JP2007025417A - Hologram recording apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve recording density while suppressing noise, by uniformly using a dynamic range of a hologram recording material. <P>SOLUTION: When interference fringes of signal light 100 and reference light not shown are subjected to multiple recording in a single layer hologram recording material 50, the data are recorded in the layer including two positions in the thickness direction of the hologram recording material 50, i.e., a position nearer the front face and a position nearer the back face, to carry out multiple layer recording to form a book (a group of holograms) 60 in two layers within the hologram recording material 50. The recording layers are selected by moving a focal position of the signal light, and the intensity ratio of the signal light 100 to the reference light at the focal position of the signal light 100 is optimized. Thus, the recording density is improved while suppressing noise, by uniformly using the dynamic range of the hologram recording material 50. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hologram recording apparatus and method for recording interference fringes of two light beams on a hologram recording material, and more particularly to multiple recording over a plurality of layers in a hologram recording material.

  In recent years, holographic data storage systems that record and reproduce large amounts of data using hologram technology have been proposed. In this holographic data storage system, the same laser beam is split into a signal beam and a reference beam, and then the signal beam and the reference beam that are spatially deviated on the data page are irradiated so as to overlap in the recording area of the hologram recording material. Light interference fringes are recorded on the hologram recording material. In order to improve the recording density of the hologram memory, a technique called multiple recording is used in which a large number of independent pages are recorded in one place. Typical examples of this multiplex recording method include angle multiplex recording, shift multiplex recording, and phase code multiplex recording. However, in the case of angle multiplexing recording, for example, the signal light intensity distribution in the hologram recording material is non-uniform, so that the recording material cannot be used uniformly, leading to a reduction in recording capacity. Therefore, it is known that the hologram recording medium has a multi-layer structure and hologram recording is performed on each layer (see, for example, Patent Document 1). However, in this case, the structure of the hologram recording medium is complicated and the manufacturing cost is increased. There is a problem that the servo mechanism for selectively recording the image becomes complicated and the apparatus becomes expensive.

  As shown in FIG. 10, the signal light 100 has a different beam thickness in the thickness direction of the hologram recording material 50, and has the smallest beam diameter at the focus position (or Fourier transform plane). This represents that the energy density is maximized at the focus position. As described above, when the energy density varies depending on the location, the intensity ratio between the signal light 100 and the reference light (not shown) also varies depending on the location, and only a part of the recording material can be recorded with an ideal intensity ratio. It will be said that. Therefore, when the overall balance is adjusted and the ratio of the signal light and the reference light is adjusted, the power density becomes too strong near the focus position as shown in FIG. 11, and this becomes a noise source (region 40) of the image. Are known.

Further, if recording as shown in FIG. 11 is continued, as shown in FIG. 12, a recording area is formed biased toward the front surface of the hologram recording material 50, resulting in non-uniform exposure. The hologram recording material 50 such as a photopolymer is known to obtain better results when exposed as uniformly as possible, and the state shown in FIG. 12 is not preferable.
JP 11-126335 A (page 5-9, FIG. 1)

  As described above, when the interference fringes between the signal light and the reference light are recorded on the hologram recording material, since the energy density of the signal light varies depending on the location in the hologram recording material, the intensity ratio of the signal light and the reference light also varies depending on the location. In other words, only a part of the recording material can be recorded with an ideal intensity ratio, and the dynamic range of the hologram recording material cannot be used uniformly, and the recording density cannot be increased. Further, if the signal light and the reference light ratio are adjusted in a balanced manner, the power density becomes too strong in the vicinity of the focus position of the signal light, resulting in a noise source.

  The present invention has been devised in view of the above circumstances, and an object of the present invention is to suppress the noise and to improve the recording density by uniformly using the dynamic range of the hologram recording material. To provide a recording apparatus and method.

  In order to achieve the above object, the present invention provides a hologram recording apparatus that multiplex-records interference fringes between reference light and intensity-modulated signal light on a single-layer hologram recording material, and has a predetermined thickness direction of the hologram recording material. It is characterized by comprising recording means for multiplex-recording the interference fringes so that the interference fringes are recorded in a plurality of recording layers that are spaced apart and spread in a direction perpendicular to the thickness direction.

  Further, the recording means of the present invention comprises a focus position changing means for selecting the recording layer by changing the focus position of the signal light to be a preset position in the thickness direction of the hologram recording material. It is characterized by doing.

  Further, the intensity ratio of the signal light and the reference light according to the present invention is adjusted to be optimal at a focus position of the signal light.

  As described above, in the present invention, for example, angle multiplex recording is performed, for example, at two locations in the vicinity of the front surface in the thickness direction and in the vicinity of the rear surface of the hologram recording material of a single layer. A book is recorded in an array to form two recording layers. At that time, by adjusting the intensity ratio of the signal light to the reference light so as to be optimal, the noise source can be prevented from being recorded and noise during recording can be suppressed. Further, by bringing the focus position of the signal light to one of the two recording layers in the thickness direction of the hologram recording material, the recording location in the thickness direction can be selected. The recording density can be improved by using the dynamic range uniformly. Further, since, for example, two-layer recording is performed using a single-layer hologram recording material, the recording density can be increased without making the configuration of the hologram recording material complicated and expensive. Further, since a hologram recording material having a single layer is used, the recording location in the thickness direction can be selected with high mechanical accuracy, and the above effect can be obtained with a simple servo system.

According to the present invention, interference fringes of signal light and reference light are recorded by angle multiplexing, for example, so that a recording layer is formed at two locations, for example, near the front surface in the thickness direction and near the back surface of a single layer hologram recording material. Then, by recording so that a plurality of books are arranged in each recording layer, noise can be suppressed and recording density can be improved by uniformly using the dynamic range of the hologram recording material.
In addition, since multiple layers can be recorded on a single-layer hologram recording material, if the recording density is maintained as before, the multiplicity of each book can be reduced, and the multiplex recording of high-quality data with reduced noise correspondingly. Playback can be performed.
Further, since, for example, two-layer recording is performed using a single-layer hologram recording material, the recording density can be increased without making the configuration of the hologram recording material complicated and expensive.
Furthermore, since a single layer hologram recording material is used, the recording location in the thickness direction can be selected with high mechanical accuracy, and the above effect can be obtained with a simple servo system.

  For the purpose of suppressing noise and improving the recording density by uniformly utilizing the dynamic range of the hologram recording material, recording is performed at two locations, for example, near the front surface in the thickness direction and near the back surface of the single layer hologram recording material. For example, the interference fringes of the signal light and the reference light are recorded by angle multiplexing so that a plurality of books are arranged in each recording layer so as to form a layer.

  FIG. 1 is a block diagram showing a schematic configuration of a hologram recording / reproducing apparatus according to the first embodiment of the present invention. The hologram recording apparatus records and reproduces data by an angle multiplexing method, and includes a laser light source 1, a shutter 2, a shutter 3, a spatial modulator (SLM) 4, a recording signal light optical system 5, a hologram recording material 50, and a reference light. A deflection mirror 6, a reproduction signal light optical system 7 and an image sensor 8, a spindle motor 9 that rotates the hologram recording material 50, an actuator 10 that moves the hologram recording material 50 in a direction perpendicular to the surface direction, and a control personal computer 30 are provided. Configured. The control personal computer 30 performs shutter control, image display on the SLM 4, angle control of the reference light deflection mirror 6, spindle motor 9, actuator 10 control, and image capture processing from the output from the image sensor 8.

  FIG. 2 is a block diagram showing detailed examples of the recording signal light optical system 5 and the reproduction signal light optical system 7 shown in FIG. The recording signal light optical system 5 includes lenses 11, 12 and 13 and an aperture 14, and the reproduction signal light optical system 7 includes lenses 15, 16 and 17 and an aperture 18. A hologram recording material 50 is inserted between the recording signal light optical system 5 and the reproduction signal light optical system 7.

  Next, the operation of this embodiment will be described. At the time of recording, the laser light emitted from the laser light source 1 is branched into the signal light 100 and the reference light 200 by PBS (not shown) or the like. The signal light 100 is intensity-modulated by the data page displayed on the SLM 4, and then passes through the recording signal light optical system 5 and is irradiated onto the recording area of the hologram recording material 50. On the other hand, the reference light 200 is irradiated to the recording area of the hologram recording material 50 through a reference light optical system (not shown), and interference fringes between the signal light 100 and the reference light 200 are recorded in the recording area. At this time, the incident angle of the reference beam 200 to the hologram recording material 50 is changed by the reference beam polarization mirror 6 in the reference beam optical system, and a large number of data are angle-multiplexed and recorded in one recording area. In this angle multiplexing, a whole hologram that is multiplexed on one page in one page is called a book.

  At the time of reproduction, the hologram recorded on the hologram recording material 50 as described above is irradiated with the same reference light (reproduced reference light) as at the time of recording to reproduce the hologram (generation of diffracted light), and the reproduced light Passes through the reproduction signal light optical system 7 and reaches the image sensor 8, where it is photoelectrically converted and read, and the recorded data is reproduced by decoding the read data by image processing or the like. The At that time, the incident angle of the reproduction reference light on the hologram recording material 50 is changed by the reference light polarizing mirror 6 in the reference light optical system, and a large number of data that are angle-multiplexed recorded in one recording area are sequentially reproduced. Note that the high frequency cut aperture 14 in the recording signal light optical system 5 in FIG. 2 cuts high-order diffracted light and the like generated in the SLM 4 so that unnecessary portions on the hologram recording material 50 are exposed. Is preventing. The high frequency cut aperture 18 in the reproduction signal light optical system 7 is used to cut the scattered light component of the light reproduced from the hologram recording material 50 and the reproduction light from an unnecessary hologram.

  FIG. 3 is a partially enlarged view of the hologram recording material 50 shown in FIG. The signal light 100 and the reference light 200 are overlapped and the interference fringes of both lights are recorded in one book. Different data are sequentially recorded in this book every time the incident angle of the reference light 200 changes. FIG. 4 shows the recording method of the present embodiment for recording in a multi-book by the angle multiplexing method.

  FIG. 4A is a cross-sectional view of the hologram recording material 50, and angle multiplexing recording is performed with the focus position of the signal light set on the upper layer so that the book 6060 is arranged in an orderly manner on the upper layer near the front surface. In this figure, the portion where the power density is large is shown by shading. FIG. 4B is a top view of the hologram recording material 50, which is a signal light irradiation range 80 when recording each book 60, and the irradiation ranges 80 are arranged in a vertical and horizontal order. When the exposure methods shown in FIGS. 4A and 4B are adopted, the books 60 overlap each other, but even if they overlap, the aperture 18 is provided in the reproduction signal light optical system 7 as shown in FIG. For example, the books 60 can be separated at the position of the aperture 18 without crosstalk. However, since the exposure is not uniform as it is, only the monomer of the upper layer portion of the hologram recording material 50 is used, and all the monomers of the hologram recording material 50 are not used. At this time, the intensity ratio of the signal light and the reference light is adjusted to be optimum at the focus position of the signal light.

  Therefore, in this embodiment, as shown in FIG. 5A, when the focus position of the signal light is set in the lower layer portion near the back surface of the hologram recording material 50 and angle multiplexing recording is performed, the book 60 is also arranged in the lower layer portion. The Also in this case, as shown in FIG. 5B, the irradiation range 80 of the signal light when recording each book 60 is arranged in a vertical and horizontal order. In this case, if the upper layer is referred to as a first layer and the lower layer is referred to as a second layer, the first layer book 60 and the second layer book 60 are arranged to face each other. Thus, exposure can be made uniform by performing angle multiplex recording so as to generate a book 60 over two upper and lower layers. The focus position of the signal light 100 can be changed by controlling the actuator 10 by the control personal computer 30 and moving the hologram recording material 50 in a direction perpendicular to the surface direction. Servo accuracy is performed with machine accuracy. The focus position of the signal light 100 can also be changed by moving all or part of the recording signal light optical system 5.

  When recording is performed over two layers in this way, the crosstalk can be removed by the aperture 18 in the reproduction signal light optical system 7 in each layer. However, regarding the front side (first layer) and the back side (second layer), crosstalk occurs in the normal exposure method. However, use of the angular selectivity of the hologram can prevent the occurrence of crosstalk. As an example, assume that the angle selectivity is 0.1 degrees. In this case, if the angle of the reference light is made different between the first layer and the second layer, crosstalk between the first layer and the second layer does not occur due to the angle selectivity. 1st layer: 0, 0.2, 0.4, ..., 2nd layer: 0.1, 0.3, 0.5, ...

  According to the present embodiment, by optimizing the intensity distribution at the focus position of the signal light 100, a noise source can be prevented from being generated, and recording without noise can be performed. Further, since recording is performed over the upper layer and the lower layer of the hologram recording material 50, the exposure of the hologram recording material 50 can be made uniform to fully utilize the dynamic range, and the recording density can be improved. Further, since a plurality of layers can be recorded on the single-layer hologram recording material 50, if the recording density is kept as before, the multiplicity of each book 60 can be reduced, and the quality of data with reduced noise is reduced accordingly. Multiple recording and reproduction can be performed.

  In this embodiment, data is recorded over the upper and lower layers of the hologram recording material 50. However, the hologram recording material 50 does not have a two-layer structure and is a single layer. The structure is simple and does not increase the manufacturing cost, and the selection of the upper and lower layers may be determined by machine accuracy, and a complicated servo system such as feedback control is not required, and a simple servo system is sufficient. Therefore, it does not increase the cost of the device.

  FIG. 6 is a diagram for explaining an angle multiplex recording method by the hologram recording apparatus according to the second embodiment of the present invention. Also in this embodiment, angle multiplex recording is performed so that the book 60 is arranged in the upper layer and the lower layer of the hologram recording material 50. In this case, the difference between the first embodiment and the book 60 is that the upper layer and the lower layer are alternately arranged. It is in the position arranged in the position. Therefore, as shown in the top view of the hologram recording material 50, the irradiation range 80 of the signal light for recording the upper layer is small, the irradiation range of the signal light for recording the lower layer is large, and these are arranged alternately.

  According to this embodiment, the books 60 arranged in the upper layer are separated from each other, the books 60 arranged in the lower layer are separated, and the upper book 60 and the lower book 60 are also separated. Since they are not located at opposite positions, hologram recording / reproduction can be performed without crosstalk without resorting to the skillful setting of the angle change of the reference light and the aperture 18 in the reproduction signal light optical system 7. Other effects are the same as those of the first embodiment.

  FIG. 7 is a diagram for explaining an angle multiplex recording method by the hologram recording apparatus according to the third embodiment of the present invention. FIG. 7A is a top view of the hologram recording material 50. The signal light irradiation range 80 for recording the upper layer is small and the signal light irradiation range 80 for recording the lower layer is large. These are alternately arranged in the vertical direction. ing. FIG. 7B is a cross-sectional view taken along the line aa of FIG. 7A, and angle multiplex recording is performed so that a large number of books 60 are arranged below the hologram recording material 50. 7A is a cross-sectional view in the same direction as the cross-sectional view taken along the line aa in FIG. 7A, and a cross-section showing a narrow signal light irradiation range 80 is not shown in FIG. The angle multiplex recording is performed so that a large number of books 60 are arranged. FIG. 7C is a cross-sectional view taken along line bb in FIG. 7A, and it can be seen that angle multiplex recording is performed so that the books 60 are alternately arranged on the upper layer and the lower layer of the hologram recording material 50. Therefore, since the horizontal position is shifted between the upper layer and the lower layer book 60, recording and reproduction can be performed without crosstalk. However, as shown in FIG. 7A, the books 60 arranged in the upper layer are close to each other, and the books 60 arranged in the lower layer are also close to each other. For this reason, there is crosstalk with the adjacent book 60, which can be separated during reproduction by the aperture 18 in the reproduction signal light optical system 7, and can be reproduced without crosstalk. Other effects are the same as those of the first embodiment.

  FIG. 8 is a block diagram showing a schematic configuration of a hologram recording / reproducing apparatus according to the fourth embodiment of the present invention. The hologram recording / reproducing apparatus records and reproduces data by speckle multiplexing, and the configuration thereof is substantially the same as that of the first embodiment. However, a diffusing plate 21 that randomly disturbs the wavefront of the reference light 200 in the reference light optical system, A reference beam 200 having a condensing lens 22 and having a very complicated wavefront is incident on the hologram recording material 50 at a constant incident angle.

  Next, the operation of this embodiment will be described. At the time of recording, the laser light emitted from the laser light source 1 is branched into the signal light 100 and the reference light 200 by PBS (not shown) or the like. The signal light 100 is intensity-modulated by the data page displayed on the spatial modulator (SLM) 4, and then passes through the recording signal light optical system 5 and is irradiated onto the recording area of the hologram recording material 50. On the other hand, the wavefront of the reference light 200 is randomly disturbed by the diffuser plate 21 and then condensed on the recording area of the hologram recording material 50 by the condenser lens 22 to record interference fringes of both lights. At this time, since the wavefront of the reference light 200 is very complex, even if the reference light 200 is slightly shifted, the wavefront mismatch occurs between the original reference light 200 and the moved reference light 200. For this reason, the shift selectivity becomes very sharp as about several μm in any direction of the hologram recording material 50, and the hologram can be overwritten, so that the recording density can be very increased. Therefore, a plurality of data are recorded by speckle multiplexing by changing the data page displayed on the SLM 4 while moving the hologram recording material 50 little by little in the track direction by the spindle motor 9.

  FIG. 9A is a cross-sectional view of the hologram recording material 50 shown in FIG. 1, in which a plurality of data are recorded by speckle multiplexing so that the signal light 100 is focused on the upper layer of the hologram recording material 50. Yes. A plurality of data is recorded by speckle multiplexing so that the signal light 100 is focused on the lower layer of the hologram recording material 50. The exposure range 80 of the signal light 100 in this case is a top view of the hologram recording material 50 in FIG. 9B. When data is recorded on the upper layer of the hologram recording material 50, the irradiation range 80 of the signal light 100 is small, and when data is recorded on the lower layer, the irradiation range 80 of the signal light 100 is large. The focus position of the signal light 100 can be changed by controlling the actuator 10 by the control personal computer 30 and moving the hologram recording material 50 in a direction perpendicular to the surface direction. Servo accuracy is performed with machine accuracy. Note that because of speckle multiplex recording, it is possible to ensure shift selectivity between data recorded in the upper layer and the lower layer.

  According to the present embodiment, by optimizing the intensity distribution at the focus position of the signal light 100, a noise source can be prevented from being generated, and recording without noise can be performed. Further, since the recording is performed over the upper and lower layers of the hologram recording material 50, the exposure of the hologram recording material 50 can be made uniform to fully utilize the dynamic range, and the recording density by speckle multiplexing is improved. be able to. Other effects are the same as those of the first embodiment.

  In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the summary, it can implement also with another various form in a concrete structure, a function, an effect | action, and an effect. For example, in the above embodiment, hologram multiplex recording is performed on two layers close to the front surface and the back surface of the hologram recording material. However, depending on the performance of the recording material, recording over three layers or more can further increase the recording density. Can do. In many cases, signal light does not enter perpendicularly to the hologram recording material surface. In this case as well, a plurality of layers can be recorded in exactly the same arrangement by changing the focus position in the depth direction, and each book can be arranged without crosstalk.

1 is a block diagram showing a schematic configuration of a hologram recording / reproducing apparatus according to a first embodiment of the present invention. FIG. 2 is a block diagram showing detailed examples of a recording signal light optical system and a reproduction signal light optical system shown in FIG. 1. It is an enlarged view of the recording part of the hologram recording material shown in FIG. It is the figure which showed the example of arrangement | sequence of the book which carries out angle multiplexing recording by the apparatus shown in FIG. It is the figure which showed the example of arrangement | sequence of the book which carries out angle multiplexing recording by the apparatus shown in FIG. It is a figure explaining the recording method by angle multiplexing by the hologram recording apparatus which concerns on the 2nd Embodiment of this invention. It is a figure explaining the recording method by angle multiplexing by the hologram recording device which concerns on the 3rd Embodiment of this invention. It is the block diagram which showed schematic structure of the hologram recording / reproducing apparatus which concerns on the 4th Embodiment of this invention. It is a figure explaining the method of speckle multiplex recording by the apparatus shown in FIG. It is a figure explaining the conventional hologram recording method. It is a figure explaining the conventional hologram recording method. It is the figure which showed the example of an arrangement | sequence of the book recorded by the conventional hologram recording method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser light source, 2, 3 ... Shutter, 4 ... Spatial modulator (SLM), 5 ... Signal optical system for recording, 6 ... Reference light deflection angle mirror, 7 ... Signal optical optics for reproduction | regeneration System, 8 ... Image sensor, 9 ... Spindle motor, 10 ... Actuator, 11, 12, 13, 15, 16, 17 ... Lens, 14, 18 ... Aperture, 21 ... Diffuser, 22 ... Condensing lens, 30 ... control PC, 50 ... hologram recording material.

Claims (8)

A holographic recording apparatus that multiplex-records interference fringes between reference light and intensity-modulated signal light on a single-layer hologram recording material,
A recording unit that multiplex-records the interference fringes so that the interference fringes that are recorded in a multiple number form a plurality of recording layers that are spaced apart in the thickness direction of the hologram recording material and spread in a direction perpendicular to the thickness direction;
A hologram recording apparatus characterized by that.   The recording means comprises focus position changing means for selecting the recording layer by changing the focus position of the signal light so as to be a preset position in the thickness direction of the hologram recording material. The hologram recording apparatus according to claim 1.   3. The hologram recording apparatus according to claim 1, wherein an intensity ratio between the signal light and the reference light is adjusted to be optimal at a focus position of the signal light.   4. The hologram recording apparatus according to claim 1, wherein the multiplex recording is angle multiplex recording.   The incident angle of the reference light to the hologram recording material in the angle multiplexing recording is set to be different for each recording layer in the thickness direction of the hologram recording material. Hologram recording device.   5. The hologram recording apparatus according to claim 4, wherein the recording layer is formed by multiple recording of interference fringes so that the focus ranges of the signal light do not overlap each other.   The hologram recording apparatus according to claim 1, wherein the multiplex recording is speckle multiplex recording. A hologram recording method in which interference fringes between reference light and intensity-modulated signal light are multiplexed and recorded on a single-layer hologram recording material,
The interference fringes are changed by changing the focus position of the signal light so that the multiple recording interference fringes are formed so as to form a plurality of recording layers that are separated by a predetermined distance in the thickness direction of the hologram recording material and spread in a direction perpendicular to the thickness direction. A holographic recording method.

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