JP4750083B2 - Hologram recording apparatus and hologram recording method - Google Patents

Description

  The present invention relates to a hologram recording apparatus that records a hologram by causing recording light and reference light to interfere with each other in a hologram recording medium, and a recording method therefor.

  In hologram recording, information to be recorded is two-dimensionally encoded and converted into light modulation data corresponding to, for example, a light and dark pixel pattern. The recording light is optically modulated based on the optical modulation data. In hologram recording, interference fringes are generated on the hologram recording medium using the recording light thus modulated and reference light emitted from the same light source as the recording light, and the interference fringes are recorded. When this interference fringe is irradiated with the same reference light as at the time of recording, reproduction light can be obtained. If the intensity of the recording light and the reference light when recording on the hologram recording medium is greatly different, the signal-to-noise ratio (SN ratio) in the reproduction light may be low, making it difficult to reproduce the original information. For this reason, in hologram recording, it is necessary to make the intensities of recording light and reference light uniform during recording. The intensity of the reference light can be controlled relatively easily, but the intensity of the recording light may change depending on the information to be recorded, and it is difficult to control the intensity. Therefore, there is a case where a balance modulation method is performed in which the information to be recorded is converted into light modulation data in which the ratio of light and dark pixels is always 1: 1 (see Patent Document 1).

  In such a balance modulation method, for example, the light modulation data is divided for each pixel block composed of four pixels, and the ratio of light and dark pixels in each divided pixel block is always 1: 1. It has become. With such light modulation data, the intensity of the recording light becomes constant, and it is possible to easily perform recording in which the intensity ratio of the recording light and the reference light is made equal to increase the SN ratio of the reproduction light.

  However, in such a balance modulation method, only a pixel pattern in which the ratio of bright and dark pixels is constant is used, so that the amount of information that can be represented by one pixel block is small. For example, when a pixel block is composed of four pixels, there are only six possible pixel patterns as shown in FIG. Such a pixel block cannot represent 3-bit information in 8 patterns. For this reason, only two bits of information can be represented by four pixels. If the ratio of the number of bits that can be expressed by one pixel block is the coding rate, the coding rate in this case is only 0.5. On the other hand, when the balance modulation method is not used, assuming that one pixel corresponds to a pixel block, two bits can be represented by one pixel, so the coding rate is 1. When the balance modulation method is used in this way, there is a problem that the coding rate is lowered and the information amount of the entire hologram recording medium is reduced.

JP 2000-228089 A

  The present invention has been conceived under such circumstances, and a hologram recording apparatus capable of improving the coding rate and performing recording capable of obtaining reproduction light having a good SN ratio, and It is an object of the present invention to provide a hologram recording method.

  The hologram recording apparatus provided by the first aspect of the present invention is a hologram recording apparatus that records a hologram by causing interference in a hologram recording medium with recording light that is light-modulated based on information to be recorded and reference light. Then, by performing a convolution operation of the information to be recorded using a plurality of check codes, convolution data generating means for generating a plurality of convolution data, and converting the plurality of convolution data into a plurality of light modulation data A data conversion unit; a light modulation efficiency selecting unit for calculating light utilization efficiency for each of the plurality of light modulation data; and selecting the light modulation data in which the light utilization efficiency falls within a predetermined range; and the selected light modulation data And spatial light modulation means for generating the recording light by performing light modulation based on the above.

  In a preferred embodiment, the data conversion means converts the convolution data into the light modulation data by two-dimensional encoding.

  In a more preferred embodiment, the data conversion means divides the convolution data into a predetermined number and performs two-dimensional encoding using a plurality of pixel patterns having different light utilization efficiency for each divided data. Then, light modulation data composed of these pixel patterns is generated.

  In another preferred embodiment, the data conversion means converts the check code used when generating the convolution data as a part of the light modulation data.

  In another preferred embodiment, light modulation data reproducing means for acquiring reproduction light by irradiating the hologram recording medium with the same reference light as at the time of recording and reproducing the original light modulation data from the reproduction light; Decoding means for obtaining the original convolution data and the check code corresponding thereto by decoding the reproduced optical modulation data, and convolution of the convolution data obtained by decoding with the check code Convolutional demodulation means for obtaining original information recorded as the hologram by demodulation.

  The hologram recording method provided by the second aspect of the present invention is a hologram recording method for recording a hologram by causing interference in a hologram recording medium with recording light that is light-modulated based on information to be recorded and reference light. Then, by performing a convolution operation of the information to be recorded using a plurality of check codes, a plurality of convolution data is generated, the plurality of convolution data is converted into a plurality of light modulation data, and the plurality of light Calculate the light utilization efficiency for each modulation data, select the light modulation data in which the light utilization efficiency falls within a predetermined range, and based on the selected light modulation data, two-dimensionally encoding the convolution data, The convolution data is divided into a predetermined number, and two-dimensional encoding is performed using a plurality of pixel patterns having different light utilization efficiency for each divided data. And by, and it generates the modulated optical data consisting of pixel patterns, by performing optical modulation on the basis of the generated light modulated data, and generates the recording beam.

  According to such a hologram recording apparatus, even when performing conversion such that the light use efficiency of the light modulation data obtained by the data conversion means takes various values, the light modulation data that the light use efficiency falls within a predetermined range. By selecting this, it is possible to keep the intensity of the recording light within a predetermined range. When conversion is performed so that the light use efficiency of the light modulation data takes various values, the number of pixel patterns increases, so that the coding rate can be easily improved. Furthermore, by keeping the intensity of the recording light within a predetermined range, the intensity ratio between the recording light and the reference light at the time of recording can be easily approached to an optimum value, and recording capable of obtaining reproduction light with a good SN ratio It can be performed. The light use efficiency of the light modulation data is expressed as a ratio of bright pixels when the light modulation data is expressed by light and dark pixels in the spatial light modulation means.

  Other advantages and features of the present invention will become more apparent from the following description of embodiments of the invention.

  Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings.

  1 to 8 show an example of an embodiment of a hologram recording apparatus according to the present invention. As shown in FIG. 1, the hologram recording apparatus A can irradiate the hologram recording medium B with recording light and reference light to record a hologram, and can reproduce the recorded information. FIG. 2 is a main part configuration diagram of the hologram recording apparatus A, and shows a configuration for generating recording light from information to be recorded. The hologram recording apparatus A includes a light source 1, a collimator lens 2, a beam expander 3, a beam splitter 4, a spatial light modulator 5, a half mirror 6, an objective lens 7 for recording light, a reflecting plate 8, a prism 9, and reference light. Objective lens 10, convolution data generation means 11, data conversion means 12, light modulation data selection means 13, light modulation data reproduction means 14, decoding means 15, and convolution demodulation means 16. . Other components not shown include a rotation mechanism for rotating the hologram recording medium B as a rotating disk, and a moving mechanism for moving the optical system such as the objective lenses 7 and 10 in the radial direction of the hologram recording medium B. I have. Furthermore, a moving mechanism for moving the objective lenses 7 and 10 in the vertical direction in FIG. 1 is also provided.

  The hologram recording medium B has a laminated structure of a substrate 90, a reflective film 91, a recording layer 92, and a protective layer 93. By irradiating the recording layer 92 with the recording light and the reference light so as to overlap with each other, a hologram as an interference fringe is recorded.

  The light source 1 is made of, for example, a semiconductor laser element, and emits laser light having a relatively narrow band and high coherence. The collimator lens 2 converts the laser light emitted from the light source 1 into parallel light. The parallel light emitted from the collimator lens 2 enters the beam expander 3. The beam expander 3 is composed of a combination lens, and guides it to the beam splitter 4 while expanding the diameter of the parallel light.

  The beam splitter 4 is a half mirror, for example, and separates the parallel light incident from the beam expander 3 into light traveling toward the spatial light modulator 5 and light traveling toward the reflecting plate 8.

  The spatial light modulator 5 is, for example, a liquid crystal screen device, and has a predetermined number of pixels that can be switched between bright and dark states. The bright pixel emits the light incident from the beam splitter 4 toward the half mirror 6. On the other hand, the dark pixel blocks light incident from the beam splitter 4. In FIG. 2, FIG. 4, and FIG. 5, bright pixels are displayed in white, and dark pixels are hatched. The spatial light modulator 5 modulates the light incident from the beam splitter 4 with such a bright and dark pixel pattern to generate recording light. The recording light generated by the spatial light modulator 5 is emitted toward the half mirror 6.

  The spatial light modulator 5 may be a deformable mirror device in which a large number of light reflecting elements are arranged.

  The half mirror 6 transmits the recording light incident from the spatial light modulator 5 and emits it toward the objective lens 7 during recording. On the other hand, during reproduction, the reproduction light incident from the objective lens 7 is reflected toward the light modulation data reproduction means 14.

  The objective lens 7 converges the incident recording light at the recording position 92a during recording, and emits the reproducing light toward the half mirror 6 during reproduction.

  The reflecting plate 8 reflects the reference light emitted from the beam splitter 4 toward the prism 9. The reference light incident on the prism 9 is refracted and enters the objective lens 10. The reference light incident on the objective lens 10 is irradiated toward the recording position 92a so as to overlap the recording light. Since the reference light is not modulated like the recording light, the intensity of the reference light has a constant value. In the present embodiment, when 37.5% of all pixels of the spatial light modulator 5 are bright, the intensity ratio between the recording light applied to the recording position 92a and the reference light applied to the recording position 92a is 1. It is set to be.

  As shown in FIG. 2, the convolution data generation means 11 includes four convolution calculators 11a, 11b, 11c, and 11d arranged in parallel, and generates four convolution data from information to be recorded. When generating convolution data from information to be recorded, an information string that acts on information to be recorded is referred to as a check code “C”. The check code “C” consists of 2 bits, for example. "00" is used as the check code "C" in the convolution calculator 11a, "01" is used in the convolution calculator 11b, "10" is used in the convolution calculator 11c, and "11" is used in the convolution calculator 11d. . FIG. 3 is an explanatory diagram for explaining the convolution calculation in the convolution calculators 11a, 11b, 11c, and 11d. In the convolution calculators 11a, 11b, 11c, and 11d, first, information to be recorded is divided every two bits. In FIG. 3, the divided information strings for every 2 bits are indicated by M1, M2, M3, M4, M5 and M6. Next, an exclusive OR of each bit of M1 and check code “C” is calculated, and a 2-bit information string obtained by the calculation is N1. Next, an exclusive OR for each bit of N1 and M2 is calculated, and a 2-bit information string obtained by the calculation is N2. Further, an exclusive OR for each bit of N2 and M3 is calculated, and a 2-bit information string obtained by the calculation is N3. By repeating this, N1, N2, N3, N4, N5, and N6 are created, and these are combined to generate convolution data.

  The data conversion means 12 comprises four two-dimensional encoders 12a, 12b, 12c and 12d arranged in parallel as shown in FIG. 2, and is a light capable of displaying the convolution data and the check code “C” on the spatial light modulation means 5. Convert to modulated data. The two-dimensional encoders 12a, 12b, 12c, and 12d are provided with a conversion table that associates a 3-bit information string and eight types of pixel patterns as shown in FIG. The two-dimensional encoders 12a, 12b, 12c, and 12d perform two-dimensional encoding that converts the convolution data into pixel patterns every 3 bits according to the conversion table of FIG. The two-dimensional encoder 12a two-dimensionally encodes the check code “00” and the convolution data generated by the convolution calculator 11a. The two-dimensional encoder 12b two-dimensionally encodes the check code “01” and the convolution data generated by the convolution calculator 11b. The two-dimensional encoder 12c two-dimensionally encodes the check code “10” and the convolution data generated by the convolution calculator 11c. The two-dimensional encoder 12d two-dimensionally encodes the check code “11” and the convolution data generated by the convolution calculator 11d. The two-dimensional encoding of the check code “C” is performed, for example, by adding 0 to the head of each check code to form 3 bits and converting according to the conversion table of FIG.

  The light modulation data selection means 13 calculates the light use efficiency of the four light modulation data obtained by the two-dimensional encoders 12a, 12b, 12c, and 12d, and the calculated light use efficiency falls within a desired range. Select the light modulation data. The light use efficiency of the light modulation data is the ratio of the bright pixels in all the pixels of the light modulation data. The desired range is, for example, 33.75% to 41.25%. When there are a plurality of light modulation data items that fall within this range, the light utilization efficiency closer to 37.5% is selected as the optimum light modulation data. When there are a plurality of optimum light modulation data, the optimum light modulation data corresponding to a smaller check code “C” is selected.

  As the number of bits of the information to be recorded and the convolution data increases, the ratio of the pixel pattern corresponding to the check code “C” in the light modulation data decreases. For this reason, the brightness of the pixel pattern corresponding to the inspection code “C” does not significantly affect the light utilization efficiency of the light modulation data. Therefore, the light use efficiency of the light modulation data may be estimated by ignoring the pixel pattern corresponding to the check code “C”.

  FIG. 5 shows a configuration diagram of a reproducing mechanism in the hologram recording apparatus A. When the interference fringes formed on the recording layer 92 of the hologram recording medium B are irradiated with the reference light at the same wavelength and incident angle as in recording, reproduction light is generated. The information recorded on the hologram recording medium B can be obtained by acquiring this reproduction light by the light modulation data reproduction means 14 and returning it to the original information by the decoding means 15 and the convolution demodulation means 16. In order to increase the SN ratio of the reproduction light, the intensity ratio between the recording light and the reference light at the time of recording needs to have a certain relationship. In general, it is preferable that the intensity ratio of the recording light and the reference light is 1. FIG. 6 is a simplified explanatory diagram showing the relationship between the intensity ratio between the recording light and the reference light during recording and the SN ratio of the reproduction light. According to FIG. 6, in order to obtain an S / N ratio necessary for sufficiently accurate reproduction, the intensity ratio between the recording light and the reference light needs to be within 1-α to 1 + α. The value of α is determined by the characteristics of the hologram recording medium B, error check accuracy, and the like, and is 0.1 here, for example. However, FIG. 6 is an example, and the optimum SN ratio is not always 1. When the optimum value is A (≠ 1), the intensity ratio is within A−α to A + α.

  The light modulation data reproducing means 14 is, for example, a CCD, and can receive the reproduction light reflected by the half mirror 6, and can read a bright and dark pixel pattern recorded as a hologram from the reproduction light. The bright and dark pixel pattern read here corresponds to the light modulation data selected by the light modulation data selection means 13.

  The decoding unit 15 is a two-dimensional decoder for returning the optical modulation data obtained by the optical modulation data reproducing unit 14 to the convolution data and the check code “C” corresponding thereto. The decoding unit 15 has a conversion table that associates a pixel pattern with a 3-bit information string in the opposite direction to the conversion table of FIG. 4, and performs two-dimensional decoding using this conversion table.

  The convolutional demodulating means 16 is an arithmetic unit for obtaining original information recorded from the convolutional data obtained by the decoding means 15 and the check code “C” corresponding thereto. As shown in FIG. 7, the convolution demodulation means 16 first divides the convolution data into N1, N2, N3, N4, N5, N6. Subsequently, M1 is restored by calculating the exclusive OR of N1 and check code “C” for each bit. Next, M2 is restored by calculating the bitwise exclusive OR of N1 and N2. Next, M3 is restored by calculating an exclusive OR for each bit of N2 and N3. Such calculation is repeated, and the original information is restored by combining M1, M2, M3, M4, M5, M6.

  Next, a hologram recording method using such a hologram recording apparatus A will be described with reference to FIG.

  First, the convolution data generation means 11 performs a convolution operation on information to be recorded input from, for example, a host computer, and transmits the obtained convolution data to the data conversion means 12. (Step S1).

  Next, the data conversion unit 12 generates optical modulation data by two-dimensionally encoding the received convolution data, and transmits the obtained optical modulation data to the optical modulation data selection unit 13 (step S2).

  Next, the light modulation data selection means 13 selects the optimum light modulation data from the received light modulation data, and transmits it to the spatial light modulation means 5 (step S3).

  Next, the spatial light modulator 5 generates recording light based on the received light modulation data, irradiates the recording light to the recording position 92a of the hologram recording medium B, and simultaneously records the recording position 92a of the hologram recording medium B. Is irradiated with reference light (step S4).

  Through the above steps S1 to S4, the hologram recording apparatus A can generate the recording light based on the information to be recorded, and perform the hologram recording by causing the recording light and the reference light to interfere at the recording position 92a.

  Next, the operation of the hologram recording apparatus A will be described with reference to a specific example shown in FIG.

  Here, for example, “100010100111” is recorded on the hologram recording medium B by using the hologram recording apparatus A. First, “100010100111” is input to the convolution data generation means 11. At this time, the convolution calculator 11a obtains “101000101100” as the convolution data using the check code “00”. In the convolution calculator 11b, “111101111001” is obtained as convolution data using the check code “01”. In the convolution calculator 11c, “000010000110” is obtained as convolution data using the check code “10”. In the convolution calculator 11d, “01011011011” is obtained as convolution data using the check code “11”.

  The convolution data obtained by the convolution calculators 11a, 11b, 11c, and 11d are transmitted to the two-dimensional encoders 12a, 12b, 12c, and 12d together with the check code “C” corresponding thereto. The two-dimensional encoder 12a converts “101”, “000”, “101”, “100” into a pixel pattern according to the conversion table of FIG. 4, and simultaneously sets the check code “00” to “000” in FIG. The pixel pattern is converted according to the conversion table. The pixel pattern obtained by such conversion is used as light modulation data and transmitted to the light modulation data selection means 13. Similarly, the two-dimensional encoders 12 b, 12 c, and 12 d convert the convolution data into a pixel pattern every 3 bits to generate light modulation data, and transmit this light modulation data to the light modulation data selection means 13.

  The light modulation data selection means 13 calculates the light use efficiency of the received light modulation data. The light use efficiency of the light modulation data obtained by the two-dimensional encoders 12a, 12b, 12c, and 12d is, for example, 25.0%, 35.0%, 40.0%, and 50.0%, respectively. Among them, the light use efficiency within the range of 33.75% to 41.25% is the light modulation data transmitted from the two-dimensional encoders 12b and 12c. Since 35.0% and 40.0% are both 2.5% different from 37.5%, the corresponding check code “C” is sent from the smaller two-dimensional encoder 12b. The light modulation data is selected.

  The spatial light modulation means 5 performs control to switch the brightness of each pixel so as to display the light modulation data transmitted from the two-dimensional encoder 12b selected in this way. When the brightness and darkness of all the pixels of the spatial light modulation means 5 are switched by the selected light modulation data, the bright pixels are 33.75% to 41.25% of all the pixels. Therefore, in the hologram recording apparatus A, the recording light is modulated by the spatial light modulation means 5 in which 33.75% to 41.25% of all pixels are bright. When the recording light 92 modulated by the spatial light modulator 5 and the reference light are irradiated onto the recording position 92a, interference fringes are recorded as a hologram. The intensity of the reference light at the recording position 92a is set so that the ratio to the intensity of the recording light when 37.5% of all the pixels of the spatial light modulator 5 is bright is 1, so that the recording position 92a The intensity ratio between the recording light and the reference light is 0.9 to 1.1.

  Further, the hologram recorded in this way can be reproduced as shown in FIG. When the recording position 92a is irradiated with reference light having the same wavelength and the same incident angle as in recording, reproduction light is generated. This reproduced light is received by the light modulation data reproducing means 14 through the objective lens 7 and the half mirror 6. The light modulation data reproducing unit 14 can acquire a pixel pattern corresponding to the selected light modulation data. When this pixel pattern is converted by the decoding means 15, “111101111001” and check code “01” obtained by the convolution calculator 11b can be restored. Further, when “111101111001” and the check code “01” are input to the convolutional demodulation means 16, the original “100010100111” can be restored.

  In such a hologram recording apparatus A, since a 3-bit information string is represented by one pixel block, the coding rate is 0.75. Furthermore, since the intensity ratio between the recording light and the reference light at the recording position 92a is 0.9 to 1.1, an SN ratio necessary for sufficiently accurate reproduction can be obtained. Thus, by performing the recording method as described above using the hologram recording apparatus A, it is possible to obtain reproduction light having an SN ratio necessary for sufficiently accurate reproduction while improving the coding rate.

  Further, in the above method, the check code “C” is 2 bits, but the number of bits can be increased. Increasing the number of bits of the check code “C” increases the number of check codes “C” and can generate more convolution data, so that light modulation data with a light utilization efficiency closer to 37.5% is obtained. Probability increases. When the light modulation data whose light utilization efficiency is close to 37.5% increases, the selected light modulation data whose light utilization efficiency is close to 37.5% increases, and the recording light and the reference light at the recording position 92a are increased. The intensity ratio is closer to 1. As described above, in the hologram recording apparatus A, it is possible to further increase the SN ratio of the reproduction light by increasing the number of bits of the inspection code “C”.

  The scope of the present invention is not limited to the above-described embodiments, and any change within the scope of the matters described in each claim is included in the scope of the present invention. For example, in the above-described embodiment, the pixel pattern for each block is used in the data conversion unit. However, even when the light conversion data is converted by simply replacing 1 and 0 with the brightness of each pixel, Thus, it is possible to obtain an effect such as preventing the increase of the extreme.

  Further, in the above embodiment, the convolution data generating means 11 arranges four convolution calculators in parallel and performs the respective calculations, but the convolution data may be sequentially calculated by one convolution calculator. Similarly, in the case of the two-dimensional encoder in the data converter 12, the conversion process may be sequentially performed by one two-dimensional encoder.

  Furthermore, in the above embodiment, the pixel pattern used in the data conversion unit is composed of four pixels, but a pixel pattern composed of more pixels may be used.

It is a block diagram which shows an example of the hologram recording device which concerns on this invention. It is a principal part block diagram of the hologram recording apparatus of FIG. It is explanatory drawing of the calculation in a convolution calculator. It is an example of the conversion table in a two-dimensional encoder. It is a block diagram of the reproduction | regeneration mechanism in the hologram recording apparatus of FIG. It is explanatory drawing which shows the relationship between the intensity ratio of recording light and reproduction | regeneration light, and SN ratio of reproduction | regeneration light. It is explanatory drawing of the calculation in a convolution demodulation means. It is a flowchart figure which shows an example of the hologram recording method which concerns on this invention. It is a pixel pattern in a conventional hologram recording apparatus.

Explanation of symbols

A Hologram recording apparatus 5 Spatial light modulation means 11 Convolution data generation means 12 Data conversion means 13 Light modulation data selection means 14 Light modulation data reproduction means 15 Decoding means 16 Convolution demodulation means

Claims (6)

A hologram recording apparatus that records a hologram by causing interference in a hologram recording medium with recording light that is light-modulated based on information to be recorded and reference light,
A convolution data generating means for generating a plurality of convolution data by performing a convolution operation of the information to be recorded using a plurality of check codes;
Data conversion means for converting the plurality of convolution data into a plurality of light modulation data;
Light modulation data selection means for calculating light utilization efficiency for each of the plurality of light modulation data and selecting light modulation data in which the light utilization efficiency falls within a predetermined range;
Spatial light modulation means for generating the recording light by performing light modulation based on the selected light modulation data;
A holographic recording apparatus comprising:   The hologram recording apparatus according to claim 1, wherein the data conversion means converts the convolution data into the light modulation data by two-dimensionally encoding the data.   The data conversion means divides the convolution data into a predetermined number and performs two-dimensional encoding using a plurality of pixel patterns having different light utilization efficiencies for each of the divided data. The hologram recording apparatus according to claim 2, which generates modulation data.   4. The hologram recording apparatus according to claim 1, wherein the data conversion unit converts the check code used when generating the convolution data as a part of the light modulation data.   Reproducing light by irradiating the hologram recording medium with the same reference light as at the time of recording, and reproducing light modulation data reproducing means for reproducing the original light modulation data from the reproduction light, and reproducing the light modulation data Decoding means for obtaining the original convolution data and the check code corresponding thereto by decoding, and convolutional demodulation of the convolution data obtained by decoding with the check code is recorded as the hologram. The hologram recording apparatus according to claim 4, further comprising convolutional demodulation means for obtaining original information. A hologram recording method for recording a hologram by causing interference in a hologram recording medium with recording light that is light-modulated based on information to be recorded and reference light,
By performing a convolution operation of the information to be recorded using a plurality of check codes, generating a plurality of convolution data, converting the plurality of convolution data into a plurality of light modulation data,
Calculate the light use efficiency for each of the plurality of light modulation data, select the light modulation data in which the light use efficiency falls within a predetermined range,
Based on the selected light modulation data, the convolution data is two-dimensionally encoded, and then the convolution data is divided into a predetermined number, and a plurality of pixel patterns having different light utilization efficiencies are used for each divided data. By performing two-dimensional encoding, light modulation data consisting of these pixel patterns is generated,
A hologram recording method, wherein the recording light is generated by performing light modulation based on the generated light modulation data.

Images