KR100657694B1 - Apparatus for controlling track servo in a holographic digital data storage system - Google Patents

Abstract

The present invention relates to a track servo control apparatus for a holographic digital data storage system, wherein a first light having a wavelength band that reacts with a recording material layer of a holographic recording medium having an initial tracking pattern is modulated into a signal light for data recording. A first optical system incident on the recording medium, a second optical system incident on the recording medium at a predetermined angle using the first light as a reference light for data recording or reproduction, and a second wavelength band not reacting with the recording material layer. A third optical system that enters light into the initial tracking pattern or data pattern as the track light, an optical detector that detects the track light diffracted by the initial tracking pattern or data pattern, and an initial stage based on the light detection value by the light detector Initial tracking pattern or data after recognizing the exact location of the tracking pattern or data pattern It includes a control unit that performs tracking servo control to adjust the data recording or reproducing position by controlling the reference light to be incident at a predetermined distance from the turn.If only the initial tracking pattern is formed, the subsequent circle uses the data pattern of the previous circle. Track servo control is performed so that multiplexing recording in the track direction is possible, so that the recording density of the holographic recording medium is improved, and when recording, the data pattern of the previous circle is used for the track servo control. There is an advantage that can be grasped.

Description

Track servo control device for holographic digital data storage system {APPARATUS FOR CONTROLLING TRACK SERVO IN A HOLOGRAPHIC DIGITAL DATA STORAGE SYSTEM}

1 is a block diagram of a general holographic digital data storage system recording / reproducing apparatus;

2 is a block diagram of a holographic digital data storage system recording / reproducing apparatus to which a track servo control apparatus according to the present invention is applied;

3A and 3B are diagrams illustrating an initial tracking pattern of a holographic recording medium for track servo control according to the present invention;

Fig. 4 is a diagram of data pattern formation recorded on the holographic recording medium by the recording process by track servo control according to the present invention, showing a part of the initial tracking pattern and a part of the data pattern being recorded.

The present invention relates to a track servo control apparatus for a holographic digital data storage system, and more particularly to a tracking servo control for recording or reproducing recorded data on a recording material layer of a holographic recording medium.

Currently, research and development of holographic recording media capable of storing hundreds to hundreds of Gbytes as optical recording media and their recording / reproducing apparatuses are being actively conducted for large-capacity and high-speed processing of data storage memories.

Holographic data recording is achieved by recording the intensity and direction of the object light reflected from the object. The intensity and direction of the light of the object is composed of the interference between the object light and the reference light to form an interference fringe, and the interference fringe is formed in a holographic recording medium made of a material that responds to the intensity of the interference fringe. When the reference beam is irradiated to the recorded interference fringe, the hologram, which is a three-dimensional image of the object, is reproduced.

The hologram data recorded on the recording medium can only be read by the reference light used in the recording process, and the hologram data passing through the hologram data recorded on the recording medium cannot be read by the reference light having a different wavelength or phase from the reference light used at the time of recording. . By using this hologram property, a large amount of hologram data can be stored in the same place of a recording medium with different reference light, thereby storing a large amount of data inside a small recording medium.

The commonly used angular multiplexing technique is to change the angle of the reference light at each recording time to create different reference light. This method allows hundreds to thousands of holograms to form binary data in pages. Can be stored in place. That is, by recording and reproducing a lot of data in the unit of a page in the same place, it is possible to record and reproduce with high storage density and fast data transfer rate.

As shown in FIG. 1, a general holographic digital data storage system includes a light source 11 for generating laser light having a predetermined wavelength, and reference light and signal light for the light generated from the light source 11. a beam splitter 13 for splitting a signal beam path, a mirror 19 for reflecting light separated from the optical splitter 13, and a light reflected from the mirror 19 for recording medium 25 ) And converts the incident angle to the rotating mirror 21 to provide the reference light, and the input data, that is, binary data of a plurality of pixels in units of pages, are converted into signal light by the light separated by the optical separator 13. The interference fringe generated by the interference of the spatial light modulator (SLM) 15 and the signal light output from the spatial light modulator (SLM) 15 and the reference light reflected from the rotation mirror 21 is recorded and the reference is made. No interference recorded by irradiation of light The recording medium 25 which diffracts and outputs the grooves and the one-page binary pixel data image recorded in the form of an interference fringe on the recording medium 25 are reproduced when the reference medium is irradiated onto the recording medium 25 and then reproduced. And a CCD 29 that converts the data image into electrical data and outputs the converted data. In the drawings, reference numerals 17 and 23 denote lenses for condensing light, and 27 denotes lenses for producing parallel light.

The holographic digital data storage system configured as described above records and plays back as follows.

First, the recording operation splits the laser light (for example, 532 nm wavelength laser light) generated by the light source 11 into two lights in the optical separator 13, which transmits the P-polarized light which is incident horizontally and is incident vertically. Reflects S-polarized light.

The P-polarized light transmitted by the optical separator 13 as it is is input to the spatial light modulator (SLM) 15 and modulated into signal light. That is, the signal light is inputted to the recording medium 25 through the lens 17 after being modulated by the data input to the spatial light modulator (SLM) 15 in units of one page of the binary data of the contrast made by the actual pixels. .

The S-polarized light reflected by the optical separator 13 is reflected by the mirror 19, converted into λ / 2 by a polarization converter (not shown), and converted into P-polarized light by the rotating mirror 21. It is reflected at an angle equal to the set recording angle and is incident on the recording medium 25 through the lens 23 as reference light. That is, the P-polarized light of the reference light whose angle of rotation mirror 21 is changed in correspondence with each stored page is incident on the optical disk which is the recording medium 25.

The P-polarized light of the signal light and the P-polarized light of the reference light cause interference in the optical disk, which is the recording medium 25 for recording the holographic digital data, and in the recording material layer of the recording medium 25 according to the intensity of the interference fringes generated at this time. A light-induced generation of mobile charge occurs to record interference fringes.

On the other hand, the operation for reproducing the data recorded on the recording medium 25 is as follows. A shutter (not shown) positioned in the signal light path blocks P polarization of the signal light transmitted from the light separator 13.

The S-polarized light reflected by the optical separator 13 is reflected by the mirror 19, converted into λ / 2 by a polarization converter (not shown), converted into P-polarized light, and preset by the rotating mirror 21. It is reflected at an angle equal to the angle at the time of recording and is incident on the recording medium 25 as a reference light through the lens 23.

If only the P-polarized light of the reference light is irradiated to the recording medium 25 without signal light, a page of binary pixel data image (i.e. checkerboard pattern) composed of original pixel contrast on the recording medium 25 on which interference data is recorded Is played.

The binary pixel data image (one page unit) reproduced from the recording medium 25 is transmitted to the CCD 29 through the lens 27, and the CCD 29 converts the reproduced data image into an electrical data signal. The converted data is restored to the original data through an image signal processor and a decoder, not shown.

In addition, as described above, the recording / reproducing process performed at a predetermined position of the recording medium is repeatedly performed while changing the position of the recording medium, thereby recording / reproducing data of several to hundreds of Gbytes using a small recording medium. Can be.

Therefore, in order to accurately record / play data during holographic recording / playback, a track servo control which is already generalized in CD or DVD recording / playback is required. In the holographic digital data storage system, the recording / playback method of CD / DVD It is completely different from the recording / reproducing method, and a new track servo control device is required.

The present invention has been proposed to solve such problems of the prior art, and an object thereof is to record an initial tracking pattern at the time of manufacturing a holographic recording medium, and to use a track using an initial tracking pattern at the beginning of track servo control during recording / reproducing. The present invention provides a track servo control apparatus for a holographic digital data storage system for recording / reproducing a data pattern through servo control and then recording / reproducing a data pattern through track servo control using a pre-formed data pattern.

As one aspect of the present invention for achieving this object, a track servo control apparatus for a holographic digital data storage system includes a holographic digital data for recording data on a holographic recording medium having an initial tracking pattern or reproducing the recorded data. A storage system, comprising: a first optical system for modulating a first light having a wavelength band that reacts with a recording material layer of a recording medium into a signal light for data recording and entering the recording medium; A second optical system incident on the recording medium as a reference light at a predetermined angle, a third optical system incident on the initial tracking pattern or data pattern using the second light having a wavelength band which does not react with the recording material layer as the track light; Light detection to detect track light diffracted by tracking pattern or data pattern After recognizing the exact position of the initial tracking pattern or data pattern based on the light detection value by the photodetector, the data recording or reproduction position is controlled by controlling the reference light to be incident at a position spaced from the initial tracking pattern or data pattern. And a control unit that performs tracking servo control to adjust.

Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings. This embodiment allows for a better understanding of the objects, features and advantages of the present invention. However, the present invention is not limited to this embodiment, of course.

FIG. 2 is a block diagram of a holographic digital data storage system recording / reproducing apparatus to which a track servo control device is applied according to the present invention. In comparison with the holographic digital data storage system shown in FIG. The sign is specified.

3A and 3B are diagrams illustrating an initial tracking pattern of a holographic recording medium for track servo control according to the present invention. As described above, in order to apply the track servo control technique according to the present invention, a circular initial tracking pattern 201 is recorded as shown in FIG. 3A when the holographic recording medium is manufactured, or a spiral initial tracking pattern (as shown in FIG. 3B). 201) should be recorded.

3A and 3B, a holographic digital data storage system for recording or reproducing data using a holographic recording medium having an initial tracking patten recorded therein generates a laser light of a first wavelength as shown in FIG. A first light source 11, an optical separator 13 for separating the light generated by the first light source 11 into a reference light and a signal light path, a mirror 19 for reflecting the light separated from the optical separator 13, In addition, the rotation mirror 21 converts the angle reflected from the mirror 19 into the recording medium 25 and provides the reference light as reference light, and input data, i.e., in units of pages, to the light separated by the optical separator 13. A spatial light modulator (SLM) 15 that carries binary data of a plurality of pixels to be converted into signal light, and the signal light output from the spatial light modulator (SLM) 15 and the reference light reflected by the rotating mirror 21. Interference pattern caused by interference A recording medium 25 which diffracts and outputs an interference fringe recorded and recorded by irradiation of a reference light, and a recording light of a single page binary pixel data image recorded in the form of an interference fringe on the recording medium 25 on the recording medium 25 The CCD 29 which reproduces when irradiated and converts the reproduced data image into electrical data, and outputs, the second light source 101 which generates laser light of a second wavelength, and the second light source 101 A lens 105 and a lens 105 for condensing the generated track light and causing the track light to enter the initial tracking patten or data pattern of the recording medium 25 in a direction opposite to the direction in which the reference light is incident on the recording medium 25; Iris 103 for adjusting the amount of light passing through the lens 105 by adjusting the aperture, and the track light diffracted by the initial tracking pattern 201 or data pattern of the recording medium 25. 2 laser light reflect and signal light (first ray) Low light) records data according to the track light mirror 107 that transmits, the light detector 109 that detects the track light reflected by the track light mirror 107, and the light detection value of the light detector 109. Or a controller (not shown) for adjusting tracking position to perform tracking servo control. In the drawings, reference numerals 17 and 23 denote lenses for condensing light, and 27 denotes lenses for producing parallel light.

The holographic data storage system according to the present invention configured as described above describes recording and reproducing operations as follows. This description makes it possible to understand the track servo control method of the present invention.

First, the recording operation splits the laser light generated by the first light source 11 (for example, green laser light having a wavelength of 532 nm) into two lights in the optical separator 13, and transmits the P-polarized light that is incident horizontally and is vertical. Reflects the S-polarized light incident on the.

The P-polarized light transmitted by the optical separator 13 as it is is input to the spatial light modulator (SLM) 15 and modulated into signal light. That is, the signal light enters the recording medium 25 through the lens 17 after being modulated by data input to the spatial light modulator (SLM) 15 in units of one page of the binary data of the contrast made by the actual pixels. do.

The S-polarized light reflected by the optical separator 13 is reflected by the mirror 19, converted into λ / 2 by a polarization converter (not shown), and converted into P-polarized light by the rotating mirror 21. It is reflected at an angle equal to the set recording angle and is incident on the recording medium 25 through the lens 23 as reference light. That is, the P-polarized light of the reference light whose angle of rotation mirror 21 is changed in correspondence with each stored page is incident on the optical disk which is the recording medium 25.

Here, the P-polarized light of the signal light incident on the recording medium 25 through the first optical system composed of the optical separator 13, the spatial light modulator 15, the lens 17 and the like, the optical separator 13, the mirror 19 , The P-polarized light of the reference light incident on the recording medium 25 through the second optical system composed of the rotating mirror 21, the lens 23, or the like is used in the optical disk which is the recording medium 25 for recording the holographic digital data. Interference is caused and a photoinduced phenomenon of the internal kinetic charge is generated in the recording material layer of the recording medium 25 according to the strength of the interference fringes generated, thereby recording the interference fringe. Track servo control is required for this.

Referring to the track servo control process, in the initial stage of the track servo control, the laser light (for example, a red laser light having a wavelength of 650 nm) generated by the second light source 101 passes through the iris 103 and the lens 105 to record the recording medium ( The light is incident on the initial tracking pattern 201 of 25 as track light.

The track light incident on the recording medium 25 through the third optical system composed of the iris 103, the lens 105, etc. is diffracted by the initial tracking pattern 201, and the track light emitted from the recording medium 25 is The light is reflected by the track light mirror 107 and detected by the light detector 109.

Here, it is preferable that the signal light for recording uses, for example, green laser light having a wavelength of 532 nm, and the track light for track servo using, for example, red laser light having a wavelength of 650 nm. The reason is that the recording material layer of the recording medium 25 by a conventional process reacts with the green laser light to cure, that is, form a polymer but does not react with the red laser light. In summary, the first light source 11 generates laser light in a wavelength band that reacts with the recording material layer of the recording medium 25, and the second light source 101 does not react with the recording material layer of the recording medium 25. Does not generate laser light in the wavelength band.

The control unit (not shown) recognizes the correct position of the initial tracking pattern 201 based on the light detection value by the photo detector 109, and positions the predetermined tracking interval with the initial tracking pattern 201 through tracking servo control. The data pattern is recorded by controlling the reference light to enter the target light. Referring to FIG. 4 to help understand the data pattern recording process, track servo control is performed while injecting the track light B2 into the initial tracking pattern 201 so that the reference light is positioned at a predetermined distance from the initial tracking pattern 201. The data pattern is recorded by controlling (B1) to be incident. At this time, as shown in FIG. 4, the data pattern may be recorded in an area overlapping the initial tracking pattern 201 to maximize the recording density.

Subsequently, when the recording of the data pattern of one circle is completed, the laser light generated from the second light source 101, that is, the track light is incident on the previously recorded data pattern as the track light. That is, when one circle of the data pattern is recorded in FIG. 4, the track light B2 incident on the initial tracking pattern 201 is incident on the data pattern of the immediately recorded circle.

Then, the track light incident on the recording medium 25 is diffracted by the previous data pattern, and the track light emitted from the recording medium 25 is reflected by the track light mirror 107 and detected by the light detector 109. do.

Here, since the track light is laser light in a wavelength band that does not react with the recording material layer of the recording medium 25, only the physical light diffraction phenomenon is generated in a state in which the pre-formed data pattern is not damaged (no chemical reaction occurs).

Then, the controller (not shown) recognizes the exact position of the previous data pattern based on the light detection value by the photo detector 109, and the reference light is incident at a position spaced a predetermined distance from the previous data pattern through tracking servo control. Record the data pattern of the next circle by controlling it.

As described above, in the present invention, since the previous data pattern is used for the track servo control, the degree of recording of the previous circle data pattern can be indirectly determined by utilizing the intensity of the signal detected by the photodetector 109. In addition, even if the track light is incident in the same direction as the reference light is incident on the recording medium 25, the previous circle data pattern is reproduced by the CCD 29 during recording or the track light is incident in the opposite direction to the reference light as shown in FIG. By reproducing the previous circle data pattern by arranging a separate CCD at the arrangement position of the photo detector 109, the recording state of the previous circle data pattern can be accurately confirmed.

On the other hand, the operation for reproducing the data recorded on the recording medium 25 is as follows. A shutter (not shown) positioned in the signal light path blocks P-polarized light of the signal light transmitted from the light separator 13.

The S-polarized light reflected by the optical separator 13 is reflected by the mirror 19, converted into λ / 2 by a polarization converter (not shown), and converted into P-polarized light by the rotating mirror 21. It is reflected at an angle equal to the set recording angle and is incident on the recording medium 25 through the lens 23 as reference light.

If only the P-polarized light of the reference light is irradiated to the recording medium 25 without signal light, a page of binary pixel data image (i.e. checkerboard pattern) composed of original pixel contrast on the recording medium 25 on which interference data is recorded Is reproduced, and track servo control is required in order to reproduce data accurately on the recording medium 25 as in the case of recording.

In order to examine the track servo control process, assuming that all data are reproduced from the beginning to the end of the recording medium 25, the laser light generated by the second light source 101 (for example, a red laser having a wavelength of 650 nm) is initially generated during the track servo control. Light) passes through the iris 103 and the lens 105 and is incident on the initial tracking pattern 201 of the recording medium 25 as track light.

The track light incident on the recording medium 25 is diffracted by the initial tracking pattern 201, and the track light exiting the recording medium 25 is reflected by the track light mirror 107 and is reflected by the light detector 109. Is detected.

Here, for example, the reference light for reproduction uses green laser light of 532 nm wavelength and the track light for track servo uses, for example, red laser light of 650 nm wavelength, for example. The reference light and the track light may be laser light having the same wavelength band. The reason is that if the recording material layer of the recording medium 250 has already been cured by reacting with the green laser light at the time of recording, even if the green laser light is incident at the time of reproduction, no chemical reaction occurs with the recording material layer of the recording medium 25. This is because only phosphor light diffraction occurs.

The control unit (not shown) recognizes the correct position of the initial tracking pattern 201 based on the light detection value by the photo detector 109, and positions the predetermined tracking interval with the initial tracking pattern 201 through tracking servo control. The data pattern is reproduced by controlling the reference light to enter the target light. In order to understand the data pattern reproducing process, referring to FIG. 4, track servo control is performed while the track light B2 is incident on the initial tracking pattern 201 so that the reference light is positioned at a predetermined distance from the initial tracking pattern 201. The data pattern is reproduced by controlling (B1) to be incident.

Subsequently, when the reproduction of the data pattern of one circle is completed, the laser light generated from the second light source 101, that is, the track light is incident on the previously reproduced data pattern as the track light. That is, when the track light B2 is incident on the initial tracking pattern 201 and the reference light B1 is incident on the data pattern in FIG. 4, when one circle of the data pattern is reproduced, the track light B2 is incident on the reproduced data pattern. The reference pattern B1 is incident on the data pattern of the next adjacent circle to reproduce the data pattern of the next circle.

Then, the track light incident on the recording medium 25 is diffracted by the previous data pattern, and the track light emitted from the recording medium 25 is reflected by the track light mirror 107 and detected by the light detector 109. do.

Then, the controller (not shown) recognizes the exact position of the previous data pattern based on the light detection value by the photo detector 109, and the reference light is incident at a position spaced a predetermined distance from the previous data pattern through tracking servo control. Control to play the data pattern of the next circle.

The binary pixel data image (one page unit) reproduced from the recording medium 25 is transmitted to the CCD 29 through the lens 27, and the CCD 29 converts the reproduced data image into an electrical data signal. The converted data is restored to the original data through an image signal processor and a decoder, not shown.

Although the foregoing description has been limited to one embodiment of the present invention, it is obvious that the technology of the present invention can be easily modified by those skilled in the art.

For example, in the above-described embodiment, the case in which the horizontally polarized P polarization is used as the signal light and the reference light has been described as an example, but the use of the vertically polarized S polarization as the signal light and the reference light is more advantageous in terms of the use efficiency of the laser light.

Such modified embodiments should be included in the technical spirit described in the claims of the present invention.

As described above, the present invention records the initial tracking pattern 201 at the time of manufacture of the holographic recording medium, and at the beginning of the track servo control at the time of recording / reproduction, the data pattern is controlled through the track servo control using the initial tracking pattern 201. After recording / reproducing the data pattern and then recording / reproducing the data pattern through the track servo control using the pre-formed data pattern, if only the initial tracking pattern 201 is formed, the track servo is controlled using the data pattern of the previous circle from the subsequent circle. Since the multiplexed recording in the track direction is possible, the recording density of the holographic recording medium is improved.

In addition, since the data pattern of the previous circle is used for the track servo control at the time of recording, the recording degree of the circle data pattern can be grasped indirectly.

Claims (7)

A holographic digital data storage system for recording data on a holographic recording medium on which an initial tracking pattern is formed or reproducing the recorded data. A first optical system for modulating a first light having a wavelength band that reacts with a recording material layer of the recording medium into a signal light for data recording and incident on the recording medium; A second optical system in which the first light is incident on the recording medium as a reference light for data recording or reproduction; A third optical system in which a second light having a wavelength band which does not react with the recording material layer is incident to the initial tracking pattern or data pattern as track light; A photo detector for detecting the track light diffracted by the initial tracking pattern or data pattern; After recognizing the correct position of the initial tracking pattern or data pattern based on the light detection value by the photo detector, controlling the reference light to be incident at a position spaced apart from the initial tracking pattern or data pattern to record or reproduce the data. Control unit to perform tracking servo control to adjust position Track servo control device of the holographic digital data storage system comprising a. The method of claim 1, The first optical system includes an optical splitter for separating the light generated by the first light source for generating the first light into a reference light and a signal light path, and a space for loading input data into the light separated by the optical splitter to convert the light into signal light. An optical modulator, The second optical system includes a mirror for reflecting light separated by the optical separator, and a rotating mirror for converting the angle reflected by the mirror to the recording medium and providing the reflected light as the reference light, The third optical system collects the track light generated by the second light source that generates the second light and enters the recording medium in a direction opposite to the direction in which the reference light is incident on the recording medium; It includes an iris to adjust the amount of light passing through the lens by adjusting the aperture of the, The optical detector detects the track light through the first optical system, and a track light mirror is disposed on the first optical system to transmit the signal light, reflect the track light, and enter the light detector. Track servo control device of holographic digital data storage system. The method according to claim 1 or 2, And wherein the first light uses green laser light and the second light uses red laser light. The method of claim 1, The initial tracking pattern is a track servo control apparatus of a holographic digital data storage system, characterized in that one circle is recorded in a circle or a spiral. The method of claim 1, The control unit records the data pattern through the track servo control using the initial tracking pattern at the beginning of the track servo control at the time of recording, and after the data pattern of one circle is recorded, thereafter the track servo control using the data pattern of the previous circle is performed. Track servo control device of holographic digital data storage system, characterized by recording the data pattern of the circle. The method of claim 1, The control unit reproduces the adjacent data pattern through track servo control using the initial tracking pattern at the beginning of the track servo control when the first position of the recording medium is reproduced, and then reproduces the data pattern of the previous circle after the data pattern of one circle is reproduced. Track servo control device of a holographic digital data storage system, characterized in that to reproduce the data pattern of the next circle by using the track servo control. The method of claim 1, The control unit controls the servo data of the holographic digital data storage system, wherein the control unit reproduces the data pattern of the next circle through the track servo control using the data pattern of the previous circle when reproducing the remaining position other than the first position of the recording medium. .

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