JP3842813B2 - Information storage device - Google Patents

Description

  The present invention relates to an information storage device for recording information on both grooves and lands of a recording medium in which grooves and lands as recording tracks are alternately formed.

  Conventionally, optical recording media have been widely used as recording media capable of recording and reproducing audio signals and image signals. In particular, magneto-optical recording media and phase change recording media are attracting attention as high-density recording media capable of rewriting information, and research and development have been extensive. In addition, research and development of information storage devices that perform information access to such optical recording media have been extensively conducted.

  An optical recording medium generally has a disk shape, and a spiral or concentric track is provided, and information is recorded on the track. In order to improve the recording density of the optical recording medium, two methods of shortening the track pitch and improving the linear recording density are conceivable. Both methods can be realized by shortening the wavelength of the semiconductor laser used for recording and reproduction. However, a semiconductor laser that stably oscillates a short wavelength such as green or blue at room temperature for a long time can be realized at low cost. It looks like it will take some time now.

  In such a situation, in a magneto-optical recording medium, magnetic super resolution (hereinafter referred to as MSR) in which a reproduction target is limited to an area smaller than a laser spot by applying a reproduction magnetic field is used. A technique for greatly improving the linear recording density by using a semiconductor laser of the current wavelength is being sought.

  In addition, as a technique for shortening the track pitch, a technique called land and groove recording in which information is recorded on both groove-like grooves and bowl-like lands alternately provided on a recording medium has been proposed. Development of information storage devices using technology is in progress. In this land and groove recording, both the groove and the land are used as tracks. For this reason, in land and groove recording, the track pitch is simply halved compared to a technique in which only one of the groove and land is used as a track, and if the linear recording density is the same, the recording density is doubled. Therefore, this is a very important technique for realizing high-density recording.

  By the way, in the case of land recording in which information is recorded only on lands, there is a groove between adjacent lands, and there is a gap between lands on which information is recorded. Therefore, information recorded on adjacent lands is reproduced information. Occurrence of mixed crosstalk is suppressed. Similarly, in the case of groove recording in which information is recorded only in the groove, since there is a land between adjacent grooves and there is a gap between the grooves in which information is recorded, the information recorded in the adjacent groove is reproduced information. The occurrence of crosstalk mixed in is suppressed. On the other hand, in the case of land and groove recording in which information is recorded on both the land and the groove, there is no separation between the tracks, so that the crosstalk occurs from the groove adjacent to the land or from the land adjacent to the groove. Inevitably affects the ability to reproduce information.

  Thus, for example, Patent Document 1 proposes a technique for reducing crosstalk from a land or a groove by appropriately selecting the depth of the groove. However, in such a groove whose depth is selected, there is a problem that the carrier level corresponding to the original reproduction information is lowered, and the level of the push-pull signal used as the tracking error signal is similarly lowered. . In addition, it has already been reported that the effect of reducing the crosstalk due to the selection of the groove depth is easily lost due to fluctuation of the Kerr ellipticity, focus error of the objective lens, spherical aberration, and the like.

Further, Patent Document 2 proposes a technique for reducing crosstalk by reversing the polarities of signals recorded in lands and grooves. However, when the polarities of the land and groove signals are reversed in magneto-optical recording, noise is generated at the boundary between the land and the groove, which is more problematic than crosstalk.
JP-A-8-7357 JP-A-9-153221

  In view of the above circumstances, an object of the present invention is to provide an information storage device that can reduce crosstalk.

The information storage device of the present invention that achieves the above object is an information storage device that records information on both grooves and lands of a recording medium in which grooves and lands as recording tracks are alternately formed.
A mark forming unit that forms a mark that is read by irradiation with light according to information to be recorded on the recording medium so as to have a mark length that is an integral multiple of a predetermined reference length;
The mark to be read out of the land and the groove forms the reference length when the mark is formed on the land by the mark forming unit and the reference length when the mark is formed on the groove by the mark forming unit. The crosstalk level that occurs when the mark formed on the land and the groove has the same reference length due to the mark formed on the other side due to the mark formed on the other side. A reference length setting section for setting each reference length to be suppressed to a level lower than the talk level;
A reading unit that reads the mark formed on the recording medium by irradiating light with a light amount equal to or less than a set maximum light amount; and
Each of the maximum amount of light when the reading unit reads the mark formed on the land and the maximum amount of light when the reading unit reads the mark formed on the groove can suppress the crosstalk to a predetermined level or less. And a maximum light amount setting unit for setting each maximum light amount.

  The inventor of the present invention has found that the crosstalk level when reading the formed mark can be reduced by appropriately setting each reference length when the mark is formed on the land or groove. A specific set reference length will be described in detail later.

  According to the information storage device of the present invention, each reference length when a mark is formed on a land or a groove by the mark forming unit is set to each reference length that suppresses the level of crosstalk, and each reference length is set. Since a mark having a mark length that is an integral multiple of is formed on the recording medium, crosstalk between adjacent tracks during information reproduction is reduced.

  In addition, by suppressing the occurrence of crosstalk, the signal-to-noise ratio is improved, and signal quality degradation can be minimized even with a narrow track pitch. Can do.

  Further, the larger the amount of irradiation light during reproduction, the larger the carrier is generated. On the other hand, large crosstalk is also generated. And the level of the crosstalk with respect to the same irradiation light quantity differs between a land and a groove. For this reason, the maximum amount of light is set so that the crosstalk is suppressed to a predetermined level or less for each of the land and the groove, and the amount of light less than the maximum amount of light is irradiated during reproduction. Information reproduction is ensured in both the land and the groove.

  As described above, according to the information storage device of the present invention, crosstalk between adjacent tracks can be reduced, and as a result, the track pitch can be narrowed to increase the information recording density. it can.

  Hereinafter, although an embodiment of the present invention is described, the technical scope of the present invention is not limited to this embodiment.

  In this embodiment, a magneto-optical disk (MO disk) is used as a recording medium, and information access to the MO disk is performed. First, the structure of the MO disk used in this embodiment will be described, and then the structure and operation of this embodiment will be described.

  FIG. 1 is a perspective view (A) and a sectional view (B) of an MO disk used in this embodiment.

  This MO disk 10 has a disk-shaped substrate 11, on which a bowl-shaped land 12 and a groove-shaped groove 13 are alternately provided concentrically. Both the land 12 and the groove 13 are used as tracks on which information is recorded. Here, as an example, the step d between the land 12 and the groove 13 is 50 nm, and the distance WG between the lands 12 and the distance WL between the grooves 13 are 1.2 μm. As a result, the track pitch TP is a narrow pitch of 0.6 μm.

  In an embodiment to be described later, while the MO disk 10 is rotated, a binary magnetization state is created in the land 12 or the groove 13 and is composed of a recording mark in one magnetization state and a space in the other magnetization state. Record information by writing a mark space string. Accordingly, both the land 12 and the groove 13 are used as recording tracks.

  FIG. 2 is a diagram showing recording marks and spaces (A) formed on lands and recording marks and spaces (B) formed on grooves.

  When no information is recorded, the entire recording track is in the same magnetization state as that of the space 21. The recording mark 20 is irradiated with light having a predetermined recording power in a spot shape on the back 12a of the land 12 shown in FIG. 2A and the bottom 13a of the groove 13 shown in FIG. As a result, the magnetization state is intermittently changed to the magnetization state of the recording mark 20 and formed. Further, the place where the magnetization state cannot be changed remains as the space 21. The mark space row formed of the recording marks 20 and the spaces 21 between the recording marks 20 formed in this way is irradiated with light of a predetermined reproduction power, and an MO signal is detected from reflected light as will be described later. Read.

  The land 12 and the groove 13 are divided into sectors in advance, and reading / writing of the mark space string is performed in units of sectors.

  FIG. 3 is a diagram showing a sector format.

  The left side of the figure is the head direction of the sector 30, and a header portion 31 is provided at the head of the sector 30. In the header portion 31, pits are formed in advance at the manufacturing stage, and predetermined information as described later is written in the pits.

  A sector mark SM32 representing the head of the sector 30 is recorded at the head of the header portion 31, and the sector mark SM32 is followed by a write cycle of ID35 which is information for the information storage device to recognize the address of the sector. A repetitive pattern ID-VFO 33 to be reproduced is described. The ID 35 is read according to the writing cycle reproduced by the repetitive pattern ID-VFO 33. Next to the repetitive pattern ID-VFO 33, an address mark AM34 for determining the reading start position of ID35 is described, and ID35 is described next to the address mark AM34.

  The header portion 31 is followed by an area where information is recorded by a mark space sequence formed by irradiation light and a recording magnetic field as described above. Immediately after the header portion 31, a repetitive pattern MO-VFO 36 that reproduces the write cycle of the data area 37 in which data is recorded is written. Data in the data area 37 is read according to the writing cycle reproduced by the repetitive pattern MO-VFO 36. It is known that the rotation unevenness occurs when the MO disk rotates. However, by reproducing the write cycle of the data area 37 by the repetitive pattern MO-VFO 36 written on the MO disk, the influence of the rotation unevenness is canceled. Data in the data area 37 can be read reliably. A data area 37 follows the repetitive pattern MO-VFO 36, and a buffer 38 is prepared after that.

  As described above, information is written in the header portion 31 by pits, and it is practically impossible to set the size of the pits to about 0.5 μm or less in consideration of the reproduction technology. On the other hand, in the case of a recording mark formed in the data area 37 or the like, there is a reproducing technique such as MSR that can be reproduced even if the size is 0.5 μm or less. It is desirable to make the mark size smaller than the pit size. Further, considering the ease of realization of the signal processing circuit, it is desirable that the pit size is an integral multiple of the size of the recording mark. Considering these circumstances, the optimum pit size is twice the size of the recording mark.

  By the way, in order to record as much information as possible in the MO disk 10 shown in FIG. However, in the embodiment to be described later, a method of writing a mark space row while rotating the MO disk 10 shown in FIG. 1 at a constant rotational speed is adopted. Therefore, if the writing speed is constant, the outer periphery of the MO disk 10 is fixed. The recording density in the vicinity is lower than the recording density in the vicinity of the center. Therefore, here, the MO disk 10 is divided into a plurality of annular bands each composed of a plurality of tracks, and a mark space string is written at a faster writing speed in a band closer to the outer periphery. Here, it is assumed that each band is associated with a band number for distinguishing the bands from each other.

  Hereinafter, the structure and operation of this embodiment will be described.

  The information storage device of the present embodiment includes an optical pickup and a magnetic head that read and write the mark space column on the MO disk in cooperation with each other, and a control unit that controls reading and writing of the mark space column by the optical pickup and the magnetic head. It has been. The optical pickup and the magnetic head cooperate with each other to operate as a mark forming unit and a reading unit according to the present invention, and the control unit serves as a reference length setting unit, a clock control unit, and a maximum light amount setting unit according to the present invention. Controls the setting of various parameters.

  FIG. 4 is a block diagram showing the periphery of the optical pickup of the information storage device of this embodiment.

  The optical pickup 60 includes a fixed optical system 40 having a laser diode and a light receiving element, a carriage 47 capable of moving a light beam along the MO disk, and an addition / subtraction circuit for obtaining various signals according to light received by the light receiving element. 52, 53, 54, 55.

  The laser diode 41 emits laser light as a diffused light beam having an elliptical cross section, and the intensity of the laser light emitted by the laser diode 41 is controlled by a laser diode drive circuit 61. The laser diode drive circuit 61 controls the laser diode 41 in accordance with the write data created by the write data creation circuit 62. Details of the write data will be described later.

  The laser light emitted from the laser diode 41 is incident on the beam splitter 44 through a coupling lens 42 that converts the diffused light beam into a parallel light beam and a perfect circle correction lens 43 that rounds the cross section of the laser light beam. The light reflected by the beam splitter 44 is collected by the lens 45 and received by the light receiving element 46 for monitoring emitted light. The output signal of the light receiving element 46 for monitoring emitted light is fed back to the laser diode drive circuit 61.

  Further, the light transmitted through the beam splitter 44 is guided to the irradiation position on the MO disk 10 by the carriage 47 and irradiated to the MO disk 10. The MO disk 10 is rotated at a constant rotational speed by a motor 71. A predetermined control signal is input to the motor 71 and the above-described laser diode drive circuit 61 and write data creation circuit 62 from a microcomputer (MPU, DSP) to be described later.

  At the time of writing the mark space string, write data corresponding to the write information DATA is created by the write data creation circuit 62, and a pulsed laser according to the write data is irradiated onto the MO disk 10. Then, the recording film of the MO disk 10 is heated to a predetermined temperature or higher by the laser light irradiated to the MO disk 10, and the recording magnetic field is applied to the region including the irradiation position on the MO disk 10 by the magnetic head 70. Is multiplied. As a result, a recording mark is formed on the MO disk 10, and information is recorded by the mark space string.

  When reading the mark space row, the MO disk 10 is irradiated with continuous light that does not overheat the recording film of the MO disk 10, and a reproducing magnetic field is applied by the magnetic head 70. When reading the concave and convex pits, reading is performed only by light irradiation, and a reproducing magnetic field is not required.

  The return light from the MO disk 10 is reflected by the beam splitter 44, passes through the cylindrical lens 49 and the composite element 50 that cause astigmatism, and is received by the light-receiving element 51 for detecting a reproduction signal.

  An output signal from the reproduction signal detecting light receiving element 51 is input to each of the four addition / subtraction circuits 52, 53, 54, and 55, and the four addition / subtraction circuits 52, 53, 54, and 55 respectively output focus error signals (FES). ), A track error signal (TES), an MO signal corresponding to the above-described mark space sequence, and an ID signal corresponding to the above-described pit are detected.

  FIG. 5 is a detailed view of the composite element 50.

  The composite element 50 is formed by bonding a Wollaston prism 50a and a lens 50b, and divides the incident light L0 into three lights of two refracted lights L1 and L2 having a plane of polarization orthogonal to each other and a straight light L3. To do.

  FIG. 6 is a detailed view of the light receiving surface of the reproduction signal detecting light receiving element 51.

  The light receiving surface of the reproduction signal detecting light receiving element 51 has six areas A, B, C, D, E, and F, and the reproduction signal detecting light receiving element 51 is appropriately positioned with respect to the composite element 50. Thus, of the three lights divided by the composite element 50, two refracted lights L1 and L2 are received in the areas E and F, respectively, and the straight light L3 is divided and received in the areas A, B, C, and D. Then, six output signals SA, SB, SC, SD, SE, and SF having a signal intensity proportional to the intensity of each light received in each of the six regions A, B, C, D, E, and F are output. .

  The addition / subtraction circuit 52 shown in FIG. 4 performs a calculation of (SA + SC) − (SB + SD) based on the astigmatism method to obtain a focus error signal. The adder / subtractor circuit 53 performs an operation of (SA + SB)-(SC + SD) based on the push-pull method to obtain a track error signal, and the adder / subtractor circuit 54 performs an operation of SE-SF to obtain an MO signal, 55 calculates SE + SF to obtain the ID signal. The focus error signal and the track error signal are used for focus control and tracking control of irradiation light by the microcomputer described above. Description of focus control and tracking control is omitted.

  Next, the mark length of the recording mark formed on the MO disk by the optical pickup and the magnetic head will be described.

  FIG. 7 is an explanatory diagram of the mark length of the recording mark.

  The upper part of FIG. 7 shows a clock signal CLK used as a reference for the mark length of the recording mark when the recording mark is formed. The cycle of the clock signal CLK is in accordance with the band number described above. Is set. As described above, since the MO disk rotates at a constant rotational speed, if it is within the range of about one band as described above, it is only a substantially constant length during the period “1T” of the clock signal CLK. It is considered that the light beam moves relative to the track. This certain length is the reference length in the present invention.

  When the mark space string is written to the MO disk, data DATA including a string of bits representing “1” or “0” representing information recorded on the MO disk by the write data creation circuit 62 shown in FIG. Are modulated according to a predetermined modulation code, and a write signal based on the clock signal CLK is generated. Here, as a modulation code, an arbitrary bit string is reversibly converted into a bit string satisfying the restriction that “1” is prohibited from being continuous and at least one “7” exists between each “1”. A modulation code RLL (1, 7) is used.

  In the lower part of FIG. 7, as an example of the write signal, a write signal having a pattern called a 2T pattern in which a recording mark having a mark length corresponding to two periods of the clock signal CLK is formed is shown. The 2T pattern write signal corresponds to a bit string “1010101...”. When the mark space sequence is written in accordance with the 2T pattern write signal, a recording mark having a mark length twice as long as the reference length is formed. When the mark space string is read, the write cycle is reproduced by the repetitive pattern MO-VFO 36 shown in FIG. 3, and the cycle of the clock signal CLK is set to the same cycle as the write cycle. In the so-called mark edge recording method, the mark edge recording method determines whether the read signal obtained from the mark space sequence written in the data area 37 mainly rises or falls in synchronization with the clock signal CLK. (That is, the mark length and space length) are recognized, and in the so-called mark position recording method, the mark position of the recording mark is recognized and data is read.

  In this embodiment, the period TL of the clock signal CLK when the recording mark is formed on the land and the period TG of the clock signal CLK when the recording mark is formed on the groove are the same as the period TL. The crosstalk level is set to be lower than the crosstalk level in the case. Here, the cause of crosstalk and the action of suppressing the crosstalk level will be described.

  FIG. 8 is a diagram illustrating a state in which a mark space column is written in both the land and the groove.

  Here, lands 12 and grooves 13 alternately provided on the MO disk are shown, and a mark space row composed of recording marks 20 and spaces 21 written in both the lands 12 and the grooves 13 is shown. An example is shown.

  For example, when the mark space sequence written on the land 12 is read out to obtain a read signal corresponding to the mark space sequence, the focused spot is tracked on the land 12. Then, the mark space row is read, but a condensing spot is applied to a part of the recording mark 20 formed on the groove 13 adjacent to the land 12, and the recording mark 20 formed on the groove 13 is read. A phenomenon occurs in which the resulting crosstalk signal is mixed with the read signal. Although this crosstalk signal is a signal having a relatively low intensity with respect to the read signal, in general, since the information storage device has been devised to increase the read sensitivity of the mark space sequence, the crosstalk signal is There will often be a situation where it is mistaken for the original read signal. The crosstalk signal thus misidentified is substantial crosstalk, and even if the signal strength of the crosstalk signal is large, the level of crosstalk is low if the frequency of misidentification is small.

  By the way, as a method for recognizing the mark length and mark position of the recording mark 20 from the read signal, the determination of the rise and fall of the read signal as described above is performed in synchronization with the clock signal CLK shown in FIG. The method is adopted. Even if the crosstalk signal has the same signal strength, if the rise and fall timings of the crosstalk signal are deviated from the clock signal CLK, the frequency with which the crosstalk signal is mistaken for the original read signal is increased. The inventors of the present invention paid attention to the fact that it was reduced. In particular, in the mark edge recording method, it was found that the possibility that a crosstalk signal is mistaken as a read signal is small because the edge of the recording mark being read is shifted from the edge of the recording mark of the adjacent track. .

  At the time of reading the mark space string, the clock signal CLK corresponding to the reference length at the time of writing in the track to be read is reproduced, and the mark space string is read by the clock signal CLK. Therefore, when the read mark is formed, if the shortest mark length in the land is different from the shortest mark length in the groove by appropriately selecting the ratio of the reference length in the land to the reference length in the groove, the edge of the recording mark As a result, when reading the mark space row, the rise and fall timing of the crosstalk signal caused by the recording mark on the track adjacent to the track to be read is adjusted. Thus, it has been thought that crosstalk can be reduced by shifting the clock signal CLK for reading. Such an effect of reducing the crosstalk by appropriately selecting the ratio of the reference lengths also occurs in the mark position recording method.

  Therefore, in the information storage device of the present invention, each reference length is set by the reference length setting unit to each reference length that shifts the rising and falling timings of the crosstalk signal with respect to the clock signal CLK. The crosstalk level when reading the mark space column is reduced. Further, as described above, in the embodiment shown in FIG. 4, the cycle TL of the clock signal CLK when writing the mark space column to the land, and the cycle TG of the clock signal CLK when writing the mark space column to the groove Each reference length is set by appropriately setting each of.

  FIG. 8 shows a recording mark 20 and a space 21 formed by setting the reference lengths of the land 12 and the groove 13 as described above. The shortest mark length of the recording mark 20 formed on the land 12 is shown. LL is different from the shortest mark length ML of the recording mark 20 formed in the groove 13.

  When the above-described modulation code RLL (1, 7) is used, since there are only mark lengths of 2, 3,..., 8 times the reference length as the mark length of the recording mark, the land 12 When the respective reference lengths are set such that the ratio of the reference lengths of the grooves 13 is shifted from the ratio A / B represented by a combination of two arbitrary natural numbers A and B from 2 to 8. It is theoretically predicted that crosstalk will be reduced. However, if the least common multiple of the two natural numbers A and B is a large value of 30 or more, even when the ratio of the reference length is equal to A / B, the timing of the rise of the crosstalk signal and the timing of the clock signal are shifted and the crosstalk Is considered to be reduced. Furthermore, the following results were obtained from specific experiments.

  When the reference length ratio is 1.00, the crosstalk level naturally exceeds the allowable level.

  The allowable level is also exceeded when the reference length ratio is 0.93 (≈13 / 14).

  When the reference length ratio is 0.9 (= 9/10), it is almost the allowable level.

  When the reference length ratio is 0.87 (≈13 / 15), it is well below the allowable level.

  When the reference length ratio is 0.81 (≈13 / 16), it is slightly below the allowable level.

  From these results, it was found that the crosstalk level can be suppressed to an allowable level or less when the reference length ratio is 0.80 or more and 0.90 or less. The range of the reference length ratio from 0.80 to 0.90 is considered not to depend on the type of modulation code. However, the ratio of the reference lengths set in the present invention is not limited to the reference length ratio of 0.80 or more and 0.90 or less. In the information storage device of the present embodiment, the control unit described below uses the cycle TL of the clock signal CLK when writing the mark space string to the land so that the reference length ratio is 13/15 = 0.87, The period TG of the clock signal CLK at the time of writing the mark space row to the groove is set.

  FIG. 9 and FIG. 10 are diagrams showing the control unit of the information storage device of this embodiment. FIG. 9 shows the operation at the time of writing the mark space sequence, and FIG. 10 shows the reading of the mark space sequence. The behavior at the time is shown.

  The control unit includes the laser diode drive circuit 61 and the write data creation circuit 62 described above, and also includes a read circuit 63, a memory 64, a clock generation circuit 65, a reference clock generation circuit 66, and a microcomputer. 67 and ROM 68 are also provided.

  The clock according to the present invention is constituted by the clock generation circuit 65 and the reference clock generation circuit 66. In the reference clock generation circuit 66, the system clock oscillator 66a oscillates a system clock that is always maintained at a constant period. The system clock is input to frequency divider 66b, and parameters M and N (M and N are natural numbers) are designated by frequency divider 66b by microcomputer 67 to have a period of M / N times the period of the system clock. A reference clock REFCLK is generated. Then, the reference clock REFCLK generated by the reference clock generation circuit 66 or the ID signal or the MO signal output from the optical pickup 60 is selected and input to the clock generation circuit 65 by the microcomputer 67. However, in FIG. 9, the output of the MO signal is not shown. The clock generation circuit 65 receives the designation of the parameter A (integer) from the microcomputer (MPU, DSP) 67 and generates and outputs a rectangular wave data clock DATACLK whose period is A times the input signal period. This data clock DATACLK is used as the clock signal CLK shown in FIGS.

  The ROM 68 stores in advance various parameters M and N corresponding to the medium type, band number, land / groove type, and the like.

  When writing the mark space string, first, the microcomputer 67 reads out the parameter for detecting the sector mark SM32 shown in FIG. The microcomputer 67 operates the switch 69 to input the reference clock REFCLK to the clock generation circuit 65 and designates a value “1” as the parameter A to the clock generation circuit 65. As a result, the data clock DATACLK having a cycle set for sector mark detection is output from the clock generation circuit 65 and input to the read circuit 63. The ID signal obtained by the optical pickup 60 is binary-determined by the read circuit 63 in synchronization with the data clock DATACLK, whereby the sector mark SM32 is detected and stored in the memory 64.

  Next, the repetitive pattern ID-VFO 33 on the MO disk is read by the optical pickup 60, and a periodic signal corresponding to the repetitive pattern ID-VFO 33 is output as an ID signal. The microcomputer 67 operates the switch 69 to input an ID signal to the clock generation circuit 65 and designates a value “4” as the parameter A in the clock generation circuit 65. As a result, the data clock DATACLK having the same period as the writing period of ID 35 is output from the clock generation circuit 65 and input to the read circuit 63. The ID signal obtained by the optical pickup 60 is binary-determined by the read circuit 63 in synchronization with the data clock DATACLK, whereby the ID 35 is read and stored in the memory 64. The ID stored in the memory 64 is used for confirming the sector address.

  Thereafter, the microcomputer 67 reads the parameter for land writing or the parameter for groove writing from the ROM 68 and designates it to the reference clock generation circuit 66 according to whether the object of data writing is a land or a groove. The microcomputer 67 operates the switch 69 to input the reference clock REFCLK to the clock generation circuit 65 and designates a value “1” as the parameter A to the clock generation circuit 65. As a result, the data clock DATACLK set in the data writing cycle is output from the clock generation circuit 65 and input to the write data generation circuit 62 as the clock CLK shown in FIG. Also, data DATA shown in FIG. 4 representing information written to the MO disk is input from the memory 64 to the write data creation circuit 62, and write data is created according to the data clock DATACLK and the data DATA as described above. . Further, as described above, write data is input to the laser diode drive circuit 61, and the laser diode 41 is controlled by the laser diode drive circuit 61.

  Hereinafter, the operation at the time of reading the mark space sequence will be described with reference to FIG. However, in FIG. 10, the above-described write data creation circuit 62, laser diode drive circuit 61, and laser diode 41 are not shown.

  At the time of reading the mark space string, the sector mark SM32 is detected and the ID 35 is read as described above.

  Thereafter, the repetitive pattern MO-VFO 36 is read by the optical pickup 60, and a periodic signal corresponding to the repetitive pattern MO-VFO 36 is output as an MO signal. The microcomputer 67 operates the switch 69 to input an MO signal to the clock generation circuit 65 and designates a value “4” as the parameter A in the clock generation circuit 65. As a result, the data clock DATACLK having the same cycle as the data write cycle of the data area 37 is output from the clock generation circuit 65 and input to the read circuit 63. Further, the microcomputer 67 sets the maximum intensity of the reproduction laser beam that the optical pickup 60 irradiates the MO disk according to whether the track to be read is a land or a groove. As a result, both generation of a sufficiently high level carrier and maintenance of a crosstalk level below the allowable level can be realized.

  The MO signal obtained by the optical pickup 60 is turned on / off by the read circuit 63 in synchronization with the data clock DATACLK, whereby the data in the data area 37 is read and stored in the memory 64. At this time, the crosstalk caused by the data stored in the data area 37 of the adjacent track is suppressed to a substantial crosstalk level because the signal on / off timing is shifted from the timing of the data clock DATACLK. Data stored in the memory 64 is output to the outside of the information storage device.

  Examples of the present invention will be described below.

  In this embodiment, in the band existing at a distance of 36.0 mm from the center of the MO disk, the clock frequency at the time of mark formation for the land is set to 67.86 MHz, and the clock frequency at the time of mark formation for the groove is 78.30 MHz. Set to. The number of revolutions of the disk is 2700 revolutions / minute. As a result, the reference length of the recording mark formed on the land (that is, the length corresponding to the clock cycle “1T”) is 0.30 μm, and the recording mark formed on the groove The reference length is 0.26 μm. Therefore, the reference length ratio between the land and the groove is 13/15 = 0.87. The mark length of the recording mark in the 2T pattern is twice the reference length, that is, 0.60 μm for the land and 0.52 μm for the groove. The mark length of the recording mark in the 8T pattern is eight times the reference length.

  With such a setting of the clock frequency or the like, a mark space string of 8T pattern was written in the groove, and the land was tracked to obtain a crosstalk signal. The obtained crosstalk signal was compared with the periodic signal of the 8T pattern at the time of mark formation to obtain a so-called error rate. Similarly, an 8T pattern mark space string was written in the land, and the groove was tracked to obtain a crosstalk signal, thereby obtaining an error rate.

  Further, as a comparative example, the error rate was obtained in the same manner as described above when the land and groove reference lengths were both 0.28 μm.

  FIG. 11 is a graph showing experimental results of Examples and Comparative Examples.

  The vertical axis of this graph indicates the error rate, and the horizontal axis indicates the intensity of the laser light irradiated on the MO disk during reproduction. A line 76 parallel to the horizontal axis indicates the allowable level of crosstalk.

  A graph 72 with a black circle and a graph 73 with a black square show experimental results of the comparative example, and a graph 74 with a white circle and a graph 75 with a white square show the experimental results of the example. Is shown.

  A graph 72 with a black circle and a graph 74 with a white circle indicate crosstalk caused by a recording mark on a land when the groove is tracked. The experimental result of the example is a comparative example. It shows a lower level of crosstalk than the experimental results. In the comparative example, in order to keep the crosstalk level below the allowable level indicated by the line 76, the laser beam intensity during reproduction must be limited to about 3.8 mW or less. It can be seen that if the light intensity is limited to about 4.3 mW or less, the level of crosstalk can be suppressed to an allowable level or less. That is, in the example, information reproduction was possible with a laser beam stronger than that in the comparative example, and the C / N ratio was improved.

  A graph 73 with a black square and a graph 75 with a white square show crosstalk caused by a recording mark on the groove when the land is being tracked. It shows a slightly higher level of crosstalk than the experimental result of the comparative example. This is probably because the mark length of the recording mark on the groove is longer than the mark length of the recording mark on the land, so that the crosstalk signal becomes strong and the false positive rate increases. However, the crosstalk level indicated by the graph 75 with the white square is sufficiently lower than the allowable level indicated by the line 76, and the maximum laser light intensity that can suppress the crosstalk level below the allowable level. Is a high laser light intensity of about 4.7 mW in both the example and the comparative example, and information reproduction with a high C / N ratio is possible. That is, it can be seen that the crosstalk level caused by the recording mark on the groove is sufficiently low in both the example and the comparative example.

  Thus, the crosstalk level in the example was suppressed to be lower than the crosstalk level in the comparative example. Further, in the embodiment, the reference length of the recording mark of the land that causes stronger crosstalk among the lands and the grooves is set to be short, and thereby the crosstalk reduction effect can be enhanced. As a result, signal quality degradation can be minimized even with a narrow track pitch, and information recording can be made dense.

  The information storage device of the present invention may be an information storage device that records information on an MSR recording medium, or may be an information storage device that records information on an MO recording medium using a magnetic field modulation method, Alternatively, it may be an information storage device that records information on a phase change optical disk.

It is the perspective view (A) and sectional drawing (B) of the MO disk used by this embodiment. It is a figure which shows the recording mark and space (A) which were formed in the land, and the recording mark and space (B) which were formed in the groove. It is a figure which shows the format of a sector. It is a block block diagram which shows the optical pick-up periphery of the information storage device of this embodiment. It is detail drawing of a composite element. It is a detailed view of a light receiving surface of a light receiving element for reproducing signal detection. It is explanatory drawing about the mark length of a recording mark. It is a figure which shows the state in which the mark space row | line was written in both land and a groove | channel. It is a figure which shows the operation | movement at the time of mark space row | line | column writing of the control part of the information storage device of this embodiment. It is a figure which shows the operation | movement at the time of the mark space row | line | column reading of the control part of the information storage device of this embodiment. It is a graph which shows the measurement result of an Example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 MO disk 11 Substrate 12 Land 13 Groove 20 Recording mark 21 Space 40 Fixed optical system 41 Laser diode 42 Coupling lens 43 Round correction lens 44 Beam splitter 45 Lens 46 Outgoing light monitoring light receiving element 47 Carriage 49 Cylindrical lens 50 Composite element 50a Wollaston prism 50b Lens 51 Reproduction signal detection light receiving element 52, 53, 54, 55 Addition / subtraction circuit 60 Optical pickup 61 Laser diode drive circuit 62 Write data creation circuit 63 Read circuit 64 Memory 65 Clock generation circuit 66 Reference clock generation circuit 66a System clock oscillator 66b Frequency divider 67 Microcomputer 68 ROM
69 switch 70 magnetic head 71 motor

Claims (1)

In an information storage device for recording information on both grooves and lands of a recording medium in which grooves and lands as recording tracks are alternately formed,
A mark forming unit that forms a mark that is read by irradiation with light according to information to be recorded on the recording medium so as to have a mark length that is an integral multiple of a predetermined reference length;
The mark to be read out of the land and the groove forms the reference length when the mark is formed on the land by the mark forming unit and the reference length when the mark is formed on the groove by the mark forming unit. The crosstalk level that occurs when the mark formed on the land and the groove has the same reference length due to the mark formed on the other side due to the mark formed on the other side. A reference length setting section for setting each reference length to be suppressed to a level lower than the talk level;
A reading unit that reads and irradiates the mark formed on the recording medium with light of a light amount equal to or less than a set maximum light amount;
Each of the maximum light amount when the reading unit reads the mark formed on the land and the maximum light amount when the reading unit reads the mark formed on the groove can suppress the crosstalk to a predetermined level or less. An information storage device comprising a maximum light amount setting unit for setting each maximum light amount.

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