JP6694376B2 - Hologram recording device and hologram recording method - Google Patents

Description

  The present invention relates to a hologram recording device and a hologram recording method, and more particularly, to a hologram recording device and a hologram recording method capable of improving data quality at the time of recording data in a hologram.

  In recent years, hologram recording has attracted attention as a large-capacity and high-speed information recording / reproducing system. In hologram recording, two coherent light beams, which are called reference light and signal light, from the same light source are caused to interfere with each other, and the resulting interference fringes are recorded and held as a refractive index change on a recording medium. The signal light is spatially modulated by a two-dimensional data image called "page data", and is irradiated onto a recording medium via a lens. It is possible to multiplex and record multiple page data at the same location on the medium while changing the conditions of the reference light (for example, incident angle to the recording medium, wavelength, phase, etc.). Is possible.

By the way, in the laser light forming the signal light or the reference light, the intensity distribution of the cross section is a Gaussian distribution and coherent noise occurs, so that the intensity distribution of the signal light cross section is not uniform.
When the signal light has an intensity distribution, the intensity distribution is superimposed on the page data, so that the data may not be recorded in a place where the intensity is low.
On the other hand, if the overall laser light intensity is too high so that recording can be performed even in a low intensity area, the exposure amount of the recording medium becomes excessive in a high intensity area, which causes extra optical noise. Furthermore, the monomer in the recording medium is partially consumed more than necessary, and the number of multiplex recordings for high density recording cannot be increased.

In order to increase the number of multiplex recordings while suppressing noise, it is necessary to make the intensity distribution of page data uniform and irradiate the recording medium with the weakest light that can record a hologram.
Up to now, the Gaussian distribution, which is the intensity distribution of the laser light, has been compensated to correct the intensity distribution of the page data.

When the page data is modulated, a signal obtained by superimposing a Gaussian distribution on the page data information is displayed on the SLM, and a signal carrying the SLM display signal information is made incident, whereby the intensity of the page data modulated by the SLM. The distribution is made uniform (Patent Document 1). Alternatively, the intensity distribution of the signal light is detected, and the intensity distribution correction element makes the laser light intensity distribution uniform based on the detected information (Patent Document 2). Further, by introducing an optical element such as a homogenizer for making the intensity distribution uniform in the signal light path, it is possible to make the intensity distribution of the page data modulated by the SLM uniform.
Further, the inventors of the present application optically compensate for the distortion of the hologram due to the contraction or expansion of the recording medium by controlling the wavefront of the reference light at the time of reproduction, and make the intensity distribution of the reproduced page data uniform. Has been proposed (Patent Document 3).

JP, 2006-139205, A JP2012-243355A JP, 2014-067017, A

  However, since the signal light is condensed by the lens and is incident on the recording medium, each ray of the signal light has various incident angles with respect to the recording medium. FIG. 2 shows an angle when an arbitrary point of the signal light which is the laser light modulated by the page data is incident on the recording medium.

Here, the plane of the recording medium is the x-axis and the y-axis, and the normal direction is the z-axis. Further, the incident angle of the signal light with respect to the z-axis is θ. In this case, the incident angle θ differs depending on the position of page data. Since the refractive index of the recording medium is different from that in air, the intensity transmitted through the recording medium varies depending on the incident angle θ.
Fig. 3 shows the relationship between the incident angle θ and the transmitted light intensity when light enters a medium with a different refractive index (the transmitted light intensity when the signal light is s-polarized light is the transmitted light intensity when the signal light is s-polarized light). Is Tp, the reflected light intensity when the signal light is s-polarized light is Rs, and the reflected light intensity when it is p-polarized light is Rp). The intensity distribution of page data in the recording medium changes from the intensity distribution just before the recording medium enters. Even if the intensity distribution just before the recording medium enters is uniform, it is not uniform in the recording medium. The quality of the information has been degraded before it was recorded.

  The present invention has been made in view of the above circumstances, and when performing hologram recording, the intensity distribution of the signal light is made uniform in the recording medium regardless of the difference in the incident angle of the signal light to the recording medium due to each light beam. It is an object of the present invention to provide a hologram recording device and a hologram recording method capable of achieving the above.

  In order to solve the above problem of making the intensity distribution of page data uniform in the recording medium, the inventors of the present application have determined that the intensity distribution of light incident on the recording medium is the transmittance according to the incident angle. From the knowledge of, we came to the idea of superimposing the reciprocal of the transmittance characteristic for the incident angle on the intensity distribution of the page data, or inserting a filter having the reciprocal of the transmittance characteristic for the incident angle as a characteristic in the signal optical path, It proposes a specific configuration relating to the following hologram recording device and hologram recording method.

That is, the first hologram recording device of the present invention is
In a hologram recording device, which is formed by separating a laser beam from a light source, causes a signal light carrying information related to page data and a recording reference light to interfere with each other, and records interference fringes related to the information on a recording medium. ,
A spatial light modulation element that causes the laser light to carry information related to the page data to be the signal light, and a predetermined calculation is performed on the information related to page data displayed on the spatial light modulation element, and the space And an arithmetic means for outputting to the light modulator,
The predetermined calculation is the reciprocal of the transmittance characteristic with respect to the light incident angle on the recording medium so that the intensity distribution of the signal light incident on the recording medium is made uniform regardless of the incident angle on the recording medium. Is an operation for superposing on the intensity distribution of the page data.

The second hologram recording device of the present invention is
In a hologram recording device, which is formed by separating a laser beam from a light source, causes a signal light carrying information related to page data and a recording reference light to interfere with each other, and records interference fringes related to the information on a recording medium. ,
A spatial light modulation element that carries the information related to the page data in the laser light to obtain the signal light, and a predetermined value for the laser light arranged in the optical path of the laser light with which the spatial light modulation element is irradiated. Equipped with a transmittance control filter that gives the intensity distribution of
The predetermined intensity distribution is the transmittance characteristic with respect to the light incident angle on the recording medium so that the intensity distribution of the signal light incident on the recording medium is made uniform regardless of the incident angle on the recording medium. The intensity distribution is obtained by superimposing the reciprocal number on the page data.

  Further, in the hologram recording device described above, the hologram recording can be applied to any multiplex recording in addition to the angle multiplex recording.

The first hologram recording method of the present invention is
In a hologram recording method, in which a signal light carrying information related to page data and a reference light for recording formed by separating laser light from a light source are interfered with each other to record interference fringes related to the information in a recording medium. ,
The reciprocal of the transmittance characteristic with respect to the light incident angle on the recording medium is related to the page data so that the intensity distribution of the signal light incident on the recording medium is made uniform regardless of the incident angle on the recording medium. The information is multiplied to obtain the page data information after the intensity distribution correction, and thereafter, the laser light is applied to the spatial light modulator on which the page data information after the intensity distribution correction is displayed to be converted into the signal light. It is characterized by that.

Further, the second hologram recording method of the present invention is
In a hologram recording method, in which a signal light carrying information related to page data and a reference light for recording formed by separating laser light from a light source are interfered with each other to record interference fringes related to the information in a recording medium. ,
The laser light is made incident on the transmittance control filter before being converted to the signal light so that the intensity distribution of the signal light made incident on the recording medium is made uniform regardless of the incident angle to the recording medium. To have a reciprocal of the transmittance characteristic with respect to the light incident angle on the recording medium as a characteristic, and thereafter, the laser light having the characteristic is applied to the spatial light modulator on which the page data is displayed. The signal light is converted into the signal light.

  According to the hologram recording apparatus and method of the present invention, the reciprocal of the light transmittance characteristic with respect to the light incident angle on the recording medium is superimposed on the intensity distribution of the page data to obtain the page data information after the intensity distribution correction. The corrected page data information is displayed on the spatial light modulation element, and the spatial light modulation element is irradiated with laser light to be converted into signal light. Alternatively, before irradiating the spatial light modulator with laser light, a transmittance control filter is used to give the reciprocal of the light transmittance characteristic with respect to the light incident angle on the recording medium as an intensity distribution, and then this laser light is used for page data. Is radiated to the spatial light modulator for displaying to convert it into signal light.

  As described above, since the signal light applied to the recording medium has the reciprocal of the light transmittance characteristic with respect to the light incident angle on the recording medium in advance as the intensity distribution of the page data, this signal light is emitted from the recording medium. When the light enters the inside, the intensity distribution of the signal light can be made uniform regardless of the difference in the incident angle between the respective rays of the signal light.

1 is a schematic diagram for explaining the configuration of a hologram recording device according to a first embodiment of the invention. FIG. 3 is a schematic diagram for explaining an incident angle θ of signal light on a recording medium. FIG. 6 is a schematic diagram showing a relationship between an incident angle θ and transmitted light intensity when light is incident on a medium having a different refractive index. 3 is a photograph showing a reproduced image of page data obtained by the hologram recording device according to the embodiment of the present invention. 6 is a photograph showing a reproduced image of page data obtained by a hologram recording device according to a conventional technique. It is a schematic diagram for explaining the configuration of a hologram recording device according to a second embodiment of the present invention.

Hereinafter, a hologram recording device and a hologram recording method according to embodiments of the present invention will be described with reference to the drawings.
<Example 1>
FIG. 1 shows the main configuration of the hologram recording apparatus according to the first embodiment.
This hologram recording device is a hologram recording / reproducing device that also has a reproducing function.

  The feature of the hologram recording apparatus according to the first embodiment is that an amplitude modulation SLM (spatial light modulation) in which laser light (signal-carrying light: p-polarized light) from the laser light source 1 carries information related to page data as signal light. The device 9 and an arithmetic means 30 for performing a predetermined arithmetic operation on the information relating to the page data displayed on the amplitude modulation SLM 9 and outputting the information to the amplitude modulation SLM 9. This predetermined calculation is performed so that the intensity distribution of the signal light incident on the hologram recording medium 11 is made uniform regardless of the incident angle of the signal light on the hologram recording medium 11 so that the light incident angle on the hologram recording medium 11 becomes uniform. Is an operation for multiplying the intensity distribution of page data by the reciprocal of the transmittance characteristic for.

Hereinafter, a specific configuration of the device according to the first embodiment will be described.
The hologram recording device shown in FIG. 1 is configured as a recording / reproducing device having a hologram recording function and a hologram reproducing function.
It should be noted that the hologram recording medium 11 is made of a photopolymer and has a structure corresponding to the phase conjugate type.
However, the material of the hologram recording medium 11 according to the device of the present invention is not limited to the photopolymer, and the optical system is not necessarily limited to the phase conjugate type.

  As shown in FIG. 1, at the time of recording, the coherent laser light flux emitted from the laser light source 1 passes through a shutter (not shown), and a beam expander including a diverging lens 2, a spatial filter 3 and a collimating lens 4 causes the light beam diameter to change. Is expanded, passes through the half-wave plate 5, is deflected at a right angle by a mirror 6, and is split into a two-system light beam by a polarization beam splitter (PBS: simply referred to as PBS hereinafter) 7.

  A light flux (light for signal carrier: p-polarized light) traveling from the PBS 7 to the left in the drawing passes through the PBS 8 and is applied to an amplitude modulation SLM (hereinafter simply referred to as SLM) 9 and spatially modulated by the SLM 9. The signal light carries page data information consisting of a digital image.

  Further, the signal light emitted (reflected) from the SLM 9 is partly changed in polarization state due to page data information from the state of being incident on the SLM 9 to become s-polarized light, which is reflected downward in the figure by the PBS 8 and the lens (FTL ) 10, it is optically Fourier-transformed and is applied to the hologram recording medium 11.

  On the other hand, the light flux (s-polarized light) traveling downward from the PBS 7 in the figure is used as reference light (reference light during recording), and the half-wave plate 14 (the optical axis of the half-wave plate 14 matches the polarization direction of the incident light). After being adjusted), the light is deflected at a right angle by the mirror 15, but is reflected by the PBS 16 because it is in the s-polarized state, and travels downward from the PBS 16 in the figure. The angle of the light flux is controlled by the galvanometer mirror 17, and the position of the signal light in the hologram recording medium 11 is irradiated via the relay lens 18 at a different angle from the signal light, whereby the recording of the recording medium 11 is performed. A change in the refractive index depending on the intensity of light having an interference fringe pattern is induced in the material, and this is held as hologram information.

Since the apparatus of the present embodiment is premised on the angle multiplex recording, the page data is displayed on the SLM 9 and the display of the page data on the SLM 9 is sequentially updated. By changing the incident angle θ of the light to the recording medium 11 little by little by the galvanometer mirror 17, it becomes possible to perform multiple recording of different page data at the same position in the recording medium 11, which enables high-density information storage. Has become.

  In addition, a measurement control unit (not shown) controls the drive of the laser light source 1 and the angle control of the galvanometer mirror 17 at the time of recording, and sends an instruction to send and display page data to the SLM 9 via the arithmetic unit 30. To do.

Incidentally, the incident angle θ of the signal light on the recording medium 11 has a different value depending on the light ray from each position of the carried page data. Since the refractive index of the recording medium 11 is different from the refractive index of air, the intensity transmitted through the recording medium 11 differs depending on the incident angle θ.
As described above, FIG. 3 shows the incident angle θ and the transmitted light intensity and the reflected light intensity when the light enters the medium having different refractive indexes (the transmitted light intensity when the signal light is s-polarized light). Is Ts, the transmitted light intensity when p-polarized is Tp, the reflected light intensity when the signal light is s-polarized is Rs, and the reflected light intensity when p-polarized is Rp). Note that FIG. 3 shows an example in which light enters from a medium (air) having a refractive index of 1.0 to a medium having a refractive index of 1.5. In this case, the transmittance of p-polarized light is 100% ( The light incident angle θ _B at which the reflectance is 0%) is 56.31 °.
As is clear from FIG. 3, the intensity distribution of page data in the recording medium 11 changes from the intensity distribution immediately before the recording medium enters, and even if the intensity distribution just before the recording medium enters is uniform. However, it is not uniform in the recording medium, and the quality of the recorded information has already deteriorated when it enters the recording medium 11.

Therefore, in this embodiment, in order to maintain the quality of recorded information in the recorded state, the intensity distribution of the signal light incident on the hologram recording medium 11 is made uniform regardless of the incident angle θ on the hologram recording medium 11. As described above, the calculation means 30 performs the calculation for superimposing the reciprocal of the transmittance characteristic with respect to the light incident angle θ on the hologram recording medium 11 on the intensity distribution of the page data, and the intensity distribution obtained by this calculation is displayed on the SLM 9. The signal light is generated by causing the laser light with which the SLM 9 is irradiated to carry the intensity distribution obtained by the calculation.
Therefore, in the first embodiment, since the reciprocal of the light transmittance characteristic with respect to the light incident angle θ on the recording medium 11 is previously superimposed as the intensity distribution of the page data to be displayed on the SLM 9, this signal light is recorded. When incident on the medium 11, the intensity distribution of the signal light can be made uniform.

Next, the reproducing function of the hologram recording apparatus according to the first embodiment will be described with reference to FIG.
As shown in FIG. 1, when reproducing the page data information recorded on the hologram recording medium 11, the position of the half-wave plate 14 is adjusted to change the polarization direction of the reproduction reference light (from s-polarized light to p-shaped light). Convert to polarized light). This reference light reaches the PBS 16 after being reflected by the mirror 15, but since it is p-polarized by the half-wave plate 14, it goes straight through the PBS 16.

  As shown in FIG. 1, the reference light transmitted through the PBS 16 is reflected by the mirror 21 and reaches the galvanometer mirror 22, and the galvanometer mirror 22 causes the incident angle for reproducing the page data recorded by the angle multiplex recording. θ is controlled.

  That is, the incident angle of the reproduction reference light on the hologram recording medium 11 is controlled by the rotation angle of the galvanometer mirror 22.

In this way, the reproduction reference light that has entered the recording medium 11 via the relay lens 23 is not incident on the recording medium 11 from the back side to the position of the recording medium 11 irradiated with the signal light. It is irradiated from the opposite direction.

As described above, the reproduction light of the predetermined page data is emitted from the hologram recording medium 11 by the irradiation of the reproduction reference light.
The emitted reproduction light is applied to the PBS 8 via the lens 10. Since the PBS 8 transmits the p-polarized reproduction light, the page data information carried by the p-polarized reproduction light enters the camera 13 and is imaged.

Hereinafter, a method for recording page data with a uniform intensity distribution in the recording medium as described above will be described in more detail.
Here, the intensity distribution of the signal light incident on the hologram recording medium 11 is obtained. A signal of page data at an arbitrary point (x, y) is A (x, y). Here, the intensity corresponding to bit 1 (bright spot) is a, and the intensity corresponding to bit 0 is 0 (black level). The incident angle θ of the light beam of the signal light passing through the point (x, y) on the page data to the recording medium 11 is obtained.

As shown in FIG. 2, assuming that the angle from the z axis on the xz plane is α and the angle from the z axis on the yz plane is β, the angles α and β can be expressed by the following formula (1 ), (2). The focal length of the lens 10 is f.

Further, the following equation (3) is geometrically established.
Thereby, the following expression (4) is established.

Further, as shown in FIG. 1, when the recording medium 11 is installed so as to be rotated around the y axis and the angle of the inclination is ω, the equation (4) is expressed by the following equation (5). To be done.

As described above, in the relationship between the incident angle and the transmittance shown in FIG. 3, when the light transmittance of the recording medium 11 with respect to the light incident angle θ is t (θ), the intensity distribution in the recording medium 11 becomes uniform. Therefore, the weight B (x, y) added to the intensity of the signal light incident on the recording medium 11 is expressed by the following equation (6).

Therefore, by setting the signal of the page data displayed on the SLM 9 as A (x, y) · B (x, y), the intensity distribution of the signal light becomes uniform after the light enters the recording medium 11, and the data becomes uniform. The page data with improved quality can be recorded in the recording medium 11. FIG. 4 shows a reproduced image of page data whose data quality is improved in this way.
According to FIG. 4, the brightness is improved in the upper part of the reproduced image, the uniformity of the intensity distribution is improved over the entire page data, and the data quality is also improved. This difference is clear when compared with the reproduced image of the page data shown in FIG. 5 obtained by using the hologram recording device according to the related art.

<Example 2>
The hologram recording apparatus according to the second embodiment shown in FIG. 6 is configured as a hologram recording / reproducing apparatus having a hologram recording function and a hologram reproducing function, as in the first embodiment.
Most of the hologram recording apparatus of the second embodiment has the same configuration as that of the first embodiment. Therefore, for these similar members, the reference numeral obtained by adding 100 to the reference numeral of the corresponding member of the first embodiment. The detailed description will be omitted.

  The feature of the second embodiment is that the laser light (signal-carrying light: p-polarized light) is caused to have a predetermined intensity distribution by the transmittance control filter 151 before being irradiated on the amplitude modulation SLM 109. It is a point that is configured in. That is, the transmittance characteristic of the light incident angle θ on the hologram recording medium 111 is adjusted so that the intensity distribution of the signal light incident on the hologram recording medium 111 becomes uniform regardless of the incident angle θ on the hologram recording medium 111. The point is that the intensity distribution related to the reciprocal is given to the laser light in advance by the transmittance control filter 151.

  As a result, in the second embodiment, of the laser light from the laser light source 101, the laser light that travels straight through the PBS 107 is first transmitted by the transmittance control filter 151 to the transmittance characteristics with respect to the light incident angle θ on the hologram recording medium 111. The intensity distribution according to the reciprocal is superposed, and then the page data information is superposed by the amplitude modulation SLM 109, and the signal light thus generated is transmitted to the hologram recording medium 111 via the PBS 108 and the lens 110. It will be irradiated.

As the transmittance control filter 151, an ND filter having a transmittance corresponding to a desired intensity distribution or a spatial light modulator such as an SLM can be used.
As the transmittance distribution of the transmittance control filter 151, B (x, y) of the equation (6) described in the above-mentioned Embodiment 1 can be used. As a result, the signal light intensity distribution of the laser light incident on the SLM 109 also becomes B (x, y), and the signal light intensity distribution modulated by the page data displayed on the SLM 109 is A (x, y) · B (x, y). Therefore, the intensity distribution of the signal light in the recording medium 111 is A (x, y), and page data with improved data quality can be recorded in the recording medium 111.

In this embodiment, the gray scale of the SLM 109 is used only for modulation of page data. Therefore, a binary ferroelectric liquid crystal can be used as the SLM 109 for page data modulation,
The data transfer rate can be improved.
On the other hand, when an element capable of gradation display is used as the SLM 109, by displaying multi-valued information on the SLM 109, it is possible to perform amplitude multi-value recording, so that it is possible to improve the recording density and the data transfer rate.

The hologram recording device and the hologram recording method of the present invention are not limited to those of the above-mentioned embodiment, but can be modified to various other modes.
For example, although the hologram recording device and the hologram recording method described above have a reproducing function, they do not necessarily have to have a reproducing function.
Further, the configuration of the optical system of the device is not limited to that of the above embodiment.

As described above, in angle-multiplexed recording and reproduction, the angle and position of the galvanometer mirror are changed little by little. Specifically, for example, the reference light is incident on the axis of the signal light. The angle θ is in the range of 55 degrees to 75 degrees (within the range in which the light emitting end structure and the emitted light do not physically interfere (vignetting) when the signal light and the reference light are incident on the recording medium), for example, 0.2. The page data information may be recorded or reproduced in the area each time it is changed.

The multiplex recording method is not limited to the angle multiplex, and various multiplex methods such as wavelength multiplex and peristrophic multiplex other than the angle multiplex can be applied.
Although the transmittance control filter used in the second embodiment is a light transmission type, a light reflection type transmittance control filter or a reflectance control mirror may be used instead.

1, 101 Laser light source 2, 102 Divergence lens 3, 103 Spatial filter 4, 104 Collimator lens 5, 105 Half-wave plate 6, 15, 21, 106, 115, 121 Mirror 7, 8, 16, 107, 108, 116 Polarized light Beam splitter (PBS)
9, 109 Amplitude Modulation SLM (SLM)
10, 18, 23, 110, 118, 123 Lens 11, 111 Hologram recording medium (recording medium)
13, 113 Cameras 17, 22, 117, 122 Galvanometer mirror 30 Computing device 151 Transmittance control filter

Claims (4)

In a hologram recording device, which is formed by separating a laser beam from a light source, causes a signal light carrying information related to page data and a recording reference light to interfere with each other, and records interference fringes related to the information on a recording medium. ,
A spatial light modulation element that causes the laser light to carry information related to the page data to be the signal light, and a predetermined calculation is performed on the information related to page data displayed on the spatial light modulation element, and the space And an arithmetic means for outputting to the light modulator,
The predetermined calculation is the reciprocal of the transmittance characteristic with respect to the light incident angle on the recording medium so that the intensity distribution of the signal light incident on the recording medium is made uniform regardless of the incident angle on the recording medium. Is a calculation for superposing on the intensity distribution of the page data. In a hologram recording device, which is formed by separating a laser beam from a light source, causes a signal light carrying information related to page data and a recording reference light to interfere with each other, and records interference fringes related to the information on a recording medium. ,
A spatial light modulation element that carries the information related to the page data in the laser light to obtain the signal light, and a predetermined value for the laser light arranged in the optical path of the laser light with which the spatial light modulation element is irradiated. Equipped with a transmittance control filter that gives the intensity distribution of
The predetermined intensity distribution is the transmittance characteristic with respect to the light incident angle on the recording medium so that the intensity distribution of the signal light incident on the recording medium is made uniform regardless of the incident angle on the recording medium. A hologram recording apparatus, which is an intensity distribution in which a reciprocal is superimposed on the page data. In a hologram recording method, in which a signal light carrying information related to page data and a reference light for recording formed by separating laser light from a light source are interfered with each other to record interference fringes related to the information in a recording medium. ,
The reciprocal of the transmittance characteristic with respect to the light incident angle on the recording medium is related to the page data so that the intensity distribution of the signal light incident on the recording medium is made uniform regardless of the incident angle on the recording medium. The information is multiplied to obtain the page data information after the intensity distribution correction, and thereafter, the laser light is applied to the spatial light modulator on which the page data information after the intensity distribution correction is displayed to be converted into the signal light. A hologram recording method characterized by the above. In a hologram recording method, in which a signal light carrying information related to page data and a reference light for recording formed by separating laser light from a light source are interfered with each other to record interference fringes related to the information in a recording medium. ,
The laser light is made incident on the transmittance control filter before being converted to the signal light so that the intensity distribution of the signal light made incident on the recording medium is made uniform regardless of the incident angle to the recording medium. To have a reciprocal of the transmittance characteristic with respect to the light incident angle on the recording medium as a characteristic, and thereafter, the laser light having the characteristic is applied to the spatial light modulator on which the page data is displayed. A hologram recording method comprising: converting the signal light into the signal light.