JP2006243262A - Hologram recording method, hologram recording medium, and hologram reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hologram recording method etc., capable of appropriately reading data out of a recording medium, especially, even if a proper wavelength band for reading the data varies with temperature. <P>SOLUTION: An embodiment of the present invention controls a recording wavelength in recording the data to the recording medium to a narrow wavelength band and, for example, a proper wavelength band, when a surface light emission laser is at ≥50°C is used. The surface light emission laser gradually decreases in proper wavelength band as the temperature rises, so the proper wavelength band when the surface light emission laser is at 50°C is very narrow and when the wavelength band of the recording wavelength is controlled under such a strict condition, the proper wavelength band expands at a temperature of <50°C to the short-wavelength side while including the wavelength band in the recording when the data are read during reproduction by using the surface emission laser, so that the data can appropriately and securely be read. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hologram recording method, a hologram recording medium, and a hologram reproducing method for recording data on a recording medium, for example, by causing reference light and data light to interfere with each other.

  Hologram recording is performed by causing recording reference light and data light including two-dimensional digital video data to interfere with a recording medium. Recording by hologram has the advantage that multiple recording can be performed in the same recording area and recording / reproduction can be performed at a high rate. There are various methods for multiplex recording, and well-known methods include angle multiplexing and wavelength multiplexing. Of these, wavelength multiplexing is advantageous in that recording is performed while changing the recording wavelength, and mechanical operation is unnecessary as in angle multiplexing.

On the other hand, in hologram reproduction, when reproduction reference light is incident on the recording medium, the reproduction reference light is diffracted by the interference fringes of data recorded on the recording medium according to the Bragg conditional expression, and reproduction light (diffracted light) Is emitted. Then, the content of the data included in the reproduction light is read out by an image pickup device such as a CCD or a CMOS.
JP 2002-3001A

  By the way, when a surface emitting laser (VCSEL) is used as the reproduction reference light, an appropriate wavelength band of the surface emitting laser varies depending on a temperature change (temperature change). FIG. 3 is a graph showing the relationship between the wavelength band and the light intensity ratio for each temperature of the surface emitting laser. The “light intensity ratio” is a ratio with a light intensity (mW) of a certain value as a reference value.

  As shown in FIG. 3, when the temperature rises, the light intensity ratio decreases and the wavelength band in which the light intensity is greater than 0 (mW) is also narrowed. Here, the “appropriate wavelength band” is defined as a wavelength band capable of obtaining a light intensity of an arbitrarily determined predetermined value or more.

  For example, it is assumed that the wavelength of the recording reference light is a wavelength λx (nm) between λ1 (nm) and λ2 (nm) shown in FIG. In this case, in principle, the incident angle of the reproduction reference light is the same as the incident angle of the recording reference light, and if the reproduction wavelength is λx (nm), the data recorded at the wavelength of λx (nm) is However, if the reproduction temperature is 40 ° C. or higher, the light intensity becomes 0 at the wavelength of λxnm as shown in FIG. 3, and reproduction is impossible. End up.

  When the temperature rises in this way, as shown in FIG. 3, the peak of the light intensity of the surface emitting laser shifts to the long wavelength side and the appropriate wavelength band gradually narrows. When the temperature at the time of reproduction is high, there is a possibility that reading cannot be performed.

  Further, when the hologram recording medium expands and contracts due to a temperature change, the pitch width of the data recorded on the recording medium changes, so that the wavelength at which light is diffracted becomes different from the wavelength of the recording reference light. In consideration of the point, it is necessary to appropriately read out all recorded data during reproduction.

  The above-mentioned Patent Document 1 focuses on the phenomenon of dimensional change due to the temperature change of the recording medium, and improves the structure of the recording medium to reduce the influence of the recorded hologram information on the temperature change. It is said. However, Patent Document 1 does not describe anything about the temperature dependency of the surface emitting laser, and therefore, naturally, there is no description of the above-described problem of the present invention and the means for solving the problem.

  Therefore, the present invention is for solving the above-described conventional problems, and in particular, even when the appropriate wavelength band for reading data recorded on the recording medium is fluctuated due to a temperature change, the data is appropriately read. It is an object of the present invention to provide a hologram recording method, a hologram recording medium, and a hologram reproducing method that are made possible.

The present invention relates to a hologram recording method for recording data on a recording medium by causing interference between a recording reference beam and a data beam.
The proper wavelength band on the high temperature side of the surface-emitting laser whose appropriate wavelength band becomes narrower as the temperature rises from the low temperature side to the high temperature side is used as the wavelength band of the recording wavelength.

  In the present invention, the recording wavelength when data is recorded on the recording medium is controlled to a narrow wavelength band, and an appropriate wavelength band on the high temperature side of the surface emitting laser is used as the reference. As shown in FIG. 3, in the surface emitting laser (VCSEL), as the temperature increases, the peak of the light intensity shifts to the longer wavelength side, and the appropriate wavelength band is gradually narrowed. The “appropriate wavelength band” is defined as an arbitrarily set wavelength band that can obtain a certain light intensity or higher.

  As shown in FIG. 3, the appropriate wavelength band of, for example, 50 ° C. on the high temperature side is very narrow. By controlling the wavelength band of the recording wavelength under such severe conditions, the surface light emission is reproduced during reproduction. When reading the data using a laser, at the reproduction temperature lower than 50 ° C. described above, the appropriate wavelength band extends to the short wavelength side while including the wavelength band at the time of recording, so the data is read appropriately and reliably. Is possible.

  The hologram recording medium of the present invention is characterized in that data is recorded by using the recording method described above. At this time, it is preferable that the recording medium expands as the temperature rises. That is, when the temperature is lowered, the recording medium contracts, the pitch width of the data recorded on the recording medium is narrowed, and the wavelength of light necessary for reading the data is shifted to the short wavelength side. For this reason, by setting the temperature at the time of recording to a temperature higher than the temperature at the time of reproduction, the above-mentioned shrinkage of the recording medium occurs at the time of reproduction, and the wavelength of light necessary for reading the data is shifted to the short wavelength side. To do. At this time, as described above, the appropriate wavelength band at the time of reproduction extends to the short wavelength side while including the wavelength band at the time of recording, so that the data required for reading is shifted to the short wavelength side appropriately and reliably. Is possible.

  The hologram reproduction method according to the present invention includes a reproduction reference beam and an imaging unit that acquires data recorded on a recording medium, uses the surface emitting laser as the reproduction reference beam, and is lower than the high temperature side. Data is read from the hologram recording medium described above at a temperature. As described above, when reading the data using the surface emitting laser at the time of reproduction, the appropriate wavelength band at the time of reproduction extends to the short wavelength side while including the wavelength band at the time of recording. Can be read appropriately and reliably. Even when the wavelength of light required for reading data shifts to the short wavelength side due to shrinkage due to the temperature drop of the recording medium, as described above, the appropriate wavelength band during reproduction is the same as the wavelength band during recording. Since it spreads to the short wavelength side while being included, it becomes possible to read the data appropriately.

  In the present invention, the recording wavelength when data is recorded on the recording medium is controlled to a narrow wavelength band, and an appropriate wavelength band on the high temperature side of the surface emitting laser is used as the reference. In the surface emitting laser (VCSEL), as the temperature increases, the peak of the light intensity shifts to the long wavelength side, and the appropriate wavelength band is gradually narrowed. For this reason, the appropriate wavelength band on the high temperature side of the surface-emitting laser is very narrow. By controlling the wavelength band of the recording wavelength under such severe conditions, the surface-emitting laser is used during reproduction. When reading the data, at a reproduction temperature lower than the high temperature side, the appropriate wavelength band extends to the short wavelength side while including the wavelength band at the time of recording, and the data can be read appropriately and reliably.

  FIG. 1 is a conceptual diagram for recording digital video data on a recording medium by a hologram recording device as an embodiment of the present invention, and FIG. 2 is a conceptual diagram for reproducing digital video data from the recording medium by a hologram reproducing device.

  In the hologram recording apparatus shown in FIG. 1, light (coherent light) emitted from a light source 20 is divided in two directions by a beam splitter (not shown). One of the divided lights is incident as a reference light (recording reference light) 28 and the other as data light 21 at a certain point on the recording medium 27. As shown in FIG. 1, the data light 21 is incident on a spatial light modulator 23. For example, image data of an object or the like is input to the spatial light modulator 23 as a binary (0, 1) digital signal (recording signal). The spatial light modulator 23 converts the digital signal into “bright, dark” two-dimensional digital video data. For example, a “0” signal is converted into “bright” digital video data, and a “1” signal is converted into “dark” digital video data. The “bright” digital video data transmits light, while the “dark” digital video data blocks light. The spatial light modulator 23 is a liquid crystal element, for example.

  The light intensity of the data light 21 is spatially modulated by passing through the air conditioning light modulator 23 and is incident on a certain point on the recording medium 27.

  As shown in FIG. 1, when the reference light 28 and the data light 21 are irradiated onto the recording medium 27, a large number of digital video data 30 is recorded in an area where the reference light 28 and the data light 21 overlap ( 4 and 5). The recorded digital video data 30 appears in the recording medium 27 as interference fringes (holograms).

  In the hologram recording apparatus, a large number of the digital video data 30 can be recorded in the same area of the recording medium 27. So-called multiplex recording is possible. As a multiplex recording method, recording is performed by changing the incident angle θ1 of the reference light 28 with respect to the surface 27a of the recording medium 27 while keeping the recording wavelength constant, or by changing the incident angle θ1. There are wavelength multiplexing, etc., in which recording is performed by changing the recording wavelength while keeping it constant.

  Next, when the digital video data 30 recorded on the recording medium 27 is reproduced using the hologram reproducing apparatus shown in FIG. 2, the reference light (reproduced reference light) 40 is emitted from the light source 41 as shown in FIG. The recording medium 27 is irradiated. At this time, when the digital video data 30 is recorded on the recording medium 27 by wavelength multiplexing as described above, the incident angle θ2 of the reference light 40 with respect to the surface 27a of the recording medium 27 is the incidence of the reference light 28 at the time of recording in FIG. It is the same value as the angle θ1. On the other hand, when the recording medium 27 is irradiated with the reference light 40 while changing the wavelength of the reference light 40, the light is diffracted by the interference fringes satisfying the Bragg conditional expression, and the reproduced light (diffracted light) 43 becomes the digital light. The video data 30 appears, and the image sensor 42 such as a CCD or CMOS is arranged on the reproduction light 43, whereby the contents of the digital video data 30 recorded on the recording medium 27 can be read. Has been. In principle, at the time of reproduction, it is possible to read out all the digital video data 30 by causing the above-mentioned light diffraction while changing the wavelength within the same wavelength band as the recording wavelength.

  The light source 41 shown in FIG. 2 is a VCSEL (surface emitting laser) array, and a surface emitting laser is irradiated from the light source 41 as reproduction reference light 40. FIG. 3 shows an example of the relationship between the wavelength and the light intensity due to the temperature change of the surface emitting laser.

  As can be seen from FIG. 3, the appropriate wavelength band gradually narrows as the temperature gradually increases. The “light intensity ratio” shown in FIG. 3 is “1” with a certain light intensity as a reference value, and is a ratio to the reference value. The “appropriate wavelength band” is defined as a wavelength band having a light intensity ratio (set to 0.5 in the present embodiment) that is not less than a predetermined value set arbitrarily.

  As shown in FIG. 3, the peak of the light intensity ratio gradually decreases as the temperature increases. Moreover, it can be seen that the peak shifts to the longer wavelength side as the temperature increases. As shown in FIG. 3, the appropriate wavelength band at 50 ° C. is narrower than any of the appropriate wavelength bands of 20 ° C., 30 ° C., and 40 ° C., and is included in each of the appropriate wavelength bands of 20 ° C., 30 ° C., and 40 ° C. Is done. Each appropriate wavelength band in the order of 40 ° C., 30 ° C., and 20 ° C. spreads toward the shorter wavelength side than the appropriate wavelength band of 50 ° C.

  In the present invention, in the hologram recording method performed using the hologram recording apparatus shown in FIG. 1, the appropriate wavelength band at 50 ° C. or higher of the surface emitting laser shown in FIG. 3 is used as the wavelength band of the recording wavelength. Therefore, the wavelength band of the recording wavelength is in the range of λy1 (nm) to λy2 (nm) (has a width of about 2 to 3 nm). Therefore, the wavelength of the light emitted from the light source 20 shown in FIG. 1 is in the range of λy1 (nm) to λy2 (nm), and the digital video data 30 is recorded on the recording medium 27 within this range, for example, wavelength multiplexing. At. The light source 20 used in the hologram recording apparatus is not particularly limited, such as a fixed laser or a gas laser.

  Next, when reproducing a hologram using the hologram reproducing apparatus shown in FIG. 2, a VCSEL array is used for the light source 41 as described above, and a surface emitting laser is irradiated from the light source 41 as the reproduction reference light 40. At this time, the temperature is not adjusted and the hologram is reproduced at the temperature. For example, when the temperature is 20 ° C., as shown in FIG. 3, the appropriate wavelength band of the surface emitting laser is in the range of λz1 (nm) to λz2 (nm) (approximately 3 to 5 nm in width), It includes λy1 (nm) to λy2 (nm) which is a wavelength band at the time of recording. Therefore, at the time of reproducing the hologram, if the wavelength of the surface emitting laser is changed within the range of λz1 (nm) to λz2 (nm) while changing the input current, all the digital video data 30 can be read out without fail. I can do it. If the temperature is 50 ° C. or lower, as described above, the wavelength band at the time of recording is included in the appropriate wavelength band at the time of reproduction, so that all the digital video data 30 can be read out appropriately. Even if the temperature at the time of reproduction becomes higher than 50 ° C., a cooling means is provided in the hologram reproducing apparatus shown in FIG. 2 so that the temperature at the time of reproduction is 50 ° C. or less by the cooling means. If the temperature is adjusted, the appropriate wavelength band at the time of reproduction fluctuates as shown in FIG. 3, and the surface emitting laser spreads while including the wavelength band at the time of recording adjusted within the appropriate wavelength band when the surface emitting laser is 50 ° C., All digital video data 30 can be read appropriately and reliably.

  By the way, the temperature at which the hologram is recorded on the recording medium 27 need not be 50 ° C. based on the graph shown in FIG. FIG. 3 shows the temperature characteristics of the wavelength of the surface emitting laser, and what is important at the time of recording is not the temperature at the time of recording but the wavelength band. That is, if hologram recording is performed within the range of λy1 (nm) to λy2 (nm) which is an appropriate wavelength band when the surface emitting laser is 50 ° C., the temperature at that time does not need to be 50 ° C. separately. However, as described below, the temperature during recording is preferably higher than the temperature during reproduction. Specifically, it is more preferable to set the temperature during recording to 50 ° C. or higher.

  The recording medium 27 has a property of expanding as the temperature rises, and FIG. 4 shows a recording state of the digital video data 30 recorded on the recording medium 27 at a certain wavelength at a certain temperature. FIG. 5 shows the recording state of the digital video data 30 when the temperature is increased and the recording medium 27 is expanded. The pitch width B between the digital video data 30 in FIG. 5 is the digital video data in FIG. The wavelength required to read the digital video data 30 recorded in FIG. 5 is larger than the wavelength required to read the digital video data 30 recorded in FIG. Also gets longer. As described above, since the pitch width of the digital video data 30 recorded on the recording medium 27 fluctuates due to temperature change, when the temperature changes, the wavelength necessary for reading the digital video data 30 is the same as that at the time of recording. It will be different from the wavelength.

  However, as shown in FIG. 3, when the wavelength band at the time of recording is set to the appropriate wavelength band when the surface emitting laser is 50 ° C. and set within the range of λy1 (nm) to λy2 (nm), When the temperature of the surface emitting laser is 20 ° C., the appropriate wavelength band of the surface emitting laser includes the appropriate wavelength band at 50 ° C. and spreads to the short wavelength side, and ranges from λz1 (nm) to λz2 (nm). Be inside. At this time, if the temperature at the time of recording is set higher than the temperature at the time of reproduction, for example, it is assumed that a certain digital video data 30 is recorded at the wavelength λy1 (nm) at the point C shown in FIG. As the temperature decreases during reproduction, the recording medium 27 contracts and changes from the recording state of FIG. 5 to the recording state of FIG. For this reason, the wavelength when reproducing the digital video data 30 recorded at the wavelength of λy1 (nm) is the wavelength at the point D on the shorter wavelength side than λy1 (nm). The appropriate wavelength band of the surface emitting laser at the time of reproduction includes the appropriate wavelength band at 50 ° C. and spreads to the short wavelength side, so that the wavelength for reading is shifted to the short wavelength side due to the shrinkage of the recording medium 27. The digital video data 30 can also be read appropriately. On the other hand, if the temperature at the time of recording is lower than the temperature at the time of reproduction, the recording wavelength is within the range of λy1 (nm) to λy2 (nm) which is an appropriate wavelength band when the surface emitting laser is 50 ° C. 3, the digital video data 30 recorded at the wavelength λy2 (nm) at the point E shown in FIG. 3 is recorded in the recording state of FIG. 4 because the temperature at the time of reproduction is higher than the temperature at the time of recording. The digital video data 30 that has changed to the recording state of FIG. 5 and has been recorded at a wavelength of λy2 (nm) is reproduced at a wavelength F higher than λy2 (nm). At this time, as shown in FIG. 3, even if the appropriate wavelength band of the surface emitting laser at the time of reproduction is set within the range of λz1 (nm) to λz2 (nm) at 20 ° C., the appropriate wavelength at the time of reproduction is set. Since the band hardly spreads to the longer wavelength side than the wavelength band of the recording wavelength, the digital video data 30 recorded at the wavelength λy2 (nm) may not be properly reproduced. For this reason, the temperature during recording is preferably higher than the temperature during reproduction. Specifically, if the temperature at the time of recording is set to 50 ° C. or higher based on FIG. 3, all the digital video data 30 is appropriately reproduced unless the temperature at the time of reproduction is higher than 50 ° C. I can do it. A temperature adjusting means is provided in the hologram recording device, and the temperature during recording is adjusted to 50 ° C. or higher. If the temperature during reproduction is higher than 50 ° C., as described above, a cooling means or the like is provided in the hologram reproducing device, and the temperature during reproduction is higher than 50 ° C. by the cooling means or the like. What is necessary is just to adjust so that it may become low temperature.

As described above, when the digital video data 30 recorded at the wavelength C is reproduced, even if the wavelength necessary for reading varies due to the shrinkage of the recording medium 27 to the point D on the short wavelength side, λz1 (nm) If reproduction is performed while changing the wavelength within ~ λz2 (nm) (appropriate wavelength band when the surface emitting laser is 20 ° C.), the reproduction reference light 40 having a short wavelength at the point D is irradiated. The digital video data 30 recorded with the wavelength at the point C can be read out. At this time, it is not necessary to check whether or not the digital video data 30 read at the wavelength at the point D is the same as the digital video data 30 recorded at the wavelength at the point C at the time of recording. All the digital video data 30 is read while changing the wavelength within the wavelength band of (nm) to λz2 (nm). The digital video data 30 also includes address data. Based on the address data, the digital video data 30 is rearranged, unnecessary digital video data 30 is erased, and the like. Play back image data.
The hologram recording method of the present invention is particularly effective for wavelength multiplexing.

Conceptual diagram (partial cross-sectional view) of recording digital video data on a recording medium by a hologram recording device, Conceptual diagram (partial sectional view) of reproducing digital video data from a recording medium by a hologram reproducing device, A graph showing a relationship between a wavelength and a light intensity at each temperature of a surface emitting laser (VCSEL); A conceptual diagram for explaining a recording state of digital video data recorded on a recording medium, FIG. 4 is a conceptual diagram for explaining a recording state of digital video data recorded on a recording medium at a higher temperature than in FIG.

Explanation of symbols

20, 41 Light source 21 Data light 27 Recording medium 28 Recording reference light 30 Digital video data 40 Reproduction reference light 43 Reproduction light 42 Image sensor A, B Pitch width

Claims (4)

In a hologram recording method for recording data on a recording medium by causing interference between a recording reference beam and a data beam,
A hologram recording method characterized in that the appropriate wavelength band on the high temperature side of the surface emitting laser, whose appropriate wavelength band becomes narrower as the temperature rises from the low temperature side to the high temperature side, is used as the wavelength band of the recording wavelength.   A hologram recording medium on which data is recorded using the recording method according to claim 1.   The hologram recording medium according to claim 2, wherein the recording medium has a property of expanding as the temperature rises.   3. A reproduction reference beam, and an imaging unit that acquires data recorded on a recording medium, wherein the surface emitting laser is used for the reproduction reference beam, and the temperature is lower than the high temperature side. 4. A hologram reproducing method comprising reading data from the hologram recording medium according to item 3.

Images