Light information device and light information control method

Abstract

To provide a technology for realizing higher speed in data recording and playback in holographic data storage.SOLUTION: In a light information recording and reproduction device 1 that irradiates a recording medium 25, which stores target information as a plurality of pieces of two-dimensional data, with light and performs at least one of recording and reproduction, light is formed where a predetermined direction is a longitudinal direction and a direction orthogonal to the aforementioned longitudinal direction is a short direction, scanning is performed in the short direction to thereby record or reproduce the two-dimensional data.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an optical information device and an optical information control method. [Background technology]

[0002] Holographic data storage has attracted attention as a technology for recording and reproducing large amounts of data. For example, Patent Document 1 discloses a technology related to a recording medium for recording at a higher density. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-080239 A Summary of the Invention [Problem to be solved by the invention]

[0004] As the amount of data that can be stored increases, faster data recording and playback (higher data transfer rates) are also essential. However, conventional technologies including the above-mentioned Patent Document 1 have not been able to provide sufficient performance.

[0005] An object of the present invention is to provide a technique for realizing high-speed recording and reproduction of data in holographic data storage. [Means for solving the problem]

[0006] The optical information recording and reproducing device of the present invention is an optical information device which performs at least one of recording and reproducing by irradiating light onto a recording medium which stores target information as two-dimensional data, The light is shaped so that a predetermined direction is a longitudinal direction and a direction perpendicular to the longitudinal direction is a transverse direction, and the two-dimensional data is recorded or reproduced by scanning in the transverse direction. It is an optical information device.

[0007] An optical information recording and reproducing method according to one aspect of the present invention is an optical information control method executed by an optical information device which performs at least one of recording and reproducing by irradiating light onto a recording medium which stores target information as two-dimensional data, the method comprising the steps of: The light is shaped so that a predetermined direction is a longitudinal direction and a direction perpendicular to the longitudinal direction is a transverse direction, and the two-dimensional data is recorded or reproduced by scanning in the transverse direction. An optical information control method. Effect of the Invention

[0008] According to the present invention, it is possible to provide a technique for realizing high-speed recording and reproduction of data in holographic data storage. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a conventional optical information recording and reproducing device using a spherical wave reference wave. [Diagram 2] FIG. 1 is a diagram showing an example of the configuration of an optical information recording / reproducing device that employs the surfing method of the first embodiment. [Diagram 3] 3 is a diagram showing an example of the shape of a signal light irradiated onto a spatial light modulator in each of the conventional optical information recording and reproducing device shown in FIG. 1 and the surfing type optical information recording and reproducing device shown in FIG. 2. [Figure 4] 3A to 3C are diagrams illustrating an example of a line beam generation method and a scanning method in the surf-riding method illustrated in FIG. 2. [Diagram 5] 3A to 3C are diagrams showing the process of recording and reproducing a hologram in the optical information recording and reproducing device of the present embodiment shown in FIG. 2. [Figure 6] FIG. 1 is a diagram showing a schematic diagram of holograms on a recording medium multiplexed by a conventional method and a surfing method. [Figure 7] This is an example of the experimental results of the laser irradiation time, the SNR of the reproduced signal, and the bit error rate (bER) when recording and reproducing were performed while changing the laser irradiation time (scanning time) for one data page. [Figure 8]This is an example of a reconstructed image captured by a CMOS camera when the laser irradiation time was 6.67 msec (equivalent to a frequency of 150 Hz). [Figure 9] The image shown is a reconstructed image from the central data page (51st page) captured by a CMOS camera when 101 pages were shift-multiplexed with a shift pitch of 5 μm at a laser irradiation time of 6.67 msec / page (150 Hz). [Figure 10] This is an example of the SNR of the central page and the brightness of the reproduced image relative to the number of shift-multiplexed pages at a laser irradiation time of 6.67 msec / page (150 Hz). [Figure 11] FIG. 3 is a diagram showing an example of a configuration for replacing the CMOS camera of the optical information recording and reproducing device shown in FIG. 2, which improves the transfer rate of reproducing data. [Figure 12] 12 is a time chart of each CIS for detecting a reproduction signal of the surfing method at high speed using the reproduction optical system shown in FIG. 11. [Figure 13] FIG. 1 is a diagram showing an example of the configuration of a conventional angle multiplexing type optical information recording and reproducing device. [Figure 14] FIG. 1 is a diagram for explaining the principle of a conventional angle multiplexing method. [Figure 15] FIG. 11 is a diagram illustrating an example of the configuration of an optical information recording / reproducing device according to a second embodiment. [Figure 16] 14 is a diagram showing an example of control of an optical deflector (galvanometer mirror) that changes the angle of a reference beam in the conventional optical information recording and reproducing device shown in FIG. 13. FIG. [Figure 17] 16 is a diagram showing an example of control of an optical deflector (galvanometer mirror and AOD) for changing the angle of a reference beam in the optical information recording and reproducing device of the present embodiment shown in FIG. 15. FIG. [Figure 18] FIG. 1 is a diagram illustrating a hologram on a recording medium multiplexed by the surfing method. [Figure 19] FIG. 16 is a diagram showing an example of a configuration for replacing the CMOS camera of the optical information recording and reproducing device shown in FIG. 15, which improves the transfer rate of reproducing data. [Figure 20] 20 is a time chart of each CMOS camera for detecting a reproduced signal of the surfing method at high speed using the example of the configuration shown in FIG. 19. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] First, an overview of holographic data storage will be given. In holographic data storage, data is recorded on a recording medium as data pages arranged two-dimensionally.

[0012] Specifically, for example, during recording, a laser beam for signal light (hereinafter referred to as "signal light") is modulated to correspond to a data page and irradiated onto the recording medium, and a laser beam for reference light (hereinafter referred to as "reference light") is irradiated onto the recording medium to cause interference. As a result, interference fringes are recorded as a hologram in the recording medium.

[0013] During playback (reading), a laser for readout light (hereinafter referred to as "readout light") is irradiated, similar to the reference light used during recording, and the laser diffracted by the hologram in the recording medium can be read out as a two-dimensional image by an image sensor.

[0014] Here, the holographic data storage allows multiplexing of recording. That is, by changing the positional relationship between the signal light and the reference light, multiple data pages can be recorded at approximately the same position. Specifically, there are methods such as a shift multiplexing method in which the position where the signal light and the reference light are irradiated is moved in the vertical, horizontal, and depth directions, an angle multiplexing method in which the angle of the reference light is changed, and a frequency multiplexing method in which the frequency of the reference light is changed. Even when reproducing a multiplexed recording medium, by irradiating the readout light in the same manner as the reference light during recording, the laser diffracted by the hologram in the recording medium can be read out as a two-dimensional image by an image sensor. That is, the reference light during recording and the readout light during reproduction basically correspond one-to-one.

[0015] Holographic data storage can record two-dimensional data in a recording medium at once and multiplex it at narrow intervals, which allows the data capacity that can be recorded on the recording medium to be dramatically increased compared to existing optical discs.

[0016] In particular, holographic data storage using a spherical reference wave (hereinafter referred to as "spherical reference wave") and a shift multiplexing method has the potential to significantly improve the amount and density of data that can be stored. In other words, holographic data storage using a spherical reference wave and a shift multiplexing method is particularly effective in increasing data capacity. In addition, holographic data storage allows for long-term storage compared to magnetic recording, etc., and therefore has many advantages as data storage in data centers.

[0017] As described above, as the amount of data that can be stored increases, faster data recording and playback (higher data transfer rates) also become essential performance. However, in order to record the interference pattern of light as a hologram, the recording medium must be stationary during recording and playback. Therefore, in shift multiplexing and angle multiplexing, the position and angle of the recording medium in the vertical, horizontal and depth directions must be repeatedly fixed and changed. In other words, the recording medium and the optical system must be repeatedly stopped and moved, which is an obstacle to increasing the speed of recording and playback of data.

[0018] In addition, by irradiating a continuously moving recording medium with a high-power short-pulse laser, it becomes possible to record and reproduce in a pseudo-stationary state. However, when using a high-power short-pulse laser, the device becomes large and it becomes difficult to change the wavelength, and it becomes impossible to adopt a wavelength-tuning method.

[0019] The present invention relates to a method and an apparatus for achieving a high data transfer rate in holographic data storage.

[0020] FIG. 1 is a diagram showing an example of the configuration of a conventional optical information recording and reproducing device using a spherical wave reference wave. The optical information recording and reproducing device SYS1 shown in Figure 1 includes a laser light source 11, a mirror 12, a beam expander 13, a half-wave plate 14, a polarizing beam splitter 15, a mirror 16, a spatial light modulator 17, a relay lens 18, a spatial filter 19, a polarizing beam splitter 20, a mirror 21, a half-wave plate 22, a condenser lens 23, an objective lens 24, a recording medium 25, a condenser lens 26, and a CMOS camera 27. The mechanism of the conventional holographic data storage system SYS1 will be described below.

[0021] The conventional optical information recording and reproducing device SYS1 shown in Figure 1 employs the one-arm method, which, among other methods proposed in the past, enables miniaturization by configuring the signal light and reference light to pass through a partially shared optical path despite being two light beams.

[0022] The laser light source 11 is a part that emits a laser having a predetermined specification. The mirror 12 is an optical element for reflecting light. In this specification, when the term "mirror" is used simply, it means a mirror that has high reflectance and does not particularly change the wavelength or polarization of light. The beam expander 13 is an optical element that expands the diameter of the incident beam (laser). The half-wave plate 14 is an optical element that converts the polarization state of light. Polarizing beam splitter 15 is an optical element that splits incident light into two different paths based on its polarization state.

[0023] That is, the laser light emitted from the laser light source 11 is reflected by the mirror 12, and the beam diameter is expanded by the beam expander 13. The laser light with the expanded beam diameter has its polarization state converted by the half-wave plate 14. The laser light with its polarization state converted is split by the polarizing beam splitter 15 at a ratio of light amounts according to the polarization state. The laser light with its polarization state converted is split by the polarizing beam splitter 15 into S-polarized reference light LREF and P-polarized signal light LSIG.

[0024] The mirror 16 is an optical element for reflecting light. The spatial light modulator 17 is a digital micromirror device (DMD), which is an optical element that digitally controls the phase, amplitude, etc. of light using extremely small mirrors. The relay lens 18 is an optical element for connecting different optical systems or lens systems. The spatial filter 19 is an optical element that controls the characteristics of light in order to adjust changes in the intensity distribution and wavefront of the light. Polarizing beam splitter 20, like polarizing beam splitter 15 described above, is an optical element that splits incident light into two different paths based on the polarization state.

[0025] The reference light LREF passes through a relay lens 18 and a spatial filter 19 and reaches a polarizing beam splitter 20 . The S-polarized reference light LREF is reflected by the polarizing beam splitter 20, passes through the half-wave plate 22, and is converted to P-polarized light, and then enters the recording medium 25 as a spherical reference wave by the condenser lens 23. Although not shown, the optical information recording and reproducing device 1 has a control unit that controls each optical element. Also, the optical information recording and reproducing device 1 has a mechanism for moving the recording medium 25. The control unit of the optical information recording and reproducing device 1 (not shown) can control the movement of the recording medium 25.

[0026] On the other hand, the signal light LSIG enters the spatial light modulator 17, and the intensity pattern of the two-dimensional information displayed on the digital micromirror device is reflected and output from the spatial light modulator 17. The P-polarized signal light LSIG output from the spatial light modulator 17 passes through a relay lens 18 and a spatial filter 19 arranged in between, and reaches a polarizing beam splitter 20. The P-polarized signal light LSIG passes through the polarizing beam splitter 20, and the intensity pattern of the information displayed by the spatial light modulator 17 is focused by an objective lens 24 on a recording medium 25 with a certain size. The certain size is usually about 1 mm. Therefore, by setting the spherical reference wave (reference light LREF) to a size of about 1 mm, the interference pattern of the reference light LREF and the signal light LSIG can be recorded on the recording medium 25 as a hologram.

[0027] When reproducing a recorded hologram, a spherical reference wave (reference light LREF) having the same conditions as when the hologram was recorded on the recording medium 25 is irradiated, so that diffracted light appears on the transmission side of the recording medium 25, and the intensity pattern of the information displayed by the spatial light modulator 17 is imaged on the CMOS camera 27 through the focusing lens 26, and is reproduced as two-dimensional information by the CMOS camera 27.

[0028] The optical information recording and reproducing device SYS1 described above can record and reproduce one data page. For example, when the shift multiplexing method is adopted, it is necessary to move the recording medium 25 and repeat the above-mentioned recording and reproduction. In other words, the recording medium and the optical system need to repeatedly stop and move, which, as described above, hinders the speedup of data recording and reproduction.

[0029] Therefore, the optical information recording and reproducing device 1 of the present embodiment described below records on a continuously moving recording medium using a reference beam that moves continuously so that the relative speed with respect to the recording medium 25 is approximately zero within one data page, and a signal beam that is time-divided into one page of two-dimensional data in a sufficiently short time, thereby forming a spatially multiplexed hologram in a pseudo-stationary state on the recording medium. During reproduction, the spatially multiplexed hologram is reproduced all at once using the reference beam. Because two-dimensional data is recorded in a time-divided manner in a sufficiently short time, this method can be called a "surf-riding method." The wave-riding method is a concept that can be utilized for both the shift multiplexing method and the angle multiplexing method. Hereinafter, the shift multiplexing method will be described as a first embodiment of the present invention, and the angle multiplexing method will be described as a second embodiment of the present invention.

[0030] First Embodiment FIG. 2 is a diagram showing an example of the configuration of an optical information recording / reproducing device that employs the shift multiplexing method of the first embodiment. The optical information recording and reproducing device 1 shown in FIG. 2 utilizes a wave-riding method in which two-dimensional data is recorded in a sufficiently short time in a time-division manner in a shift multiplexing method. In the following description of FIG. 2, the same components as those in the conventional optical information recording and reproducing device SYS1 are given the same reference numerals, and the description thereof will be omitted as appropriate.

[0031] The optical information recording / reproducing device 1 shown in FIG. 2 is realized by adding an optical system between the laser light source 11 and the beam expander 13 of the conventional one-arm type optical system shown in FIG. Specifically, an optical deflector 30, a half-wave plate 31, a polarizing beam splitter 32, a relay lens 33, a mirror 34, an anamorphic prism 35, a mirror 36, a cylindrical lens 37, and a polarizing beam splitter 38 are added.

[0032] The optical deflector 30 is an optical element that changes the direction (angle) of light. Note that the optical deflector 30 of this embodiment will be described as being an acoustic optical deflector (AOD). The control unit of the optical information recording and reproducing device 1 can control the optical deflector 30. The anamorphic prism 35 is an optical element that transforms the beam shape. The cylindrical lens 37 is an optical element used to focus or diffuse light in a specific direction. The cylindrical lens 37 of this embodiment is used to convert light into a line beam (approximately linear or highly flattened elliptical shape) as described below. The half-wave plate 31 , the polarizing beam splitters 32 and 38 , the relay lens 33 , and the mirrors 34 and 36 are basically the same optical elements as the half-wave plate 14 , the polarizing beam splitters 15 and 20 , the relay lens 18 , and the mirror 12 .

[0033] The laser light emitted from the laser light source 11 has the angle of the emitted beam scanned by the optical deflector 30. Then, the laser light is split into P-polarized signal light LSIG and S-polarized reference light LREF by the polarizing beam splitter 32. The light intensity ratio between the signal light LSIG and the reference light LREF is determined by the half-wave plate 31. First, the reference light LREF passes through a relay lens 33, and after the beam shape is changed by an anamorphic prism 35, it is reflected by a polarizing beam splitter 38 and is multiplexed with the signal light LSIG. Meanwhile, the signal light LSIG enters a cylindrical lens 37, where it is converted into a line beam, and passes through the polarizing beam splitter 38 to be multiplexed with the reference light LREF.

[0034] The optical system thereafter is the same as the conventional one-arm type optical system, except for the presence or absence of the half-wave plate 14. That is, the optical signal LSIG and the reference light LREF combined in the explanation of the optical information recording and reproducing device 1 in Fig. 2 above are processed in the same optical system as the optical signal LSIG and the reference light LREF of the optical information recording and reproducing device SYS1 in the explanation of Fig. 1. Note that specific control of the optical deflector 30 and the like will be described later with reference to Fig. 3 and subsequent figures.

[0035] FIG. 3 is a diagram showing an example of the shape of a signal light irradiated onto a spatial light modulator in each of the conventional optical information recording and reproducing device shown in FIG. 1 and the surfing type optical information recording and reproducing device shown in FIG. 3 shows the rectangular spatial light modulator 17 and the irradiation range of the circular or elliptical signal light LSIG. The octagonal area of ​​the spatial light modulator 17 where the intensity pattern of two-dimensional information is reflected by the digital micromirror device is shown with checkered hatching.

[0036] As shown in FIG. 3A, in the conventional method, two-dimensional information on the spatial light modulator 17 is irradiated all at once with a large circular beam.

[0037] On the other hand, as shown in FIG. 3(B), in the surfing method, a two-dimensional area corresponding to one data page is divided in one direction, and a line beam that covers only each of the divided strip-shaped blocks (blocks B1 to B50 in FIG. 3) is irradiated, and the line beam is scanned in the short axis direction to irradiate so as to cover all the two-dimensional information of the spatial light modulator 17.

[0038] In the example of Fig. 3(B), for convenience of explanation, the two-dimensional information of the spatial light modulator 17 is divided into strip-shaped blocks. That is, the line beam does not irradiate each block, but it is sufficient to scan at a constant speed. That is, in reality, there is no finite area called a block. However, in the following description, for the sake of convenience, the description will be given assuming that a block exists virtually, and therefore, hereinafter, this will be referred to as a virtual block.

[0039] In the surfing method shown in Figure 3(B), the laser energy density (laser energy per piece of information on the digital micromirror device) is increased by shaping it into a line beam, making it possible to record in a shorter time than with conventional methods.

[0040] Specifically, for example, if the width of the short axis of the line beam is made 1 / 50 of the diameter of the large circular beam used in the conventional method, 50 times the energy density can be obtained. In other words, by scanning a high-energy-density line beam in the short axis direction and recording in virtual blocks in a short time, it becomes possible to record holograms in a pseudo-stationary state on a continuously moving recording medium (using a continuous-light emitting low-power laser).

[0041] FIG. 4 is a diagram showing an example of a line beam generating method and a scanning method in the surf-riding method shown in FIG. FIG. 4(A) shows an example of an optical system for generating a line beam. That is, the laser emitted from the laser light source 11 is incident on the optical deflector 30. Next, the laser light passing through the optical deflector 30 is converted into a small line beam without energy loss by the cylindrical lens 37. After that, the beam is expanded by the beam expander 13, and the desired line beam can be projected onto the spatial light modulator 17. In addition, the focal lengths (f50, f11, f120) of the optical elements (lenses) and the distances between the lenses in FIG. 4(A) are merely examples.

[0042] FIG. 4B shows an example of the operation of the optical deflector 30. As shown in FIG. Here, the angle of the emitted beam is determined by the applied voltage of the optical deflector 30. As described above, an acoustic optical deflector (AOD) is used for the optical deflector 30 in this embodiment, so the applied voltage is appropriately frequency converted by a driver, and an emitted beam with an angle corresponding to the frequency is obtained. That is, the horizontal axis of the graph shown in FIG. 4B is time, and the vertical axis is the angle θ of the beam output from the optical deflector 30, which is the voltage applied to the optical deflector 30 of the acoustic optical deflector (AOD).

[0043] As shown in Fig. 4(B), by changing the applied voltage and the angle θ of the beam output from the optical deflector 30 in a sawtooth wave shape over time, it is possible to scan the output angle from the optical deflector 30. Note that the example shown in Fig. 4(B) is an example in which three data pages (three pieces of two-dimensional information) are recorded. Therefore, three periods of the sawtooth wave are shown in Fig. 4(B).

[0044] In other words, by applying a sawtooth voltage with a constant period as shown in Figure 4(B), the line beam scans the data page at a constant speed, and while the next data page is being displayed, the line beam is quickly returned to its original position, and the process of scanning the line beam at a constant speed again can be repeated. The spacing between the sawtooth waves represents the laser exposure time for each data page. In this way, by executing the control shown in Figure 4(A) above, the optical information recording and reproducing device 1 having the configuration shown in Figure 2 can cause the line beam to scan the spatial light modulator 17 without changing its shape.

[0045] Next, with reference to FIG. 5, we will explain how a hologram is recorded on a continuously moving recording medium 25 and how it is reconstructed using a signal light LSIG in which two-dimensional data of one data page is time-divided over a sufficiently short period of time. FIG. 5 is a diagram showing the process of recording and reproducing a hologram in the optical information recording and reproducing device of the present embodiment shown in FIG.

[0046] Fig. 5(A) is a schematic diagram showing the process of recording one data page, which shows three stages, an initial stage, an intermediate stage, and a final stage, of the process of recording one data page.

[0047] The figures show the positions of the reference light and signal light as seen from a fixed optical system, from the start of scanning the first data page by the optical deflector 30, through the midpoint, to the end of the scan. Also shown is the recording medium, which moves at a constant speed because it is a fixed optical system, and the associated positions of the holograms of each recorded block. Here, the position of the reference light on the recording medium changes as the optical deflector 30 scans, but the position of the signal light on the recording medium does not change. As the optical deflector 30 scans, the position of the reference light on the recording medium moves in sync with the movement of the recording medium. In the recording process (FIG. 5(A)), at the start of scanning, a hologram of block B1 is recorded by the reference light located at the left end. Because the reference light is a spherical wave, there is sufficient interference even if there is a distance between the positions of the reference light and the signal light. This is also true for subsequent intermediate points and up to the end of scanning. At the midpoint, the hologram of block B25 is recorded by the reference light located at the center. At this time, the holograms of B1 to B24 have already been recorded in a row on the right side of the optical system due to the movement of the recording medium. At the end of the scan, the hologram of block B50 is recorded by the reference light located at the right end. At this time, the holograms of B1 to B49 have already been recorded in a row on the right side of the optical system due to the movement of the recording medium. At this time, the movement distance of the recording medium from the start of the scan to the end of the scan is made to match the (inter-page) shift pitch of the shift multiplexing. Then, recording is performed by roughly matching the movement distance of the reference light with the movement distance of the recording medium. The movement distance of the reference light is adjusted by the relay lens 33 and anamorphic prism 35 in FIG. 2. FIG. 5(B) shows the regeneration process. Next, in the reproduction process shown in FIG. 5(B), the reference light with the same conditions as in the recording process (FIG. 5(A)) is irradiated onto the moving recording medium. At this time, a reproduction signal is selectively obtained from the hologram of the block where the relative positions of the signal light and the reference light at the time of recording coincide, and at the start of scanning, all holograms of blocks B1 to B50 are reproduced by the reference light located at the left end. This is because the relative relationship between the reference light and blocks Ba to B50 is the same as the relative relationship at the time of recording shown in FIG. 5(a). Even at the midpoint, all holograms of blocks B1 to B50 are reproduced by the reference light located at the center. At the end of scanning, all holograms of blocks B1 to B50 are reproduced by the reference light located at the right end. In other words, since a reproduction signal can be obtained from all holograms of blocks B1 to B50 throughout the entire scanning, the same amount of reproduction signal light as in the past can be secured. This is achieved by roughly matching the moving distance of the reference light with the moving distance of the recording medium. The above has been explained in terms of recording a one-page hologram, but shift multiplexing can be achieved by repeatedly scanning a laser beam with a sawtooth waveform as shown in FIG. 4(B). FIG. 6 is a schematic diagram showing holograms on a recording medium multiplexed by the conventional method and the surfing method. As an example, the shift-multiplexed holograms of the first to third data pages are shown. In the conventional method, three holograms are recorded at an (inter-page) shift pitch. In the conventional method, the recording medium must be stopped, recorded, moved, stopped, and recorded repeatedly, resulting in a low data transfer rate. On the other hand, in the surfing method, block holograms are repeatedly recorded at regular intervals during the (inter-page) shift pitch. Here, the shift selectivity during playback that determines the lower limit of the (inter-page) shift pitch is effective for the distance between holograms of the same block number on adjacent pages, so recording and playback can be performed at the same (inter-page) shift pitch as in the past. In addition, since recording and playback can be performed from a continuously moving recording medium, the data transfer rate can be increased to the maximum display frequency (display speed) of the spatial light modulator 17 for recording and the maximum frame rate of the CMOS camera for playback. In other words, by using the surfing method, a significantly higher data transfer rate can be achieved with the same data recording capacity as the conventional method.

[0048] Next, some examples (experimental results) of this method are shown below. The laser power was 50 mW, and a line beam of 20 x 0.3 mm was used for the display area of ​​the spatial light modulator 17 of 10 x 10 mm (element size 10.8 um).

[0049] Figure 7 shows an example of experimental results of the SNR and bit error rate (bER) of the reproduced signal versus the laser irradiation time when recording and reproducing were performed while changing the laser irradiation time (scanning time) for one data page. The moving distance of the recording medium was fixed at 5 um. As a result, sufficient SNR and bER were obtained for laser irradiation times up to 5 msec (equivalent to a frequency of 200 Hz).

[0050] Figure 8 shows the reconstructed image captured by the CMOS camera when the laser irradiation time was 6.67 msec (150 Hz in frequency conversion). The image was reconstructed without any problems over the entire surface. SNR=3.4, bER=1.3%.

[0051] Figure 9 shows the reconstructed image from the central data page (51st page) captured by a CMOS camera when 101 pages were shift-multiplexed with a shift pitch of 5um at a laser irradiation time of 6.67msec / page (150Hz). The entire surface was reproduced without any problems. SNR=2.7, bER=4.4%.

[0052] FIG. 10 shows the SNR of the central page and the brightness of the reconstructed image versus the number of shift-multiplexed pages at a laser irradiation time of 6.67 msec / page (150 Hz). As the number of shift-multiplexed pages increases, both the SNR and the brightness of the reconstructed image decrease, but this is due to the decrease in diffraction efficiency caused by multiplexing, and a similar decrease is seen in the conventional method. In any case, we confirmed that shift-multiplexed recording of 201 pages with a shift pitch of 5 um was possible, and demonstrated the effectiveness of this method.

[0053] As mentioned above, with this method, the transfer rate of recording data can be increased to the maximum display speed of the spatial light modulator 17 for recording and the maximum frame rate of the CMOS camera for playback. However, the maximum display speed of the spatial light modulator 17 is generally high at over 20 kHz, while the maximum frame rate of a CMOS camera is about 2 kHz. In other words, the transfer rate of playback data is significantly lower than the transfer rate of recording data. Therefore, an option was invented to improve the transfer rate of playback data.

[0054] FIG. 11 is a diagram showing an example of a configuration for replacing the CMOS camera of the optical information recording and reproducing device shown in FIG. 2, which improves the data transfer rate during reproduction. As shown in Figure 11, the light reproduced from the recording medium is detected by multiple CMOS cameras (hereinafter, sometimes referred to as "CIS" where appropriate). In this case, the CIS must be placed on the image plane of the reproduced signal. Therefore, by repeatedly extracting part of the signal to the reflection side using a half-wave plate and a polarizing beam splitter and detecting it with the CIS, and re-imaging the remainder with a relay lens, it is possible to arrange multiple CISs in series to detect the reproduced signal. The last CIS can also be placed on the transmission side of the polarizing beam splitter. In this example, six CISs are described, but the number of CISs is not limited to this, as long as the optical system is expanded in a similar manner.

[0055] FIG. 12 is a time chart of each CIS for detecting a reproduction signal of the surfing method at high speed using the reproduction optical system shown in FIG. The frame rate of a CIS is about 2 kHz, but the shutter speed is generally fast, at 1 / 10,000 seconds or less. Therefore, if the scanning of the optical deflector 30 is synchronized (a trigger signal is generated) and the playback signal of each CIS is detected by the trigger shutter operation, a faster playback data transfer rate determined by the frequency of the optical deflector 30 (the display speed of the spatial light modulator 17) can be realized. In this example, the frequency of the optical deflector 30 is set to 12 kHz, and the shutter speed of the six CISs is 1 / 12,000 seconds, resulting in a frame rate of 2 kHz, which is achievable with currently available CISs, resulting in a total playback frame rate of 12 kHz.

[0056] The optical information recording / reproducing device 1 according to the first embodiment has been described above with reference to FIGS. The optical information recording / reproducing device 2 of the second embodiment will be described below with reference to FIGS.

[0057] As with the shift multiplexing method, the angle multiplexing method also requires faster data recording and playback (higher data transfer rates) as the amount of data that can be stored increases. However, in order to record the interference pattern of light as a hologram while changing the angle of the reference light, the reference light must be stopped and the angle transition must be repeated, which takes time in the conventional mechanical angle transition method, and this is an obstacle to high-speed data recording and reproduction. Also, since it is not possible to record and reproduce another hologram multiplexed with the same reference light angle, the recording medium must be moved after performing a series of angle multiplex recordings in a stationary state, and the flow of performing the next series of angle multiplex recording must be repeated, which takes time in the conventional mechanical recording medium movement method, and this also prevents high-speed data recording and reproduction. Until now, there has been no practical method that simultaneously satisfies high data capacity and high data transfer rate, i.e., high data transfer rate in the angle multiplex method.

[0058] FIG. 13 is a diagram showing an example of the configuration of a conventional angle multiplexing type optical information recording / reproducing device. The optical information recording and reproducing device SYS2 shown in Figure 13 includes a laser light source 11, a mirror 12, a beam expander 13, a mirror 16, a spatial light modulator 17, a relay lens 18, a spatial filter 19, an objective lens 24, a recording medium 25, a focusing lens 26, a CMOS camera 27, a half-wave plate 41, a polarizing beam splitter 42, a galvanometer mirror 43, a half-wave plate 44, a mirror 45, a relay lens 46, and a mirror 47. The mechanism of the conventional holographic data storage system SYS2 will be described below. Incidentally, the same components as those in the optical information recording and reproducing device SYS1 described above are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[0059] The laser light emitted from the laser light source 11 is split by the polarizing beam splitter 42 into P-polarized signal light LSIG and S-polarized reference light LREF. The light intensity ratio between the signal light LSIG and the reference light LREF is determined by the half-wave plate 41. First, the reference light LREF is reflected by the galvanometer mirror 43, which is a beam deflector, passes through the half-wave plate 44 and is converted into P-polarized light, passes through the relay lens 46, and is incident on the recording medium 25 as a parallel light whose incident angle is changed by the galvanometer mirror 43. On the other hand, the beam diameter of the signal light LSIG is expanded by the beam expander 13. Thereafter, it is incident on the spatial light modulator 17 and exits the spatial light modulator 17 with an intensity pattern of two-dimensional information displayed by the spatial light modulator 17. The P-polarized signal light LSIG emitted from the spatial light modulator 17 passes through a relay lens 18 and a spatial filter 19 arranged in between, and the intensity pattern of the information displayed by the spatial light modulator 17 is focused by an objective lens 24 onto a recording medium 25 with a certain size. The certain size is usually about 1 mm. Therefore, by setting the size of the above-mentioned parallel reference light LREF to about 1 mm, the interference pattern of the reference light LREF and the signal light LSIG can be recorded on the recording medium 25 as a hologram. The recorded hologram is reproduced by irradiating the recording medium 25 with a parallel reference beam at the same angle of incidence as when it was recorded, so that diffracted light appears on the transmission side of the recording medium 25, and the intensity pattern of the information displayed by the spatial light modulator 17 is imaged on the CMOS camera 27 through the focusing lens 26, and is reproduced as two-dimensional information by the CMOS camera 27.

[0060] <Second embodiment> FIG. 14 is a diagram for explaining the principle of the conventional angle multiplexing method. Holographic data storage using the angle multiplexing method, like the shift multiplexing method, is particularly effective in increasing data capacity. In addition, holographic data storage has many advantages as data storage in data centers, since it can store data for long periods of time, a feature of optical recording. In the angle multiplexing method, a hologram is recorded on a recording medium by changing the angle of a reference light relative to signal light of multiple pieces of 2D information. During playback, the recorded 2D information can be selectively played back by changing the angle of the reference light and irradiating it. Note that the recording medium is stationary when recording or playing back using the angle multiplexing method. Therefore, after a series of angle multiplexing recordings is performed, the recording medium is moved to perform the next series of angle multiplexing recordings. In other words, the recording medium is repeatedly moved and stopped on a stage that determines its position. In other words, similar to the shift multiplexing method, the recording medium and the optical system must repeatedly stop and move, which is an obstacle to increasing the speed of data recording and reproduction.

[0061] FIG. 15 is a diagram showing an example of the configuration of an optical information recording / reproducing device according to the second embodiment. The optical information recording / reproducing device 2 shown in FIG. 15 is realized by adding an optical system to the conventional optical system shown in FIG. 13 and by partially changing the arrangement. Specifically, an optical deflector 30, a half-wave plate 31, a polarizing beam splitter 32, a relay lens 33, a mirror 34, and a cylindrical lens 26 are added. In the description of FIG. 15, the same components as those in the conventional optical information recording and reproducing device SYS2 and the above-mentioned optical information recording and reproducing device 1 are denoted by the same reference numerals, and the description thereof will be omitted as appropriate. Although not shown, the optical information recording and reproducing device 2 has a mechanism for moving the recording medium 25. The optical information recording and reproducing device 2 also has a control unit for controlling each optical element. The optical information recording and reproducing device 2 shown in FIG. 15 utilizes a surfing method in which two-dimensional data is recorded in a sufficiently short time in a time-division manner in an angle multiplexing method.

[0062] The angle of the emitted beam of laser light emitted from the laser light source 11 is scanned by an optical deflector 30, which is an Acoustic Optical Deflector (AOD). Next, the light is split into P-polarized signal light LSIG and S-polarized reference light LREF by the polarizing beam splitter 32. The light intensity ratio between the signal light LSIG and the reference light LREF is determined by the half-wave plate 31. First, the deflection angle of the reference light LREF is adjusted by the relay lens 33, and then the reference light LREF is incident on the galvanometer mirror 43, and thereafter the same process as in the conventional reference light optical system. The galvanometer mirror 43 is an optical deflector, and is an optical element for precisely controlling the direction of the laser.

[0063] On the other hand, the signal light LSIG is incident on a cylindrical lens 37, converted into a line beam, and passes through a beam expander 13. After that, the process is the same as in the conventional signal light optical system.

[0064] In the angle multiplexing method, the difference between the conventional method and the surfing method in the shape of the laser beam that irradiates the spatial light modulator 17 is basically the same as that in the shift multiplexing method described with reference to FIG. In the case of simultaneous irradiation as shown in the conventional method in FIG. 3(A), the signal light LSIG is irradiated to the spatial light modulator 17 at a different angle due to the change in angle of the optical deflector 30, which results in a lateral shift on the recording medium 25, making it impossible to record a stable interference pattern (hologram). On the other hand, in the case of the surfing method shown in Figure 3(B), the angle change of the optical deflector 30 is converted into a lateral shift by the cylindrical lens 37, and the spatial light modulator 17 can be scanned with a line beam having a constant irradiation angle, so that a stable interference pattern (hologram) that avoids lateral shift on the recording medium 25 can be recorded.

[0065] An example of a method for generating a line beam and a method for scanning in the surf-riding method shown in FIG. 15 are basically similar to the example in FIG. 4 described above. That is, the laser light that has passed through the optical deflector 30 is converted into a small line beam without any energy loss by the cylindrical lens 37. After that, the laser light is expanded by the beam expander 13, and the desired line beam can be projected onto the spatial light modulator 17.

[0066] FIG. 16 is a diagram showing an example of control of an optical deflector (galvanometer mirror) that changes the angle of the reference light in the conventional optical information recording and reproducing device shown in FIG. That is, one of the factors that limits the data transfer rate of recording and reproduction in the conventional optical information recording and reproducing device SYS2 is the optical deflector (galvanometer mirror 43) that changes the angle of the reference light LREF. When recording and reproducing each data page while changing the angle of the reference light LREF, the galvanometer mirror 43 mechanically moves the mirror angle, so a waiting time (waiting time shown in FIG. 16) is required between pages for angle transition and settling. Therefore, the data transfer rate of recording and reproduction is limited to a low value.

[0067] The optical information recording and reproducing device 2 of this embodiment performs recording and reproducing while changing the angle with the optical deflector 30 so as to cancel the angular transition of the reference beam caused by the galvanometer mirror for a certain period of time for recording and reproducing per page while moving the galvanometer mirror 43 at a constant speed. The amount of angle change caused by the optical deflector 30 is adjusted by the relay lens 33 arranged as the optical system of the reference beam LREF shown in FIG.

[0068] FIG. 17 is a diagram showing an example of control of two optical deflectors (a galvanometer mirror and an acoustic optical deflector (AOD)) that change the angle of the reference beam in the optical information recording and reproducing device of this embodiment shown in FIG. As shown in Fig. 17(A), the galvanometer mirror 43 is controlled to move at a constant speed. Furthermore, as explained using Fig. 4(B), the AOD optical deflector 30 is controlled to have a sawtooth wave shape for each data page. At this time, the AOD optical deflector 30 is controlled in a direction that cancels the angle control by the galvanometer mirror 43. Since the AOD optical deflector 30 is an optical deflector, it is capable of high-speed angle change.

[0069] Fig. 17(B) shows an example of the angle change of the reference beam LREF during multiplex recording and reproduction obtained as a result of the control in Fig. 17(A). Since the angle transition of the reference beam by the galvanometer mirror 43 is cancelled by the angle change of the optical deflector 30, even if the angle of the galvanometer mirror 43 changes continuously, the angle of the reference beam incident on the recording medium changes in a stepped manner, thereby realizing the angle multiplexing method. The waiting time for the angle transition and settling of the galvanometer mirror 43 between each data page, which was necessary in the conventional method, is significantly reduced.

[0070] Another factor limiting the data transfer rate for recording and playback in conventional angle multiplexing methods is the delay caused by the repeated movement and stopping of the stage carrying the recording medium. This problem is also solved by the surfing method, which makes it possible to record holograms in a pseudo-stationary state on a continuously moving recording medium.

[0071] The angle multiplexing method can also enjoy the advantages described above with reference to Fig. 3. That is, the line beam increases the energy density of the laser (the laser energy per piece of information of the spatial light modulator 17), making it possible to record in a shorter time than with the conventional method. Hereinafter, as with the shift multiplexing method, the method will be described using the band-shaped blocks (virtual blocks) for convenience described with reference to Fig. 3.

[0072] FIG. 18 is a schematic diagram showing a hologram on a recording medium multiplexed by the surfing method. The holograms of each virtual block of each data page are recorded in a pseudo-stationary state while shifting little by little relative to the continuously moving recording medium. The holograms of each block (B1 to B50) of the same data page (e.g., page 1) are recorded at the same reference beam angle (R1), so they are simultaneously reconstructed at the same reference beam angle (R1). Meanwhile, the holograms of other pages (pages 2 and 3) are not reconstructed at that reference beam angle (R1). Similarly, the hologram of page 2 is also reconstructed at the reference beam angle (R2), but the holograms of other pages (pages 1 and 3) are not reconstructed. In this way, each data page is recorded in order using angle multiplexing, and after recording with the final reference beam angle is completed, recording begins again with the first reference beam angle. At this time, the speed at which the recording medium moves is determined so that the holograms of pages recorded with the same reference beam angle do not overlap spatially, so angle selectivity is guaranteed, and angle multiplexing recording and playback is possible with a continuously moving recording medium.

[0073] To summarize the above, in the conventional method, multiplex recording or playback must be repeated while stationary, waiting for the angle transition of the galvanometer mirror 43 and moving the recording medium 25, resulting in a low data transfer rate. On the other hand, in this method, multiplex recording and playback are performed while the galvanometer mirror transitions angle at a constant speed and the recording medium moves at a constant speed. The response speed of the AOD is very fast, so as a result, the recording data transfer rate can be increased to the maximum display speed of the spatial light modulator 17, and the playback transfer rate can be increased to the maximum frame rate of the CMOS camera. In other words, by using this method, it is possible to achieve a significantly higher data transfer rate with the same data recording capacity as the conventional method.

[0074] The data transfer rate in the surfing method can be as high as the maximum display speed of the spatial light modulator 17 during recording, and as high as the maximum frame rate of the CMOS camera during playback. Generally, the maximum display speed of the spatial light modulator 17 is high, exceeding 20 kHz, while the maximum frame rate of the CMOS camera is about 2 kHz. In other words, the data transfer rate for playback is significantly lower than the data transfer rate for recording. By using the configuration shown below, the transfer rate of playback data can be improved.

[0075] FIG. 19 is a diagram showing an example of a configuration for replacing the CMOS camera of the optical information recording and reproducing device shown in FIG. 15, which improves the transfer rate of reproduction data. As shown in Figure 19, the light reproduced from the recording medium is detected by multiple CMOS cameras. At this time, the CIS must be placed on the image plane of the reproduced signal. Therefore, by repeatedly extracting part of the signal to the reflection side using a half-wave plate and a polarizing beam splitter and detecting it with a CIS, and re-imaging the remainder with a relay lens, it is possible to arrange multiple CISs in series to detect the reproduced signal. The last CIS can also be placed on the transmission side of the polarizing beam splitter. In this example, six CISs are described, but the invention is not limited to this, as long as the optical system is expanded in a similar manner.

[0076] FIG. 20 is a time chart of each CMOS camera for detecting a reproduced signal of the surfing method at high speed using the example of the configuration shown in FIG. The frame rate of a CIS is about 2 kHz, but the shutter speed is generally fast, at 1 / 10,000 seconds or less. Therefore, if synchronization is achieved with the scanning of the optical deflector 30 (a trigger signal is generated) and time-division detection is performed in each CIS using trigger shutter operation, a faster playback data transfer rate determined by the frequency of the optical deflector 30 (the display speed of the spatial light modulator 17) can be achieved. In this example, the frequency of the optical deflector 30 is set to 12 kHz, and the shutter speed of the six CISs is 1 / 12,000 seconds, resulting in a frame rate of 2 kHz, which is achievable with currently available CISs, resulting in a total playback frame rate of 12 kHz.

[0077] Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within the scope that can achieve the object of the present invention are considered to be included in the present invention.

[0078] For example, the hardware configurations of the optical information recording and reproducing device 1 shown in FIG. 2 and the optical information recording and reproducing device 2 shown in FIG. 15 are merely examples for achieving the object of the present invention, and are not particularly limited. That is, in the above-mentioned embodiment, the method and arrangement of each optical element are described as an example, but the present invention is not limited to this. That is, it is sufficient that each optical element has the same function as an optical element and adopts a method that satisfies the same specifications. In addition, the position and direction of splitting and multiplexing of the optical system can be changed within a range that performs the same function.

[0079] Furthermore, the series of control processes described above can be executed by hardware or software. Furthermore, one functional block may be configured as a single piece of hardware, a single piece of software, or a combination of both.

[0080] When the series of processes is executed by software, the program constituting the software is installed into a computer or the like from a network or a recording medium. The computer may be a computer implemented with dedicated hardware. Furthermore, the computer may be a computer capable of executing various functions by installing various programs thereon, such as a server, a general-purpose smartphone, or a personal computer.

[0081] A recording medium containing such a program may be composed not only of a removable medium (not shown) that is distributed separately from the device body in order to provide the program to the user, but also of a recording medium that is provided to the user in a pre-installed state in the device body.

[0082] In this specification, the steps of describing a program to be recorded on a recording medium include not only processes that are performed chronologically according to the order, but also processes that are not necessarily performed chronologically but are executed in parallel or individually.

[0083] In summary, it is sufficient for an information processing device to which the present invention is applied to have the following configuration, and various embodiments can be adopted.

[0084] In other words, the information processing system to which the present invention is applied can take various forms having the following configurations. That is, an optical information device to which the present invention is applied (for example, the optical information recording / reproducing devices 1 and 2 in FIG. 2 and FIG. 15) In an optical information device, the target information (data to be recorded or reproduced) is stored as two-dimensional data (multiple pages of data) on a recording medium and light is irradiated onto the recording medium to perform at least one of recording and reproduction, The light is shaped so that a predetermined direction is the longitudinal direction and a direction perpendicular to the longitudinal direction is the lateral direction, and the two-dimensional data is recorded or reproduced by scanning in the lateral direction.

[0085] Moreover, the light includes a signal light, The optical information device comprises: A spatial light modulator (e.g., the spatial light modulator 17 in FIG. 2 or the spatial light modulator 17 in FIG. 15) that displays the two-dimensional data; an optical deflector (for example, the optical deflector 30 in FIG. 2 or the optical deflector 30 in FIG. 15) that scans the spatial light modulator; It can be provided with:

[0086] The light also includes a reference light, The optical information device comprises: A mechanism for moving the recording medium; Equipped with The reference beam can be moved at approximately the same speed as the recording medium.

[0087] The light also includes a reference light, the optical information device comprises two optical deflectors; The angle of the reference beam can be controlled in a stepped manner by the continuous operation of a first optical deflector (e.g., galvanometer mirror 43 in FIG. 15) and the periodic operation of a second deflector (e.g., optical deflector 30 using an AOD in FIG. 15).

[0088] Moreover, the optical information device The reference light is controlled to perform a periodic motion in which the reference light scans the two-dimensional data and then quickly repeats scanning from the initial position (for example, the control shown in FIG. 4 or the control shown in FIG. 17), thereby enabling at least one of recording and reproducing a plurality of two-dimensional data to be performed.

[0089] The optical deflector can perform scanning with the signal light and scanning with the reference light by deflecting light before the signal light and the reference light are separated. [Explanation of symbols]

[0090] Reference Signs List 1...optical information recording and reproducing device, 2...optical information recording and reproducing device, 11...laser light source, 12...mirror, 13...beam expander, 14...half-wave plate, 15...polarizing beam splitter, 16...mirror, 17...spatial light modulator, 18...relay lens, 19...spatial filter, 20...polarizing beam splitter, 21...mirror, 22...half-wave plate, 23...condensing lens, 24...objective lens, 25...recording medium, 26...condensing lens Optical lens, 27...camera, 30...optical deflector, 31...half-wave plate, 32...polarizing beam splitter, 33...relay lens, 34...mirror, 35...anamorphic prism, 36...mirror, 37...cylindrical lens, 38...polarizing beam splitter, 41...half-wave plate, 42...polarizing beam splitter, 43...galvanometer mirror, 44...half-wave plate, 45...mirror, 46...relay lens, 47...mirror

Claims

1. An optical information device that performs at least one of recording and reproducing by irradiating light onto a recording medium that stores target information as two-dimensional data, The light is shaped so that a predetermined direction is a longitudinal direction and a direction perpendicular to the longitudinal direction is a lateral direction, and the two-dimensional data is recorded or reproduced by scanning in the lateral direction. Optical information device.

2. the light includes a signal light, The optical information device comprises: a spatial light modulator for displaying the two-dimensional data; an optical deflector for scanning the spatial light modulator; The optical information device according to claim 1 .

3. The light includes a reference light, The optical information device comprises: A mechanism for moving the recording medium; Equipped with The reference beam is moved at a speed substantially equal to that of the recording medium.

3. The optical information device according to claim 2.

4. The light includes a reference light, the optical information device comprises two optical deflectors; controlling the continuous operation of the first optical deflector with the periodic operation of the second deflector; 3. The optical information device according to claim 2.

5. The optical information device comprises: After scanning the two-dimensional data with the reference light, control is performed to perform a periodic motion in which scanning is quickly repeated from an initial position, thereby performing at least one of recording and reproducing a plurality of two-dimensional data.

5. The optical information device according to claim 4.

6. the optical deflector deflects light before the signal light and the reference light are separated, thereby performing scanning with the signal light and scanning with the reference light.

6. The optical information device according to claim 5.

7. An optical information control method executed by an optical information device that performs at least one of recording and reproducing by irradiating light onto a recording medium that stores target information as two-dimensional data, comprising: The light is shaped so that a predetermined direction is a longitudinal direction and a direction perpendicular to the longitudinal direction is a lateral direction, and the two-dimensional data is recorded or reproduced by scanning in the lateral direction. Optical information control method.

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