JP4332390B2 - Holographic playback device - Google Patents

Description

  The present invention relates to a holographic recording / reproducing method, a holographic reproducing apparatus, and a holographic recording / reproducing apparatus for recording interference fringes by irradiating a holographic recording medium with object light and reference light.

  In this conventional holographic recording / reproducing method or holographic recording / reproducing apparatus, recording and reproduction are performed by laser light from the same laser light source. In the case of wavelength multiplex recording, recording and reproduction are performed in units of holograms with the same light source and laser light having the same characteristics.

  As described above, in the conventional holographic recording / reproducing method, the same laser light source is used for recording and reproducing. However, when a solid laser or gas laser is used as the laser light source, the coherency of the laser beam during recording ( Coheremcy) and good laser power can be obtained, but there are problems in that it is large and expensive, and the recording / reproducing apparatus is not suitable for mass production.

  Further, when a laser diode is used as a laser light source, it is small and inexpensive, and a recording / reproducing apparatus is suitable for mass production, but there is a problem that performance is inferior in terms of coherency and power of laser light during recording.

The present invention has been made in view of the above problems, and is capable of obtaining a reproduced image by laser light from a laser diode while maintaining sufficient coherency and power during reproduction of holographic recording . an object of the present invention is to provide an e b graphics playback equipment.

  As a result of diligent research, the present inventor has made the laser diode multimode oscillation so that the wavelength of a part of the laser beam for reproduction coincides with the laser beam at the time of recording. It turns out that can be obtained.

  That is, the following problems can be solved by the present invention described below.

  (1) Information to be recorded by branching laser light from any one of a solid-state laser, a gas laser, a surface emitting laser, and a single-mode oscillation laser diode into object light and reference light, and using an amplitude spatial light modulator The holographic recording medium is irradiated with the reference light to record interference fringes, and when reproducing the recording, the longitudinal mode waveform of the reproducing laser beam emitted from the reproducing laser diode is converted into a multimode, The hologram is controlled according to a deviation of the laser beam wavelength for reproduction from the laser beam wavelength at the time of recording so that one of the oscillation wavelengths substantially coincides with the wavelength of the laser beam at the time of recording. Graphic recording and playback method.

  (2) The holographic recording / reproducing method according to (1), wherein the longitudinal mode waveform is converted into a multimode by using the oscillation transient characteristic of the reproducing laser beam by the reproducing laser diode by a high frequency superimposing method. .

  (3) The holographic recording / reproducing method according to (2), wherein a single-mode oscillation laser diode is used for the recording, and the laser diode is used as a reproducing laser diode by multi-mode oscillation.

  (4) At the time of recording the interference fringes, the reference light is spatially modulated by modulating the phase of some of the pixels in the phase spatial light modulator as modulation pixels, and becomes the address of the data page to be recorded. A phase distribution is provided to obtain phase code multiplex recording. During recording and reproduction, the reproduction laser beam is spatially modulated by the reproduction phase spatial light modulator so as to have the same phase pattern as that during recording, and the holographic recording is performed. (2) or (3) characterized in that the unit of the modulation pixel in the reproduction phase spatial light modulator is changed so that the medium is irradiated, the generated diffracted light quantity is detected, and the detected light quantity is maximized. ) Holographic recording and playback method.

  (5) Interference fringes between the object light modulated by the amplitude spatial light modulator according to the information to be recorded and the reference light provided with the phase distribution serving as the address of the data page recorded by the phase spatial light modulator Is a holographic recording device that reproduces the information by the generated diffracted light by irradiating a reproducing laser beam having the same wavelength as that of the reference light onto a holographic recording medium on which is recorded, A laser diode that emits a reproduction laser beam in a wavelength band including the spectrum, a spectrum control device that converts a longitudinal mode waveform of the reproduction laser beam emitted from the laser diode into a multimode, and a reproduction laser that passes through the holographic recording medium A light detector for detecting the amount of light, and the spectrum control device is configured to detect the amount of transmitted light detected by the light detector. As a small, holographic reproducing apparatus characterized in that it is adapted to control the longitudinal-mode waveform of the reproduction laser beam.

  (6) The spectrum control device is a high-frequency superimposing circuit that multiplies the longitudinal mode waveform by using the oscillation transient characteristic of the laser beam for reproduction by the laser diode. Graphic playback device.

  (7) A reproduction phase spatial light modulator that spatially modulates the reproduction laser beam so as to have the same phase pattern as the reference light at the time of recording is provided, and the spectrum control device maximizes the amount of diffracted light. As described above, the holographic reproducing device according to (5), wherein the holographic reproducing device is a pixel control device configured to change a unit of a modulation pixel in the reproduction phase spatial light modulator.

  (8) Recording laser light source comprising any one of a solid-state laser, gas laser, surface emitting laser, and single mode oscillation laser diode, and holographic recording of object light and reference light branched from the laser light from the recording laser light source An object optical system and a reference optical system that lead to a medium; an amplitude spatial light modulator that is provided in the object optical system and modulates object light according to information to be recorded; and a reference light that is disposed in the reference optical system. A phase spatial light modulator that provides a phase distribution serving as an address of a data page recorded on the holographic recording medium on which interference fringes between the object light and the reference light are recorded, via the reference optical system, A holographic recording / reproducing apparatus that irradiates a reproducing laser beam having the same wavelength as that of a reference light and reproduces the recording by the generated diffracted light, and includes the wavelength of the reference light A reproduction laser diode that emits a reproduction laser beam in a wavelength band, a spectrum control device that converts the longitudinal mode waveform of the reproduction laser beam emitted from the reproduction laser diode into a multimode, and the holographic recording medium transmitted A light detector for detecting the amount of transmitted light generated by the interference fringes based on the irradiation of the reproduction laser beam, and the spectrum control device includes a light amount of diffracted light detected by the light detector. A holographic recording / reproducing apparatus, wherein a longitudinal mode waveform of the reproducing laser beam is controlled so as to be minimized.

  (9) The spectrum control device is a high-frequency superimposing circuit that multiplies the longitudinal mode waveform by using the oscillation transient characteristic of the reproducing laser beam by the reproducing laser diode (8). Holographic recording and playback device.

  (10) The phase spatial light modulator spatially modulates the reproduction laser light so as to have the same phase pattern as the reference light at the time of recording, and the spectrum control device maximizes the amount of diffracted light. As described above, the holographic recording / reproducing apparatus according to (8), wherein the holographic recording / reproducing apparatus is a pixel control apparatus configured to change a unit of a modulation pixel in the phase spatial light modulator.

  (11) The recording laser light source is a single-mode oscillation laser diode, and the reproduction laser diode is also used as the recording laser light source, and is oscillated in a multi-mode to emit reproduction laser light. The holographic recording / reproducing apparatus according to (8), (9) or (10), wherein

  During holographic recording, recording is performed using any one of a solid-state laser, a gas laser, a surface emitting laser, and a laser diode of single mode oscillation, and at the time of recording / reproducing, a reproducing laser beam emitted from the reproducing laser diode The above-mentioned object is achieved by controlling the wavelength of the reproduction laser beam by the high frequency superposition method so that one of the oscillation wavelengths substantially coincides with the wavelength of the laser beam at the time of recording.

  The first embodiment of the present invention will be described below with reference to FIGS.

  FIG. 1 shows a recording optical system 10 for holographic recording on a holographic recording medium 12 in the holographic recording / reproducing method of the present invention. The recording optical system 10 includes a recording laser light source 14 composed of any one of a solid laser, a gas laser, and a surface emitting laser, and a part of the laser beam emitted from the recording laser light source 14 as a reference light. A reference optical system 16 for guiding to the graphic recording medium 12 and an object optical system 18 for guiding the remainder of the branched laser light as object light to the holographic recording medium 12 are provided.

  The laser light from the recording laser light source 14 is reflected, for example, by an s-polarized component by the polarizing beam splitter 20 and enters the reference optical system 16 as reference light, and the p-polarized component passes through the polarizing beam splitter 20. Thus, the light beam is incident on the object optical system 18 as object light.

  In the reference optical system 16, a half-wave plate 22, a phase spatial light modulator 24, and a Fourier lens 26 are arranged in this order from the polarization beam splitter 20 side.

  In the object optical system 18, an amplitude spatial light modulator 28 and a Fourier lens 30 are arranged in this order from the polarization beam splitter 20 side.

  The diffracted light generated by the object light and the reference light irradiated on the holographic recording medium 12 is guided to the CCD 34 through the inverse Fourier lens 32 so that the recording state can be monitored.

  The amplitude spatial light modulator 28 in the object optical system 18 may or may not modulate the amplitude for each pixel in accordance with information (data) to be recorded.

  Here, in general, encoding is performed so that the ON pixel ratio of the recorded data page (the ratio of ON pixels to all pixels, that is, the ratio of pixels that allow laser light to pass) is constant for all pages.

  The phase spatial light modulator 24 in the reference optical system 16 spatially modulates the reference light by modulating the phase of some pixels as modulation pixels, and the data page recorded on the holographic recording medium 12. The phase distribution of the address is given, so that phase code multiplex recording is performed.

  For example, as shown in FIGS. 2A, 2B, and 2C, by applying a phase difference to each pixel of the phase spatial light modulator 24, a hologram recorded on the holographic recording medium 12 is formed. An address is allocated.

  2A to 2C, between the pixels indicated by diagonal lines and the pixels indicated by white lines, there is a phase difference of π, that is, ½ wavelength, between the laser beams that have passed through the respective pixels. It shows that it is given.

  Here, the phase spatial light modulator 24 gives a spatial distribution only to the phase of the laser beam passing therethrough, and its amplitude is not changed. Therefore, energy loss as a whole of the laser beam does not occur.

  Next, a holographic reproducing device 40 for reproducing the recording of the holographic recording medium 12 holographically recorded by the recording optical system 10 will be described with reference to FIG.

  The holographic reproducing device 40 includes a laser diode 42, a reproducing phase spatial light modulator 44 that phase-modulates laser light emitted from the laser diode 42, and a Fourier lens 46.

  Further, a CCD 48 that receives the diffracted light generated by irradiating the holographic recording medium 12 with the laser light that has passed through the Fourier lens 46 and an inverse Fourier disposed between the CCD 48 and the holographic recording medium 12. The lens 50, a photodetector 52 for detecting the amount of laser light transmitted through the holographic recording medium 12, and the laser so that the output is minimized based on the output of the photodetector 52 And a spectrum controller 54 for controlling the diode 42.

  The spectrum control unit 54 converts the longitudinal mode waveform of the reproduction laser beam emitted from the laser diode 42 into a multimode, and includes a high frequency superimposing circuit 56 as shown in FIG. Yes.

  The high-frequency superimposing circuit 56 includes the laser diode 42 and includes an oscillation circuit 58 and an impedance matching circuit 60 as signal generators.

  The impedance matching circuit 60 is for converting the output impedance of the oscillation circuit 58 into the impedance of the laser diode 42, and efficiently transmits the output of the oscillation circuit 58 to the laser diode 42 and is connected to the laser diode 42. The direct current output from the APC circuit 62 is cut.

  The high-frequency superimposing circuit 56 converts the longitudinal mode waveform into a multimode by using the transient characteristics of the laser beam.

  More specifically, the ON time of the optical output of the laser diode 42 is shorter as the frequency of the signal generator (oscillation circuit 58 and impedance matching circuit 60) is higher, and the number of longitudinal modes in the laser diode 42 is larger as the ON time is shorter. Therefore, in order to keep the multi-mode state continuous, the frequency of the signal generator is set to several hundred MHz, and the optical output of the laser diode 42 is turned on and off.

  In the first embodiment, when holographic recording is performed on the holographic recording medium 12 by the laser light from the recording laser light source 14, the relationship between the wavelength of the laser light and the laser output is shown in FIG. As described above, the wavelength λw laser light is emitted with almost no spectral line width.

  Further, when a laser diode is used for the recording laser light source 14, as shown in FIG. 5B, oscillation is performed in a single mode with a narrow spectral line width. For this purpose, for example, a current sufficiently larger than the threshold current may be applied, or a distributed feedback laser, a Bragg reflection laser, a surface emitting laser, or the like may be used.

  When reproducing the data recorded on the holographic recording medium 12, the holographic reproducing device 40 shown in FIG. 3 is used. Here, the reproducing laser beam from the laser diode 42 is applied to the holographic recording medium 12. The diffracted light obtained by irradiation is incident on the CCD 48 via the inverse Fourier lens 50. Further, the laser light transmitted through the holographic recording medium 12 enters the photodetector 52, and the light intensity is detected.

  The spectrum control device 54 controls the laser diode 42 based on the output from the photodetector 52 so that the output is minimized. Specifically, the ON time of the laser diode 42 is increased or decreased using the high frequency superimposing circuit 56. The longitudinal mode waveform of the laser diode 42 decreases as the ON time increases, but the wavelength of each longitudinal mode waveform also changes.

  Therefore, by controlling the ON time, as shown in FIG. 5C, when one wavelength of the longitudinal mode waveform matches the wavelength of the laser beam of the recording laser light source 14, the holographic recording medium The diffraction efficiency at 12 is maximized.

  Next, with reference to FIG. 6, a holographic reproducing device 70 according to Embodiment 2 of the present invention will be described.

  The holographic reproduction device 70 is provided with a second spectrum control device 72 different from the spectrum control device 54 with respect to the holographic reproduction device 40.

  Since other configurations are the same as those of the holographic reproducing device 40, the same parts are denoted by the same reference numerals, and description thereof will be omitted.

  The second spectrum control device 72 in the second embodiment spatially modulates the reproducing laser beam emitted from the laser diode 42 so as to have the same phase pattern as the reference beam at the time of recording. The pixel control device changes the unit of the modulation pixel.

  More specifically, the unit of the modulation pixel in the reproduction phase spatial light modulator 44 is changed so that the amount of diffracted light received from the CCD 48 from the holographic recording medium 12 is maximized. .

  Referring back to FIG. 2, for example, using the phase code shown in FIG. 2B, interference fringes are recorded on the holographic recording medium 12 by the recording optical system 10 by the laser light having the wavelength λ. Think about the case.

  Note that the modulation pixel unit of the phase code does not necessarily need to be a unit pixel (the smallest square in FIG. 2) of the phase spatial light modulator 24. In FIGS. 2A, 2B, and 2C, respectively. 5 × 5, 6 × 6, and 7 × 7 pixels are used as modulation pixel units.

  Here, consider a case where phase code multiplex recording is performed on the holographic recording medium 12 using a laser beam having a wavelength λ for recording and the phase code shown in FIG.

  Vol. 16, No. 3 / March 1999 / J. Opt. Soc. Am. According to Aps 563 to 564, it is known that the period of a modulation pixel that minimizes crosstalk during recording and reproduction varies depending on the wavelength of the reference laser beam. That is, the phase code modulation unit (the maximum frequency of the phase code pattern) functions as a parameter for the Bragg condition as well as the wavelength of the laser beam and the incident angle of the laser beam.

  Therefore, by changing the modulation unit of the phase code, the Bragg condition can be changed, that is, the wavelength shift can be compensated.

  Next, the wavelength spectrum of the reproduction laser beam from the laser diode 42 is actually detected by the second spectrum control device in the second embodiment, and the modulation unit of the phase code in the reproduction phase spatial light modulator 44 is changed. The process of compensating for the wavelength shift will be described.

  As described above, since the ON pixel ratio of the data page as shown in FIGS. 2A to 2C is encoded so as to be constant in all pages, the CCD 48 should detect it during reproduction. The total amount of light is known in advance from reproduction laser light intensity × propagation efficiency of optical system × diffraction efficiency per hologram × ON pixel ratio. Therefore, by monitoring the total amount of light detected by the CCD 48, it is possible to know how much the setting including the oscillation wavelength of the reproducing laser beam satisfies the Bragg condition in the holographic recording medium 12.

  If the Bragg condition is not completely satisfied, that is, if the total amount of light detected by the CCD 48 is less than the expected value, it is considered that the wavelength of the reproduction laser beam is deviated from the wavelength of the laser beam during recording. On the other hand, as described above, the wavelength shift of the reproduction laser beam can be compensated by changing the phase code modulation pixel unit in the reproduction phase spatial light modulator 44.

  Actually, for example, if the modulation pixel unit is increased and the amount of light detected by the CCD 48 is increased, the modulation pixel unit is continuously increased until it approaches the maximum value, and if the detected light amount is decreased, the modulation pixel unit is decreased. The second spectrum control device 72 may perform servo control according to an algorithm such as

  When the deviation of the reproduction laser beam from the Bragg condition in the holographic recording medium 12 is caused by the wavelength shift of the reproduction laser beam, the compensation of the Bragg condition by the phase code as described above is also applied to different data pages (holograms). If the amount of reproduction light obtained by the CCD 48 is reduced while the reproduction operation is repeated, the compensation operation may be performed again.

  With this Bragg condition compensation method using phase code modulation, whether the wavelength of the reproduction laser beam is shifted to the longer wavelength side or the shorter wavelength side with respect to the wavelength of the laser beam during recording is used. Even if the Bragg condition is changed due to the setting of the holographic recording medium or the change of the optical system, it is possible to compensate within the range that can be achieved by the modulation pixel unit.

  In the case of multiplex recording of holograms using phase codes, Applied Optics / Vol. 39, No. According to 23/10 August 2000, p4160-4166, theoretically, it is possible to form approximately 4.3 billion phase codes in the orthogonal direction by 32 × 32 pixel modulation pixels, which is practically sufficient. Is a number. On the other hand, currently available phase spatial light modulators have hundreds of thousands to millions of pixels. For example, a phase spatial light modulator of 1024 × 1024 pixels forms a phase code consisting of 32 × 32 modulation pixels. In this case, one modulation pixel includes 32 × 32 = 1024 pixels, and finer control than the example of FIG. 2 is possible.

  Embodiments 1 and 2 above are cases where a holographic recording medium recorded by a recording laser light source is reproduced by a holographic reproducing device, but the present invention is not limited to this, and is shown in FIG. 7, for example. As in the third embodiment, the same laser diode may be used during recording and reproduction.

  In this case, the holographic recording / reproducing apparatus 80 according to the third embodiment is controlled by a spectrum control apparatus 54 as shown in FIG. 3 instead of the recording laser light source 14 in the optical system of the recording optical system 10 in FIG. A laser diode 82 is used, and during recording, the laser diode 82 is set to single mode oscillation, and during reproduction, multimode oscillation is set as in the case of FIG.

  In other configurations, the same portions as those in FIGS. 1 and 3 are denoted by the same reference numerals, and description thereof is omitted.

  Further, like the holographic recording / reproducing apparatus 90 according to the fourth embodiment shown in FIG. 8, a reproducing laser diode 92 is added to the recording optical system 10 shown in FIG. Multi-mode oscillation may be performed.

1 is an optical system diagram showing a recording optical system used in a holographic recording method according to Embodiment 1 of the present invention. The top view which shows typically the state of the pixel in the data page in the phase spatial light modulator used with the recording optical system and reproduction | regeneration optical system Optical system diagram showing a holographic reproducing apparatus in the first embodiment A circuit diagram showing a spectrum control device in the holographic reproduction device The diagram which shows the relationship between the wavelength of the laser beam at the time of recording and the reproduction | regeneration in the holographic recording / reproducing method of the Example 1, and a laser output Optical system diagram showing a holographic reproducing apparatus according to Embodiment 2 of the present invention Optical system diagram showing a holographic recording and reproducing apparatus according to Embodiment 3 of the present invention Optical system diagram showing a holographic recording and reproducing apparatus according to Example 4 of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Recording optical system 12 ... Holographic recording medium 14 ... Recording laser light source 16 ... Reference optical system 18 ... Object optical system 24 ... Phase spatial light modulator 28 ... Amplitude spatial light modulator 40, 70 ... Holographic reproduction apparatus 42 82, 92 ... Laser diode 44 ... Reproducing phase spatial light modulator 48 ... CCD
52 ... Photo detector 54 ... Spectrum control device 56 ... High frequency superposition circuit 72 ... Second spectrum control device 80, 90 ... Holographic recording / reproducing device

Claims (3)

Interference fringes between the object light modulated by the amplitude spatial light modulator according to the information to be recorded and the reference light provided with the phase distribution serving as the address of the data page recorded by the phase spatial light modulator are recorded. Holographic recording medium is irradiated with a reproducing laser beam having the same wavelength as the reference light, and the information is reproduced by the generated diffracted light,
A laser diode that emits reproducing laser light in a wavelength band including the wavelength of the reference light;
A spectrum control device for converting the longitudinal mode waveform of the reproduction laser beam emitted from the laser diode into a multimode;
A photodetector for detecting the amount of reproduction laser light transmitted through the holographic recording medium;
Having
The holographic reproduction device characterized in that the spectrum control device controls the longitudinal mode waveform of the reproduction laser beam so that the amount of transmitted light detected by the photodetector is minimized. . 2. The holographic reproduction according to claim 1 , wherein the spectrum control device is a high-frequency superimposing circuit for converting a longitudinal mode waveform into a multimode by using an oscillation transient characteristic of a reproduction laser beam by the laser diode. apparatus. The reproduction phase spatial light modulator according to claim 1 , wherein the reproduction laser light is spatially modulated so as to have the same phase pattern as the reference light at the time of recording.
The spectral control device is a pixel control device configured to change a unit of a modulation pixel in the reproduction phase spatial light modulator so that the diffracted light quantity is maximized. .

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