitors a timing at which the angle error signal becomes a predetermined threshold, and sets a value obtained by adding a predetermined value to the output value of the angle detection unit at the timing as the target angle. A featured hologram reproducing apparatus.
The hologram reproducing apparatus according to claim 2,
When an angle formed by at least two light beams having different propagation directions is Δφ,
The target angle setting unit adds the value approximately half of Δφ to a value detected by the angle detection unit when the angle error signal becomes a predetermined threshold value to obtain the target angle. A hologram reproducing apparatus.
The hologram reproducing apparatus according to claim 2,
At least two light beams having different propagation directions of the optical axis branching portion are present in an incident plane including the optical axis of the reference light and the normal line of the hologram recording medium,
The hologram reproducing apparatus, wherein the incident angle changing unit is capable of changing an incident angle at which the reference light is incident on the hologram recording medium within the incident surface.
The hologram reproducing apparatus according to claim 2,
Information recorded on the hologram recording medium is recorded by angle multiplexing,
The optical axis branching unit branches the reference light into two light beams having different intensities,
When continuously reproducing the angle-multiplexed hologram, the incident angle changing unit includes a light beam having a lower intensity among at least two light beams having different propagation directions branched by the optical axis branching unit. The hologram reproducing apparatus is characterized in that the incident angle is changed in a direction from the incident angle toward the incident angle of the light beam having the stronger intensity.
The hologram reproducing apparatus according to claim 2,
The optical axis branching unit branches the reference light into two light beams having different intensities,
Of the at least two light beams having different propagation directions branched by the optical axis branching unit, the light beam having the stronger intensity travels straight through the optical axis branching unit.
The hologram reproducing apparatus according to claim 1,
The target angle setting unit acquires a value of the angle error signal at every predetermined sampling time, and based on at least two values before and after the angle error signal crosses a predetermined threshold, the angle error signal is A hologram reproducing apparatus characterized by calculating a timing that crosses a threshold value.
The hologram reproducing apparatus according to claim 1,
It has a temperature measurement unit that measures temperature,
The incident angle changing unit sets a target angle set in the target angle setting unit using an output of the temperature measuring unit, and the incident angle control unit controls the incident angle changing unit based on the target angle. The hologram reproducing apparatus, wherein the target angle setting unit changes the target angle based on the angle error signal during a period in which the incident angle of the reference light is changed.
A hologram reproducing method used in a hologram reproducing apparatus for reproducing information recorded on a hologram recording medium,
A light source that emits reference light;
An incident angle changing unit capable of changing the incident angle of the reference light incident on the hologram recording medium;
An angle error signal generation unit that generates an angle error signal using reference light incident on the hologram recording medium;
A target angle setting unit that sets a target angle of the incident angle of the reference light using the angle error signal generated by the angle error signal generation unit;
With the target angle set by the target angle setting unit as a control target, an incident angle control unit that controls the incident angle change unit,
The incident angle control unit controlling the incident angle changing unit to change the incident angle of the reference light;
And a step of changing the target angle based on the angle error signal by the target angle setting unit.