JP4933984B2 - Hologram recording / reproducing device - Google Patents

Description

  The present invention relates to a hologram recording / reproducing apparatus using a holographic memory.

  Holograms that can record two-dimensional data such as images at high density are known. A feature of this hologram recording is that a diffraction grating is formed on a hologram recording medium by an optical interference pattern between signal light carrying recorded information and reference light emitted from the same light source as the signal light and having no recorded information. is there. That is, the optical paths of the reference light and the signal light are spatially separated from each other, the two are crossed in the hologram recording medium, and data is recorded by forming interference fringes.

  Also, the recording capacity can be dramatically increased by performing multiple recording of the optical interference pattern on the hologram recording medium. For example, in the angle multiplexing method, the recording information that differs for each angle in the same area is maintained in the hologram recording medium at the time of recording by slightly changing the so-called crossing angle of the reference light with respect to the signal light and maintaining the angle for a certain time Can be recorded multiple times.

  Reproduction of the data recorded on the hologram recording medium is different from the time of recording in that no signal light is input to the hologram recording medium, and only the reference light is input at the same incident angle as at the time of recording, and the data is recorded in the hologram recording medium. This is performed by detecting the diffracted light from the interference pattern being detected by the image sensor.

FIG. 1 shows a data reproduction method using a phase conjugate reproduction method known as a method for reproducing data recorded on a hologram recording medium. In a recording / reproducing apparatus employing the phase conjugate reproduction method, a reflection mirror 2 is disposed on the opposite side of the recording medium 1 from the incident side of the reproduction reference light A. Then, the reproduction reference light A is incident on the recording medium 1 at the same incident angle as that during recording, and the transmitted reproduction reference light A is specularly reflected by the reflection mirror 2 and is incident on the recording medium 1 again. Thereby, diffracted light (phase conjugate light as reproduction light) is obtained from the recording medium 1, and this is detected by the image sensor 3 arranged on the same side as the incident side of the reproduction reference light A, and data is reproduced. Here, in the conventional hologram recording / reproducing apparatus adopting the phase conjugate reproduction method, the reflection mirror for generating the phase conjugate light rotates in conjunction with the galvanometer mirror for making the incident angle of the reference light variable. Is configured to do. That is, the angle of the reflection mirror is controlled so that the reference light is always perpendicularly incident on the light reflection surface. For this reason, even during data recording, the recording reference light is regularly reflected by the reflection mirror, and is reflected back to the recording medium as it is. Such reflected light is unnecessary at the time of data recording, and has been an obstacle to normal data recording. In view of this point, the hologram recording / reproducing apparatus described in Patent Document 1 controls the angle of the reflection mirror so that the recording reference light transmitted through the recording medium does not re-enter the recording medium during recording. The optical path is changed.
JP 2007-17661 A

  In a hologram recording / reproducing apparatus employing a phase conjugate reproduction method, the influence of recording noise is eliminated by changing the optical path so that the recording reference light transmitted through the recording medium does not re-enter the recording medium, and appropriate data recording However, not only can the optical path of the recording reference light transmitted through the recording medium be changed, but this can also be used to control the recording / reproducing apparatus, thereby realizing more accurate data recording. It becomes possible.

  The present invention has been made in view of the above points, and in the hologram recording / reproducing apparatus adopting the phase conjugate reproduction method, while preventing re-incident to the recording medium of the recording reference light transmitted through the recording medium at the time of recording, An object of the present invention is to provide a hologram recording / reproducing apparatus capable of realizing data recording with higher accuracy by using recording reference light for various controls of the apparatus.

  The hologram recording / reproducing apparatus according to the present invention is based on recording information for one of two divided laser beams, a laser light source, splitting means for splitting the laser light emitted from the laser light source into two, and Irradiating the recording medium with the spatially modulated laser light as signal light and irradiating the recording medium with the other of the two laser lights as reference light. An optical system for recording the recording information on a recording medium, a reflection mirror provided on an optical path of reference light transmitted through the recording medium, and having a reflection surface for reflecting the reference light; and reflected by the reflection mirror and Reproducing means for reproducing the recorded information recorded on the recording medium based on the reference light re-incident on and transmitted to the recording medium, the hologram recording / reproducing apparatus comprising: The direction of the incident surface is positioned at different positions according to the operation mode, and an optical path control means for controlling the optical path of the reference light transmitted through the recording medium and a light detection signal having a signal level corresponding to the received light intensity are generated. The optical path control means, wherein the optical path control means receives the reference light transmitted through the recording medium in the recording mode or in the standby mode before shifting to the recording mode or the reproduction mode on the light receiving surface of the photodetector. It is characterized by guiding.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings shown below, substantially the same or equivalent components and parts are denoted by the same reference numerals.

(First embodiment)
FIG. 2 is a block diagram showing the overall configuration of the hologram recording / reproducing apparatus of the present invention, and FIG. 3 shows the configuration of a pickup 100 mounted on the hologram recording / reproducing apparatus of the present invention.

  A hologram recording medium 1 (hereinafter referred to as a recording medium) has a recording layer made of a photosensitive material, and is sandwiched between a substrate or a protective layer such as a resin or glass. As the photosensitive material, for example, a polymer or a photorefractive material lithium niobate single crystal is used. Hereinafter, the case where the shape of the recording medium 1 is a disk shape will be described as an example. However, the shape of the recording medium 1 is not limited to the disk shape, and may be a card shape or other shapes.

  The recording / reproducing light source 10 is configured by, for example, a semiconductor laser diode (LD) or the like, and emits a blue-violet laser beam having a wavelength of 405 nm, for example, in accordance with a light source driving signal supplied from the light source driving circuit 41. The light source drive circuit 41 generates the light source drive signal according to the control signal supplied from the main controller 300. A laser beam emitted from the recording / reproducing light source 10 is shaped into a parallel light beam by a collimator lens 11 and divided into signal light and reference light by a beam splitter 12. The signal light is incident on a spatial light modulator (SLM) 13 constituted by a transmissive TFT liquid crystal panel or the like.

  The spatial light modulator 13 forms a bright and dark dot pattern according to the recording data to be recorded on the recording medium 1. More specifically, the encoder 80 converts a recording data signal composed of a one-dimensional digital signal sequence into a two-dimensional data sequence, that is, performs page processing and adds an error correction code to the two-dimensional data sequence to obtain a two-dimensional Generate a data signal. The SLM drive circuit 42 generates an SLM drive signal based on the two-dimensional data signal supplied from the encoder 80 and the control signal supplied from the main controller 300 to drive the spatial light modulator 13. The spatial light modulator 13 has a modulation processing unit of, for example, vertical 480 pixels × horizontal 640 pixels, and forms a two-dimensional light / dark dot pattern based on the SLM drive signal. When the signal light passes through the spatial light modulator 13, it is optically modulated by the bright and dark dot pattern. That is, the spatial light modulator 13 modulated the signal light having a wavelength of 405 nm emitted from the light source 10 by turning on / off the light for each pixel (pixel) according to the two-dimensional data signal from the encoder 80. A modulated signal light beam is generated. The modulated signal light beam is incident on the objective lens 16 through the polarization beam splitter (PBS) 14 and the quarter wavelength plate 15 and is condensed on the recording layer in the recording medium 1.

  On the other hand, the reference light split by the beam splitter 12 is aperture-limited by the aperture 17, then reflected by the first galvanometer mirror 18, and passed through the 4f relay lenses 19 and 20 to the signal light irradiation position of the recording medium 1. Incident at a predetermined angle. The reference light intersects with the signal light inside the recording medium 1 to form an optical interference pattern, and the optical interference pattern corresponding to the two-dimensional data signal is recorded as a change in refractive index. The first galvanometer mirror 18 has a light reflecting surface, is rotatably provided by a driving unit (not shown), and the direction of the light reflecting surface is variable. That is, when the first galvanometer mirror 18 is rotated, the irradiation angle of the reference light is changed, whereby multiple recording is performed by angle multiplexing on a predetermined recording area of the recording medium 1. The first galvanometer mirror drive circuit 70 generates a drive signal based on the control signal supplied from the main controller 300 and supplies it to the drive section (not shown) of the first galvanometer mirror 18. 18 angular positions are positioned.

  The second galvanometer mirror 30 is disposed on the optical path of the reference light that is irradiated and transmitted toward the recording medium 1. The second galvanometer mirror 30 has a light reflecting surface, is rotatably provided by a drive unit (not shown), and the direction of the light reflecting surface is variable. The second galvanometer mirror drive circuit 71 generates a drive signal based on the control signal supplied from the main controller 300, supplies it to the drive section of the second galvanometer mirror 30, and determines the angular position of the second galvanometer mirror 30. Perform positioning. Specifically, the second galvanometer mirror driving circuit 71 is configured so that the data reflection surface of the second galvanometer mirror 30 intersects perpendicularly with the reproduction reference light irradiated and transmitted to the recording medium 1 during data reproduction. Perform angle control. Thus, the reproduction reference light transmitted through the recording medium 1 is specularly reflected by the light reflecting surface of the second galvanometer mirror 30 and reenters the recording medium 1 along the same optical path as the incident optical path. When the reproduction reference light is incident again on the recording medium 1, diffracted light (phase conjugate light as reproduction light) is obtained from the recording medium 1. Then, the reproduction light is guided to the image sensor 21 through the objective lens 16, the quarter wavelength plate 15, and the polarization beam splitter 14. Note that, when sequentially reproducing the data multiplexed and recorded on the recording medium 1, the second galvanometer mirror driving circuit 71 rotates the reflecting mirror 30 stepwise in accordance with the irradiation angle of the reproduction reference light, and the recording medium 1 The angle control of the second galvanometer mirror 30 is performed so that the reproduction reference light that has passed through is always regularly reflected.

  On the other hand, at the time of data recording, the second galvanometer mirror driving circuit 71 controls the angle of the second galvanometer mirror 30 so as to guide the recording reference light irradiated and transmitted to the recording medium 1 to the light receiving surface of the photodetector 32 described later. Do.

  The image pickup device 21 is configured by a charge coupled device (CCD) having a light receiving region of 480 vertical pixels × 640 horizontal pixels, for example. The image sensor 21 receives the reproduction light generated by the reference light passing through the recording medium 1, converts it into an electric signal for each pixel, and supplies this to the reproduction signal detection circuit 43 as an image output signal. The reproduction signal detection circuit 43 detects a reproduction signal from the imaging output signal and supplies it to the decoder 81. The decoder 81 performs a reverse conversion to the page conversion performed by the encoder 80 on the reproduction signal to generate time-series reproduction data.

  The photodetector 32 has a light receiving surface on which light receiving elements such as a plurality of photodiodes are arranged, and receives the recording reference light guided by the second galvanometer mirror 30 and the condenser lens 31 on the light receiving surface. The photodetector 32 supplies an electrical signal obtained by photoelectrically converting the received recording reference light by each of the light receiving elements to the reference light detection circuit 44 as a light detection signal.

  Based on the light detection signal output from the light detector 32, the reference light detection circuit 44 and the reference light intensity detection signal indicating the light intensity of the recording reference light and the reference light indicating the irradiation angle of the recording reference light to the recording medium 1 An irradiation angle detection signal is generated and supplied to the main controller 300. Detailed configurations of the photodetector 32 and the reference light detection circuit 44 will be described later.

  The pickup driving unit 50 moves the pickup 100 in the radial direction of the recording medium 1 in accordance with the drive signal supplied from the pickup driving circuit 52 and controls the irradiation position of the recording / reproducing beam with respect to the recording medium 1. The pickup drive circuit 52 generates the drive signal based on a control signal from the main controller. The position of the pickup 100 on the moving stroke is detected by a pickup position detection circuit 51 including a position sensor, and is supplied to the main controller 300 as a pickup position detection signal.

  The recording medium 1 is fixed to the spindle motor 60 by a clamp mechanism and is driven to rotate. Thereby, the irradiation position of the recording / reproducing beam in the tangential direction of the recording medium is controlled. The spindle motor drive circuit 62 generates a drive signal based on the control signal supplied from the main controller 300, supplies this to the spindle motor 60, and controls the rotation of the spindle motor 60. The rotational angle position and rotational speed of the spindle motor 60 are detected by the rotary encoder 80, and supplied to the main controller 300 as a rotation detection signal for recognition.

  The main controller 300 controls the entire apparatus, and supplies control signals and the like to the various drive circuits described above based on detection signals from the various detection circuits and operation commands from the operation input unit 200. Responsible for operation control of the entire apparatus.

  Next, detailed configurations of the photodetector 32 and the reference light detection circuit 44 will be described with reference to FIG. The light receiving surface of the photodetector 32 has a light receiving region in which a plurality of light receiving elements are arranged in stripes and divided for each light receiving element. When the irradiation angle of the recording reference light changes during angle multiplexing recording, the beam spot of the recording reference light formed on the light receiving surface of the photodetector 32 intersects with the arrangement direction of the light receiving elements (FIG. 4A). (The direction indicated by the middle arrow). The formation pitch of each light receiving element coincides with the moving distance of the beam spot when the irradiation angle of the recording reference light changes by one step angle, for example. That is, when the irradiation angle of the recording reference light is changed by one step by the rotation of the first galvanometer mirror 18, the beam spot formed on the light receiving surface of the photodetector 32 moves by a distance corresponding to the formation pitch of the light receiving elements. The formation pitch of the light receiving elements may be defined by the width dimension of the light receiving elements in the arrangement direction. Each of the light receiving elements photoelectrically converts the received recording reference light, and supplies a light detection signal having a signal level corresponding to the amount of received light to the reference light detection circuit 44. That is, each of the light receiving elements outputs a light detection signal having a higher signal level as the intensity of the received light is stronger and as the light receiving area is larger.

  The reference light detection circuit 44 includes a differential amplifier circuit 44a and an adder circuit 44b. Each of the light receiving elements arranged in the stripe shape is alternately connected to the inverting input terminal and the non-inverting input terminal of the differential amplifier circuit 44a according to the arrangement order. That is, one of the light receiving elements adjacent to each other is connected to the inverting input terminal of the differential amplifier circuit 44a and the other is connected to the non-inverting input terminal. The differential amplifier circuit 44a outputs an output signal corresponding to the difference between the light detection signals input via the two input terminals from the output terminal OUT1 as a reference light irradiation angle detection signal, and supplies this to the main controller 300. To do.

  FIG. 4B shows the signal level of the reference light irradiation angle detection signal when the beam spot formed on the light receiving surface of the photodetector 32 moves on the light receiving surface according to the irradiation angle of the recording reference light. Is. When the beam spot moves along the direction intersecting the arrangement direction of the light receiving elements, the reference light irradiation angle detection signal varies within a certain range of positive potential and negative potential. That is, the signal level of the reference light irradiation angle detection signal changes according to the incident angle of the recording reference light. In such a configuration, when the recording reference light is irradiated so that the center of the beam spot comes to the boundary between the light receiving elements adjacent to each other of the photodetector 32, the signal level of the reference light irradiation angle detection signal becomes zero. For example, this zero cross point can be made to correspond to the positioning point of the irradiation angle of the reference light. That is, in this case, when the irradiation angle of the recording reference light is appropriate in the angle multiplex recording, the signal level of the reference light angle detection signal is zero, and the main controller 300 indicates that the signal level of the reference light angle detection signal is zero. Alternatively, when the angle is within a predetermined range near zero, it is determined that the irradiation angle of the recording reference light is appropriate. The main controller 300 is also supplied with an identification signal indicating from which light receiving element the light detection signal is output from the reference light detection circuit 44, so that the absolute irradiation angle of the recording reference light is also recognized. Be able to.

  On the other hand, the light detection signal generated by each light receiving element of the light detector 32 is also supplied to the adding circuit 44b. The adder circuit 44b outputs a signal obtained by adding the light detection signals supplied from each of the light receiving elements from the output terminal OUT2 as a reference light intensity detection signal, and supplies this to the main controller 300. That is, the reference light intensity detection signal has a signal level corresponding to the light intensity of the recording reference light received by the light receiving surface of the photodetector 32. Therefore, the main controller 300 can determine whether or not the emission intensity of the recording reference light is within an appropriate range based on the signal level of the reference light intensity detection signal.

  The formation pitch of each light receiving element may be 1 / N (N is a positive integer) of the moving distance of the beam spot when the irradiation angle of the recording reference light changes by one step angle. That is, when the irradiation angle of the recording reference light changes by one step, the beam spot formed on the light receiving surface of the photodetector 32 moves by a distance corresponding to N times the formation pitch of the light receiving elements. Here, FIG. 5A shows a case where the formation pitch of each light receiving element is set to one half of the moving distance of the beam spot when the irradiation angle of the recording reference light is changed by one step angle. FIG. 5B shows the signal level of the reference light irradiation angle detection signal when the beam spot moves according to the irradiation angle of the recording reference light, and corresponds to FIG. . Even in this case, the zero cross point of the graph shown in FIG. 5B can be made to correspond to the positioning point of the reference light irradiation angle, and if the irradiation angle of the recording reference light is appropriate in the angle multiplex recording, the reference is made. The signal level of the light angle detection signal is zero.

  Further, as shown in FIG. 6, in the photodetector 32, the formation pitch of the light receiving elements arranged on the light receiving surface may be non-uniform in consideration of the characteristics of the optical system. That is, the diameter of the beam spot formed on the light receiving surface of the photodetector 32 changes according to the irradiation angle when the recording reference light is irradiated onto the light receiving surface. Therefore, by making the width dimension of each light receiving element different according to the position, more accurate detection angle of the reference light can be detected.

  Next, the operation of the hologram recording / reproducing apparatus having the above configuration will be described. In the hologram recording / reproducing apparatus of the present invention, the recording mode or the reproducing mode is not selected by the mode selection command from the operation input unit 200, and the recording / reproducing process is executed under the control of the main controller 300. First, the operation in the recording mode will be described with reference to the flowchart of FIG.

  When a command for performing data recording on the recording medium 1 is issued from the operation input unit 200, the main controller 300 sends a control signal for positioning the second galvanometer mirror 30 at a predetermined position during recording to the second galvanometer mirror driving circuit 71. To supply. The second galvanometer mirror drive circuit 71 generates a drive signal in response to the control signal, rotates the second galvanometer mirror, and causes the recording reference light transmitted through the recording medium 1 to be guided to the photodetector 32. The direction of the light reflecting surface of the two galvanometer mirror 30 is positioned (step S1).

  Next, the main controller 300 supplies control signals to the spindle motor drive circuit 62 and the pickup drive circuit 52, and drives the spindle motor 60 and the pickup drive unit 50 to position the beam irradiation position (step S2).

  Next, when the main controller 300 supplies a control signal to the SLM drive circuit 42, the SLM drive circuit 130 generates a drive signal corresponding to the two-dimensional data signal generated by the encoder 80, and supplies this to the spatial modulator 15. Supply. As a result, a light and dark dot pattern corresponding to the two-dimensional data signal is formed in the spatial light modulator 15 (step S3).

  Next, the main controller 300 sends a control signal to the first galvanometer mirror driving circuit 70 to position the angular position of the first galvanometer mirror 18 so that the irradiation angle of the reference light corresponds to the recording of the first page (step S4). .

  Next, the main controller 300 supplies a control signal to the light source driving circuit 41 to turn on the recording / reproducing light source 10. The laser light emitted from the recording / reproducing light source 10 is split into signal light and reference light (recording reference light) by the beam splitter 12. When the signal light passes through the spatial modulator 13, the signal light is optically modulated by the bright and dark dot pattern formed in the spatial modulator 13 according to the recording data, and is applied to the recording medium 1 via the quarter-wave plate 15 and the objective lens 16. Incident. On the other hand, after the aperture of the recording reference light is limited by the aperture 17, the irradiation angle is controlled by the first galvanometer mirror 18, and the recording reference light is positioned at the same position as the signal light irradiation position of the recording medium 1 via the 4f relay lenses 19 and 20. Incident. The signal light and the reference light interfere in the recording medium 1, and the interference fringes are held in the recording medium 1 as recording data (step S5).

  The recording reference light transmitted through the recording medium 1 is reflected by the light reflecting surface of the second galvanometer mirror 30 and guided to the light receiving surface of the photodetector 32 through the condenser lens 31. The recording reference light received by the light detector 32 is photoelectrically converted by each of a plurality of light receiving elements provided on the light receiving surface of the light detector 32 and supplied to the reference light detection circuit 44 as a light detection signal. The adder circuit 44b constituting the reference light detection circuit 44 outputs a signal obtained by adding the signal group photoelectrically converted by each of the plurality of light receiving elements as a reference light intensity detection signal. The reference light intensity detection signal indicates the light intensity of the recording reference light irradiated on the photodetector 32. Further, the differential amplifier circuit 44a constituting the reference light detection circuit 44 outputs a signal corresponding to the difference between the signal levels of the signal group photoelectrically converted by each of the plurality of light receiving elements as a reference light irradiation angle detection signal. . The reference irradiation angle detection signal has a signal level corresponding to the irradiation position of the recording reference light irradiated to the photodetector 32, and indicates the irradiation angle of the recording reference light to the recording medium 1. The reference light detection circuit 44 supplies the reference light intensity detection signal and the reference light irradiation angle detection signal to the main controller 300 (step S6).

  Based on the reference light intensity detection signal supplied from the reference light detection circuit 44, the main controller 300 determines whether or not the recording medium is attached to the recording / reproducing apparatus, and the recording medium is not attached to the recording / reproducing apparatus. If it is determined, the recording operation is interrupted (step S7). That is, the main controller 300 determines whether or not the recording medium is mounted based on the reference light intensity detection signal that exhibits a different signal level depending on whether or not it has passed through the recording medium.

  Subsequently, the main controller 300 determines whether or not the light intensity of the recording reference light is within the appropriate range based on the reference light intensity detection signal. A control signal is supplied to control the output power of the recording / reproducing light source 10 so that the light intensity of the recording reference light falls within an appropriate range (step S8).

  Further, the main controller 300 determines, based on the reference light angle detection signal, whether the irradiation angle of the reference light is within an appropriate range, that is, whether it is within a predetermined irradiation angle range corresponding to the recording page. If it is determined that it is out of the proper range, a control signal is supplied to the first galvanometer mirror driving circuit 70 so that the irradiation angle of the recording reference light falls within a predetermined angle range corresponding to the recording page. The direction of the light reflecting surface of the mirror 18 is corrected.

  When performing angle multiplex recording on the recording medium 1, the main controller 300 supplies a control signal to the first galvanometer mirror driving circuit 70 when the current page recording is completed, and the first galvanometer mirror 18 is moved to a predetermined amount. Rotate to make the recording reference light irradiation angle correspond to the new page recording. By repeating this operation, the first galvanometer mirror 18 is rotated stepwise, and the angle multiplex recording is performed by sequentially changing the irradiation angle of the recording reference light.

  Next, the operation of the reproduction mode of the hologram recording / reproducing apparatus will be described with reference to the flowchart of FIG. When a command to reproduce the data recorded on the recording medium 1 is issued from the operation input unit 300, the main controller 300 supplies control signals to the spindle motor drive circuit 62 and the pickup drive circuit 52, and the spindle motor 60 and The pickup driving unit 50 is driven to adjust the beam irradiation position to the area where the data to be reproduced is recorded (step S21).

  Next, the main controller 300 supplies a control signal to the SLM drive circuit 42 to block all the pixels constituting the spatial modulator 15 in the dark state and block the optical path of the signal light (step S22).

  Next, the CPU 300 supplies a control signal to the first galvanometer mirror driving circuit 70 and the second galvanometer mirror 71 to reproduce the angular positions of the first galvanometer mirror 18 and the second galvanometer mirror 30, that is, the irradiation angle of the reproduction reference light. Correspond to the record page to be. At this time, the angle of the second galvanometer mirror 30 is controlled so that the light reflection surface intersects the reproduction reference light transmitted through the recording medium 1 perpendicularly (step S23).

  Next, the CPU 300 supplies a control signal to the light source driving circuit 41 to turn on the recording / reproducing light source 10 (step S24). The laser light emitted from the recording / reproducing light source 10 is split into signal light and reference light (reproduction reference light) by the beam splitter 12. The signal light is blocked by the spatial modulator 15 and is not irradiated onto the recording medium 1. On the other hand, after the aperture of the reproduction reference light is limited by the aperture 17, the irradiation angle is controlled by the first galvanometer mirror 18 and enters the recording medium 1 through the 4f relay lenses 19 and 20. The reproduction reference light transmitted through the recording medium 1 is regularly reflected by the light reflecting surface of the second galvanometer mirror 30. The reproduction reference light specularly reflected by the second galvanometer mirror 30 reenters the recording medium 1 along the same optical path as the incident optical path. When the reproduction reference light is incident again on the recording medium 1, diffracted light (phase conjugate light as reproduction light) is obtained from the recording medium 1. The reproduction light is guided to the image sensor 21 through the objective lens 16, the quarter wavelength plate 15, and the polarization beam splitter 14. The imaging element 21 converts the brightness of the received reproduction light into an electrical digital signal for each pixel, and supplies this to the reproduction signal detection circuit 43 as an imaging output signal. The reproduction signal detection circuit 43 determines “0” or “1” in the imaging output signal at a predetermined slice level, detects the reproduction signal of the recording data, and supplies this to the decoder 81. The decoder 81 performs a reverse conversion to the page conversion performed by the encoder 80 on the reproduction signal to generate time-series reproduction data, and supplies this to an output circuit (not shown) as reproduction output data ( Step S25).

  In the case of sequentially reproducing a plurality of recording pages that are multiplexed and recorded on the recording medium 1, the main controller 300 drives the first galvanometer mirror driving circuit 70 and the second galvanometer mirror when the reproduction of the current recording page is completed. A control signal is supplied to the circuit 71, the first galvanometer mirror 18 is rotated to change the irradiation angle of the reproduction reference light, and the second galvanometer mirror is rotated according to the change of the irradiation angle of the reproduction reference light. The light reflection surface is controlled to be orthogonal to the reproduction reference light. That is, the second galvanometer mirror 30 is driven in conjunction with the first galvanometer mirror. By repeating this operation, the first galvanometer mirror 18 and the second galvanometer mirror 30 are rotated stepwise, and the recording data recorded by angle multiplexing is read by sequentially changing the irradiation angle of the reproduction reference light.

  As is clear from the above description, according to the hologram recording / reproducing apparatus of the present invention, the recording reference light transmitted through the recording medium is guided to the photodetector without re-entering the recording medium during recording. Since the operation control at the time of data recording is performed based on the light intensity and the irradiation angle of the recorded reference light, recording noise is reduced and highly accurate data recording is achieved.

  In the above-described embodiment, the recording reference light is guided to the photodetector when the operation mode of the hologram recording / reproducing apparatus is the recording mode. However, the reference light is always sent to the photodetector except in the reproduction mode. It may be guided. For example, even when the operation mode of the hologram recording / reproducing apparatus is the recording mode or the standby mode before the transition to the reproducing mode, the reference light is guided to the photodetector to detect the intensity of the laser light as shown in the above embodiment. It is also possible to determine whether or not the recording medium is mounted.

(Second embodiment)
FIG. 9 shows the configuration of a pickup 100 ′ mounted in the hologram recording / reproducing apparatus according to the second embodiment of the present invention. The pickup 100 'differs from the first embodiment in the configuration of the second galvanometer mirror. That is, a photodetector is coupled to the second galvanometer mirror 30 'according to the second embodiment, a light reflecting surface 30a is formed on one surface, and a light receiving surface 32a of the photodetector is formed on the back side thereof. Has been. A plurality of light receiving elements are arranged on the light receiving surface 32a of the photodetector. The second galvanometer mirror 30 'has a drive unit (not shown) as in the first embodiment, and is rotationally controlled by the second galvanometer mirror drive circuit 71 so that the directions of the light reflecting surface 30a and the light receiving surface 32a are variable. .

  Hereinafter, the operation of the second galvanometer mirror 30 ′ during recording and reproduction will be described. First, at the time of data reproduction, the reproduction reference light transmitted through the recording medium 1 is specularly reflected by the light reflecting surface 30a and re-incident on the recording medium 1 as in the first embodiment. Further, when reproducing a plurality of recording pages that are multiplexed and recorded, the angle control is performed in conjunction with the first galvanometer mirror 18 so that the light reflecting surface 30a is always orthogonal to the reproduction reference light. Thereby, phase conjugate reproduction is achieved as in the first embodiment.

  On the other hand, at the time of data recording, the second galvanometer mirror 30 ′ is rotated approximately 180 degrees from the state at the time of reproduction, and receives the recording reference light transmitted through the recording medium 1 by the light receiving surface 32 a. At this time, the light receiving surface 32a does not necessarily need to be orthogonal to the recording reference light, and is not interlocked with the first galvanometer mirror 18 for angle multiplexing recording. That is, at the time of recording, the second galvanometer mirror 30 'is fixed at a predetermined angular position so that the recording reference light transmitted through the recording medium 1 can be received by the light receiving surface 32a. The recording reference light received by the light receiving surface 32a is photoelectrically converted by each of the plurality of light receiving elements and supplied to the reference light detection circuit 44 as a light detection signal. Since the other parts are the same as those in the first embodiment, the description thereof is omitted.

  As described above, according to the hologram recording / reproducing apparatus in the second example, the light receiving surface of the photodetector is provided on the back side of the light reflecting surface of the second galvanometer mirror. There is no need to provide an optical system for guiding, and the recording reference light can be directly received by the photodetector only by rotationally driving the second galvanometer mirror. As a result, the same effects as the first embodiment can be obtained, and the pickup can be configured compactly.

It is a figure which shows the reproducing | regenerating method by the conventional phase conjugate reproducing | regenerating system. It is a figure which shows the structure of the pick-up with which the hologram recording / reproducing apparatus based on this invention is equipped. 1 is a block diagram of a hologram recording / reproducing apparatus according to the present invention. (A) is a block diagram showing a configuration of a photodetector and a reference light detection circuit according to the present invention, and (b) is reference light irradiation when a beam spot of recording reference light moves on the light receiving surface of the photodetector It is a graph which shows the change of the signal level of an angle detection signal. (A) is a block diagram showing another configuration of the photodetector according to the present invention, (b) is a reference light irradiation angle detection signal when the beam spot of the recording reference light moves on the light receiving surface of the photodetector. It is a graph which shows the change of the signal level of. It is a block diagram which shows the other structure of the photodetector which concerns on this invention. It is a flowchart which shows the operation | movement at the time of the recording mode of the hologram recording / reproducing apparatus based on this invention. It is a flowchart which shows the operation | movement at the time of the reproduction | regeneration mode of the hologram recording / reproducing apparatus concerning this invention. It is a figure which shows the other structure of the pick-up with which the hologram recording / reproducing apparatus based on this invention is equipped.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Recording / reproducing light source 11 Collimator lens 12 Beam splitter 13 Spatial modulator 16 Objective lens 18 1st galvanometer mirror 21 Imaging element 30 2nd galvanometer mirror 32 Photo detector 41 Light source drive circuit 44 Reference light detection circuit 70 1st galvanometer mirror drive Circuit 71 Second galvanometer mirror drive circuit

Claims (8)

A laser light source;
Splitting means for splitting the laser light emitted from the laser light source into two;
Spatial modulation means for performing two-dimensional spatial modulation on one of the two divided laser beams based on recording information;
An optical system that irradiates the recording medium with spatially modulated laser light as signal light and irradiates the recording medium with the other of the two laser lights as reference light and records the recording information on the recording medium;
A reflection mirror provided on the optical path of the reference light transmitted through the recording medium and provided with a reflective surface for reflecting the reference light;
Replaying means for replaying recorded information recorded on the recording medium based on reference light reflected by the reflecting mirror and re-entered and transmitted to the recording medium,
An optical path control means for controlling the optical path of the reference light transmitted through the recording medium by positioning the direction of the reflecting surface of the reflecting mirror at different positions according to the operation mode;
A light detector that generates a light detection signal having a signal level corresponding to the received light intensity, and
The optical path control means guides the reference light transmitted through the recording medium to a light receiving surface of the photodetector in a recording mode or in a standby mode before shifting to a recording mode or a reproducing mode. apparatus. The photodetector is located away from the reflecting mirror;
The optical path control means positions the reflecting surface so that reference light transmitted through the recording medium and reflected by the reflecting surface of the reflecting mirror during recording is directed toward the light receiving surface of the photodetector. The hologram recording / reproducing apparatus according to claim 1. The photodetector is coupled to the reflecting mirror, and has a light receiving surface on the back side of the reflecting surface of the reflecting mirror;
2. The hologram according to claim 1, wherein the optical path control unit positions the reflecting surface so that the reference light transmitted through the recording medium is received by the light receiving surface of the photodetector during recording. Recording / playback device. The photodetector has a plurality of light receiving elements arranged on the light receiving surface thereof,
4. The hologram recording / reproducing apparatus according to claim 1, wherein the light detection signal includes a signal group received and photoelectrically converted by each of the light receiving elements. 5.   5. The hologram recording / reproducing apparatus according to claim 1, further comprising emission intensity control means for controlling the emission intensity of the laser light source based on the light detection signal. The optical system includes an angle control unit that changes an irradiation angle of the reference light to the recording medium;
6. The hologram recording / reproducing according to claim 1, further comprising angle detection means for detecting an irradiation angle of the reference light to the recording medium based on the light detection signal. apparatus.   The correction means for correcting the irradiation angle of the reference light controlled by the angle control means when the irradiation angle of the reference light detected by the angle detection means is not within a predetermined range. 6. The hologram recording / reproducing apparatus according to 6.   8. The hologram recording / reproducing apparatus according to claim 1, further comprising a determination unit that determines the presence / absence of the recording medium based on the light detection signal.

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