KR20080064359A - Method and apparatus for recording data on a holographic storage medium, and holographic storage medium - Google Patents

Abstract

A method and an apparatus for recording data on a holographic storage medium, and a holographic storage medium are provided to increase tilt tolerance when a reference light is inclined in a tangential direction by using a light processor. An apparatus for recording data on a holographic storage medium(100) comprises a light processor(410), a control part(420), and a memory(430). The control part controls the light processor to record data in the medium and to play the data from a medium. The light processor includes a laser source(411), a beam splitter(412), a first reflector(413), a spatial light modulator(414), a first lens(415), a second reflector(416), a second lens(417), a third lens(418), and a detection part(419). The light processor records the data so that a tangential incidence angle is smaller than an incidence angle perpendicular to the tangential direction.

Description

Method and apparatus for recording data on a holographic storage medium, and holographic storage medium

1 is a reference diagram for explaining recording and reproduction in optical holography.

2 is a reference diagram for explaining changes in angles and diffraction effects of recording and reproducing light in optical holography.

3 is a diagram illustrating an example of a reproduced image when tilt is generated.

4 is a block diagram showing a schematic configuration of a hologram recording device according to an embodiment of the present invention.

5 is a reference diagram for explaining formation of signal light during data recording according to the present invention.

6A is a diagram illustrating a direction of an SLM according to an embodiment of the present invention.

6B is a diagram illustrating an arrangement of an SLM according to an embodiment of the present invention.

7 is a view showing an optical processing unit of a data recording apparatus according to another embodiment of the present invention.

8 is a flowchart illustrating a method of writing data to a holographic storage medium according to an embodiment of the present invention.

9 is a flowchart illustrating a method of writing data to a holographic storage medium according to another embodiment of the present invention.

The present invention relates to an apparatus and method for recording data in a holographic storage medium, and to a holographic storage medium.

In optical holography, data is stored through the volume, not the surface of the recording medium. The light containing the signal interferes with the reference light in the recording medium to produce an interference grating called a data page. A plurality of gratings are superposed by changing the optical properties of the reference light. This process is called multiplexing. In reading out data, a single reference light is incident on the recording medium under the same conditions as was used for data recording, thereby producing diffracted light representing the stored data page. The diffracted light is detected by a detection array, which extracts the stored data bits from the measured intensity pattern. The data page contains a large number of data bits or pixels. By superimposing such a plurality of data pages on the same volume, the data storage capacity can also be increased.

The hologram is recorded using a reference light and a signal light containing data. At the time of recording, as shown in Fig. 1A, the reference light R and the signal light S interfere with each other to generate an interference pattern, and the interference pattern is transmitted to the medium. At the time of reproduction, as shown in Fig. 1B, when the original reference light R is irradiated to the hologram recorded on the medium, this causes diffraction phenomenon of the recorded hologram to produce the output signal light S. At this time, when the reference light differs from the original light used at the time of recording, the amount or direction of reproduction light changes differently from the originally recorded light. In general, when the difference is larger, the amount of light decreases in the form of a sinc function.

 FIG. 2 is a reference diagram for explaining selectivity according to angles and tilts of recording and reproducing light in optical holography. As the grating recorded by the two plane waves and the conditions of the reference light during reproduction are not satisfied, the angle of the reproduction light changes and the selectivity becomes large.

When the tilt of the disk occurs in the holographic storage medium, that is, when the surface of the disk to be flat is inclined, the angle of the reference light does not coincide with that at the time of recording, resulting in signal degradation. At this time, the tilt of the disk occurs in two directions, a radial direction and a tangential. The radial direction is the scan direction of the reference light, and the tangential direction is a direction perpendicular to the radial direction. The tilt in the radial direction can be compensated by changing the angle of the reference light. That is, the tilt in the radial direction does not cause a big problem in reproducing, but the tilt in the tangential direction deteriorates the reproduction signal unless there is a separate control to compensate for this.

,

는 각각 신호광과 참조광의 웨이브 벡터, z 벡터는 매체에 수직한 방향의 단위 벡터를 나타낸다.

는 y, z 평면으로부터 신호광의 각도,

은 y,z 평면으로부터 참조광의 각도로서 래디얼 방향으로 틸트가 얼마나 발생했는지를 가리키며,

는 x,z 평면으로부터의 신호광의 각도,

은 x,z 평면으로부터의 참조광의 각도로서 탄젠셜 방향으로 틸트가 얼마나 발생했는지를 가리킨다. 틸트의 발생으로 인해서 기록시와 재생시의 참조광 조건이 다르면, 벡터들이 Bragg 조건을 만족하지 못하고 벗어나며, 신호의 세기가 떨어진다. Bragg 조건이란, 특정한 참조광으로 기록된 홀로그램이 동일한 참조광으로 재생될 때 강한 회절 효율을 제공하는 것을 말한다. 독출시의 참조광의 웨이브 벡터가 실질적으로 다를 때, 회절 효율은 작아진다. 참조광 및 신호광의 각도를 이용하여, 틸트에 따른 셀렉티비티를 근사적으로 계산하면 다음과 같다.Referring to FIG. 2, the selectivity by the tangent tilt can be calculated. here,

,

Are the wave vectors of the signal light and the reference light, respectively, and the z vector represents the unit vector in the direction perpendicular to the medium.

Is the angle of the signal light from the y, z plane,

Indicates how much tilt occurred in the radial direction as the angle of the reference light from the y, z plane,

Is the angle of the signal light from the x, z plane,

Is the angle of the reference light from the x, z plane and indicates how much tilt occurred in the tangential direction. If the reference light conditions at the time of recording and reproduction are different due to the occurrence of the tilt, the vectors do not satisfy the Bragg condition, and the signal intensity drops. Bragg condition refers to providing a strong diffraction efficiency when holograms recorded with a particular reference light are reproduced with the same reference light. When the wave vector of the reference light at the time of reading differs substantially, diffraction efficiency becomes small. Using the angles of the reference light and the signal light, the selectivity according to the tilt is approximately calculated as follows.

는 파장을 의미한다. 일반적으로 참조광의 틸트는 0이며, 신호광은 페이지에서의 위치에 따라서 틸트 각도가 달라지게 된다. 따라서 페이지에서 데이터의 위치에 따라 틸트에 대한 셀렉티비티가 변한다. 예를 들어, 미디어의 두께가 2mm, 파장이 205nm일 때, 신호광의 탄젠셜 방향의 틸트에 따른 셀렉티비티는 다음과 같다.Where L is the thickness of the media,

Means wavelength. In general, the tilt of the reference light is zero, and the tilt angle of the signal light varies according to its position on the page. Therefore, the selectivity for the tilt changes depending on the position of the data on the page. For example, when the thickness of the media is 2 mm and the wavelength is 205 nm, the selectivity according to the tilt in the tangential direction of the signal light is as follows.

Signal Light Tilt Selection

0

5.293

One

1.131

5

0.226

10

0.112

20

0.056

30

0.037

As described above, the selectivity decreases as the tilt increases, and the playback image when there is a tilt appears as shown in FIG. 3. If there is a tilt in the tangential direction, the signal in the center portion of the image is well reproduced, whereas the signal is relatively weak at the top and bottom of the image. In order to increase the tolerance (selectivity) with respect to the scan direction tilt, the tilt of the signal light needs to be reduced.

Accordingly, an object of the present invention for solving the above problems is to provide a data recording method, a recording apparatus, and a holographic storage medium on a holographic storage medium for increasing the allowable tolerance for tilt.

According to an aspect of the present invention, there is provided an apparatus for recording data in a holographic storage medium, comprising: an optical processor configured to record data in the holographic storage medium using light modulated signal light and reference light; And a control unit for controlling the light processing unit to record the data, wherein the light processing unit has an incident angle in a radial direction that is a scanning direction of a reference light among angles at which the modulated signal light is incident on the holographic storage medium. This is achieved by a data recording apparatus characterized in that data is recorded so as to be larger than a tangential direction perpendicular to the direction.

The optical processing unit may further include an optical modulator for modulating signal light, and a length of a tangential direction perpendicular to the radial direction is shorter than a length of the radial direction in which the reference light is scanned on the surface of the optical modulator.

The light processor may further include an objective lens unit that blocks the signal light at the edge of the signal light in the direction in which the reference light is scanned from the signal light.

On the other hand, the technical problem, according to another field of the present invention, in the method for recording data in a holographic storage medium, a tangential direction perpendicular to the radial direction than the length of the radial direction in which the signal light is received and the reference light is scanned Modulating the signal light so that the length of the signal is short; And recording data on the holographic storage medium using the light modulated signal light and reference light.

In addition, the technical problem is a method of recording data in a holographic storage medium, comprising the steps of: modulating the signal light; Condensing the modulated signal light such that an incident angle in a radial direction, which is a scan direction of a reference light, is greater than a tangential direction perpendicular to the radial direction among the angles at which the modulated signal light is incident on the holographic storage medium; And recording data on the holographic storage medium using the focused modulated signal light and reference light.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

4 is a block diagram showing a schematic configuration of a hologram recording device according to an embodiment of the present invention.

Referring to FIG. 4, the holographic recording / reproducing apparatus according to the exemplary embodiment of the present invention records data in the optical processing unit 410 into which the holographic storage medium 100 is inserted or in the holographic storage medium 100. The controller 420 controlling the light processor 410 to reproduce data from the 100 and the data read from the holographic storage medium 100 may be temporarily stored or data to be recorded on the holographic storage medium 100 may be stored. Memory 430 for temporary storage. The light processor 410 may include a laser light source 411, a beam splitter 412, a first reflector 413, a spatial light modulator 414, a first lens 415, a second reflector 416, and a second lens ( 417, a third lens 418, and a detector 419.

The controller 420 controls the light processor 410, and also generates a data page including record data, transmits the data page to the light processor 410, and processes the signal reproduced from the light processor 410. When data is recorded on the holographic storage medium 100, coherent laser light output from the laser light source 411 is incident on the beam splitter 412 and is separated into a reference light and a signal light. The signal light is incident on the spatial light modulator 414, and the signal light incident on the spatial light modulator 414 for displaying recording data is spatial light modulation (amplitude modulation). The modulated signal light is condensed on the holographic storage medium 100 by the first lens 415. On the other hand, the reference light is reflected by the second reflector 416 and irradiated to the holographic storage medium 100 by the second lens 417. Therefore, the interference fringe formed by overlapping the signal light and the reference light is recorded in the holographic storage medium 100 as a fine dense pattern.

이

보다 크게 되도록 하여 변조된 신호광을 집광한다. 이를 위한 구체적 실시예는 도 6, 7, 8과 관련하여 후술한다.In particular, the light processing unit 410 according to the present invention has a radial direction in which the tangent direction is perpendicular to the tangent direction among the angles at which the signal light modulated by the spatial light modulator 414 is incident on the holographic storage medium. Record the data so that it is smaller than the angle of incidence. That is, as shown in FIG. 5, when the signal light is modulated by the SLM 414 and condensed on the holographic storage medium 100 by the objective lens unit 415, an angle is obtained.

this

It becomes larger so as to condense the modulated signal light. Specific embodiments for this will be described later with reference to FIGS. 6, 7 and 8.

6A illustrates the direction of an SLM according to an embodiment of the present invention, and FIG. 6B illustrates an arrangement of the SLM according to an embodiment of the present invention.

The arrangement of the light modulator 414 may be adjusted so that the incident angle of the modulated signal light focused on the holographic storage medium 100 appears larger in the radial direction than in the tangential direction. The light modulator 414 is generally a spatial light modulator (SLM) using an element such as an LCD or a DMD, and the signal light passing through the SLM is modulated in the form of a page composed of a plurality of pixels. The SLM is usually manufactured in a rectangular shape. In the surface of this SLM, the SLM is disposed so that the length of the direction perpendicular to the reference light scanning direction is shorter than the length of the direction in which the reference light is scanned. As shown in FIG. 6A, the SLM is disposed to have a shorter length in the tangential direction than the length in the radial direction. That is, the length of a in FIG. 6B is shorter than the length of b so that the modulated signal light passing through the SLM has the form as shown in FIG. 6A.

정도로 할 수 있다. 그러나 SLM의 가로/세로를 반대로 배열한다면 틸트 허용 공차는 0.05

정도로 감소하게 된다.For example, in the case where the focal point of the objective lens is 20mm, the SLM pixel size is 10um, and the DMD of 1366 * 768 is used as the SLM, and the SLM is arranged so that the long axis 1366 of the DMD faces the radial direction, Applying Equation 1 sets the disc's tilt tolerance to 0.1

I can do that. However, if the horizontal / vertical arrangement of the SLMs is reversed, the tilt tolerance is 0.05

To a degree.

7 is a view showing an optical processing unit of a data recording apparatus according to another embodiment of the present invention. FIG. 7 is shown at an angle different from that of the light processor of FIG. 6 for convenience of description.

Referring to FIG. 7, the edge portion of the objective lens unit 415 in the tangential direction may be blocked to adjust the signal light not to pass through. As the signal light at the edge in the tangential direction from the modulated signal light passing through the SLM 414 does not pass through the objective lens, the incidence angle of the modulated signal light focused on the holographic storage medium 100 is radial than the tangential direction. It can be made larger in the direction.

According to another embodiment of the present invention, it is also possible to limit the NA in the tangential direction of the objective lens 415 (the numerical aperture of the objective lens that focuses the signal light) to adjust the size of the signal light. If the light does not seek to be below a certain angle from the central axis, the light refracts out, and the sine of the maximum angle at which light propagates and propagates within the lens without refracting out is called NA. If the NA is made small, the reflection of the signal at the edge of the axis in the tangential direction reduces the tilt tolerance. For this purpose, the objective lens should be a specially manufactured lens such as a cylindrical lens, not a general spherical lens. According to the present embodiment, the incident angle of the modulated signal light focused on the holographic storage medium 100 may be larger in the radial direction than in the tangential direction.

8 is a flowchart illustrating a method of writing data to a holographic storage medium according to an embodiment of the present invention.

In operation 810, the signal light is modulated such that the length of the tangential direction perpendicular to the radial direction is shorter than the length of the radial direction in which the reference light is scanned. The optical modulator 414 is generally a rectangular SLM, and arranges the SLM such that the radial direction in which the reference light is scanned is the long axis, so that the length in the radial direction is longer than the length in the tangential direction.

In step 820, data is written to the holographic storage medium using the reference light and the signal light modulated by the optical modulator 414.

9 is a flowchart illustrating a method of writing data to a holographic storage medium according to another embodiment of the present invention.

In step 910, the optical modulator 414 modulates the signal light, and in step 920, the angle of incidence in the radial direction, which is the scan direction of the reference light, among the angles at which the objective lens unit 415 enters the holographic storage medium. The modulated signal light is condensed so as to be larger than the incident angle in the tangential direction perpendicular to the radial direction.

In order to make the incident angle in the radial direction larger than the incident angle in the tangential direction, the NA in the tangential direction of the objective lens unit 415 may be limited. By reducing the NA in the tangential direction, the allowable tolerance due to tilt can be increased. For this purpose, a cylindrical lens or the like can be used as the lens used in the objective lens unit 415. In order to reduce the angle of incidence in the tangential direction, the objective lens unit 415 may also be achieved by blocking the edge portion of the tangential direction and adjusting the signal light not to pass.

In step 930, data is recorded on the holographic storage medium using the focused modulated signal light and the reference light.

Meanwhile, the above-described embodiments of the present invention can be written as a program that can be executed in a computer, and can be implemented in a general-purpose digital computer that operates the program using a computer-readable recording medium.

The computer-readable recording medium may be a magnetic storage medium (for example, a ROM, a floppy disk, a hard disk, etc.), an optical reading medium (for example, a CD-ROM, a DVD, etc.) and a carrier wave (for example, the Internet). Storage medium).

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

According to the present invention as described above, in the case where the tilt occurs in the tangential direction to the reference light, a data recording apparatus and method and a holographic storage medium are provided in a holographic storage medium which increases the allowable tolerance for the tilt.

Claims (5)

An apparatus for recording data on a holographic storage medium, An optical processor configured to record data on the holographic storage medium using light modulated signal light and reference light; And A control unit for controlling the light processing unit to record the data, The optical processing unit records data by making the incident angle of the radial direction, which is the scan direction of the reference light, larger than the tangential direction perpendicular to the radial direction among the angles at which the modulated signal light is incident on the holographic storage medium. Data recording device. The method of claim 1, The light processor further includes an optical modulator for modulating the signal light, And a length in the tangential direction perpendicular to the radial direction is shorter than a length in the radial direction in which the reference light is scanned on the surface of the optical modulator. The method of claim 1, And the optical processing unit further comprises an objective lens unit for blocking the signal light at the edge of the signal light in the direction in which the reference light is scanned from the signal light. In a method of recording data on a holographic storage medium, Modulating the signal light so that the length of the tangential direction perpendicular to the radial direction is shorter than the length of the radial direction from which the reference light is scanned; And And recording data on the holographic storage medium using the light modulated signal light and reference light. In a method of recording data on a holographic storage medium, Modulating the signal light; Condensing the modulated signal light by making the incident angle in the radial direction, the scan direction of the reference light, larger than the incident angle in the tangential direction perpendicular to the radial direction among the angles at which the modulated signal light is incident on the holographic storage medium; And And recording data on the holographic storage medium using the focused modulated signal light and reference light.

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