OPTICAL TRACK FORMAT FOR HOLOGRAPHIC STORAGE OPTICAL DISC AND ENCODING METHOD THEREOF

Abstract

An optical track format of a holographic storage optical disc includes a lead-in area, a data area and a lead-out area. The data area is provided with data holographic positioning marks for marking reading/writing position of data holograms on the optical track and start positioning marks for marking position on the optical track where data holograms start to be recorded. The start positioning marks may also contain address encoding information. Such optical track can be encoded by performing binary encoding by length of the optical track between two consecutive notches, or performing binary encoding by high and low levels of a level signal.

Claims

1. An optical track format for a holographic storage optical disc, comprising a lead-in area, which is configured for storing characteristic information, product information, and reading/writing parameters of the holographic storage optical disc, and calibration holograms for calibrating an incident light; a data area, which is configured for recording data holograms loaded with data; and a lead-out area, which is configured for storing sealing information of the holographic storage optical disc, wherein the data area is provided with two kinds of marks including data holographic positioning marks for marking reading/writing position of the data holograms on an optical track, and start positioning marks for marking position on the optical track where the data holograms start to be recorded, each start positioning mark includes address encoding information, the lead-in area is provided with calibration holographic positioning marks for marking position of the calibration holograms on the optical track, and the data holographic positioning marks, start positioning marks, and calibration holographic positioning marks on the optical track are capble of being positioned or read information therein by the incident light.

2. The optical track format for the holographic storage optical disc according to claim 1, wherein the optical track comprises a plurality of ridges or grooves on an inner surface of a substrate of the holographic storage optical disc, each ridge or groove is provided with a plurality of notches, and each of two ends of each notch has a descending end with a reduced height and an ascending end with a raised height, and the reduced height and the raised height are equal, which are less than or equal to ¼ of wavelength of an incident light, the notches provided in the lead-in area are configured for storing the characteristic information, product information, and reading/writing parameters of the holographic storage optical disc, and the calibration holograms for calibrating the incident light, and the notches provided in the lead-out area are configured for storing the sealing information of the holographic storage optical disc; each holographic positioning mark includes one notch on the optical track or the ascending end or the descending end thereof; each start positioning mark includes at least one of the notches on the optical track and a plurality of sections of the ridges or grooves separated by the at least one of the notches.

3. The optical track format for the holographic storage optical disc according to claim 2, wherein the optical track is in form of concentric circles with a certain spacing, the optical track is divided into a plurality of sectors by the plurality of start positioning marks, and the lead-in area is formed by at least one of the concentric circles closest to a center of the optical disc, the lead-out area is formed by at least one of the concentric circles furthest away from the center of the optical disc, and the data area is formed by the concentric circles between the lead-in area and the lead-out area.

4. The optical track format for the holographic storage optical disc according to claim 3, wherein each start positioning mark comprises a front end, an address field and a back end, the address field is located between the front end and the back end, and the address field are recorded with optical track information and sector information.

5. The optical track format for the holographic storage optical disc according to claim 2, wherein the optical track is in form of an equidistant spiral line from the inside to the outside, the lead-in area is formed by a plurality of spiral turns of the spiral line closest to a center of the optical disc, the lead-out area is formed by a plurality of spiral turns of the spiral line furthest away from the center of the optical disc, the data area is formed by the spiral turns of the spiral line between the lead-in area and the lead-out area, and a head end and a tail end of the data area is each provided with one start positioning mark.

6. The optical track format for the holographic storage optical disc according to claim 5, wherein the start positioning mark comprises a front end and a back end.

7. The optical track format for the holographic storage optical disc according to claim 2, wherein when a spot of the incident light covers the ascending end and the descending end of each notch at the same time and is located at a center of the corresponding notch, light reflected is diverged into three light beams along the optical track direction, and light intensity of the light beams on sides are equal; when a spot of the incident light covers the ascending end or the descending end of each notch and deviates from a center of the corresponding notch, light reflected is diverged into three light beams along the optical track direction, and light intensity of the light beams on sides are unequal, and wherein the light beams reflected are received by a light intensity sensor to conduct comparison of the light intensity, and the light beams reflected is converted into an analogue voltage signal, which is referred to as a tangential push pull signal.

8. The optical track format for the holographic storage optical disc according to claim 7, wherein each notch on the optical track has a fixed length so that the incident light spot covers both the ascending end and the descending end of each notch at the same time, the tangential push pull signal of the corresponding notch is converted into a single high-level signal, and the tangential push pull signal at the remaining positions is converted into a low-level signal.

9. The optical track format for the holographic storage optical disc according to claim 7, wherein the incident light spot does not cover the ascending end and the descending end of each notch at the same time, the tangential push pull signal of the ascending end and the descending end of each notch is respectively converted into a high-level signal, and the tangential push pull signal at the remaining positions is converted into a low-level signal;

10. A method for encoding the optical track format for the holographic storage optical disc according to claim 8, comprising steps of performing binary encoding by a length of the optical track between two consecutive notches, the length of the optical track between two consecutive notches determines a time interval between the ascending edges of two consecutive high-level signal, wherein spatial distance between the ascending ends of two consecutive data holographic positioning marks or calibration holographic positioning marks and the time interval between the ascending edges of two corresponding consecutive high-level signal are defined as a code element length T of a spatial domain and a time domain, respectively, “0” is encoded as the optical track with a distance T between the ascending ends of two notches; and “1” is encoded as the optical track with a distance nT between the ascending ends of two notches, in which n is a positive integer, n≠1.

11. The method for encoding according to claim 10, wherein in the start positioning marks, distance between the ascending ends of the two notches on two sides of the front end or duration between corresponding ascending edges of the two high-level signals is aT, in which a is a positive integer, a>n, and distance between the ascending ends of the two notches on two sides of the back end or duration between corresponding ascending edges of the two high-level signals is bT−(b+1)T, in which b is a positive integer, b>n, and b≠a, and the n, a and b is in different value.

12. A method for encoding the optical track format for the holographic storage optical disc according to claim 8, comprising steps of performing binary encoding by high or low level of a level signal, wherein “1” is encoded as a high level corresponding to each notch or the ascending end or the descending end of the notch, duration of the high-level signal is defined as a code element length T, and “0” is encoded as a low level, duration of the low level is an integer multiple of the code element length which is the number of “0”.

13. The method for encoding according to claim 12, wherein the front end and the back end of each start positioning mark are respectively a section of the optical track which is detected as a level signal with a unique waveform.

14. A method for encoding the optical track format for the holographic storage optical disc according to claim 9, comprising steps of performing binary encoding by high or low level of a level signal, wherein “1” is encoded as a high level corresponding to each notch or the ascending end or the descending end of the notch, duration of the high-level signal is defined as a code element length T, and “0” is encoded as a low level, duration of the low level is an integer multiple of the code element length which is the number of “0”.

15. The method for encoding according to claim 14, wherein the front end and the back end of each start positioning mark are respectively a section of the optical track which is detected as a level signal with a unique waveform.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 is a schematic diagram showing distribution of start positioning mark s and holographic positioning marks on an optical track in form of concentric circles of an optical disc according to one embodiment.

[0035] FIG. 2 is a schematic diagram showing encoding of the start positioning mark s and a part of the start positioning marks on the optical track in form of concentric circles according to one embodiment.

[0036] FIG. 3 is a schematic diagram showing encoding of the start positioning mark s and a part of the start positioning marks on the optical track in form of concentric circles according to one embodiment.

[0037] FIG. 4 is a schematic diagram showing encoding of the start positioning mark s and a part of the start positioning marks on the optical track in form of concentric circles according to one embodiment.

[0038] FIG. 5 is a schematic diagram of a hologram storage trajectory on the optical track in form of concentric circles of the optical disc according to one embodiment.

[0039] FIG. 6 is a signal receiving and light spot intensity distribution diagram of a four-quadrant detector according to one embodiment.

[0040] FIG. 7 is a schematic diagram of a tangential push pull signal and a level signal of a short notch according to one embodiment.

[0041] FIG. 8 is a schematic diagram of a tangential push pull signal and a level signal of a long notch according to one embodiment.

[0042] FIG. 9 is a schematic diagram of an optical track in form of spiral line and start positioning mark s and holographic positioning marks on the optical track of the optical disc according to one embodiment.

DETAILED DESCRIPTION

[0043] The accompanying drawings of the present invention are only used for exemplary illustration, and should not be construed as limitation to the present invention. In order to better illustrate the following embodiments, some parts of the drawings may be omitted, enlarged or reduced, which do not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0044] An optical track format for a holographic storage optical disc is provided according to one embodiment, which includes a lead-in area 3, a data area 4 and a lead-out area 5. The lead-in area is configured for storing characteristic information, product information, and reading/writing parameters of the optical disc, and holograms for calibrating an incident light, etc. The data area is configured for recording holograms loaded with data. The lead-out area is used for storing disc sealing information. Two kinds of marks exist in the data area, including data holographic positioning marks 2 for marking a reading/writing position of the data hologram on the optical track and start positioning marks 1 for marking a position on the optical track where the data hologram starts to be recorded. The start positioning marks can also contain address encoding information. Calibration holographic positioning marks 2 are provided in the lead-in area, which are configured for marking the position of a calibration hologram on the optical track. All the marks on the optical track are able to be positioned or read information therein by the incident light.

[0045] The configuration of the start positioning marks 1 and the data holographic positioning marks 2 in the data area can effectively divide the information on the optical disc, the optical track and the reading/writing position of the data holograms can be positioned according to the marks, so that the incident light can quickly position and address the reading/writing position, thereby improving the reading/writing efficiency of the hologram. By arranging the calibration holographic positioning marks 2 in the lead-in area, a reference beam during reproducing can be calibrated by the calibration holograms at the calibration holographic positioning marks. When recording data, the calibration hologram is written at each calibration holographic positioning mark in the lead-in area, and when reading data, by reproducing the calibration holograms, the irradiation position and angle of reproducing reference light is calibrated to reach maximum diffraction efficiency and signal-to-noise ratio of the calibration holograms, so that the data can be accurately reproduced.

[0046] According to one embodiment, the optical track includes a plurality of ridges or grooves on the inner surface of a substrate of the holographic storage optical disc. Each ridge or groove is provided with a plurality of notches, and two ends of each notch includes a descending end with a reduced height and an ascending end with a raised height. The heights of the ascending end and the descending end are equal, and the height thereof is less than or equal to ¼ of the wavelength of incident light. At least one notch provided in the lead-in area and the lead-out area are for storing relevant information. The data holographic positioning marks and the calibration holographic positioning marks are the notches on the optical track or the ascending end or descending end of the notches. The start positioning mark is comprised of at least one notch on the optical track and a plurality of sections of the ridges or grooves separated by the notch. With a plurality of notches in the lead-in area and the lead-out area of the optical track, the characteristic information, product information, reading/writing parameters and sealing information of the optical track can be stored in the plurality of sections of the ridge or groove separated by the notches.

[0047] As shown in FIG. 1, in this embodiment, the optical track is in form of concentric circles with a certain spacing tp, and the distance between two adjacent holographic positioning marks is Δ L. A plurality of start positioning marks are provided in the optical track to divide the optical track into a plurality of sectors, so that the light beam can determine the optical track located and the sector located according to the start positioning marks, and can further determine the reading/writing position of the hologram in the sector by the holographic positioning marks. According to this embodiment, two concentric circles of the optical track closest to the center of the optical disc form the lead-in area 3, the concentric circle of the optical track furthest away from the center of the optical disc forms the lead-out area 5, and the other concentric circles form the data area 4. The concentric circle with the smallest radius in the lead-in area records the characteristic information, product information and reading/writing parameters of the optical disc. In the lead-in area, a plurality of start positioning marks 1 and calibration holographic positioning marks 2 are provided on the concentric circle of the optical track with a larger radius. The start positioning marks 1 are used for positioning the incident light and the calibration holographic positioning marks 2 are used for calibrating the incident light. The holographic positioning mark of the optical track in FIG. 1 is only partially shown as a schematic illustration. Referring to FIG. 2, each start positioning mark on the optical track includes a front end, an address field and a back end, the address field is located between the front end and the back end and configured for recording the optical track information and sector information. The front end and the back end are used for identifying the start positioning mark, and the optical track information and the sector information recorded in the address field are used for identifying the position of the start positioning mark in the optical track.

[0048] FIG. 9 shows another optical track format of a holographic storage optical disc according to one embodiment. The optical track in this embodiment is in form of an equidistant spiral line from inside to outside, tp is the distance between the spiral line of the optical track, and the distance between two adjacent holographic positioning marks is L. A section of the spiral line closest to the center of the optical disc forms the lead-in area, a section of spiral line farthest away from the center of the optical disc is the lead-out area. The head end and the tail end of the data area are respectively provided with a start positioning mark. The start positioning mark at the head end of the data area is used for positioning a place on the optical track where the data hologram starts to be recorded, and the start positioning mark at the tail end of the data area is used for positioning a place where the recording of the data hologram ends. The section of the spiral line in the lead-in area closest to the center of the optical disc records the characteristic information, product information and reading/writing parameters of the optical disc, and other section of the spiral line in the lead-in area are provided with the calibration holographic positioning marks for calibrating the incident light. Since the optical track in form of spiral line is not divided the optical track into sectors, the start positioning marks in the optical track in form of spiral line does not need to record optical track information and sector information, so that the start positioning mark in the optical track in form of the spiral line thus only contains a front end and a back end for identifying the start positioning mark.

[0049] In the optical track in form of concentric circles, when the hologram is recorded, the shift multiplexing distance L along the optical track direction is an integer multiple of the interval ΔL between the holographic positioning marks, namely, L=c×ΔL, c≥1, wherein c is a positive integer, and the radial shift multiplexing distance r of the hologram is an integer multiple of the distance tp between adjacent concentric circles of the optical track, namely, r=d×tp, d≥1, wherein d is a positive integer. While in the optical track in form of the spiral line, when the hologram is recorded, the shift multiplexing distance L in the optical track direction is an integer multiple of the interval ΔL between the holographic positioning marks, namely, L=c×ΔL, c≥1, wherein c is a positive integer, and the radial shift multiplexing distance r of the hologram is equal to the distance tp between adjacent optical tracks, namely, r=tp.

[0050] Specifically, as exemplary illustration, FIG. 5 shows a holographic storage optical disc with the optical track in form of concentric circles, when recording, the characteristic information, product information and reading/writing parameters of the optical disc are firstly read on the concentric circle of the optical track closest to the center of the optical disc in the lead-in area 3. One start positioning mark 1 in the lead-in area 3 is then positioned and a plurality of calibration holograms for calibration are recorded in the sector at such start positioning mark 1 in the lead-in area. One start positioning mark 1 on the optical track in the data area 4 is then positioned and the data holograms are recorded in the sector where such start positioning mark 1 in the data area 4 is located. When the sector where the start positioning mark 1 is located is recorded the data holograms completely, another start positioning mark 1 of the optical track is positioned and the data holograms are recorded in the sector where such start positioning mark 1 is located. When reading, the characteristic information, product information and reading and writing parameters of the optical disc are firstly read on the concentric circle of the optical track closest to the center of the optical disc in the lead-in area 3. Then, through the start positioning mark and the calibration holographic positioning mark in the lead-in area 3, the calibration hologram in the lead-in area for calibration is positioned, and by reproducing the calibration hologram, the irradiation position and angle of a reproducing reference beam is adjusted to reach the maximum diffraction efficiency and the signal-to-noise ratio of the calibration hologram. The start positioning mark on the optical track in the data area is then positioned and the data holograms are read in the sector where the start positioning mark in the data area is located, and the data holograms in other sectors of the optical track are then read sequentially. When the data holograms in the data area is read completely, the lead-out area is positioned, the sealing information of the optical disc is read, and the reading process is thus completed.

[0051] A method for encoding the optical track format for the holographic storage optical disc mentioned above is provided according to one embodiment. As shown in FIG. 6, when an incident light spot covers the ascending end and the descending end of the corresponding notch at the same time and is located at the center of the notch, light reflected is diverged into three light beams in the optical track direction, and the light intensities of light beams on two sides are equal. When an incident light spot covers the ascending end or/and the descending end of the notch and deviates from the center of the notch, light reflected is diverged into three light beams in the optical track direction, and the light intensities of the light beams on two sides are unequal. The reflected light beams are received by a four-quadrant photodetector to conduct comparison of light intensity, and each reflected light beam is converted into an analogue voltage signal, namely, a tangential push pull signal (TPP). The four-quadrant photodetector includes four areas A, B, C and D for receiving light reflected back from the optical track. The difference of light intensity signals of the two areas AB and CD in the optical track direction is the tangential push pull signal, TPP=(I.sub.A+I.sub.B)−(I.sub.C+I.sub.D).

[0052] Preferably, all the notches in the optical track are all short notches with fixed length. The holographic positioning mark is one notch on the optical track, and a section of the ridge or the groove between two adjacent holographic positioning marks is a minimum continuous unit on the optical track, and the length of the minimum continuous unit is greater than the length of the notch. FIG. 2 shows a partial structure of the optical track.

[0053] Referring to FIG. 7, when the notch is a short notch, the incident light spot can cover both the ascending end and the descending end thereof at the same time, the tangential push pull signal thereof is further converted into a single high-level signal, and the tangential push pull signals corresponding to the remaining positions are further converted into low-level signals. The structure of the optical track can be identified according to different level signals.

[0054] Since the notches of the holographic positioning marks are all short notches, namely, the incident light spot can cover the ascending end and the descending end thereof at the same time, the tangential push pull signal corresponding to the holographic positioning marks is the single high-level pulse signal, so that the holographic positioning marks can be identified by the single high-level pulse signal without encoding.

[0055] By encoding the above-mentioned optical track format, the relevant information in the lead-in area, the lead-out area and the start positioning marks of the optical track thus can be quickly identified.

[0056] The specific encoding method includes, as shown in FIG. 2, performing binary encoding by length of the optical track between two consecutive notches, such optical track length can determine the time interval between two consecutive high-level ascending edges. The spatial distance between the ascending ends of two holographic positioning marks and the time interval between their corresponding high-level ascending edges defined as a code element length T in spatial domain and time domain, respectively.

[0057] In this method “0” is encoded as the optical track with a distance T between the ascending ends of two notches, and “1” is encoded as the optical track with a distance 4T between the ascending ends of two notches.

[0058] As exemplary illustration, FIG. 2 shows encoding of a section of the start positioning mark. The address field in FIG. 2 has seven notches, the distance between the first notch and the second notch from left to right is T, thus encoding as 0, the distance between the second notch and the third notch is 4T, thus encoding as 1, and the distance between the third notch and the fourth notch, between the fourth notch and the fifth notch, between the fifth notch and the sixth notch, and between the sixth notch and the seventh notch is T, so that the four spacing are encoded as 0, respectively. Code of the address field shown in FIG. 2 thus is 010000.

[0059] Preferably, in the start positioning mark, the distance between the ascending ends of the notches on two sides of the front end or the duration between corresponding ascending edges of the high-level signals is correspondingly 12T, and the distance between the ascending ends of the notches on two sides of the back end or the duration between corresponding ascending edges of the high-level signals is correspondingly 8T-9T.

[0060] During moving of the incident light spot from left to right along the optical track, when a low-level signal with a duration of 12T is identified, it indicates that the front end of the start positioning mark of the optical track is reached, so that an optical track number and a sector number in the address field start to be read. When a low-level signal with a duration of 8T-9T is identified, it indicates that the back end of the start positioning mark is reached, the identification of the start positioning mark ends, then reading/writing of data holograms in the sector starts, or moving to other positions to identify other start positioning marks.

[0061] By binary coding, the relevant information in the lead-in area, the lead-out area and the start positioning mark are recorded in the optical track. The binary encoding method proposed in this embodiment herein is simple and efficient, without involving a complicated encoding process, and can effectively screen out useful information in the optical track.

[0062] Another method for encoding the optical track format of the holographic storage optical disc mentioned above is provided according to one embodiment. As shown in FIG. 6, when an incident light spot covers the ascending end and the descending end of the notch at the same time and is located at the center of the notch, the light reflected is diverged into three light beams in the optical track direction, and the light intensities of the light beams on two sides are equal; when an incident light spot covers the ascending end or/and the descending end of the notch and deviates from the center of the notch, the light reflected is diverged into three beams in the optical track direction, and the light intensities of the light beams on two sides are unequal. The light beams reflected are received by a four-quadrant photodetector to conduct comparison of light intensity and is converted into an analogue voltage signal, namely, a tangential push pull signal (TPP). The four-quadrant photodetector includes four areas A, B, C and D for receiving light reflected back from the optical track. The difference of light intensity signals of the two areas AB and CD in the optical track direction is the tangential push pull signal, TPP=(I.sub.A+I.sub.B)−(I.sub.C+I.sub.D).

[0063] Preferably, all the notches in the optical track are all short notches with fixed length. The holographic positioning mark is the notch on the optical track, and a section of the ridge or the groove between two adjacent holographic positioning marks is a minimum continuous unit on the optical track, and the length of the minimum continuous unit is greater than the length of the notch. FIG. 3 shows a partial structure of the optical track.

[0064] Referring to FIG. 7, when the notch is the short notch, the incident light spot can cover both the ascending end and the descending end thereof at the same time, the tangential push pull signal thereof is further converted into a single high-level signal, and the tangential push pull signals corresponding to the remaining positions are further converted into low-level signals. The specific structure of the optical track can be identified according to different level signals.

[0065] Since the notches of the holographic positioning mark are all short notches, namely, the incident light spot can cover the ascending end and the descending end thereof at the same time, the tangential push pull signal corresponding to the holographic positioning mark is the single high-level pulse signal, so that the holographic positioning mark can be identified by the single high-level pulse signal without encoding.

[0066] By encoding the above-mentioned optical track format, the relevant information in the lead-in area, the lead-out area and the start positioning marks of the optical track can be quickly identified.

[0067] The specific encoding method includes: as shown in FIG. 3, performing binary encoding by high and low levels of a level signal. “1” is encoded as a high level corresponding to the notch or the ascending end or descending end thereof, the duration of the high-level signal is defined as a code element length T; and “0” is encoded as a low level, the duration of a continuous low level is an integer multiple of the code element length, i.e. the number of “0”.

[0068] As exemplary illustration, FIG. 3 shows encoding of the start positioning mark in a section of optical track in form of concentric circles. The address field in FIG. 3 shows a total of seven notches, each notch corresponding to a high-level signal, each is thus encoded as “1”. The distance between the first notch and the second notch from left to right is 2T, thus encoding as 00; the distance between the second notch and the third notch is 11T, thus encoding as 00000000000; the distance between the third notch and the fourth notch, between the fourth notch and the fifth notch, between the fifth notch and the sixth notch, and between the sixth notch and the seventh notch is 2T, so that the four spacing are encoded as 00, respectively. Code of the address field shown in FIG. 3 thus is 1001000000000001001001001001.

[0069] Preferably, in the start positioning mark, the front end and the back end are respectively a section of the optical track in a level signal with a certain unique waveform.

[0070] During moving of the incident light spot from left to right along the optical track, when the level signal of a certain unique waveform of the front end is identified, it indicates that the front end of the start positioning mark of the optical track is reached, and an optical track number and a sector number in the address field start to be read; when the level signal of a certain unique waveform of the back end is identified, it indicates that the back end of the start positioning mark is reached, the identification of the start positioning mark ends, then reading/writing of the data holograms in the sector starts, or moving to other positions to identify other start positioning marks.

[0071] By binary coding, the relevant information in the lead-in area, the lead-out area and the start positioning mark is recorded in the optical track. The binary encoding method proposed in this embodiment herein is simple and efficient, without involving a complicated encoding process, and can effectively screen out useful information in the optical track.

[0072] Another method for encoding an optical track format of a holographic storage optical disc mentioned above is provided according to one embodiment. As shown in FIG. 6, when an incident light spot covers the ascending end and the descending end of the notch at the same time and is located at the center of the notch, the light reflected is diverged into three light beams in the optical track direction, and the light intensities of the light beams on two sides are equal; when an incident light spot covers the ascending end or/and the descending end of the notch and deviates from the center of the notch, the light reflected is diverged into three light beams in the optical track direction, and the light intensities of the light beams on two sides are unequal. The reflected light beams are received by a four-quadrant photodetector to conduct comparison of light intensity and is converted into an analogue voltage signal, namely, a tangential push pull signal (TPP). The four-quadrant photodetector includes four areas A, B, C and D for receiving light reflected back from the optical track. The difference of light intensity signals of the two areas AB and CD in the optical track direction is the tangential push pull signal, TPP=(I.sub.A+I.sub.B)−(I.sub.C+I.sub.D).

[0073] Preferably, all the notches in the optical track are all long notches. The holographic positioning mark is the notch on the optical track, and a section of the ridge or the groove between two adjacent holographic positioning marks is a minimum continuous unit on the optical track, and the length of the minimum continuous unit is greater than the length of the notch. FIG. 4 shows a partial structure of such optical track

[0074] As shown in FIG. 8, when the notch is the long notch, the incident light spot cannot cover the ascending end and the descending end thereof at the same time, and the tangential push pull signals corresponding to the ascending end and the descending end thereof are respectively further converted into two high-level signals; and the tangential push pull signals corresponding to the remaining positions are further converted into low-level signals. Accordingly, the specific structure of the optical track can be identified according to different level signals.

[0075] Since the holographic positioning mark is the long notch on the optical track, the incident light spot cannot cover the ascending end and the descending end thereof at the same time, the tangential push pull signal corresponding to the holographic positioning mark is two high-level pulse signals, so that the holographic positioning mark can be identified by the pulse signals without encoding.

[0076] By encoding the above-mentioned optical track format, the relevant information in the lead-in area, the lead-out area and the start positioning marks of the optical track can be quickly identified.

[0077] The specific encoding method includes, as shown in FIG. 4, performing binary encoding by high and low levels of a level signal. “1” is encoded as a high level corresponding to the notch or the ascending end or descending end thereof, the duration of the high-level signal is defined as a code element length T; and “0” is encoded as a low level, the duration of a continuous low level is an integer multiple of the code element length, i.e. the number of “0”.

[0078] As exemplary illustration, FIG. 4 shows encoding of the start positioning mark in a section of the optical track in form of concentric circles. The address field shows two sections of the ridge or the groove in FIG. 4, and the two ends of each notch respectively correspond to a high-level signal. The right end of the first notch from left to right corresponds to a high-level signal, encoding as “1”; the distance between the first notch and the second notch is 8T, thus encoding as 00000000; the distance between the second notch and the third notch is 8T, thus encoding as 00000000; the left and right ends of the second notch respectively correspond to two high-level signals, encoding as 1, respectively, and the middle corresponds to a low-level signal, encoding as 00; the left end of the third notch corresponds to a high level signal, encoding as 1. Code of the address field shown in FIG. 4 thus are 1000000001001000000001.

[0079] Preferably, in the start positioning mark, the front end and the back end are respectively a section of the optical track in a level signal corresponding to a certain unique waveform.

[0080] During moving of the incident light spot from left to right along the optical track, when the level signal of a certain unique waveform of the front end is identified, it indicates that the front end of the start positioning mark of the optical track is reached, and an optical track number and a sector number in the address field start to be read; when the level signal of a certain unique waveform of the back end is identified, it indicates that the back end of the start positioning mark is reached, the identification of the start positioning mark ends, then reading/writing of the data hologram in the sector starts, or moving to other positions to identify other start positioning marks.

[0081] By binary coding, the relevant information in the lead-in area, the lead-out area and the start positioning mark is recorded in the optical track. The binary encoding method proposed in this embodiment herein is simple and efficient, without involving a complicated encoding process, and can effectively screen out useful information in the optical track.

[0082] Obviously, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the technical solutions of the present invention, and are not intended to limit the specific embodiments of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the claims of the present invention shall be included within the protection scope of the claims of the present invention.