JP2014098797A - Hologram recording and reproducing device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve recording density by enabling shift multiple recording even to a recording medium film thickness direction (z direction) during performing shift multiple recording using a spherical reference wave.SOLUTION: A hologram recording and reproducing device for recording interference fringes obtained by interfering signal light carrying data information with reference light in a recording medium as data information, or reproducing the data information by irradiating the reference light to the recording medium 6 with the data information recorded includes an objective lens 13 for irradiating spherical reference light as the reference light. The objective lens 13 performs shift multiple recording at least toward a medium film thickness direction (z axis) by being relatively moved in a vector direction including the medium film thickness direction (z axis) at least in the recording medium 6.

Description

  The present invention relates to a hologram recording / reproducing apparatus and method suitable for constructing a large-capacity optical memory by multiplexly recording a two-dimensional digital bit pattern as a hologram on a recording medium.

  2. Description of the Related Art Conventionally, a recording / reproducing apparatus for a hologram recording medium has been proposed in which digital information is recorded two-dimensionally using a hologram and reproduced. In this recording / reproducing apparatus, when digital information is recorded, a transmissive or reflective spatial light modulator composed of a plurality of pixels is used to spatially modulate coherent signal laser light based on the digital information to be recorded. Then, two-dimensional diffracted light is generated by causing interference between the spatially light-modulated signal laser light and a separately generated coherent reference laser light. Then, the image formed by the diffracted light is recorded on the hologram recording medium as two-dimensional information corresponding to the digital information.

  The main recording / reproducing methods in such a hologram recording medium include (1) angle multiplex recording, (2) shift multiplex recording, (3) speckle reference beam multiplex recording, and the like (for example, see Non-Patent Document 1). ).

  In the method (1), the multiplex recording of the hologram is performed by changing the angle of the reference beam little by little. In the method (1), the multiple recording is performed under the condition that the film thickness of the recording medium is as large as 1 mm or more and the Bragg diffraction condition is angularly severe. Then, hologram multiplex recording is performed in book units, and new hologram multiplex recording is performed in book units at positions that do not overlap by moving on the medium.

  In the method (2), hologram recording is performed using the reference light as a spherical wave. The recorded hologram is reproduced under the Bragg diffraction condition. However, when the recording medium is slightly shifted, the Bragg diffraction condition is canceled and the hologram cannot be reproduced. For this reason, a new hologram can be recorded by slightly shifting the recording medium.

  The method (3) performs shift multiplex recording similar to the method (2), but the reference light is modulated with a speckle pattern. For this reason, when reproducing the information recorded on the hologram on the recording medium, if the speckle pattern is the same as that at the time of recording, the information can be reproduced. However, if the recording medium is shifted over a small distance, the hologram pattern is not matched and information cannot be reproduced. For this reason, a new hologram can be recorded by slightly shifting the recording medium.

Tsutomu Shimura (edition): Holographic memory system and materials, CMC Publishing, Tokyo (2006)

  In (1) angle multiplex recording, which has been mainly studied conventionally, it is necessary to set the reference beam angle with an accuracy of about 0.01 ° to 0.02 °. The angle adjustment in such an order is within a range that is easily affected by a slight environmental temperature change or drive vibration. For this reason, a more advanced angle control technique is required in an actual use environment. In addition, it is difficult to expand the angle change region in the optical system, and it is difficult to improve the recording density.

  On the other hand, the collinear or co-axis type shift multiplex recording which has been studied conventionally has a drawback that the depth direction of the thick film medium cannot be effectively used from the recording principle. This is because the reference light and the signal light are arranged on the same optical axis and focused on the medium by the objective lens. In this case, the area where both interfere with each other is limited within the medium, and effective use of the medium film thickness is effective. Densification is hindered. For this reason, there is a problem that it is impossible to increase the density of information recording by increasing the film thickness.

  Further, the reference light needs to be subjected to randomized amplitude or phase modulation such as a speckle pattern, but these generate a lot of noise and lower the signal-to-noise ratio. This is also a factor that hinders higher density.

  In the conventional shift multiplex recording method using spherical reference waves, multiplex recording in the medium track direction (x direction) can be realized with a shift of about several microns, but the radial direction (y direction: disk) In the radial direction), the shift selectivity is loose, and a shift amount of about several hundred μm is necessary to actually perform multiplex recording. For this reason, it is difficult to increase the density substantially in two dimensions. In this shift multiplex recording method using a spherical reference wave, interference between the signal light and the reference light is possible over the entire film thickness as compared with the collinear type, but the recording density in the y-axis direction cannot be improved and the recording density is increased. There were restrictions.

  Therefore, the present invention has been devised in view of the above-described problems, and an object of the present invention is to provide an information recording / reproducing method for recording digital information two-dimensionally using a hologram and reproducing the same, and Hologram recording / reproduction capable of improving recording density by enabling shift multiplex recording in the film thickness direction (z direction) of the recording medium when performing shift multiplex recording using a spherical reference wave. It is to provide an apparatus and method.

  The hologram recording / reproducing apparatus according to claim 1 causes the signal light carrying the data information to interfere with the reference light, and records the obtained interference fringes on the recording medium as the data information, or the data information is recorded. In a hologram recording / reproducing apparatus for reproducing the data information by irradiating the recording medium with the reference light, the hologram recording / reproducing apparatus includes a reference light objective lens that irradiates a spherical reference light as the reference light, and the reference light objective lens includes at least The shift multiplex recording is performed at least in the medium film thickness direction (z axis) by relatively moving in the vector direction including the medium film thickness direction (z axis) in the recording medium.

  According to a second aspect of the present invention, there is provided the hologram recording / reproducing apparatus according to the first aspect, wherein the reference light objective lens is transmissive to the signal light by irradiating the spherical reference light from both surfaces of the recording medium. Shift multiplex hologram recording is performed using both hologram recording and reflection hologram recording.

  According to a third aspect of the present invention, there is provided a hologram recording / reproducing apparatus according to the first or second aspect of the present invention, in a vector direction including a medium film thickness direction (z axis) with respect to the recording medium on which the shift multiplex recording has been performed. Data information is reproduced by relatively moving the reference beam objective lens.

  The hologram recording / reproducing method according to claim 4 causes the signal light carrying the data information to interfere with the reference light, and records the obtained interference fringes on the recording medium as the data information, or the data information is recorded. In a hologram recording / reproducing method of reproducing the data information by irradiating the recording medium with the reference light, the spherical reference light is irradiated as the reference light, and the reference light objective lens is at least a medium film in the recording medium. Shift multiple recording is performed at least in the medium film thickness direction (z-axis) by relatively moving in the vector direction including the thickness direction (z-axis).

  According to a fifth aspect of the invention, there is provided a hologram recording / reproducing method according to the fourth aspect of the invention, wherein the reference light objective lens is irradiated with the spherical reference light from both sides of the recording medium, thereby transmitting the signal light. Shift multiplex hologram recording is performed using both hologram recording and reflection hologram recording.

  According to a sixth aspect of the present invention, there is provided a hologram recording / reproducing method according to the fourth or fifth aspect of the present invention, in a vector direction including a medium film thickness direction (z axis) with respect to the recording medium on which the shift multiplex recording has been performed. Data information is reproduced by relatively moving the reference beam objective lens.

  According to the present invention having the above-described configuration, when performing shift multiplex recording using a spherical reference wave, the recording density can be improved by enabling shift multiplex recording in the film thickness direction (z direction) of the recording medium. It becomes possible to plan.

It is a conceptual diagram of the shift multiplex recording by the hologram recording and reproducing apparatus to which the present invention is applied. 1 is a block configuration diagram of a hologram recording / reproducing apparatus to which the present invention is applied. It is a figure which shows the shift selectivity experiment result of a x-axis direction. It is a figure which shows the shift-selectivity experiment result of a y-axis direction. It is a figure which shows the shift selectivity experiment result of az axis direction. It is a figure for demonstrating experimental conditions. It is a figure which shows the example which uses together a transmission type hologram recording and a reflection type hologram recording. It is a figure for demonstrating the shift selectivity of the x-axis direction in reflection type recording.

  Hereinafter, a hologram recording / reproducing apparatus as an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a conceptual diagram of shift multiplex recording by a hologram recording / reproducing apparatus to which the present invention is applied. The recording medium 6 is irradiated with the signal light 1 and the spherical reference light 2 is irradiated. Each direction of the recording medium 6 is defined by a track direction 3 (x-axis direction), a medium film thickness direction 4 (z-axis direction), and a medium radial direction 5 (y-direction). This recording medium 6 is made of, for example, a photopolymer or the like and is made of a monomer, and the portion irradiated with light is made of a material that is polymerized. A refractive index difference is generated between the polymerized region and the non-polymerized region, and data can be reproduced by reading this difference.

  Such signal light 1 and spherical reference light interfere in the recording medium 6 to form a hologram. When performing multiple recording, the irradiation position is shifted independently in the x, y, and z axis directions, or a new hologram is recorded by shifting the irradiation position over a short distance using both the x and z axis directions. To do.

  FIG. 2 is a block diagram of a hologram recording / reproducing apparatus 30 to which the present invention is applied. The hologram recording / reproducing apparatus 30 records a hologram on the recording medium 6 by using so-called transmission type recording and reflection type recording in combination.

  The hologram recording / reproducing apparatus 30 includes a blue laser light source 7, a first shutter 8a, a half mirror 9, an ND filter 10, an optical path separation mirror 11, a second shutter 8a, and a first mirror 12a. , A third mirror 12c, and a second objective lens 13b. The hologram recording / reproducing apparatus 30 includes a fourth shutter 8b and a first objective lens 13a. Further, the hologram recording / reproducing apparatus 30 includes a second mirror 12b, a third shutter 8c, a lens 14a, a lens 14b, a spatial modulator 15, a third lens 14c, and a fourth lens 14d. And a CCD (Charge Coupled Device) camera 16.

  The blue laser light source 7 is a light source that emits blue laser light. The first shutter 8a to the third shutter 8c adjust the diameter of the laser beam to be propagated to a predetermined value. The half mirror 9 is disposed on the emission side of the first shutter 8a, and reflects a part of the incident laser beam in a direction substantially perpendicular to the laser beam and transmits a part thereof. Here, it is assumed that the transmitted light by the half mirror 9 is used as spherical reference light and the reflected light is used as signal light, but the opposite may be possible.

  The ND filter 10 is used to reduce the light amount of the laser light emitted from the blue laser light source 7. The ND filter 10 is configured in gray or black, and the amount of light reduction of the laser light emitted from the blue laser light source 7 is determined according to the degree of the darkness.

  The optical path separation mirror 11 includes a half mirror (not shown) disposed obliquely in the optical path emitted from the ND filter 12. The optical path separation mirror 11 divides the laser beam from the ND filter 10 and transmits a part thereof as it is and reflects the remaining part.

  Each of the first mirror 12a to the third mirror 12c is disposed to change the direction of the optical path. The objective lenses 13a and 13b are lenses for condensing spherical reference light toward the recording medium 6, respectively. The lenses 14a to 14d are for adjusting the spot diameter of the signal light or condensing it toward the recording medium 6, respectively.

  The spatial modulator 15 forms an image pattern by operating each element in accordance with input data. Each pixel of the spatial modulator 15 has a one-to-one correspondence with each pixel of the CCD camera 16.

  The CCD camera 16 is composed of a camera that takes an image from the back side of the recording medium 6. The CCD camera 16 includes a lens for forming an image light and a CCD image sensor that generates an electrical imaging signal based on a subject image incident through the lens. As a result, the CCD camera 16 can receive the signal light reproduced from the recording medium 6. The CCD camera 16 can acquire information on the recording medium 6 from the information on the signal light.

  Next, a recording operation by the hologram recording / reproducing apparatus 30 to which the present invention is applied will be described.

  First, the signal light carrying the data information is caused to interfere with the reference light. The interference fringes thus obtained are recorded on the recording medium 6 as data information. As this reference light, spherical reference light is irradiated. The spherical reference light is irradiated through the first objective lens 13a and the second objective lens 13b.

  First, when irradiating spherical reference light only through the first objective lens 13a, so-called transmission hologram recording is performed. In such a case, the first objective lens 13a is relatively moved in the vector direction including the medium film thickness direction (z axis) in the recording medium 6. The vector direction including the medium film thickness direction (z-axis) here means a vector direction set between the medium film thickness direction 4 (z-axis direction) and another direction as shown in FIG. To do. The other directions here include the track direction 3 (x-axis direction) and the medium radial direction 5 (y-axis direction), or any other direction on the xy plane.

  When recording data information on the recording medium 6, the first objective lens 13a is moved in the vector direction while emitting spherical reference light from the first objective lens 13a. Since the vector direction includes the medium film thickness direction (z-axis), the hologram is shift-multiplex-recorded at least in the medium film thickness direction (z-axis). Further, since the vector direction includes components in all directions on the xy plane, the hologram is also shift-multiplex recorded on the xy plane on the recording medium 6.

  Note that, if the first objective lens 13a is fixed and the recording medium 6 is moved instead of moving the first objective lens 13a in the vector direction, the same effect as described above can be obtained. It becomes possible. That is, the first objective lens 13a only needs to be relatively moved in the vector direction including at least the medium film thickness direction (z axis) in the recording medium. In other words, this includes relative movement in the xz plane and relative movement in the yz plane.

  The results obtained experimentally for the shift selectivity of the transmissive recording are shown in FIG. 3, FIG. 4, and FIG. In this experimental example, the NA of the objective lens that forms the spherical reference light is 0.4. As the NA increases, the shift selectivity improves. In the conventional research, examination including the x-axis or y-axis was the main result. However, the following experimental example is characterized in that the feasibility of shift multiplex recording of a hologram in the z-axis direction is particularly verified.

  FIG. 6 shows the experimental conditions. In FIG. 6, in particular, the configuration of the medium proximity region of the spherical reference light is extracted and described. In the experiment, first, shift multiplexing in the x-axis direction was performed 20 times at intervals of 10 μm. Next, the recording medium 6 is moved over 20 μm at an angle inclined about 30 ° with respect to the z-axis direction, and 20 times are multiplexed again in the x-axis direction at intervals of 10 μm. Confirmed that it was possible.

  For separation in the z-axis direction, 20 μm is sufficient, and recording of 10 or more multiplexes on the z-axis is possible. This makes it possible to achieve a recording capacity that is 10 times or more than before. On the other hand, the shift multiplexing in the x-axis direction was performed 20 times at intervals of 10 μm, and then the recording medium 6 was moved 300 μm in the y-axis direction, and the shift multiplexing in the x-axis direction was similarly performed 20 times at intervals of 10 μm. In both cases, it was confirmed that each hologram could be separated and reproduced. Multiple recording is possible if the y-axis direction is shifted by about 200 μm, leading to an improvement in recording density several times that of the x-axis direction alone. Thus, it was confirmed that shift multiplex recording can be performed in the x-, y-, and z-axis directions, respectively, and it has become clear that high density can be achieved.

  On the other hand, the present invention is also characterized by the combination of transmission hologram recording and reflection hologram recording. As shown in FIG. 7, in the transmissive recording and the reflective recording, the direction of the reference light incident on the signal light is different, and the interference fringes of the formed hologram are formed so as to be relatively orthogonal. In such a case, by transmitting spherical reference light from both surfaces of the recording medium 6 via the first objective lens 13a and the second objective lens 13b, transmission hologram recording and reflection hologram recording are performed on the signal light. Is used in combination with the shift multiple hologram recording.

  Therefore, even if recording is performed at the same location, the holograms can be separated and reproduced independently without interfering with each other. Therefore, an improvement in recording density can be expected. Conventionally, the reflection type recording has been difficult to use because the reproduced image deteriorates due to the shrinkage in the film thickness direction of the medium. However, the present invention has found that the influence of shrinkage can be reduced by increasing the film thickness of the medium. The media thickness of 1.5mm was found to be at a level that was not problematic, and the prospect of practical use was obtained. FIG. 8 shows the result of comparing the specific shift selectivity with the transmissive recording. Shift selectivity comparable to the transmission type is obtained. Also, the reproduced image is good and practical use is possible.

  Note that the hologram recording / reproducing apparatus 30 to which the present invention is applied moves the objective lens 13 in the vector direction including the medium film thickness direction (z axis) with respect to the recording medium 6 on which the shift multiplex recording has been performed. Information may be reproduced. At this time, of course, the objective lens 13 may be fixed and the recording medium 6 may be moved.

  Further, in the present invention, it is a matter of course that a plurality of recording media 6 may be bonded together, and transmission hologram recording and reflection hologram recording may be performed on different media for the same signal light.

DESCRIPTION OF SYMBOLS 1 Signal light 2 Spherical reference light 3 Track direction 4 Medium thickness direction 5 Medium radial direction 6 Recording medium 7 Blue laser light source 8 Shutter 9 Half mirror 10 ND filter 11 Optical path separation mirror 12 Mirror 13 Objective lens 14 Lens 15 Spatial modulator 16 Camera 30 Hologram recording / reproducing device

Claims (6)

The signal light carrying the data information is interfered with the reference light, and the obtained interference fringes are recorded as data information on the recording medium, or the recording medium on which the data information is recorded is irradiated with the reference light. In the hologram recording / reproducing apparatus for reproducing the data information,
A reference light objective lens that irradiates spherical reference light as the reference light,
The reference beam objective lens performs the shift multiplex recording at least in the medium film thickness direction (z axis) by moving relatively in the vector direction including the medium film thickness direction (z axis) in the recording medium. A hologram recording / reproducing apparatus characterized by the above. The reference light objective lens irradiates the spherical reference light from both sides of the recording medium, thereby performing shift multiplex hologram recording using the transmission hologram recording and the reflection hologram recording in combination with the signal light. The hologram recording / reproducing apparatus according to claim 1, wherein: Data information is reproduced by relatively moving the reference light objective lens in a vector direction including a medium film thickness direction (z axis) with respect to the recording medium on which the shift multiplex recording is performed. The hologram recording / reproducing apparatus according to claim 1 or 2. The signal light carrying the data information is interfered with the reference light, and the obtained interference fringes are recorded as data information on the recording medium, or the recording medium on which the data information is recorded is irradiated with the reference light. In the hologram recording / reproducing method for reproducing the data information,
Irradiate spherical reference light as the reference light,
Shift multiple recording is performed at least in the medium film thickness direction (z-axis) by moving the reference light objective lens at least in the vector direction including the medium film thickness direction (z-axis) in the recording medium. A method for recording and reproducing holograms. By irradiating the spherical reference light from both surfaces of the recording medium with the reference light objective lens, shift multiplex hologram recording is performed on the signal light by using both transmission hologram recording and reflection hologram recording. The hologram recording / reproducing method according to claim 4, wherein: Data information is reproduced by relatively moving the reference light objective lens in a vector direction including a medium film thickness direction (z axis) with respect to the recording medium on which the shift multiplex recording is performed. The hologram recording / reproducing method according to claim 4 or 5.

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