KR100317766B1 - High Density Information Recording and Playback Method - Google Patents

Abstract

A recording laser having a first output and a wavelength and a reproduction laser having a second output lower than the first output portion and a second wavelength shorter than the first wavelength are used, and the laser for recording and reproduction is about 0.55. A spot which is optically determined from the wavelength of the recording laser and the NA of the objective lens by a shielding plate in the optical system that irradiates onto the disc-shaped recording medium using an objective lens and irradiates the recording characteristics of the disc-shaped recording medium and the laser. A micro mark of about 1/4 or less in comparison with the size is formed on the recording medium, and in the recording method, two-dimensional recording is performed in which marks are arranged at grid points of a two-dimensional grid that extends in the track direction and the track radius direction. As a method, a reproduction signal from the mark on a two-dimensional lattice point is detected, and information that processes the signal by using the reproduction signals from each mark is detected. It is disclosed in optical recording and reproducing method.

Description

High Density Information Recording Playback Method

This application is part of US patent application Ser. No. 08/321619, filed October 12, 1994, and US Patent application Ser. No. 08/285003, a continuing application of the August 2, 1994 application of US patent application Ser. No. 07/704227, now abandoned; In a continuation-in-part, the disclosures of US patent applications 08/321619 and 08/285003 are incorporated into the present invention.

At present, the surface density of the optical disk device of the product is about 880 megabits per square inch (Mb / in ² ), and at the research and development level, it is possible to comprehensively realize the strictness of the environmental conditions in which the optical disk is used. What you can do is about three times the product level. The wavelength of the optical disk device made of the product is 780 nm, the NA of the objective lens is 0.55, the recording ice type is mark length recording, and the servo method is continuous servo. The reference is a specification document of ECMA (European Computer Manufacturing Association).

It is an object of the present invention to realize the most dense recording and reproducing characteristics of an optical disc by using the presently feasible components. The value of the realized recording density is 10 Gbit / in ² .

[Initiation of invention]

The purpose of the present invention is as follows.

(1) The recording laser employs a semiconductor laser having a power of 50 mW and a wavelength of 680 nm, and a reproducing SHG (second harmonic generation) light source that oscillates at a wavelength of 530 nm with an output of 15 mW or more.

(2) The NA of the objective lens is 0.55, and the chromatic aberration is corrected for the wavelengths for recording and reproduction.

(3) As the recording medium, a micromark of 1/4 or less can be produced in comparison with the spot size determined from the wavelength and the NA of the objective lens. In addition, a medium having super resolution characteristics using a difference in magnetic properties with respect to the temperature of each layer of the magnetic multilayer film is also used.

(4) As the optical system, a super resolution optical system that can be made smaller on the disk plane than the spot size determined from the wavelength and NA of the objective lens is used. Also, a plurality of spots are created at the time of recording or reproduction.

(5) In the recording method, two-dimensional recording is performed in which marks of the same circular shape are arranged at grid points of a two-dimensional grid extending in the track direction and the track radial direction.

(6) The reproduction method detects a reproduction signal from a mark on a two-dimensional lattice point, performs signal processing using each of the reproduction signals from each mark, and detects information. At this time, the timing is synchronized with the lattice point. Irradiating light with a peak power larger than that irradiated with a direct current light from a light source is pulsed, and the reflected light is detected by the timing synchronized with a grating point.

(7) Tracking uses sample servo, creates a write and redefine clock from discretely installed embedded bits, and detects a tracking error signal from the wobble mark.

Recording is done using a high power laser with a wavelength of 680 nm, which is currently available as a light source and can be directly modulated, with a spot size of about 1.23 microns. Moreover, the spot size is reduced to 0.87 microns, which is about seven percent, while giving an optical super-resolution effect and considering the efficiency of light output. This spot is used to record a mark having a diameter of 0.22 microns on a medium capable of forming a mark of 1/4 or less of the recording spot. As the structure of this medium

(1) A buried mark layer in which a micromark having a shape aimed at about 0.22 microns is recorded in advance, a recording spot is placed thereon by a sample servo, and a click is made from the embedded bit. Therefore, the information mark is recorded in the reproduction layer depending on whether or not the buried mark is self-transferred. The mark recorded in the reproduction layer becomes a buried mark shape and becomes a micro mark that does not depend on the recording spot.

(2) A micro mark that does not depend on the recording spot is created by locally changing the recording sensitivity characteristic in the micro area. As a specific means, a laser beam is irradiated to the recording film, and the structure is loosened locally to weaken the coercive force.

(3) A pattern of minute unevenness is preliminarily provided on the substrate of the optical disk by injection, and the recording marks are easily formed locally by the nucleus of the formation of the magnetic marks. This creates a micromark that does not depend on the recording spot.

A plurality of or a single spot is positioned on the mark formed by the above using sample servo, pulse irradiation is performed when the light spot is positioned on the two-dimensional lattice point according to the clock generated from the buried mark, and the reflected light is directed to the lattice point. Detection is performed at the synchronized timing, and each sample is sampled. The amount of interference from the adjacent grid points is obtained in advance in the learning area, and a process of removing the amount of interference from the detection signal after the sample holder is performed to detect the presence or absence of a mark recorded at the grid point.

The present invention relates to a high density of an apparatus for optically recording and reproducing information, particularly an optical disc apparatus for recording and reproducing information on a disc-shaped medium.

1 is a plan view for explaining the relationship between a recording mark and a recording / reproducing spot of the present invention.

2 is a block diagram of the optical system of the optical super resolution of the present invention.

3 is an explanatory diagram of the optical filter configuration of the optical super resolution of the present invention.

4 is a block diagram illustrating the effect of the optical super resolution of the present invention.

5 is a block diagram explaining the relationship between the coercive force and the temperature on the recording film.

6 is an explanatory diagram of a recording process of a magnetization mark.

7A and 7B are diagrams illustrating the configuration and measurement results of one embodiment of the medium of the present invention, respectively.

8A and 8B are diagrams illustrating the configuration and measurement results of another embodiment of the present invention, respectively.

9A and 9B are views for explaining the configuration and measurement results of another embodiment of the medium of the present invention, respectively.

10A and 10B are block diagrams of the control performance of the magnetization marks of the TbFeCo composition.

11 is a block diagram of a temperature distribution according to light spot irradiation.

12 is a graph of coercive force and recording temperature.

13 is a graph of variation in mark diameter due to variation in recording power of RE rich composition.

14 is a graph of variation in mark diameter due to variation in recording power of TM rich composition.

Fig. 15 is a block diagram of the recording and reproducing system of the present invention.

16 is a plan view of the spot arrangement of the recording and reproduction system of the present invention.

17 is an explanatory diagram of a tracking error signal detection process of the present invention.

18 is a block explanatory diagram of an arithmetic circuit for detecting the tracking error signal of the present invention.

19 is a graph illustrating the tracking error signal detected in accordance with the present invention.

20 is a circuit diagram of a control circuit using the tracking error signal detected according to the present invention.

21 is a plan view for explaining the track layout of the recording method of the present invention.

22 is a plan view for explaining another track layout of the recording method of the present invention.

23 is a plan view of the explanation of learning the interference coefficient for reproduction of the present invention.

24 is a schematic block diagram of a data write circuit of the present invention.

25 is a block diagram illustrating a data detection unit of the present invention.

26 is a block diagram for explaining a data selection section of the present invention.

Fig. 27 is a block diagram for explaining an embodiment of the data recording section of the present invention.

28 is a schematic block diagram of the data reproducing circuit of the present invention.

Fig. 29 is a block diagram for explaining the almost detection unit in the data reproduction of the present invention.

30 is a block diagram illustrating a synchronous correction unit of recording and reproducing of the present invention.

31 is a block diagram for explaining reproduction signal processing of the present invention.

32 is a diagram illustrating an area recognition circuit of the present invention.

33 is an explanatory diagram of an interference coefficient.

34 is a graph of the spectral characteristics of a polyaryl ethene derivative.

35 is a configuration diagram of the photodetector of the present invention.

36 is a graph showing the relationship between the incident energy density and the transmittance of the photochromic material.

37 is a graph showing the relationship between the incident power density and the transmitted light power density of the photochromic material.

38A and 38B are principle diagrams of magnetic super resolution.

39A, 39B, 39C, and 39D are views for explaining mark arrangement and signal processing in the recording and reproducing method of the present invention.

40 is a diagram for explaining a signal and a processing area detected from marks existing in the grid point intervals of the present invention.

41 is an explanatory diagram of partial responses 1 and 1 in the optical disk.

42 is a view for explaining the partial response process which eliminates the interference from the adjacent track of the present invention.

43A and 43B are diagrams for explaining waveforms of partial responses when the interference from adjacent tracks of the present invention is removed and not removed.

44A to 44D are diagrams for explaining the principle of the pulse regeneration method.

45 is a graph showing the frequency spectrum of the signal level and the noise level.

46 is a graphical representation of the frequency spectrum of individual noise levels.

FIG. 47 is a graph of regenerative power dependency characteristics of signal level and noise level.

48 is a graph illustrating regenerative power dependency characteristics of SN.

49 is a temperature dependent characteristic graph of Kerr rotation angle.

50 is a graph showing the relationship between the linear velocity and the peak temperature holding power and the SN at that time.

51 is a graph of temperature distribution at the time of direct current irradiation and pulse irradiation.

52A to 52D are explanatory diagrams of the second pulse regeneration method.

Best Mode for Carrying Out the Invention

1 shows the appearance on the recording medium of the present invention.

The recording spots 101, 101 'and 101 "perform optical superresolution in the radial direction of the disc using a semiconductor laser having a wavelength of 685 nm as a light source. The laser from the semiconductor laser is formed on the disc surface using an optical system having a numerical aperture of 0.55. The size of the recording spot 101 is 1.24 mu m in the circumferential direction and 0.87 mu m in the radial direction, and the size of the information mark 102 to be recorded is 0.22 mu m in the disk circumferential direction and about 0.30 mu m in the radial direction. The minimum spacing between the information marks 102 is about 0.22 占 The pitch of the track is about 0.30 占 The reproduction spots 103a, 103b, 103c are magnetic super-resolutions (FADs), which describe lasers having a wavelength of 533 nm. And an optical super-resolution, with a size of 0.96 mu m in the circumferential direction of the disk and 0.67 mu m in the radial direction, and the clock mark 104, wobble mark 105, and address mark (before the information mark 102). 106) the back Formed.

2 shows a concrete configuration of an optical super resolution. The light from the semiconductor laser 261 is made into a parallel beam by the coupling lens 202, guided to the objective lens 205 through the prism 204, and the like and formed on the imaging surface 206. The shield plate 203 is inserted in this optical path.

3 shows the shield plate 203 in detail. The shield plate 206 shields a part of the beam of diameter r by the diameter r 'about the optical axis. Shielding (alpha) is defined as ratio (r '/ r) of (r) and (r'). When the shielding ratio d is increased, separate light spots are seen on both sides of the center spot focused on the imaging surface 206, and the center intensity of the center spot decreases. However, the spot size in the middle becomes small. These spots correspond to reference numerals 101, 101 ′, 101 ″ in FIG. 1.

4 shows the relationship between the shielding ratio α and the spot size. exp. is an experimental value, cal. is a calculated value, and the reference value of the normalized spot diameter is a case where the shielding ratio (alpha) is zero. When the spot size is reduced to about seven, the chape ratio is about 0.7, and the spot center strength is about 50%. At this time, the intensity of the spots on both sides is about 20% of the intensity of the spot in the middle, and there is no problem because the spots on both sides are not recorded at the time of recording.

Using the above-described recording spot, the principle of formation of a mark having a size of about 1/4 of the spot size will be described. The magnetic wall of the magneto-optical mark is determined by the stable conditions of magnetic energy. The sum of the magnetic field Htotal, which is the basis of the force that makes the magnetic domain wider when σw is the magnetic domain energy per unit area, Ms is the saturation magnetization, r is the radius of the magnetic domain, Hd is the anti-magnetic field acting on the magnetic wall, and Hext is the external magnetic It is represented by the following formula (1).

Htotal = Hext + Hd-σw / 2rMs

The magnetic wall is determined where the balance between the coercive force Hc of the recording film and the Htotal is obtained.

5 shows the relationship between the general coercive force and the temperature of the coercive force Hc. The temperature distribution on the recording film is changed by the irradiation of the laser, and the magnetic domain wall is stopped at the place where the temperature Trec where Htotal and Hc is balanced in FIG. 5 is formed, and an inverted magnetization mark is formed. The stability of the recording mark can be expressed by the change of the position of the magnetic wall with respect to the power fluctuation, that is, the shape change amount of the magnetization mark.

6 shows the formation principle of the magnetization mark. At the same time as the light beam 602 is irradiated to the vertical magnetization film 601, an external magnetic field 603 is applied to form magnetization marks. Normally, as indicated by the dotted line, the recording temperature Trec is the same on the front of the disc. Then, the magnetic walls of the magnetization marks are determined at the intersection of the temperature distribution 604 formed by the irradiation of the light beam and the recording temperature Trec, and a magnetic force 605 is formed on the vertical magnetization film 601. The width of the mark 606 at this time is about half of the spot size to be stable.

However, in the present invention, the coercive force characteristic of FIG. 5 or the recording temperature at which Htotal is locally changed is set to T'rec, and the recording temperature characteristic on the disk surface is locally lowered. Then, if the light spot is irradiated to the portion where the recording temperature is locally lowered to form the temperature distribution 604a, the intersection of the recording temperature T'rec and the temperature distribution 604a becomes the peak portion of the temperature distribution. Therefore, the magnetic wall 605a is formed on the vertical magnetization film, and the width of the magnetization mark 606a is smaller than the width of the conventional magnetization mark 606. In the peak portion of the conventional temperature distribution, the variation of the intersection point was not very stable even with the change of the temperature distribution. However, according to the present invention, the slope with respect to the position of the recording temperature is reverse polarity with the slope with respect to the position of the temperature distribution. For the change, the variation of the intersection is suppressed. As a result, it is possible to stably form the micromark with a lower recording energy than before.

There are two ways to change the recording temperature. One is to change the coercive force characteristics of the media locally, and the other is to locally change the Htotal. A method of locally changing the coercive force characteristic of the medium will be described with reference to FIGS.

7 shows an example of causing local relaxation on the disc. Structural relaxation can locally weaken the coercive force of the recording medium by weakening magnetic anisotropy by annealing.

FIG. 7A shows a situation where recording is performed by the light beam 702 on the recording medium 701 which caused the structure relaxation. In the part 703 which causes the structure relaxation, the coercive force characteristic of the temperature shown in FIG. 5 locally decreases, but since Htotal does not change, the effective recording temperature 704 decreases. Therefore, when the temperature distribution 705 is formed by the light beam, small magnetization marks 706 are formed. The decrease in coercive force depends on the energy given for the annealing. As an annealing method, there is a method of locally irradiating high energy light and causing structural relaxation depending on temperature. In this method, the amount of decrease in local coercive force changes due to the high energy distribution, and thus the recording temperature changes. In order to narrow the local area, it is preferable to record by a spot smaller than the recording spot. Currently, the recording spot is determined with a recording wavelength of 680 nm and a numerical aperture of 0.55, but a short-wavelength laser and a high numerical aperture lens used when creating the disc of the optical disk can be used to cause structure relaxation. The combination of lasers and lenses currently in use allows the spot size to be around 0.45 microns, thus narrowing the anneal area to about 0.2 microns.

FIG. 7B shows measurement data 707 of the reproduction output at the time of generating structure relaxation and recording thereon in comparison with the conventional data 708. FIG. When the recording power is lowered, in the conventional method, the intersection of the recording temperature and the temperature distribution approaches the peak point, the mark changes rapidly due to the power variation, and the reproduction output decreases. However, when the mark is recorded after the structure is relaxed, when the mark is larger than the structure relaxed area when the recording power is large, most marks of the same style as in the prior art are formed, so that there is no deviation in the reproduced signal. However, if the recording power is lowered and the recording mark is caught in the structure relaxation area, the change in mark width with respect to the change in recording power becomes small, so that the change in output level becomes small.

In FIG. 8, an example is described in which the region forming the recording mark of the recording medium is made the same as the conventional coercive force, and the coercive force of the other regions can be increased.

8A shows the medium of the present invention. In this vertical magnetization film 701, the coercive force is improved by making the surface roughness other than the portion where the magnetization mark 706 is formed. That is, only the portion where the magnetization mark 706 is formed is called the flat end portion 801. Therefore, below the flat portion 801, the surface energy for stopping the magnetic wall may increase, and the apparent coercive force may increase. By this configuration, the recording temperature 604 is relatively lowered in the mark area.

As a method of roughening the surface roughness, first, light is irradiated to the micromark portion in the form of a two-dimensional lattice point by using a resist having a characteristic of crossing only in a region where light is irradiated and insoluble in a developing solution. In the development process, the surface from which the two-dimensional lattice points have been removed is roughened by etching in a concentrated developer. In this way, the surface roughness around a micro mark can be roughened by creating a stamper from the created disk and stamping the surface roughened with plastics. 8B shows the relationship between the width of the magnetic domain and the recording power. When a stripe flat portion having a width of 0.2 占 퐉 is formed and the surface roughness on both sides is roughened, the relationship between the width of the formed magnetic domain and the recording power becomes as shown by reference numeral 807. It can be seen that the width of the formed magnetic domain is smaller than that of the data 808 when the surface roughness is not roughened.

9 shows an example in which the magnetic field is locally changed.

As shown in FIG. 9A, a layer 903 is provided in which the micromagnetization mark 902 is embedded in contact with the recording film 901 magnetically. The micro-magnetization marks 902 are arranged in two dimensions, and the effective Htotal is changed by increasing the external magnetic field on the recording layer 901 in contact with the buried layer 903 by only the magnetic field generated by the magnetization marks 902.

Referring to FIG. 5, the operation of the recording film is lowered from Trec to T'rec even if the magnetic properties of the recording film do not change, but change from Hc to H'total due to magnetization by a buried mark. do. Therefore, in order to reduce the recording temperature 904 on the buried mark in FIG. 9A, if the temperature on the recording film is raised as shown by the curve 705, the recording mark 706 corresponding to the lowered area of the recording temperature 904 is formed. Is formed. Fig. 9B shows the relationship between the mark forming power at the time of recording and the output signal at the time of reproducing this mark.

Next, a method of forming the micro domains by changing the composition of the recording film will be described. The basic structure of the magneto-optical recording film has a three-atomic amorphous structure of TbFeCo. Depending on the ratio of Tb and Fe, there is a difference in the perpendicular magnetic properties.

FIG. 10A shows the relationship between coercive force and temperature in a Fe rich TM rich and a Tb rich RE rich. The slope of the coercive force characteristic with respect to temperature is steeper compared to the TM rich. Regarding the relationship between the recording temperature and the recording mark, if the coercive force characteristic described in FIG. 5 becomes the same as that of FIG. 10, fine marks can be formed more stably than before, and variations in the recording mark are suppressed in response to variations in Htotal. do.

10B shows the relationship between the write power and the signal output. For the reason described above, the dependence of the output signal on the write power is less in RE rich.

This reason will be described in more detail with reference to FIGS. 11, 12, 13, and 14.

FIG. 11 shows the temperature distribution for each medium when the laser light is irradiated on the medium at room temperature 20 degrees. It can be seen that the temperature distribution on the medium is almost the same when the short pulse is irradiated.

FIG. 12 shows the coercive force characteristic of each medium corresponding to FIG. 10A. This coercive force characteristic and the recording temperature determined from Htotal form a recording mark of 0.2 micron.

The relationship between the displacement of the mark and the coercive force due to the temperature distribution in FIG. 11 is shown in FIG. 13 for the RE rich medium and in FIG. 14 for the TM rich medium. Mark variation when the recording power is changed from 0.9 to 1.1 times from a value capable of recording a 0.2 micron recording mark is obtained from the intersection of Htotal and the coercive force characteristic. As a result, it can be seen that the RE rich side has less mark width variation. When recording at the same spot using the recording film structure of FIGS. 7 to 9 and a RE-rich recording medium, recording marks having a width about half of the conventional one can be formed.

15 is a configuration diagram of the recording and reproducing apparatus of the present invention.

Laser light having a wavelength of 532 nm from the SHG 300 which is a reproducing light source is focused in one direction by the cylindrical lens 303 through the slit 302. Reference numeral 301 denotes a detector system that controls the A / O driving circuit 377 to detect a part of the lens light and control the intensity of the lens light. Light focused at the cylindrical lens 303 is input to the A / O modulator 304 and the transmitted diffracted light is converted by the cylindrical lens 305 to the original beam diameter. The light converted to the original beam system is enlarged and converted, for example, by 3 times by the beam expander 307 via the slit 306. The converted beam is bent into the diffraction grating 311 by bending an optical path along the deflection mirror 309 and the reflection mirror 310. The diffraction grating 311 divides the light into three beams of 0th order and ± 1st order diffracted light, passes through the optical filter 308 for super resolution, and then enters the prism 3l2 for optical path synthesis.

The laser from the semiconductor laser light source 378 having a wavelength of 685 nm, which is a recording light source, is collimated by an optical system 399 such as a coupling lens, and then the beam is passed through an optical filter 313 for super resolution. The light passing through the filter 313 is incident on the optical path synthesis prism 316 by bending the optical path with the optical deflector 314 and the reflection mirror.

A laser beam having a wavelength of 532 nm and 685 nm is synthesized by the optical path synthesis prisms 312 and 316 and moves over the optical disk 398 after passing through the reflection mirror 318 and the beam separation prism 3 l9. Towards the optical system 320. In the moving optical system 320, the beam from the fixed optical system 321 is bent toward the surface of the optical disk 398 attached to the spindle motor with a deflection mirror. The curved beam is focused on the optical disk 398 by the objective lens to form a light spot. The formed light spot has the same positional relationship as the recording spot 101 and the reproduction spot 103 in FIG. The moving optical system 320, which incorporates an objective lens and an optical deflection mirror, is placed on a moving table moving at a high speed in the radial direction 380 of the optical disk to perform an axing operation and simultaneously track an optical spot to the track. In this case, the moving table and the optical deflection mirror are interlocked to move.

Reflected light from the optical disk is bent to the beam separation prism 319 through the optical deflection mirror and then to the reflection mirror 353 to the sub-signal and clock signal detection optics 355 by the 685 nm separation prism 354. Incident. The 532 nm light passes through the prism 354 and is incident on the magneto-optical signal detection system 357 by the 532 nm separation prism 356.

The light incident on the magneto-optic signal detector 357 rotates the polarization angle about 45 degrees with the half wave plate 358, and three beams of s-polarized light and p-polarized light passed through the sp polarized light separating prism 359. Is detected by the three-segment detector (360, 370), the output difference from the photo detector corresponding to the reproduction spots (103a, 103b, 103c) shown in FIG. Detection is made as a signal 381. The magneto-optical signal 381 is input to the recording / playback control circuit 372 and subjected to the processing described later.

The servo signal / clock signal detection optical system 355 detects a mark (104, 105, 106, etc.) shown in FIG. The detected signal 382 is input to the data clock generation circuit 373, the servo circuit 374, and the recording / playback control circuit 372, respectively, and generates clock signals, tracking control, control operation of autofocus control, and recording / playback. The following control of the operation is performed.

The spindle 383 for rotating the disk sends a signal from the encoder attached to the spindle to the rotation control system 375, and controls the spindle through the spindle driver 384 so as to be a fixed speed in synchronization with the reference clock. The position of the moving optical system 320 is controlled by giving the servo circuit 374 a command of a control operation from the recording / playback control circuit 372. The drive of the A / O deflector 304 which sends a signal and recording data for controlling the power level of the recording and reproducing from the recording and reproducing control circuit 372 to the laser control circuit 376 and controls the output from the SHG 300. The regenerative output is controlled through the circuit 377. On the other hand, the recording laser uses the APC (automatic power control) control signal 385 for controlling the DC force, the set level command value 386 of the recording power, and the binarization data 387 which is the recording data, and the high speed driver 378 of the laser. Enter

FIG. 16 shows the arrangement relationship of the optical spots on the optical disc 398. FIG. A wobble pit 331, 332, 333, 334, 335 and a clock pit 336, 337, 338, which have a recording 685 nm spot 101, are disposed in the head and are formed in a concave-convex shape in advance by the recording spot 101. Detect. A well-known technique obtains a detection signal for tracking servo from a wobble pit that is offset by a small amount left and right with respect to the track center, and a clock signal, which is a timing reference for recording and reproducing a mark on a disk surface, from the clock pit. Write.

The 685 nm spot 101 generates side lobes 101 'and 101 "by wavefront manipulation after passing the optical super resolution filter on both sides of the spot. The optical super resolution is to appear in the radial direction of the track and Do not appear in the circumferential direction.

The 532nm laser beam for reproduction is separated into three spots 103a, 103b and 103c by a diffraction grating, and side lobes 103a ', 103b', 103c ', 103a "and 103b" 103c "on both sides of each spot. The diffraction grating 311 of FIG. 17 is rotated in a plane perpendicular to the beam such that the three spots 103a, 103b, 103c are located on the centerlines 350, 351, 352 of the virtual tracks adjacent to each other. The deflector on the moving system 320 is controlled by a control signal detected by the light spot 101 of 685 nm, and simultaneously moves the spots 103a, 103b, and 103c of 532 nm. Is fine-tuned by the deflector 314 of the 532 nm light source shown in Fig. 15. Focusing is similar to tracking error detection using a spot aberration of 685 nm using an astigmatism scheme in an unshown focus area. The focus error is detected and controlled by driving the objective lens of the mobile system.

The virtual track spacing should be narrowed down to 0.3 microns, but the size of the spot for detecting track error is large, 0.87 microns, which is large compared to the virtual trans spacing. The conventional track pitch was about the size of a spot. Thus, a control signal capable of positioning finer than the track pitch is generated using a conventional sample servo prepit. The prepit spacing here is 1.2 microns and the wobble spacing of the wobble pit is 0.3 microns.

A method of forming a track error signal is described in FIG. Create a clock signal that generates timing based on the signal detected from the click mark, and use it to sample a signal signal for detecting the signal levels of the wobble mark A333, the clock mark 338, and the wobble mark B335. A, B, C) (1702, 1703, 1704) are written. The signals A, B, and C are used to sample-hold the level of the total light quantity signal 1701 from each mark.

18 illustrates a specific configuration of the servo circuit 374 in which the track error signal is present. The sample holder circuits 150a, 150b, and 150c sample-hold the total light quantity signal modulated by the wobble mark 333, the clock mark 338, and the wobble mark 335, respectively. The subtraction circuits 152a, 152b, and 152c take differentials between the sample-bound signals, respectively, and create tracking signals A 1801, B 1802, C 1803, and D 1804. These signals become control signals for positioning the optical spots on the virtual track centerlines N, N + 1, N + 2, and N + 7 by dividing the track pitch shown in FIG.

FIG. 19 shows the relationship between the virtual track centerline and tracking signals 1801, 1802, 1803, and 1804 shown in FIG. Tracking control can be performed using this relationship.

20 shows a circuit for forming a specific control signal. The amplitudes of the tracking signals C 1803 and D 1804 are adjusted by the gain controls 2061 and 2002. In addition, the tracking signals A ', B', C ', and D' (2003 to 2006) are created by adjusting the polarity with the polarity inversion circuits 2003, 2004, 2005 and 2006. These signals are switched by the switching circuit 2007, processed by the phase compensation circuit 2008, input as a control signal of the control system, and the optical deflector inside the moving optical system 320 is controlled.

21 is an example of the recording form of the present invention in which the reproduction information block is composed of three information tracks. The information to be recorded is recorded as an information block 211 formed by three rows of information marks 102. The information block has a conventional sector concept in the circumferential direction of the optical disc, and consists of, for example, an address area, a timing area, an interference coefficient learning area, and a data storage area in order from the head. Marks (including prepits) included in these areas are formed on the predetermined grid point 213 at predetermined intervals from the head position of the sector. Information marks on three information tracks are reproduced in three reproduction spots 103a, 103b, 103c.

FIG. 1 shows the appearance of FIG. 21 as a perspective view. In the address area, a specific pattern, a sector address, or the like indicating that the head of the sector is formed in advance as the prepit 106. The timing mark 104 is formed in advance in the timing area at the position on the grid point 213 on each column of information marks. It is used when recording an information mark on a grid point or sampling a signal on the grid point, and a strobe pulse is created or hearing using a PLL circuit based on the detection signal of this timing mark. In the interference coefficient learning region described later, a learning mark for learning the interference coefficient required for the signal processing operation during information reproduction is recorded.

21 shows a part of the data storage area. The information mark 102 to be recorded is recorded on the grid point 213. Specifically, the time corresponding to the predetermined interval using the strobe pulse generated based on the timing mark described above. , ti-1, ti, ti + 1,... The information mark 102 is recorded accordingly. Thus, the information is expressed by whether or not the information mark 102 exists on the grid point 213 to be recorded.

22 shows an example of another recording method. In the example of FIG. 21, the lattice points 213 are aligned in the radial direction of the optical disc and the circumferential direction of the optical disc. In the example of FIG. 22, the lattice point periods on the adjacent information tracks are shifted by half the period. At this time, the crosstalk in the radial direction of the optical disk at each lattice point becomes smaller than in the case of FIG. For this reason, the lattice point spacing can be further narrowed in the radial direction of the optical disk as compared with the recording system row in FIG. 21, and much higher density can be made in the optical disk radial direction.

23 is an example of the learning mark described above. The learning mark 231 may be recorded as an isolated mark located on the grid point of the center precision track among the three information tracks. The learning mark 231 may be previously formed as a prepit or may be recorded at the time of shipment of the disc.

At the time of information reproduction, first, the interference coefficient is learned. The interference coefficient, which is a function of the light spot shape, the information mark shape and the grid point spacing, must be learned in the actual optical disk device. For this reason, when the information is reproduced, the learning mark 231 is detected as an optical spot and the interference coefficient is learned.

In the case where the reproduction information block is composed of three information tracks, the interference coefficient has characteristics such as a to n shown in FIG.

First, when the center of the light spot 103c reaches the lattice points M-2 and N + 1, q (j) is measured as the amount of interference in the diagonal direction, and the lattice points M-1 and N + 1 are measured. When q is reached, q (k) is measured as the amount of interference in the diagonal direction, and then q (l) is measured as the amount of radial interference when the lattice points M and N + 1 are reached. Next, when the center of the light spot 103b reaches the lattice points M-2 and N, q (f) is measured as the amount of interference in the circumferential direction, and when the lattice points M-1 and N are reached. Q (g) is measured as the amount of interference in the circumferential direction, and then the isolated signals S, M, N of the interference coefficient learning mark 231 are detected when the grid points M, N are reached.

Based on the above measurements, the interference coefficient j in the diagonal direction is given by the ratio q (j) / SM, N of the interference amount q (j) in the diagonal direction and the isolated signals S, M, and N. Similarly, the radial interference coefficient l is given by the ratio q (l) in the radial direction and the ratio q (l) / SM, N of the isolated signals SM and N, and the interference coefficient f in the circumferential direction is It is given by the ratio q (f) / SM, N of the interference amount q (f) and the isolation signal SM, N.

Similarly, the interference coefficients n and m in the diagonal directions are obtained when the center of the light spot 103c reaches the lattice points M + 1 and N + 1, and the center of the light spot 103c is the lattice point M. It can be detected when it reaches +2, N + 1). Incidentally, the interference coefficients d and e in the diagonal directions are obtained when the center of the light spot 103a reaches the lattice points M + 1 and N-1, and the center of the light spot 103a is the lattice point M. Obtained when +2, N-1) is reached. Furthermore, the circumferential interference coefficients h and i take the ratio of the spot 103b to the isolated signals SM and N of values obtained at the lattice points M + 1 and N and M + 2 and N. Find the interference coefficient. In addition, the learning can be performed several times, and the results can be averaged to increase the learning accuracy of the interference coefficient. As an example, a method of providing a plurality of marks for interference coefficient learning is considered.

The signal processing operation for reducing the crosstalk noise component is performed by using each interference coefficient obtained by the above means and a detection signal sampled at each lattice point position by the strobe pulse described above. At this time, when the strobe pulse corrected by the PLL circuit is used, the information mark detection signal at the grid point position can be sampled more accurately.

In the case of the information mark column as shown in FIG. 21, a detection signal on the grid points M and N and a detection signal on the grid points near 14 (5 x 3-1 = 14) adjacent to the grid points M and N are used ( Shown in FIG. 33).

FIG. 40 shows a matrix of the magnitude of the signal amplitude at each grid point when only the recorded marks with two tracks adjacent to the three tracks 1, 2 and 3 also exist in isolation. Here, since only three tracks can be detected simultaneously in this embodiment, it is considered to accurately detect the mark of the area surrounded by the dotted lines. Here, formula (2) representing an isolated signal obtained at each grid point position

In Eq., The calculated value obtained by ignoring E is a value to be obtained in which crosstalk is reduced. Here, S (j, k) is a column vector whose component is an isolated signal obtained at 21 lattice point positions, and K (i, j) is a 21st-order square matrix whose component is an interference coefficient, S '(i, j). Denotes a column vector having a detection signal obtained at 21 grid point positions, and E denotes a column vector representing crosstalks from grid points other than the 21 grid points. Here, if the influence of crosstalk is completely interrupted, the isolated signal S (i, j) at each lattice point can be computed using Formula (3).

S (i, j) = K- ¹ (i, j) (S '(i, j) -E)... (3)

However, since there are parts inside the column vector E that cannot be detected by the three spots, an operation value obtained by ignoring E is calculated. In other words, the signal S ″ at the grid points i and j is calculated using the inverse of K from the signal detected using the equation (4).

As described above, by using the recording method and the signal processing calculation method of the present invention, recording and reproducing with higher density than the conventional method can be realized. Further, in the reproduction signals from all the light spots used at the time of information reproduction, a signal obtained by sufficiently reducing the crosstalk noise component is obtained, so that the data transfer rate is also improved compared to the conventional method.

In the following, a recording apparatus for realizing the above-described information recording method and signal processing calculation method will be described taking the case where the information block is composed of three information tracks as an example.

First, for the tracking and autofocus of the optical system and the plurality of light spots for realizing the plurality of light spots, means described in JP-A-52-021336 may be used. At this time, as shown in FIG. 21, the axis connecting the plurality of optical spots is inclined with respect to the information block radius, and as a result, a constant time difference occurs between the optical spots with respect to the circumferential direction of the optical disk. If this time difference is not a multiple of the grid point spacing, in order to simultaneously record and reproduce the information mark 102 on the grid point 213 by using the plurality of light spots 103a to 103c, a strobe pulse unique to each light spot is applied. You need to prepare. In other words, each strobe pulse is accurately synchronized with a lattice point on each information track, and each light spot records and reproduces information in accordance with the timing of each strobe pulse. At this time, the time difference between each strobe pulse corresponds to the time difference of each light spot.

FIG. 24 shows a block diagram of a write circuit for performing the above write. This recording circuit includes a detection unit 201a to 201c having the same number of light spots for detecting that the light spot has entered the learning area, a data selection unit 202 for selecting learning data and precision data, and a data recording unit 203. It consists of. The data recorder 203 is controlled by the clock 2310.

25 shows an example of the detector 201 of FIG. The detector 210 detects a mark on the optical disk in correspondence with each light spot. The detection signal from the detector 210 extracts a predetermined timing signal from the gates 2501a and 2501b. The PLL circuit 2110 forms a timing signal from a signal corresponding to the timing mark output from the gate 2501a. The sector head recognition circuit 212 recognizes the head of the sector from the signal corresponding to the header mark recorded in the head of the area output from the gate 2501b. The area recognition circuit 2130 is a part that controls the detector 201.

The operation of the detector 201 is also shown with reference to the time chart of FIG. The area recognition circuit 2130 recognizes the position of the light spot by counting the strobe pulse 215 output from the PLL circuit 2110, and as a result, the address area signal 217, the timing area signal 218, and the interference coefficient The learning area signal 219 and the data storage area signal 220 are output.

Specifically, the count value of the strobe pulse 215 is first reset to zero by the pulse signal 223 output from the sector head recognition circuit 222. The sector area recognition circuit 222 detects a specific pattern representing a head of a sector formed in the address area 2170 based on the output signal 214 from the photodetector, and pulses when detecting the specific pattern. Outputs a signal 223.

Since the light spot exists in the address area 2170 between count values 0 to a, only the address area signal 217 is turned on and output. When the address area signal 217 is turned on, the output signal 214 from the photodetector is output to the address recognition circuit 212 through the gate circuit 2501b. The address recognition circuit 212 is a circuit for detecting address information formed in the address area 2170 based on the output signal 214.

Since the light spot exists in the timing area 2180 between count values a to b, only the timing area signal 218 is turned on and output. When the typing area signal 218 is turned on, the output signal 214 from the photodetector is input to the PLL circuit 2110 through the gate circuit 2501a. The PLL circuit 2110 detects a timing mark formed in the timing region 2180 based on the output signal 214 from the photo detector, and writes the detection result to correct the timing error between the strobe pulse and the grid point position. Correct it. The PL circuit 211 outputs a strobe pulse 215, which is a gate circuit 2501c when the interference coefficient learning area signal 219 is on or the data storage area signal 220 is on. It is output from the detection unit 201 through ().

Since the light spot exists in the interference coefficient learning region 2190 between the coefficient values b and c, only the interference coefficient class region signal 219 is turned on, and the optical spot has a data storage region 2200 between the coefficient values c and d. ), Only the data storage area signal 220 is turned on and output. These interference coefficient learning region signals 219 and data storage region signals 220 become output signals of the detection unit 201. Accordingly, each of the detection units 201a to 201c outputs the strobe fields 215a to 215c, the interference coefficient learning area signals 219a to 219c, and the data storage area signals 220a to 220c.

FIG. 26 shows an example of a block diagram of the data selection unit 202. As shown in FIG. The user data 204, the plurality of data storage area signals 220a to 220c and the plurality of interference coefficient learning area signals 219a to 219c, which are outputs from the respective detection units 201a to 201c, are input to the data selection unit 202. do. At this time, for example, when at least one of the data storage area signals 220a to 220c is turned on, the data selector 202 outputs the user data 204 as the serial data 225. In addition, when at least one of the interference coefficient learning region signals 219a to 219c is turned on, an information mark necessary for learning the interference coefficient is recorded in the interference coefficient learning region, so that it is stored in the interference coefficient learning data ROM 226. The data thin is output as serial data 225. In this case, the data string expresses an isolation mark as shown in FIG.

FIG. 27 shows an example of the data recording section 203. As shown in FIG. The data recording strobe pulse 221 and the serial data 225 are input to the data recording unit 203. At this time, the serial data 225 is converted by the serial-parallel conversion circuit 230 which operates with the reference clock 231 of higher frequency than the respective strobe pulses 221. The converted data 232 is stored in the FI / FO (first in / first out) memory 233 and read out from the FI / FO memory 233 by the strobe pulse 221 for writing. These read data 234 are input to the modulator 235. The modulated data 236 is inputted to the driving circuit 237 of the laser, and the mark is recorded by the intensity modulation of the light spot 238.

Here, in the case where one of the spots 101 in FIG. 1 is recorded in the information block 211 of the three information tracks shown in FIG. 21, one information track is written for each rotation of the disc using the above circuit. Recording is done on three information tracks. In addition, a three-beam laser array having a wavelength of 685 nm is used as the recording light source, and the recording spots are placed on three information tracks in the information block, respectively, and the FI / FO memory 233, modulator 235 shown in FIG. What is necessary is just to provide three systems of the laser drive circuit 273. Alternatively, three SHG lasers having a wavelength of 532 nm may be provided without using a laser having a wavelength of 685 nm, and recording and reproduction may be performed using three beams using three A / O modulators.

28 shows a block diagram of an information reproducing circuit for reproducing recorded information. This reproducing circuit has the same number of detectors 251a to 251c as the number of light spots for detecting the incidence of light spots entering each region shown in FIG. 32, and a synchronization correcting unit for synchronizing detection signals from the respective detectors ( 252 and arithmetic unit 253.

FIG. 29 shows an example of a block diagram of the detector 251. As shown in FIG. The detector 251 is mainly composed of a detector 267, a sample holder circuit 256, a PLL circuit 257, a sector head recognition circuit 258, and an area recognition circuit 259 corresponding to each light spot. The PLL circuit 257, the sector head recognition circuit 258, the area recognition circuit 259, and the address recognition circuit 267 are the same as those described in the above-described recording circuit, and the detector 251 is a detector in the write circuit. Similarly to 201, it is controlled by the area recognition circuit 259. First, when the light spot enters the timing area, the timing area signal 218 output from the area recognition circuit 213 is turned on, and the timing mark signal detected by the light spot is transferred to the PLL circuit 257 in the detection unit. Is entered. The PLL circuit 257 corrects phase shift with the strobe pulse 264 due to irregularities in disc rotation or the like based on the timing mark signal. Then, when the interference coefficient learning region signal 262 is turned on or the data storage region signal 273 is turned on, the strobe pulse 264 that is the output of the PLL circuit 257 is clocked 205 of the sample holder circuit 256. Becomes The sample holder circuit 256 samples the signal value on the lattice point of the detection signal 255 as an input according to the clock 265. The sampled value is the output of the detection unit 251 as the detection signal 266 and is input to the synchronization correction unit 252.

The output from the sample holder circuit 256 which generates a pulse corresponding to the lattice point only when the interference coefficient learning area signal 262 is on or the data storage area signal 263 is on is a detection unit as the control clock 265. An output of 251 is input to the synchronous correction circuit 252.

30 shows an example of a block diagram of the synchronization correction unit 252. As shown in FIG. The synchronization correction unit 252 is mainly composed of a FI / FO memory and a read clock control circuit. Each detection signal 266a to 266c output from each detection unit 251a to 251c and input to the synchronization correction unit 252 is similarly output from each detection unit 251a to 251c and input to the synchronization correction unit 252. The FI / FO memories 271a to 271c are stored in correspondence with the clocks 265a to 265c. Further, the signal which is turned on when each of the interference coefficient learning force signals 262a to 262c output from each of the detection units 251a to 251c is all on is the interference coefficient learning area signal 275 and each data storage area output from each detection unit. If the signal to be turned on when the signals 263a to 263c are turned on is the data storage area signal 276, the read clock control circuit 272 makes a reference clock 277 when either of these two signals is turned on. Outputs The frequency of the reference clock 277 is below the frequency of the control clocks 265a to 265c.

Each detection signal 266a to 266c stored in each of the FI / FO memories 271a to 271c is read out according to the output signal 277 of the read clock control circuit 272 and synchronized with the detection signals 278a to 278c. As a result, the synchronous correcting unit 252 is output and input to the calculating unit 253. The interference coefficient learning area signal 275 and the data storage area signal 276 are output from the synchronization correction unit 252 and are input to the calculation unit 253.

31 shows an example of the calculation unit 253. The detection signals 278a to 278c further output from the synchronous correcting unit 252 and input to the calculating unit 253 are input to the calculating unit 286. At this time, when the interference coefficient learning region signal 276, which is an input from the synchronization correction unit 252, is on, the calculator 280 calculates the interference coefficient by performing the above calculation based on the detection signals 278a to 278c, The inverse matrix is calculated based on these interference coefficients (Equation (4)), and the calculation coefficients are calculated. The calculated calculation coefficient is stored in the calculation coefficient memory 281.

When the data storage area signal 276, which is an input from the synchronous correction unit 252, is on, the calculator 280 calculates the equation (2) based on the detection signals 278a to 278c and the calculation coefficient calculated by the means. The calculations shown in (3) and (4) are performed, and the calculation results 283a to 283c obtained by reducing crosstalk noise are output to the comparator 284. The comparator 284 determines the presence or absence of an information mark based on the calculation value 283. The discrimination results 285a to 285c are demodulated by the demodulator 286, which are output as the reproduction signals 287a to 287c.

In addition, the serial data 289, i.e., user data, is reproduced by the parallel-serial conversion circuit 288.

The above is an example of three-track simultaneous playback in which three information tracks are configured as one information block and one information block information is simultaneously reproduced. Only one track scanned by the spot 103b in the middle of the playback spots is scanned. It is also possible to record and play back.

In this system, only the track scanned by the spot 103b needs to be playable. Spots 103a and 103c are used to detect signal leakage from adjacent tracks that seep into the information tracks that spot 103b irradiates. Accurate information can be detected even if the leakage (cross talk) of the signal detected by the spots 103a and 103c is removed from the signal detected by the spot 103b and the information block interval shown in FIG. 21 is narrowed. Therefore, the recording density can be further increased. In the case of recording, similarly to the configuration shown in FIG. 1, recording is performed in the recording spot 101 of 685 nm, and information track data on the spot 103b is reproduced in three spots 103a, 103b, and 103c of 532 nm.

Specifically, when the surface density is calculated, the spot size W becomes 0.96 micron when the reproduction wavelength is 530 nm and the numerical aperture is 0.55. With optical superresolution, the spot size in the track direction is substantially 0.7 times and 0.67 microns. In the playback method adopted this time, the track pitch can be reduced to about 0.4 times W, so that a track pitch of 0.3 micron can be realized.

Optical super resolution generates side lobes on the disc surface, and signals leak from the tracks caught in the side lobes. In order not to detect this on the detector surface, a shielding plate for inserting the side lobe is usually inserted in the middle of the beam after passing through the objective lens. However, since at least three beams are present and the beams are arranged inclined with respect to the track direction, the same shielding plate is difficult to set.

Fig. 35 shows an example of a photo detector that solves the problem of the side lobe. The nonlinear transmissive material 351 was coated on the photo detector 350. As this material, the diaryl ethene derivative which is a photochromic medium, for example is preferable.

34 shows the spectral characteristics of the diaryl ethene derivative. When there is sufficient energy intensity (diaryl ethene A open-ring), the transmittance characteristic curve becomes from curve 342 to curve 341 and the transmittance changes nonlinearly with respect to the energy intensity of the regenerated light at 530 nm.

36 shows the state of the transmittance change with respect to the energy intensity of the regenerated light. In the case of light with little change in intensity, energy is equivalently expressed in average power.

37 shows the principle of signal reproduction. When the nonlinear characteristics of the incident power density and the transmission power density become the curve 407, only the light intensity portion reaches the photodetector example reproduction light. Therefore, the intensity distribution of the incident light spot 401 becomes the same intensity distribution as the light spot 400 after transmission. Here, the weak light in the incident light spot 401 compared to the main lobe 402 such as the side lobe 403 is significantly lower in intensity compared to the main lobe such as the side lobe 405 after transmission, and the photodetector The side lobe 405 hardly receives a signal from the mark to be irradiated. If the position where the light detector is placed is the farfield plane away from the position where the photo detector is placed, the reproduction spot starts tracking with the optical deflector. The spot moves on the photodetector plane. In this state, it is necessary to always excite this material with the light different from the reproduction so that the nonlinear effect occurs as the spot moves so that only the light of the main lobe is transmitted at all times.

For this reason, as shown in FIG. 35, the light 352 of the short wavelength blue light emitting diode 3520 other than the reproduction light 353 is irradiated to the whole surface of this material. As the wavelength of the light emitting diode, one of 480 nm is selected from the wavelength band 420 having the transmission characteristic in the curve 342 which is another spectral characteristic (diaryl ethene A closed-ring). The characteristic of the curve 342 is obtained by irradiation light of this wavelength range. The curve 342 has absorption characteristics at 530 nm, which is the wavelength of light for detecting a signal, so that 530 nm of light is absorbed by the entire nonlinear material. However, when the light energy intensity is strong, it becomes a characteristic of the curve 341 so that 530 nm light is transmitted. Can be configured. Therefore, nonlinearity can be controlled by the power of the light emitting diode which irradiates as a whole. Also, in general, nonlinear materials of this kind are slow in responsiveness, but can sufficiently cope with a response such as following a tracking error. As described above, the leakage from the side lobe due to the optical super resolution can be eliminated with a simple configuration by using a nonlinear material, so that the assembly and adjustment of the optical system are easy.

In FIG. 38A, front aperture detection (FAD), which is a kind of magnetic super-resolution, is described for improving the circumferential reproduction resolution. In the recording medium, a cut layer 382 made of TbDyFe and a reproduction layer 383 made of GdFeCo are placed on a recording layer 381 such as TbFeCo shown in FIGS. 7 and 8. When the light spot 384 is irradiated onto the medium of this structure and moved in the direction of the arrow 385, the temperature distribution 387 on the track center on the medium has a high temperature deformed extension behind the spot. The mark 389 recorded on the recording layer 381 based on a certain external magnetic field 386 is transferred to the reproduction layer 383 by the magnetization of the mark through the cutting layer 282 when the temperature is low. However, if the temperature exceeds a certain value 3809, the magnetization disappearance region 3811 of the cut layer 382 will not be transferable. That is, when viewed from the reproduction layer 383, a mask 380, which appears as an oblique line, is formed in the laser spot 384, and the mark recorded using the region having a low temperature as the opening 3800 is detected. For this reason, the spot 384 seems to become substantially small, and the resolution of the circumferential direction can be improved. However, since the shape of this opening 3800 is crescent-shaped, the signal waveform obtained even if the mark computed from the recording mark is a round mark is a waveform asymmetric in the advancing direction.

In the two-dimensional equalization described later, the asymmetry can be compensated by taking the interference coefficients in front, rear, left, and right directions. In addition, since the resolution of the detection signal depends on the temperature distribution and the positional shift of the spot, when the temperature distribution approaches the center of the spot, the opening is narrowed and the resolution is improved. For this purpose, the A / O deflector is used to adjust the regenerated light into a pulse shape at the position where the mark is recorded, and to steep the temperature distribution to bring it closer to the center. The timing for modulating the reproduction light intensity is made from a clock signal generated by starting the PLL from a prepit formed on the disk surface as described above. For this reason, the timing which sample-holds a signal within the irradiation period of detection light is set.

Another magnetic superresolution RAD (rear aperture detection) in FIG. 38B is described. The switch layer 3801 and the reproduction layer 3802 are formed on the recording layer 381 described with reference to FIGS. The RAD gives an initial magnetic field 3804 of the light spot 3803, and initializes the reproduction layer 381. In a place where the temperature is low, the SW layer 3801 transfers the mark of the recording layer 301 to the reproduction layer 3802. When the temperature is increased by the light spot 3803, the mark 389 of the recording layer 301 is transferred to the reproduction layer 3802. In this manner, a mask 3812 is formed, and an opening 3811 is generated behind the spot 3803 in the advancing direction. When the reproduction light of the recording mark 389 is irradiated in a pulse shape, the position of the opening 3811 can be positioned at the center of the light spot, so that the asymmetry of the reproduction waveform can be reduced.

Fig. 39 explains the principle of detecting the information recorded in this way.

As shown in FIG. 39A, the recording mark 102 is recorded by the non-return-to-zero (NRZ) rule in which the presence or absence of the mark at the grid point 213 corresponds to " 1 " and " 0 " It is. Thus, the signal to be detected takes only two levels.

39C shows a track 2 signal (eye pattern) detected from the spot 103b. Cross talks from adjacent tracks 1 and 3 hardly open the eye level, so that data cannot be detected accurately.

As shown in Fig. 39D, it is necessary to process a signal in which the child is open and can read data accurately.

FIG. 39B shows a configuration of a two-dimensional equivalent processing circuit for compensating for the cross talk to obtain a signal similar to that in FIG. 39D from the signal in FIG. 39C. Here, after learning the interference coefficient, the result of calculating the inverse matrix of K and using the signals from track 1, track 2, and track 3 is used to find an operation coefficient to remove the amount of interference.

In the two-dimensional equivalent processing circuit example, signals x (t) (3900-1,3900-2, 3900-3) reproduced from each track are converted into seven types of transverse filters (391-1, 391-2, 391-3). Pass it on. The transverse filter 391 has a delay circuit 392, an attenuator 395, and an adder 396, and shapes signal waveforms for each track. Thereafter, the signal g (t) from each track is weighted by the weighting circuits 397-1, 397-2, and 397-3, and summed by the addition circuit 393. The coefficients of the delay circuit and attenuator of the transverse filter 391 passing the signals from each track and the coefficients weighted by the weighting circuit 397 to the signals from each track are obtained from the inverse matrix as described above. The delay circuits 394a and 394b have a delay time corresponding to the distance r (sec) between the reproduction spots 103.

In FIG. 39A, the grid point spacing is 0.25 micron, the track spacing is 0.3 micron, and the mark diameter is 0.22 micron. The time corresponding to the grid point interval is T, and the time interval of three spots is t. The signal processing in the two-dimensional direction is given a time delay to compensate for the time delay between tracks in advance. All of the signal processing digitally makes it possible to use a clock written in a PLL, making it easy to control the time delay in the t interval.

If the circumferential spot does not have the effect of magnetic superresolution, the spot diameter in the circumferential direction is about 0.96 micron, so that a signal cannot be detected from a lattice of 0.5 micron period. Thus, we apply a partial response that is well known in the transmission field. A simpler partial response in an optical disc that exhibits a candid response from direct current to the high frequency range is the response characteristic of PR (1, 1). This is a characteristic that when an optical disk is regarded as a transmission path, a response to an input pulse exists only in two portions of a detection time slot, and no response appears in other slots.

In FIG. 41, the signal processing flow of the PR (1, 1) will be described. The user data ak is converted into the modulation data bk by the processing of the precoder. The role of the precoder is to apply the reverse characteristics of the optical disk to the recording data in advance in order to prevent error propagation due to defects on the optical disk or the like.

The recording pulse 411 is created in accordance with the modulation data, and the recording mark 102 is recorded on the grid point 213 based on the clock signal in accordance with the recording pulse 411. If the size of the substantial reproduction spot 103 is as shown in the figure, the mark cannot be decomposed even from the reproduction signal waveform 412 even if one lattice gap is opened between the mark and the mark. However, the mark arrangement can be known as the level takes the intermediate value of the saturation level. The saturation level occurs when a plurality of marks are arranged in succession. It can be seen that the detection level takes three values due to the interference between the marks. Two slice levels 413a and 413b are provided to detect whether they are at any level, and any one of three values divided into two levels for each time slot is detected. The obtained 3 values are calculated by mod2 and regarded as 2 values of demodulation data. This makes it possible to detect signals even at low density. Although a signal from one track has been described as an example, in the present invention, a waveform suitable for the partial response cannot be detected due to interference from an adjacent track. Means for obtaining this will be described below.

42 shows an arrangement for inputting detection signals 3900 from three spots into a two-dimensional equalization circuit. The detection signals 3900-1 (S'bc to S'bi) from the track 1 are input in chronological order. The detection signal 3900-2 (S'cc to S'ci) from track 2 is input to the equalization processing circuit 4201 to the detection signal 3900-3 (S'dc to S'di) from track 3. do. From these signals, a signal 4200 (S " cc to S " ci) of track 2 from which interference from adjacent marks is removed at each timing is obtained. This signal is an arrangement of reproduction signals from isolated recording marks, and the amount of interference necessary for partial response is eliminated. Therefore, r3 is newly added and added from the interference amount r-3 between adjacent marks to become the characteristic of the partial response (1, 1). As a result, a signal S '"cf is obtained which eliminates interference from adjacent tracks and has an optimum partial response characteristic. The signal is obtained from a mark in the middle of 21 mark columns surrounded by dotted lines in FIG. It corresponds to signal of.

FIG. 43 shows the result of the equalization process simulation of FIG. The calculation was performed at minute intervals every 0.0125 micron indentation by dividing the grid point spacing by 20, and a signal waveform corresponding to S '"cf regarded as continuous was obtained.

43A shows waveforms when a random pattern is placed on tracks 1, 2, and 3, only track 2 is reproduced, and only signal processing for partial response is performed. It can be seen that the eye opening necessary for signal detection is not obtained due to interference from adjacent tracks.

43B shows the result of applying the partial response signal processing after detecting the signals of the tracks 1 and 3, removing the interference between adjacent marks by the above-described two-dimensional equalization. Compared with the 43A, a sufficient eye opening 4300 is obtained, and it can be seen that three values can be reliably determined at the signal detection point 4302 using two slice levels 413a and 413b. Compared with NRZ, the recording position is a lattice point, but the signal detection point is an intermediate point of the lattice point. In addition, although the simulation showed the state of the wave form processing close to the continuous waveform, in the present invention, all the signal processing is performed digitally in synchronization with the clock. Thus, the grid point spacing T corresponds to the slot spacing and the time slot is the midpoint of each grid point. Therefore, in the above-described embodiment, the signal is sampled at each lattice point, but in the present embodiment, each reproduction detection signal is sampled at each time slot to process the signal. Reference numeral 4301 corresponds to an amplitude of a reproduction signal of an isolated mark.

The embodiments thus far used the optical superresolution effect for the track radial direction, but the magnetic transfer structure shown in FIG. 9 as the medium is difficult to use the above-described partial response because the magnetic superresolution is difficult. However, it is possible by the present invention to perform optical super-resolution in the circumferential direction in order to achieve higher density and to have a margin with 10 Gb / in ² . That is, the optical super-resolution effect is isotropically performed by using a circular shielding plate or a circular phase plate as an optical filter. Moreover, even if the track pitch and the lattice point spacing are changed by the ellipse shape, it can respond. Detection can eliminate the effects of side lobes by applying a non-linear transmissive material onto the detector face as described above.

Next, an embodiment for performing high SN playback is shown below.

44 shows a principle diagram of high SN detection. FIG. 44A shows the situation on the medium, FIG. 44B shows the clock signal, FIG. 44C shows the intensity of the laser to be irradiated, and FIG. 44D shows the temperature distribution on the medium. The reproduction spot 4401 irradiates and reproduces the normal DC light 441 in the sample region 500 in which the prepit mark 4400 is formed to extract the tracking signal and the clock. In the data area 501, pulses of light 442 having a peak power level 503 greater than the reproduction level 502 are pulsed at a timing synchronized with the grid point, and the reflected light is timing 504 synchronized with the grid point. ) Is detected. A gap region 505 is formed between the sample region 500 and the data region 501.

The reason why high SN reproduction is possible is explained below.

45, in the reproducing system having a wavelength lambda 532nm and a numerical aperture NA of a focusing lens of 0.6, the repetition of the maximum repetition frequency of 12.5 [MHz], i. The spectrum of frequencies measured by the spectrum analyzer when the pattern is reproduced is shown. Here, the double cycle of the interval of the lattice points corresponds to the highest repetition frequency. As for the signal 4500 corresponding to the repetition period of the mark, the signal component C corresponds to the signal component C1 and the base level signal 4501 corresponds to the total noise N.

FIG. 46 shows measured values of spectrums of various noises including the noise level 4501 shown in FIG. Regenerative light power was 1 mW. The noise component 4501 is composed of system noise 506 including amplifier noise, short noise 507 generated in the photodetector, and disc noise 508 including modulated noise due to nonuniformity of the mark at the time of recording. do. Here, the noise of the laser itself is at a level that can be sufficiently ignored because it uses an SHG laser. As a result of the measurement, the disk noise 508 prevails in the low frequency region around the frequency fmin = 11 [MHz], and the short noise 507 prevails in the high frequency region.

FIG. 47 shows the relationship between the signal level Sp-p, the amount of loosening N of each kind, and the power of the reproduced light focused on the medium surface. The signal level Sp-p corresponds to the peak value of the signal 4500 of FIG. It corresponds to the value multiplied by, and the noise corresponds to the amount of noise integrated in the region from the frequency 0 to the cutoff frequency shown in FIG. The abscissa is standardized by a number of standards with the regenerative power PO as one. The sign 509 is The theoretical curve of the short noise expressed, symbol 510 is The theoretical curve of the signal level to be expressed, symbol 511 is The theoretical curve of the disk noise, which is represented, 500 is the theoretical curve of the system noise.

Considering only the change in the amount of light on the detector, the system noise 500 does not depend on the power of the reproduction light. On the other hand, the short noise becomes a theoretical curve 509 proportional to the power P of the reproduction light. The signal level and the disc noise become theoretical curves 510 and 511 in proportion to the power of the reproduction light. Here, the short noise that dominates the high frequency region of the signal band by raising the reproduction power can be reduced with respect to the disk noise, and the amount of noise determined by the integration in the band can be reduced.

FIG. 48 shows the relationship between the reproduction power, the reproduction signal Sp-p, and the total noise Nrms. Reference numeral 512 is a theoretical curve of the relationship with the reproduction power at the time of reproduction light DC irradiation, reference numeral 517 is an actual value when DC irradiation is performed at a linear speed of 20 m / sec, and reference numeral 518 is a linear speed. It is an actual value at the time of pulse irradiation of reproduction light at 10 m / sec. The signal band at this time was fmax = V / (λ / 2NA) [MHz] = 22.5 MHz, which is an optical cutoff frequency.

As can be seen from the theoretical curve 512, when the regenerative power is set from 1 mW to 2 mW and 1.8 dB and 4 mW, it can be seen that the improvement is 2.8 dB and SN. However, in an actual system, the following problem occurs when increasing the reproduction power.

This problem is explained with reference to FIG. Curve 513 in FIG. 47 is the measured value of the signal level in the case of DC irradiation of light at a linear velocity of 10 m / sec. Curve 514 is a measured value of the disk noise level when DC irradiation of light at a linear velocity of 10 m / sec.

First, the signal level is lower than the theoretical curve 510, such as the measured curve 513. This is because the Kerr rotation angle of the magnetic film that controls the furnace level decreases with temperature, as shown in FIG. 49, so that the temperature of the film surface increases and the signal level decreases with the increase of the regenerative power. .

Second, as in the measurement curve 514, the disk noise level increases with the increase of the reproduction power than the theoretical curve 511. This is because the magnetization of the magnetic film becomes unstable and the disk noise rises when the temperature of the film surface rises.

In order to solve the above problem, it is considered that the temperature of the film surface does not rise even when the linear speed is increased to increase the regenerative power.

Referring to FIG. 47, the curve 515 is an actual value of the signal level when the reproduction light is irradiated with DC at 20 m / sec, which is twice the linear velocity, and the curve 516 is an actual value of the disc noise level. Curves 515 and 516 show that the regenerative power can be raised to about 3 mW. However, the measured SN with respect to the regenerative power can only be improved by about 0.5 dB as shown by the measured curve 517 of FIG. The reason is that the signal band should be increased proportionally with the increase of the linear velocity. As can be seen from FIG. 46, the amount of noise in the band of the short noise which dominates the noise in the high frequency region increases, and as a result, the SN Falls. This phenomenon will be described later.

FIG. 50 shows the result of obtaining the regenerative power 5000 at which the peak temperature of the film surface is maintained for each linear velocity, and obtaining the SN 5001 for the linear velocity by obtaining SN for the obtained regenerative power. As can be seen from this result, even if the linear velocity is increased from 10 m / sec, it is understood that almost no SN improvement is obtained.

In view of the above, in the present embodiment, in order to increase the reproduction power without raising the signal band, the signal is reproduced while irradiating a pulse at the detection point of data at the time of reproduction and not raising the temperature of the film surface. As shown in FIG. 44C, the intensity of the regenerated light is irradiated pulsed at the lattice point with light having a third intensity level Pp 503 which is larger than the regeneration level Pdc 502 irradiated from the light source with the normal DC light.

FIG. 51 shows the measured temperature distribution of the surface of the recording film of various pulse widths during direct current light reproduction under the recording and reproducing conditions. The wave height of the irradiation power was 2 mW, the linear velocity of the optical spot was 10 m / sec, and the pulse width was changed to 10 ns, 20 ns, 30 ns, and DC irradiation. Curve 511 is a pulse width of 10 ns, curve 512 is a pulse width of 20 ns, curve 513 is a pulse width of 30 ns, and curve 514 is the arrival temperature in the case of DC irradiation. When the pulse width is 10 ns, it can be seen that half of the DC light irradiation becomes the peak temperature and 2 mW of regenerative power can be irradiated at 10 m / s.

In FIG. 47, the curve 4700 shows the measured value of the reproduced signal when the reproduced light is irradiated in the pulse shape at a linear velocity of 10 m / s, and the curve 4701 similarly shows the measured value of the disc noise. Reference numeral 517 in FIG. 48 likewise shows an actual measurement curve of SN with respect to regenerative power. As can be seen from this, SN could increase by 2.3 dB at 10 m / s rapidity and 3 mW of regenerative power.

Here, the following problem arises at the time of irradiation of FIG. 44C. As shown in FIG. 44D, when moving from the sample area 500 which is irradiating light with DC to pulse irradiation, the temperature level rises due to the remaining heat at the lattice point by the direct current irradiation (4400). However, at the next pulse irradiation, since the remaining heat becomes smaller, the temperature level falls (4401). And the temperature level after several pulse irradiation turns into a normal value. A gap region 505 is formed between the sample region and the data region in order to keep this temperature level from fluctuating.

52 shows a method of making the temperature level constant without forming a gap region. A pulse having a third intensity level 503 greater than the reproduction level 502 irradiated from the light source with the direct current light is pulsed at the lattice point, the period of intensity zero is narrowed, and the regeneration level 502 between the lattice points. Pulses for the remaining heat of the second intensity level 519 greater than). As shown in FIG. 52C, even if a direct light spot enters the data area 501 from the sample area 500, the temperature level by pulse irradiation can be made constant as shown in FIG. 52D.

The operation during concrete playback will be described below.

In the sample area 500 for extracting the tracking signal and the clock at the time of reproduction, irradiation and reproduction is performed with DC light, and the recording circuits shown in FIGS. 24, 25 and 26 degrees in the data area 501 are also used during reproduction. The strobe pulse 221 drives the AO drive circuit 377 shown in FIG. 15 at a timing synchronized with the lattice point at the time of reproduction to modulate the reproduction light. Here, since the reproduction spot 4400 constitutes three spots by a diffraction grating, the AO driving circuit 377 is modulated by mixing the pulses from each recording strobe 221 so that individual spots generate pulses at the lattice points. do.

However, when one spot irradiates a pulse at a lattice point, the other spot irradiates a pulse at a non-grid point and the temperature rises. In practice, the pulse width is about one-third so that the temperature does not rise even if pulse irradiation by two different spots occurs. Further, the diffraction grating 311 shown in FIG. 15 may be rotated so that three spots are always located at the same point in the lattice point interval in the spot scanning direction. As a result, the pulse is irradiated at each lattice point of three spots by one recording strobe pulse 221, so that the reproduction pulse condition can be satisfied in one spot condition. In addition, you may independently modulate by using three light sources and three AO drive circuits as a financial light source, without using a diffraction grating.

The reproducing circuit applies the configuration of FIGS. 28 and 29 as it is, detects the reflected light at the timing 504 synchronized with the lattice point in the reproducing pulse irradiation period, and detects the level with the sample holder. Here, the sample clock 265 does not have to be the same as the pulse irradiation time, but may be optimized by controlling the position so that the SN is maximized by providing a learning area. At this time, it is also possible to learn and optimize the time constant at the time of sample.

In the embodiment, the reproduction pulse condition for pulse reproduction is defined as the peak temperature of the film surface. However, since the mark has a finite width, the mark can be further optimized by considering the temperature distribution in the mark width. In the case of performing partial response signal processing, pulse irradiation may be performed at the detection point in the class. The optical super resolution spot can also be combined by optimizing the pulse condition with respect to the effective spot diameter, i.e., (λ / NA x (spot micronization rate due to the optical super resolution, 0.8 in the embodiment)).

According to the present invention, a density of about 1 digit or more can be realized by using a light source, an optical element, and a recording / reproducing technique currently available for a recording density of about 1 Gbit / in ² in an existing optical disk device.

Claims (12)

In the high density information recording and reproducing method, A recording laser light having a wavelength of 680 nm is irradiated onto the medium by using a super resolution optical system, and a recording spot is formed on the medium, and the heat energy of the recording spot is about one quarter or less of the size of the recording spot on the medium. Forming a; And Reproducing a signal from the mark using regenerated laser light having a wavelength of 530 nm How to include. A method according to claim 1, wherein in said irradiating step, two-dimensional recording is performed in which circular marks similar to each other are arranged at grid points of a two-dimensional grid on the medium extending in a track direction and a radial direction perpendicular to the track direction. In the high density information recording and reproducing method, A recording laser light of a first wavelength is irradiated onto the medium by using a super resolution optical system to form a recording spot on the medium, and a mark having a size equal to or less than a quarter of the recording spot on the medium by the thermal energy of the recording spot. Forming a; And Reproducing a signal from the mark using reproducing laser light of a second wavelength shorter than the first wavelength 2. The method of claim 2, wherein the irradiating step arranges circular marks that are similar to each other at grid points of a two-dimensional grid on the medium extending in a track direction and a radial direction perpendicular to the track direction. The method according to claim 2 or 3, wherein the information is detected by performing signal processing using the signal reproduced from the mark. 5. The method of claim 4, further comprising generating a recording clock signal and a reproducing clock signal from discretely provided clock marks on the medium, and detecting a tracking error signal from the wobble marks provided on the medium. . 4. The shape of the recording spot according to claim 2 or 3, wherein a strong laser light is previously applied to the medium to locally relax the structure to weaken the coercive force, thereby changing the recording sensitivity characteristic of the medium locally in a minute region. Forming a micro mark that is not dependent on the method. 4. The method according to claim 2 or 3, wherein the core is formed by injection to form an image microconcave-convex pattern of the optical disk substrate to provide a nucleus for forming a magnetic mark, thereby facilitating local formation of a recording mark. Forming a micro mark that does not depend on the shape of the recording spot, and locally changing the recording sensitivity characteristic of the medium in the micro area to form a micro mark that does not depend on the shape of the recording spot. The method according to claim 2 or 3, wherein at least one spot is positioned on the formed mark by using a sample servo to sample the detection signal according to a clock signal generated from the buried mark when the light spot is located at the lattice point. Holding, The method, Determining an amount of interference from adjacent grid points in the learning area, and Removing the amount of interference from the detection signal after the sample / hold is performed to determine the presence or absence of the mark recorded at the grid point How to include. The method according to claim 1, wherein a buried mark layer in which a micro mark having a predetermined shape is recorded on the medium is provided in advance, and the recording spot is positioned with respect to the buried mark layer to determine whether the buried mark is magnetically transferred. Recording an information mark on a reproduction layer of said medium by said recording spot. In the information recording and reproducing apparatus, A recording laser of 680 nm wavelength; A recording spot disposed on the optical path from the recording laser to the medium and blocking a portion of the recording laser to form a recording spot on the medium, wherein a mark having a size of one quarter or less of the recording spot is located in the recording spot. A shielding plate to be formed on the medium by means of thermal energy; And A recording laser of 530 nm wavelength for reproducing a signal from the mark recorded on the medium by the recording laser. Device comprising a. 11. The apparatus of claim 10, further comprising means for generating a write clock signal and a playback clock signal from discretely provided clock marks on the medium, and detecting a tracking error signal from the wobble marks provided on the medium. In the high density information recording and reproducing method, A recording laser light of a first wavelength is irradiated onto the medium by using a super resolution optical system to form a recording spot on the medium, and the recording energy on the medium is less than one quarter the size of the recording spot on the medium. Forming a mark having; And Reproducing a signal from the mark using a reproducing laser light of a second wavelength shorter than the first wavelength And a buried mark layer in which a micro mark having a mark of a predetermined shape is recorded on the medium, and before the irradiation step, the buried mark layer is positioned with respect to the buried mark layer so that the buried mark is magnetic. And an information mark is recorded in the reproduction layer of the medium by the recording spot according to whether or not it is transferred.