JPH0877640A - High density information recording/reproducing method - Google Patents

Abstract

PURPOSE: To realize a surface density not less than 10 Gbit/sq.in. by a method wherein the recording/reproduction of fine marks which overcomes the optical diffraction limit is achieved by using presently available light source, optical devices and recording/reproducing technology. CONSTITUTION: A laser beam with a wavelength of 532nm is emitted from a reproduction light source SHG 300 and converged into one direction by a cylindrical lens 303 through a slit 302. The converged beam is inputted to an A/0 modulator 304. The transmitted diffracted beam is converted into a beam having an original beam diameter by a cylindrical lens 305 and the beam is converted into a beam having a diameter, for instance, 3 times the original diameter by a beam expander 307 through a slit 306. The light path of the converted light beam is bent by a deflection mirror 309 and a return mirror 310 and the light beam is inputted to a diffraction lattice 311. The beam is divided into three light beams, i.e., 0-order beam and ± 1 order diffracted beams, by the diffraction lattice and, after passing through a superresolution optical filter 308, enters a light path synthesizing prism 312. Then, the beam is emitted toward a moving optical system 320 which is moving on an optical disc 398 through a return mirror 318 and a light beam splitting prism 319.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for optically recording and reproducing information, and more particularly to increasing the density of an optical disc device for recording and reproducing information on a disk-shaped medium.

[0002]

2. Description of the Related Art At present, the surface density of an optical disk device, which is a product, is about 880 megabits / square inch, and even at the research and development level, it is possible to overcome the harsh environmental conditions in which the optical disk is used. It is said that it can be realized at about three times the product level. In addition, the optical disc device used as a product has a wavelength of 780 nm, the objective lens has an NA of 0.55, and the recording method is mark length recording.
The servo system is continuous servo. Reference is ECMA
(European Computer Manufacturers Association) standard document.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to realize the highest density recording / reproducing characteristics of an optical disk by utilizing the components that can be realized at present. The value of the recording density realized is 10 Gbit / in ² .

[0004]

The gist of the present invention is as follows.

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

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

(3) The recording medium has a wavelength and NA of the objective lens.
The size of a spot that can be formed is about 1/4 or less compared to the spot size determined by Further, a medium having super-resolution characteristics using the difference in magnetic characteristics with respect to 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 surface than the spot size determined by the wavelength and NA of the objective lens is used. In addition, a configuration is adopted in which a plurality of spots are created during recording or reproduction.

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

(6) In the reproducing system, the reproduced signals from the marks on the two-dimensional lattice points are detected, and the reproduced signals from the respective marks are used to perform signal processing to detect information. On this occasion,
Light having a larger peak power than that emitted from direct current light is emitted from the light source in a pulsed manner at the timing synchronized with the lattice points, and the reflected light is detected at the timing synchronized with the lattice points.

(7) For tracking, a so-called sample servo is used, recording and reproducing clocks are made from embedded pits provided discretely, and a track deviation signal is detected from the wobble mark.

The structure of the medium is as follows: (1) An embedded mark layer in which fine marks having a target shape of about 0.22 μm are recorded in advance,
A recording servo is positioned on this by a sample servo, a clock is created from the embedded pits, and the embedded mark is magnetically transferred according to this clock, and the information mark is recorded in the reproducing layer depending on whether or not. The marks recorded on the reproducing layer follow the embedded mark shape and become minute marks that do not depend on the recording spot.

(2) The recording sensitivity characteristic is locally changed in a minute area to form a minute mark that does not depend on the recording spot. As a concrete means, the recording film is irradiated with a strong laser beam to locally generate structural relaxation and weaken the coercive force.

(3) A fine concavo-convex pattern is preliminarily provided on the substrate of the optical disc by injection to serve as a core for forming the magnetic mark, thereby facilitating local formation of the recording mark. As a result, a minute mark that does not depend on the recording spot is created.

When a plurality of or singular spots are positioned on the mark formed as described above by using a sample servo, and an optical spot is positioned on a two-dimensional lattice point according to a clock created from the embedded mark. Pulse irradiation is performed, and the detectors sample and hold the reflected light at the timings synchronized with the lattice points. The amount of interference from adjacent lattice points is obtained in advance in the learning area, and the process of removing the amount of interference from the detection signal after sample hold is performed to detect the presence or absence of the mark recorded at the lattice point.

[0016]

The recording uses a high power laser having a wavelength of 680 nm which is currently available as a light source and can be directly modulated, and the spot size is set to about 1.23 μm. Furthermore, the spot size is reduced to about 70% of 0.87 μm while giving an optical super-resolution effect and considering the efficiency of light output.

A recording medium having a diameter of 0.22 μm is recorded by using a recording medium capable of forming a mark of ¼ or less of a recording spot.

As a recording method, marks are arranged on a two-dimensional lattice and two-dimensional recording for recording is adopted to increase the recording density.

As described above, by using the presently feasible constituent elements, recording / reproduction of minute marks that have broken the optical diffraction limit can be realized, and a recording density of 10 Gbit / in ² can be realized.

[0020]

EXAMPLE FIG. 1 shows a state on a recording medium of the present invention.

The recording spots 101, 101 ', 101 "use a semiconductor laser having a wavelength of 685 nm as a light source and perform optical super-resolution in the disk radial direction. The laser from the semiconductor laser uses an optical system with a numerical aperture of 0.55. Converge on the disk surface, and the size of the recording spot 101 is 1.24 μm in the disk circumferential direction and 0.87 μm in the radial direction.The size of the information mark 102 to be recorded is about 0.22 in the disk circumferential direction.
μm, approximately 0.30 μm in the radial direction. The minimum distance between the information marks 102 is about 0.22 μm. Track pitch is about
It is 0.30 μm. The reproduction spots 103a, 103b, 103c have a wavelength of 5
The size of the 33 nm laser is 0.96 μm in the disk circumferential direction and 0.67 μm in the radial direction by using magnetic super resolution (FAD) and optical super resolution described later. Further, prior to the information mark 102, a clock mark 104, a wobble mark 105, an address mark 106, etc. are formed in an uneven shape.

FIG. 2 shows a specific structure of the optical super-resolution. The light from the semiconductor laser 201 is converted into a parallel light flux by the coupling lens 202, and the objective lens 205 is passed through the prism 204 and the like.
To form an image on the image plane 206. Shield plate 2 in this optical path
Insert 03.

FIG. 3 shows the details of the shielding plate 203. The shield plate shields a part of the light flux having the diameter r by the diameter r ′ centered on the optical axis.
The shielding ratio α is defined by the ratio of r and r ′ (r ′ / r). As the shielding ratio α is increased, another light spot appears on both sides of the focused spot on the image plane 206, and the central intensity of the center spot decreases. However, the spot size in the middle becomes smaller. These spots are 101, 101 ', 101 "in FIG.
Corresponding to.

FIG. 4 shows the relationship between the shielding ratio α and the spot size. exp. Is an experimental value, cal. Is the calculated value,
The standard value of the standardized spot diameter is taken when the shielding ratio α is 0. When the spot size is reduced to about 70%, the shielding ratio is about 0.7, and the central intensity of the spot is about 50%. The intensity of the spots on both sides at this time is about 20% of the intensity of the spot in the middle, and there is no problem because the spots on both sides do not record at the time of recording.

The principle of forming a mark having a size of about 1/4 of the spot size using the above-described recording spot will be described. The domain wall of the magneto-optical mark is determined by the stable condition of magnetic energy. Let σw be the domain wall energy per unit area, Ms be the saturation magnetization, r be the radius of the magnetic domain, Hd be the demagnetizing field acting on the domain wall, and Hext be the external magnetic field, the sum of the magnetic fields that are the source of the force to expand the domain wall. Htotal
Is expressed by the following formula.

Htotal = Hext + Hd−σw / 2rMs (Equation 1) The domain wall is determined when the coercive force Hc of the recording film and the above Htotal are balanced.

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

FIG. 6 shows the principle of formation of magnetization marks. Irradiation of the light beam 602 to the perpendicular magnetization film 601 and the external magnetic field
603 is applied to form a magnetization mark. Usually, as indicated by the dotted line, the recording temperature Trec is the same on the entire surface of the disk.
Then, the temperature distribution 604 formed by the irradiation of the light beam
The magnetic domain wall of the magnetization mark was determined at the intersection of the recording temperature Trec and the magnetic domain wall 605 was formed on the perpendicular magnetization film 601. At this time, the width of the mark 606 was about half of the spot size and was in a stable state.

However, in the present invention, the coercive force characteristic of FIG. 5 or the above Htotal is locally changed to set the recording temperature to T'rec, and the recording temperature characteristic on the disk surface is locally reduced. Then, when a light spot is irradiated to a portion where the recording temperature is locally lowered to form a 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 domain wall 605a is formed on the perpendicular magnetization film, and the width of the magnetization mark 606a is narrower than that of the conventional magnetization mark 606. Conventionally, in the peak portion of the temperature distribution, the variation of the intersection is large and not stable with respect to the variation of the temperature distribution, but according to the present invention, the gradient with respect to the position of the recording temperature has the opposite polarity to the gradient with respect to the position of the temperature distribution. Therefore, the variation of the intersection can be suppressed against the variation of the temperature distribution. In this way, the fine marks can be stably formed with a recording energy lower than that of the conventional one.

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

FIG. 7 shows an example in which structural relaxation is locally caused on the disk. Structural relaxation means locally weakening the coercive force of the recording medium by weakening the magnetic anisotropy by the annealing action.

FIG. 7a shows a state in which recording is performed by the light beam 702 on the recording medium 701 having the structural relaxation. In the portion 703 where the structural relaxation is caused, the coercive force characteristic at the temperature shown in FIG. 5 is locally reduced, but since the Htotal is not changed, the effective recording temperature 704 is reduced. Therefore, when the temperature distribution 705 is formed by the light beam, the small magnetization mark 706 is formed. The amount of decrease in coercive force depends on the energy applied for annealing. As an annealing method, there is a method of locally irradiating high energy light to cause structural relaxation depending on temperature. In this method, the amount of local decrease in coercive force changes due to the high energy distribution, and the recording temperature changes accordingly. In order to narrow the local area, it is preferable to perform recording with a spot smaller than the recording spot. Currently, the recording spot is determined by 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 forming a master of an optical disc can be used to cause structural relaxation. The spot size is 0.45 with the current combination of laser and lens.
It can be made in the order of microns, and thus the annealed region can be made as narrow as 0.2 microns.

FIG. 7b shows the measured data 707 of the reproduced output when the structural relaxation is caused and recording is performed thereon, in comparison with the conventional data 708. When the recording power is lowered, the intersection of the recording temperature and the temperature distribution approaches the peak point in the conventional method, and the mark fluctuates abruptly due to the power fluctuation and the reproduction output is lowered. However, if the mark is recorded after the structure is relaxed, when the recording power is high, the mark is almost the same as the conventional one if the mark is larger than the region of the structure relaxation, and there is no difference in the reproduced signal. However, as the recording power decreases, the change in the mark width with respect to the change in the recording power decreases when the recording mark reaches the structural relaxation region.
The change in output level becomes small.

FIG. 8 illustrates an example in which the area where the recording mark of the recording medium is formed is the same as the conventional coercive force, and the coercive force of other areas is increased.

FIG. 8a shows the medium of the present invention. In the perpendicular magnetic film 701, the surface roughness other than the portion where the magnetic mark 706 is formed is roughened to improve the coercive force. That is, only the portion where the magnetization mark 706 is formed is the flat portion 801. Therefore, the surface energy for stopping the domain wall is increased except for the flat portion 801, and the apparent coercive force can be increased. With this configuration, the recording temperature 804 relatively decreases in the mark area.

As a method of roughening the surface roughness, first, a resist having a characteristic that only light is cross-linked when it is cross-linked and is insoluble in a developing solution is used, and light is applied to a minute mark portion of a two-dimensional lattice point. Irradiate. In the development process, the surface excluding the two-dimensional lattice points is roughened by etching with a developer having a high concentration. By forming a stamper from the master thus prepared and stamping the roughened surface on the plastic, the surface roughness around the minute mark can be roughened.

FIG. 8b shows the relationship between the magnetic domain width and the recording power. When a striped flat portion having a width of 0.2 μm is formed and the surface roughness on both sides thereof is made rough, the relation between the width of the magnetic domain to be formed and the recording power is 807. It can be seen that the width of the magnetic domain formed is smaller than the data 808 when the surface roughness is not roughened.

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

As shown in FIG. 9, a layer 903 which is in magnetic contact with the recording film 901 and in which the minute magnetization marks 902 are embedded in advance is formed.
Is provided. The minute magnetized marks 902 are arranged two-dimensionally,
The effective Htotal is changed by increasing the external magnetic field on the recording layer 901 in contact with the embedded layer 903 by the amount of the magnetic field generated by the magnetization mark 902.

This effect will be described with reference to FIG. 5. Even if the magnetic characteristics of the recording film do not change, the recording temperature changes from Trec when changing to H'total due to the magnetization due to the embedded mark as compared with the conventional Htotal. T'rec. Therefore, in FIG. 9A, the recording temperature 904 lowers above the embedded mark. Therefore, when the temperature on the recording film is increased as shown by the curve 705, the recording mark 706 corresponding to the lowering region of the recording temperature 904 is formed. . FIG. 9b shows the relationship between the mark forming power during recording and the output signal when this mark is reproduced.

Next, a method of forming a minute domain by changing the composition of the recording film will be described. The basic structure of the magneto-optical recording film is an amorphous structure of 3 atoms of TbFeCo. The perpendicular magnetic characteristics differ depending on the ratio of Tb and Fe.

FIG. 10a shows the relationship between the coercive force and the temperature in the TM rich with a large amount of Fe and the RE rich with a large amount of Tb. The slope of the coercive force characteristics with respect to temperature is RE compared to TM rich.
Rich is steeper. Regarding the relationship between the recording temperature and the recording mark, when the coercive force characteristic explained in FIG. 5 becomes the characteristic shown in FIG. 10, a finer mark can be formed more stably than in the conventional case, and the recording mark is changed against the change of Htotal. Fluctuation can be suppressed.

FIG. 10b shows the relationship between the recording power and the signal output. For the above-mentioned reason, the dependence of the signal output on the recording power is also less in RE rich.

The reason for this will be described in more detail with reference to FIGS.
This will be described with reference to FIGS. 13 and 14.

FIG. 11 shows the temperature distribution of each medium when the medium at room temperature of 20 degrees is irradiated with laser light. It is known that the temperature distribution on the medium is almost equal to the spot distribution when irradiated with a short pulse.

FIG. 12 is a diagram showing coercive force characteristics of each medium corresponding to FIG. 10a. This coercive force characteristic and Htotal
1 for the RE-rich medium in which a recording mark of 0.2 μm is formed by the recording temperature determined by
4 shows the relationship between the mark displacement and the coercive force due to the temperature distribution of FIG. 11 for the TM rich medium. From the value that can record a recording mark with a recording power of 0.2 micron, 0.9
Changes 1.1 times from Htota
It is obtained from the intersection of l and the coercive force characteristic. As a result, it can be seen that the mark width variation is smaller in RE rich. By using the recording film structure of FIGS. 7 to 9 and the RE-rich recording medium, it is possible to form a recording mark having a width about half that of the conventional case when recording is performed at the same spot.

FIG. 15 is a block diagram of the recording / reproducing apparatus of the present invention.

Laser light having a wavelength of 532 nm emitted from the reproducing light source SHG 300 is converged in one direction by the cylindrical lens 303 through the slit 302.
301 is a detector system that controls a A / O drive circuit 377 in order to detect a part of the laser light and control the intensity of the laser light.
The light converged by the cylindrical lens 303 is input to the A / O modulator 304, and the transmitted diffracted light is converted into the original luminous flux diameter by the cylindrical lens 305. The light that has been converted into the original light beam system is expanded by the beam expander 307 through the slit 306 so that the diameter of the light beam is expanded to, for example, three times. The optical path of the converted light flux is bent by the deflecting mirror 309 and the folding mirror 310, and the diffraction grating 31
1 is incident. The diffraction grating 311 splits the light into three luminous fluxes of 0th order and ± 1st order diffracted light, and an optical filter 3 for super-resolution is used.
After passing through 08, it is incident on the prism 312 for optical path combination.

A laser from a 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 light flux is passed through an optical filter 313 for super-resolution. The light passing through the filter 313 has its optical path bent by an optical deflector 314 and a folding mirror 315, and enters a prism 316 for combining optical paths.

Laser light having wavelengths of 532 nm and 685 nm is combined by the optical path combining prisms 312 and 316, passes through the folding mirror 318 and the light beam separating prism 319, and is then emitted toward the moving optical system 320 moving on the optical disk 398. . In the moving optical system 320, the fixed optical system 32
The light flux emitted from the beam No. 1 is bent by the deflecting mirror toward the surface of the optical disk 398 attached to the spindle motor. The bent luminous flux is converted into an optical disc by an objective lens.
It is focused on 398 to form a light spot. The formed light spot has a positional relationship like the recording spot 101 and the reproducing spot 103 in FIG. The moving optical system 320 with a built-in objective lens and light deflection mirror is mounted on a moving table that moves at high speed in the radial direction 380 of the optical disk to perform an access operation, and at the time of tracking to make a light spot follow a track, Move the light deflection mirror in conjunction.

The reflected light from the optical disk has its optical path bent by the light beam separating prism 319 via the light deflecting mirror.
Bent by the folding mirror 353, 685 nm
The separating prism 354 enters the servo signal and clock signal detecting optical system 355. Further, the light of 532 nm passes through the prism 354, and the 532 nm separating prism 356.
Then, it is made incident on the magneto-optical signal detection system 357.

The light incident on the magneto-optical signal detection system 357 is 2
The polarization angle is rotated to about 45 degrees by the one-half wavelength plate 358, and the three light beams of s-polarized light and p-polarized light that have passed through the s- and p-polarized light separating prism 359 are detected by the three-division detectors 360 and 370. The difference between the outputs from the photodetectors corresponding to the reproduction spots 103a, 103b, 103c shown is formed by the differential amplifier 371 and detected as a magneto-optical signal 381. The magneto-optical signal 381 is input to the recording / reproducing control circuit 372 and subjected to the processing described later.

Servo signal / clock signal detection optical system 355
Then, marks such as 104, 105, and 106 in FIG. 1 are detected. The detected signal 382 is input to the data clock generation circuit 373, the servo circuit 374, and the recording / reproduction control circuit 372,
The control operations of clock signal generation, tracking control, automatic focus control, and recording / reproducing operation will be described later.

A spindle 383 for rotating the disk sends a signal from an encoder attached to the spindle to a rotation control system 375, and drives the spindle via a spindle driver 384 so as to achieve a constant rotation speed in synchronization with a reference clock. Control. The recording / reproducing control circuit 372 gives a control operation command to the servo circuit 374 to move the moving optical system.
Control the position of 320. A signal for controlling the power level of recording and reproduction and recording data are sent from the recording and reproduction control circuit 372 to the laser control circuit 376, and the reproduction output is controlled through the drive circuit 377 of the A / O deflector 304 which controls the output from the SHG 300. To do. On the other hand, to the recording laser, an APC (auto power control) control signal 385 for controlling the DC power, a command value 386 of a set level of the recording power, and binarized data 387 which is recording data are input to a high speed driver 378 of the laser.

FIG. 16 shows the arrangement relationship of the light spots on the optical disk 398. The recording 685 nm spot 101 is arranged at the head, and wobble pits 331, 332 formed in advance in an uneven shape by the recording spot 101.
333, 334, 335 and clock pits 336, 33
7,338 is detected. A detection signal for tracking servo is obtained by a well-known method from the wobble pits that are slightly offset to the left and right with respect to the track center, and a mark for recording and reproducing a mark on the disk surface is obtained from the clock pits. Create a reference clock signal.

The 685 nm spot 101 generates side lobes 101 'and 101 "on both sides of the spot by wavefront manipulation after passing through the optical super-resolution filter. The optical super-resolution is made to appear in the track radial direction, Avoid appearing in the circumferential direction.

The reproducing 532 nm laser beam is separated into three spots 103a, 103b, 103c by the diffraction grating,
And side lobes 103a ', 10 on both sides of each spot
3b ', 103c', 103a ", 103b", 103c "are generated. The diffraction grating 311 of FIG. 17 is arranged so that the three spots 103a, 103b, 103c are located on the virtual track centerlines 350, 351, 352 adjacent to each other. Is rotated in a plane perpendicular to the light beam.
Controlled by the control signal detected in 1, the 532 nm spots 103a, 103b, 103c are also moved at the same time. 532nm and 6
The 85 nm alignment is finely adjusted by the deflector 314 of the 532 nm light source system shown in FIG. Focusing is performed by using a spot 685 nm 101 as in the case of detecting the track shift, detecting the focus shift using an astigmatism method in a focusing region (not shown), and driving the objective lens of the moving system.

Although the virtual track interval must be narrowed to 0.3 μm, the spot size for detecting the track deviation is as large as 0.87 μm, which is larger than the virtual track interval. The conventional track pitch is about the size of the spot. Therefore, a control signal that can perform finer positioning than the track pitch is generated by using the conventional prepits for sample servo. Here, the pre-pit interval is 1.2 μm and the wobble interval of the wobble pits is 0.3 μm.

A method of forming the track deviation signal will be described with reference to FIG. Sample and hold signals A, B, C (1702) for detecting the signal levels of the wobble mark A333, the clock mark 338, and the wobble mark B335 by using the signals detected from the clock marks to create a clock signal for generating timing. , 1703,1704) is created. The level of the total light amount signal 1701 from each mark is sampled and held by these signals A, B and C.

A specific configuration of the servo circuit 374 for forming the track deviation signal will be described with reference to FIG. The sample hold circuits 150a, 150b, 150c sample and hold the total light amount signals modulated by the wobble mark 333, the clock mark 338, and the wobble mark 335, respectively. Subtraction circuit 152a, 1
52b and 152c respectively take a differential between the sampled and held signals to obtain tracking signals A (1801), B (1802), C (180
3), D (1804) is created. These signals are control signals for positioning the light spot on the virtual track center lines N, N + 1, N + 2, N + 7 obtained by dividing the track pitch shown in FIG. 16 into eight. FIG. 19 shows the relationship between the virtual track center line shown in FIG. 16 and the tracking signals 1801, 1802, 1803, 1804. Tracking control can be performed using this relationship. FIG. 20 shows a specific control signal forming circuit.
The amplitudes of the tracking signals C (1803) and D (1804) are adjusted by gain controls 2001 and 2002. Further, the polarities are adjusted by the polarity reversing circuits 2003, 2004, 2005 and 2006 to create the tracking signals A ′, B ′, C ′ and D ′ (2003 to 2006). These signals are switched by the switching circuit 2007, processed by the phase compensation circuit 2008, and input as control signals for the control system.
0 Controls the internal light deflector.

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

FIG. 1 shows the state of FIG. 21 as a perspective view. In the address area, a specific pattern indicating the beginning of a sector, a sector address, etc. are stored in the pre-pit 106.
Is formed in advance. In the timing area, the timing mark 104 is formed in advance on the grid point 213 on each information mark row. Record information marks on grid points,
The strobe pulse used when sampling the signal on the grid point is the PLL based on the detection signal of this timing mark.
Created or corrected using circuitry. A learning mark for learning an interference coefficient required for signal processing calculation at the time of reproducing information is recorded in an interference coefficient learning area described later.

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

FIG. 22 shows an example of another recording method. Figure 21
22, the grid points 213 are aligned in the radial direction of the optical disc and the circumferential direction of the optical disc, but in the example of FIG. At this time, the crosstalk in the radial direction of the optical disc at each lattice point is smaller than that in the case of FIG. For this reason,
Compared with the example of the recording method of FIG. 21, it is possible to further reduce the lattice point spacing in the radial direction of the optical disc, and it is possible to further increase the density in the radial direction of the optical disc.

FIG. 23 shows an example of the learning mark described above. Three
The learning mark 231 may be recorded as an isolated mark located on the grid point of the central information track of the two information tracks. The learning mark 231 may be formed in advance as a pre-pit, or may be recorded when the disc is shipped.

When reproducing information, the interference coefficient is first learned. The interference coefficient, which is a function of the light spot shape, the information mark shape, and the lattice point spacing, must be learned by an actual optical disk device. Therefore, at the time of reproducing information, the learning mark 231 is detected by the light spot and the interference coefficient is learned.

When the reproduction information block is composed of three information tracks, the interference coefficient has the characteristics a to n shown in FIG.

First, when the center of the light spot 103c reaches the lattice point (M-2, N + 1), q (j) is measured as the amount of interference in the diagonal direction, and the lattice point (M-1, N +) is measured.
When 1) is reached, q (k) is measured as the amount of diagonal interference, and when the lattice point (M, N + 1) is subsequently reached, q (l) is measured as the amount of radial interference. I'll do it.
Next, the center of the light spot 103b is a lattice point (M-2,
When N) is reached, q (f) is measured as an interference amount in the circumferential direction, and when reaching a lattice point (M-1, N), q (g) is measured as an interference amount in the circumferential direction. Incidentally, when the grid point (M, N) is subsequently reached, the interference coefficient learning mark 23
The isolated signal SM, N of 1 is detected.

Based on the above measured values, the interference coefficient j in the diagonal direction is given by the ratio q (j) / SM, N between the diagonal interference amount q (j) and the isolated signal SM, N. Similarly, the interference coefficient l in the radial direction is determined by the interference amount q (l) in the radial direction and the isolated signal S.
The interference coefficient f in the circumferential direction is given by the ratio q (l) / SM, N with respect to M, N, and the ratio q (f) / SM, with the interference amount q (f) in the circumferential direction and the isolated signal SM, N. Given by N.

Similarly, the interference coefficients n and m in the diagonal direction are determined when the center of the light spot 103c reaches the lattice point (M + 1, N + 1) and when the center of the light spot 103c reaches the lattice point (M + 2, N + 1). It can be detected when it reaches. The diagonal interference coefficients d and e are obtained when the center of the light spot 103a reaches the grid point (M + 1, N-1) and when the center of the light spot 103a reaches the grid point (M + 2, N-1). Gained when reached. Furthermore, the interference coefficient h, i in the circumferential direction
Indicates that the spot 103b has grid points (M + 1, N), (M +
2. The interference coefficient is obtained by taking the ratio of the value obtained in (2, N) to the isolated signal SM, N. Further, the learning accuracy of the interference coefficient can be improved by performing the above-mentioned learning several times and averaging the results. As an example, a method of providing a plurality of interference coefficient learning marks can be considered.

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

In the case of the information mark string as shown in FIG. 21,
The detection signal on the grid point (M, N) and the detection signals on the grid points in 14 neighborhoods (5 × 3-1 = 14) adjacent to the grid point (M, N) are used (shown in FIG. 33).

FIG. 40 shows a matrix of the signal amplitude at each lattice point when two tracks adjacent to the three tracks 1, 2 and 3 are also included and only recorded marks exist in isolation. Indicates. Here, since only three tracks can be detected at the same time in this embodiment, it is considered to accurately detect the mark in the area surrounded by the dotted line.

Therefore, an arithmetic expression representing an isolated signal obtained at each lattice point position

[0075]

[Equation 1]

In the above, the calculation value obtained by ignoring E is the value to be obtained with reduced crosstalk. Here, S (j, k) is a column vector having an isolated signal as a component obtained at 21 grid point positions, K (i, j) is a 21st-order square matrix having an interference coefficient as a component, and S ′ (i , J) is 21
A column vector having a detection signal obtained at the respective grid point positions as a component, and E is a column vector representing crosstalk from grid points other than the above-mentioned 21 grid points. Here, if the influence of the crosstalk is completely removed, the isolated signal S (i, j) at each lattice point can be calculated using Equation 2.

[0077]

[Equation 2]

However, since the column vector E has a portion that cannot be detected by three spots, the calculated value obtained by ignoring E is calculated. That is, the signal S ″ at the grid point (i, j) position is calculated using the inverse matrix of K from the signal detected using equation 3.

[0079]

(Equation 3)

As described above, by using the recording method and the signal processing calculation method according to the present invention, it is possible to realize recording and reproducing at a higher density than the conventional method. Further, in the reproduced signals from all the light spots used during information reproduction, a signal in which the crosstalk noise component is sufficiently reduced can be obtained, so that the data transfer rate is also improved as compared with the conventional method.

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

First, for the optical system for realizing the plurality of light spots, and the tracking and autofocusing of the plurality of light spots, for example, the means described in Japanese Patent Publication No. 58-021336 may be used. At this time, as shown in FIG. 21, the axis connecting the plurality of light spots has an inclination with respect to the information block radius, and as a result, a certain time difference occurs between the light spots in the optical disc circumferential direction. If this time difference is not a multiple of the grid point interval, in order to simultaneously record and reproduce the information mark 102 on the grid point 213 using the plurality of light spots 103a to 103c, it is necessary to prepare a strobe pulse unique to each light spot. There is.
That is, each strobe pulse is accurately synchronized with the lattice point on each information track, and each light spot records and reproduces information according to the timing of each strobe pulse. At this time, the time difference between the strobe pulses corresponds to the time difference between the light spots.

FIG. 24 shows a block diagram of a recording circuit for performing the above recording. This recording circuit includes detection units 201a to 201c as many as the number of light spots for detecting that light spots have entered the learning area, a data selection unit 202 for selecting learning data and information data, and data recording. It is composed of the unit 203. The data recording unit 203 is controlled by the clock 2310.

FIG. 25 shows an example of the detecting section 201 of FIG. The detector 210 detects a mark on the optical disc corresponding to each light spot. The detection signals from the detector 210 are extracted at predetermined timings by the gates 2501a and 2501b. The PLL circuit 2110 forms a timing signal from the signal corresponding to the timing mark output from the gate 2501a. The sector head recognition circuit 212
The head of the sector is recognized from the signal corresponding to the header mark recorded at the head of the area output from the gate 2501b. The area recognition circuit 2130 is a part that controls the detection unit 201.

Referring also to the time chart of FIG. 32, the detection unit
The operation of 201 is shown. The area recognition circuit 2130 is a PLL circuit 211.
The position of the light spot is recognized by counting the strobe pulse 215 output from 0, and as a result,
Address area signal 217, timing area signal 218,
The interference coefficient learning area signal 219 and the data storage area signal 220 are output.

More specifically, the count value of the strobe pulse 215 is first reset to 0 by the pulse signal 223 output from the sector head recognition circuit 222. The sector area recognition circuit 222 outputs the output signal 21 from the photodetector.
4 is a circuit for detecting a specific pattern indicating the head of a sector formed in the address area 2170 based on 4, and outputs a pulse signal 223 when the specific pattern is detected.

Since the light spot exists in the address area 2170 between the count value 0 and a, the address area signal 21
Outputs only 7 as on. When the address area signal 217 is turned on, the output signal 214 from the photodetector is output to the address recognition circuit 212 via the gate circuit 2501b. The address recognition circuit 212 is a circuit that detects the address information formed in the address area 2170 based on the output signal 214.

Since the light spot exists in the timing region 2180 while the count value is between a and b, only the timing region signal 218 is turned on and output. Timing domain signal 2
When 18 is turned on, the output signal 214 from the photodetector is input to the PLL circuit 2110 via the gate circuit 2501a. P
The LL circuit 2110 detects the timing mark formed in the timing region 2180 based on the output signal 214 from the photodetector, and uses the detection result to correct the timing deviation between the strobe pulse and the lattice point position. To do. PL
The L circuit 211 outputs a strobe pulse 215, which is the interference coefficient learning region signal 2
When the signal 19 is ON or the data storage area signal 220 is ON, the signal is output from the detection unit 201 via the gate circuit 2501c.

Since the light spot exists in the interference coefficient learning area 2190 while the count value is from b to c, only the interference coefficient learning area signal 219 is turned on, and the light spot stores data while the count value is from c to d. Since it exists in the area 2200, only the data storage area signal 220 is output as ON. These interference coefficient learning area signal 219 and data storage area signal 220
Is an output signal of the detection unit 201. Therefore, the detection units 201a to 201c have the strobe pulse 215a.
˜215c, the interference coefficient learning area signals 219a to 219c and the data storage area signals 220a to 220c are output.

FIG. 26 shows an example of a block diagram of the data selection unit 202. The data selection unit 202 includes user data 204 and the detection units 201a to 201.
a plurality of data storage area signals 220a output from c
-220c and a plurality of interference coefficient learning area signals 219a-
219c is input. At this time, for example, when at least one of the data storage area signals 220a to 220c is turned on, the data selection unit 202 outputs the user data 204 as serial data 225. Further, when at least one of the interference coefficient learning area signals 219a to 219c is turned on, an information mark necessary for learning the interference coefficient is stored in the interference coefficient learning data ROM 226 for recording in the interference coefficient learning area. The output data string is output as serial data 225. In this case, the data string may represent an isolated mark as shown in FIG.

FIG. 27 shows an example of the data recording section 203. In the data recording section 203, the data recording strobe pulse 221 and the serial data 2 are recorded.
25 is input. At this time, the serial data 225 is
Serial-parallel conversion circuit 23 operating with a reference clock 231 having a frequency higher than that of each recording strobe pulse 221.
Converted by 0. The converted data 232 is F
The data is stored in the I / FO (first-in / first-out) memory 233 and read from the FI / FO memory 233 by the recording strobe pulse 221. The read data 234 are input to the modulator 235. The modulated data 236 is input to the laser drive circuit 237, and a mark is recorded by the intensity modulation of the light spot 238.

Here, when recording is performed in the information block 211 of the three information tracks shown in FIG. 21 with one spot of the spot 101 in FIG. 1, one information track is used for each rotation of the disk by using the above circuit. By recording 3
Record on one information track. Further, using a three-beam laser array having a wavelength of 685 nm as a recording light source, the recording spots are respectively positioned on the three information tracks in the information block, and the F1 / F0 memory 233, modulator 235, and laser driving circuit 273 shown in FIG. 27 are arranged. 3 systems should be provided. Further, instead of using the laser having the wavelength of 685 nm, three SHG lasers having the wavelength of 532 nm may be provided, and three systems of A / O modulators may be used to record / reproduce with three beams.

FIG. 28 is a block diagram of an information reproducing circuit for reproducing recorded information. This reproducing circuit has the same number of detection units 251a to 251 as the number of light spots for detecting that the light spots have entered the respective areas shown in FIG.
c, a synchronization correction unit 2 for synchronizing detection signals from each detector
52 and an arithmetic unit 253.

FIG. 29 shows an example of a block diagram of the detecting section 251. The detection unit 251 mainly includes a detector 267 corresponding to each light spot, a sample hold circuit 256, a PLL circuit 257, and a sector head recognition circuit 2.
58 and a region recognition circuit 259. PLL circuit 25
7, 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-mentioned recording circuit, and the detection unit 251 is the same as the detection unit 201 in the recording circuit, and Controlled. 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 in the detection unit.
It is input to the circuit 257. The PLL circuit 257 corrects the phase shift of the strobe pulse 264 due to the disk rotation irregularity based on the timing mark signal. Then, when the interference coefficient learning area signal 262 is on or the data storage area signal 263 is on, the strobe pulse 264 output from the PLL circuit 257 becomes the clock 265 of the sample hold circuit 256. The sample hold circuit 256 samples the signal value of the input detection signal 255 on the grid point according to the clock 265.
The sampled value is detected by the detection unit 25 as a detection signal 266.
It becomes an output of 1 and is input to the synchronization correction unit 252.

The sample hold circuit 25 which generates the 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.
The output from 6 is detected by the detection unit 25 as a control clock 265.
It becomes an output of 1 and is input to the synchronization correction unit 252.

FIG. 30 shows an example of a block diagram of the synchronization correction section 252. The synchronization correction unit 252 mainly includes an FI / FO memory and a read clock control circuit. The detection signals 266a to 266c output from the detection units 251a to 251c and input to the synchronization correction unit 252.
Similarly, each control clock 265a output from each detection unit 251a to 251c and input to the synchronization correction unit 252.
To 266c, the FI / FO memories 271a to 271
It is stored in 71c. In addition, each of the detection units 251a to 251
The interference coefficient learning area signals 262a to 262 output from c
A signal that is turned on when all of 62c are on is an interference coefficient learning area signal 275, and a signal that is turned on when all of the data storage area signals 263a to 263c output from each detection unit are on is a data storage area signal 276. Then, when either one of these two signals is turned on, the read clock control circuit 272 outputs the reference clock 277. The frequency of the reference clock 277 is set to be equal to or lower than the frequencies of the control clocks 265a to 265c.

Each of the above FI / FO memories 271a to 271
The detection signals 266a to 266c accumulated in c are read according to the output signal 277 of the read clock control circuit 272, and the detected signals 278a to 278c are synchronized.
Is output from the synchronization correction unit 252 and input to the calculation 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 input to the calculation unit 253.

FIG. 31 shows an example of the calculation unit 253. Output from the synchronization correction unit 252, the calculation unit 25
Each of the detection signals 278a to 278c input to No. 3 is input to the calculator 280. At this time, when the interference coefficient learning area signal 276, which is the input from the synchronization correction unit 252, is on, the calculator 280 calculates the interference coefficient by performing the above-described calculation based on the detection signals 278a to 278c, An inverse matrix is calculated based on these interference coefficients (Equation 3), and the calculation coefficient is calculated. The calculated calculation coefficient is stored in the calculation coefficient memory 28.
Stored in 1.

When the data storage area signal 276, which is an input from the synchronization correction unit 252, is ON, the arithmetic unit 280
Is the calculation result 283a to 28 which reduces the crosstalk noise by performing the calculation shown in Formula 1, Formula 2 and Formula 3 based on the detection signals 278a to 278c and the calculation coefficient calculated by the above means.
3c is output to the comparator 284. Comparator 28
4 determines the presence or absence of the information mark based on the calculated value 283. The determination results 285a to 285c are demodulated by the demodulator 286 and output as reproduced signals 287a to 287c.

Further, the parallel-serial conversion circuit 288
Thus, the serial data 289, that is, the user data is reproduced.

The above is an example of three-track simultaneous reproduction in which three information track groups are regarded as one information block and information of one information block is reproduced at the same time. Scanning of the spot 103b in the middle of the reproduction spot is performed. It is also possible to record / reproduce only one track to be recorded.

In this method, only the track scanned by the spot 103b needs to be reproduced. Spot 103a
And 103c are used to detect the leak of the signal from the adjacent track which leaks to the information track irradiated with the spot 103b. Spots 103a and 10
By canceling the signal leakage (crosstalk) detected in 3c from the signal detected in the spot 103b, accurate information can be detected even if the information block interval shown in FIG. 21 is narrowed. Therefore, the recording density can be further increased. The recording is similar to that shown in FIG.
Recording is performed with the recording spot 101 of 5 nm, and 3 of 532 nm is recorded.
Spot 10 at spots 103a, 103b, 103c
Reproduce the data of the information track above 3b.

Specifically, when the area density is calculated this time, the spot size W is 0.96 micron when the reproduction wavelength is 530 nm and the numerical aperture is 0.55. The optical super-resolution effectively increases the spot size in the track direction by 0.7 times to 0.67 μm. In the reproducing method adopted this time, the track pitch can be reduced to about 0.4 times W, so that the track pitch of 0.3 micron can be realized.

When optical super-resolution is performed, side lobes are generated on the disk surface, and a signal leaks from the tracks on the side lobes. In order not to detect this on the detector surface, a shield plate for cutting side lobes is usually inserted in the middle of the light flux after passing through the objective lens. However, there are at least three beams this time,
Moreover, since the luminous flux is arranged to be inclined with respect to the track direction, it is difficult to set it with the same shielding plate.

FIG. 35 shows an example of a photodetector that solves the side lobe problem. Non-linear transmission material 351 was coated on photodetector 350. As this material, for example,
A diarylethene derivative that is a photochromic medium is preferable.

FIG. 34 shows the spectral characteristics of the diarylethene derivative. When there is sufficient energy intensity (ring opening of diarylethene A), the transmittance characteristic curve is curve 342.
Thus, a curve 341 is obtained, and the transmittance changes non-linearly with respect to the energy intensity of the reproduction light of 530 nm.

FIG. 36 shows how the transmittance changes with the energy intensity of the reproduction light. In the case of light with almost no change in intensity, the energy is equivalently represented by the average power.

FIG. 37 shows the principle of signal reproduction. If the incident power density and the transmission power density have non-linear characteristics as shown by the curve 407, the reproduction light reaches only the portion with high intensity at the photodetector. Therefore, the intensity distribution of the incident light spot 401 becomes an intensity distribution like the light spot 400 after transmission. Here, in the incident light spot 401, light that is weaker than the main lobe 402 such as the side lobe 403 has a significantly reduced intensity as compared with the main lobe after the transmission, as in the side lobe 405. Side lobe 40
Almost no signal is received from the mark illuminated by 5.
Further, if the position where the photodetector is placed is the far field surface away from the image forming position, when the reproduction spot starts tracking by the optical deflector, the spot moves on the photodetector surface. Even in this state, a non-linear effect occurs depending on the spot movement so that only the light from the main lobe can be transmitted at all times, so this material is always excited with light different from the reproduction light over the entire surface where the spot moves. It is necessary to keep it.

Therefore, as shown in FIG.
In addition to 353, light 352 of short wavelength blue light emitting diode 3520 is applied to the entire surface of this material. Another spectrum characteristic of the wavelength of the light emitting diode (diarylethene A
A wavelength band 420 to 480 nm having a transmission characteristic is selected on the curve 342 which is a closed ring. The characteristic of the curve 342 is obtained by the light irradiation in this wavelength region. The curve 342 has the absorption characteristic at the wavelength of 530 nm of the light for detecting the signal, so that the nonlinear material as a whole absorbs the light of 530 nm, but if the light energy intensity is strong, the characteristic of the curve 341 is obtained and the light of 530 nm is transmitted. Can be configured to The non-linearity can therefore be controlled by the power of the light emitting diode that is totally illuminated. Further, generally, this type of non-linear material has a slow response, but can sufficiently deal with a response that follows a track deviation. As described above, the leakage from the side lobes due to the optical super-resolution can be removed with a simple structure using the nonlinear material, and the assembly and adjustment of the optical system becomes easy.

FAD (Front Aperture Detection), which is a kind of magnetic super resolution, for improving the reproduction resolution in the circumferential direction will be described with reference to FIG. 38a. The recording medium is Tb on the recording layer 381 such as TbFeCo shown in FIGS. 7 and 8.
A cutting layer 382 made of DyFe and a reproducing layer 383 made of GdFeCo are placed. When a light spot 384 is irradiated onto the medium of this structure and moved in the direction of arrow 385, the temperature distribution 387 on the center of the track on the medium has a distorted spread of high temperature behind the spot. Under a certain external magnetic field 386, the recording layer 381
The mark 389 recorded on the cutting layer 382 is recorded when the temperature is low.
The magnetization of the mark is transferred to the reproducing layer 383 via. However, if the temperature exceeds a certain value 3809, transfer cannot be performed due to the demagnetization region 3811 of the cutting layer 382. That is, the reproduction layer
When viewed from 383, the mask 380 indicated by diagonal lines is formed on the laser spot 384, and the mark recorded as the aperture 3800 in the region of low temperature is detected. For this reason, it looks like the spot 384 has actually become smaller,
The resolution in the circumferential direction can be improved. But,
Since the shape of this aperture 3800 is a crescent shape, even if the mark transferred from the recording mark is a round mark, the signal waveform obtained is asymmetric in the traveling direction.

In the two-dimensional equalization to be described later, the asymmetry can be compensated by taking in the interference coefficient in all of the front, rear, left and right sides and calculating it. Further, the resolution of the detection signal depends on the temperature distribution and the positional deviation of the spot, and when the temperature distribution is brought closer to the center of the spot, the aperture becomes narrower and the resolution is improved. For that purpose, the A / O deflector is used to irradiate the reproducing light in a pulse shape at the position where the mark is recorded to make the temperature distribution steep and bring the temperature distribution close to the center. The timing for modulating the reproduction light intensity is generated from the clock signal generated by activating the PLL from the prepits formed on the disk surface as described above. Therefore, the timing for sampling and holding the signal is set within the irradiation period of the detection light.

Another magnetic super-resolution, RAD, is shown in FIG. 38b.
Explain (Rear Aperture Detection). FIG.
The switching layer 3801 and the reproducing layer 380 are formed on the recording layer 381 described in 8.
Form 2. The RAD gives an initial magnetic field 3804 in front of the traveling of the light spot 3803 to initialize the reproducing layer 381. When the temperature is low, the SW layer 3801 reproduces the mark on the recording layer 301 from the reproducing layer 3
The mark 389 of the recording layer 301 is transferred to the reproducing layer 3802 when the temperature of the light spot 3803 rises so as not to transfer to the 802. In this way, the mask 3812 is formed, and the aperture 3811 is generated behind the spot 3803 in the traveling direction. When the reproduction light of the recording mark 389 is irradiated in a pulse shape,
Since the position of the aperture 3811 can be located at the center of the light spot, the asymmetry of the reproduced waveform can be reduced. The principle of detecting the information recorded in this manner will be described with reference to FIG.

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

FIG. 39c shows the signal (eye (eye) pattern) of the track 2 detected from the spot 103b. The eye level is hardly opened due to the crosstalk from the adjacent tracks 1 and 3, and the data cannot be accurately detected.

As shown in FIG. 39d, it is necessary to process a signal with which the eye is opened and data can be accurately read.

FIG. 39b shows a circuit for compensating for the above crosstalk to obtain a signal as shown in FIG. 39d from the signal as shown in FIG. 39c.
The structure of a dimensional equivalent processing circuit is shown. Here, after learning the interference coefficient, the calculation coefficient for removing the interference amount is obtained using the result of calculating the inverse matrix of K and the signals from track 1, track 2, and track 3.

In the two-dimensional equivalent processing circuit, the signals x (t) 3900-1,3900-2,3900-3 reproduced from each track are passed through 7-tap transversal filters 391-1,391-2,391-3. The transversal filter 391 has a delay circuit 392, an attenuator 395, and an adder 396, and shapes the signal waveform for each track. After that, the signal g from each track
(t) is weighted by weighting circuits 397-1, 397-2, and 397-3, and the addition circuit 393 calculates the sum. The coefficients of the delay circuit and the attenuator of the transversal filter 391 that pass the signal from each track and the weighting coefficient that the signal from each track is multiplied by the weighting circuit 397 are obtained from the inverse matrix as described above. Delay circuit 39
4a 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 0.2.
It is 2 microns. Let T be the time corresponding to the grid point interval and τ be the time interval of the three spots. The signal processing in the two-dimensional direction is previously given a time delay in order to compensate for the time delay between tracks. It is easy to control the time delay of the τ interval because the clock generated from the PLL can be used when all the signal processing is processed digitally.

If the spot in the circumferential direction does not have the effect of the magnetic super-resolution, the spot diameter in the circumferential direction is about 0.96 μm, so that the signal cannot be detected from the 0.5 μm period grating as it is. . Therefore, the partial response well known in the field of transmission lines is applied. In an optical disc that shows a further response from DC to a high range, a simpler partial response has a response characteristic of PR (1,1). This is a characteristic that when the optical disk is regarded as a transmission line, the response to the input pulse exists only in two of the detection time slots and no response appears in other slots.

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

The recording pulse 411 is created according to the modulation data, and the recording mark 102 is recorded on the grid point 213 according to the recording pulse 411 based on the clock signal. When the size of the effective reproduction spot 103 is set as shown in the figure, the mark cannot be separated from the reproduced signal waveform 412 even if there is one lattice interval between the marks. However, the mark arrangement can be known when the level takes an intermediate value of the saturation level. The saturation level occurs when a plurality of marks are continuously arranged. It can be seen that the detection level takes three values due to the interference between the marks. Two slice levels 413a and 413b to detect which level
Is provided to detect which of three values is divided into two levels for each time slot. The obtained 3 values are mod
It is calculated by 2 and converted into binary demodulated data. This allows signals to be detected even at densities with reduced resolution. Although the signal from one track has been described as an example, the present invention cannot detect a waveform suitable for a partial response due to interference from adjacent tracks. The means for obtaining this will be described below.

FIG. 42 shows detection signals from three spots.
An array for inputting the 3900 to a two-dimensional equalization circuit is shown. The detection signals 3900-1 (S'bc to S'bi) from the track 1 are input in time order. Moreover, the detection signal 3900-2 from the track 2
(S'cc to S'ci) is the detection signal 3900-3 from the truck 3.
(S'dc to S'di) is input to the equalization processing circuit 4201. From these signals, the signal 4200 (S ″ cc to S ″ ci) of the track 2 is obtained by removing the interference from the adjacent mark at each timing. This signal is an array of reproduced signals from isolated recording marks, and the amount of interference required for partial response is removed. Therefore, interference amounts γ-3 to γ3 between adjacent marks are newly added and added so that the partial response (1, 1) characteristic is obtained. As a result,
It is possible to obtain the signal S '''cf having the optimum partial response characteristic while eliminating the interference from the adjacent tracks. This signal corresponds to the signal from the middle mark in the 21 mark rows surrounded by the dotted line in FIG.

FIG. 43 shows the simulation result of the equalization processing of FIG. The calculation is performed by dividing the grid point interval into 20 equal steps with a fine interval of 0.0125 microns.
A signal waveform corresponding to S '''cf that can be regarded as continuous was obtained.

FIG. 43A shows a waveform when random patterns are arranged 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 required for signal detection is not obtained due to interference from adjacent tracks.

FIG. 43B shows the result of performing signal processing for partial response after detecting the signals of tracks 1 and 3 and removing the interference between adjacent marks by the above-mentioned two-dimensional equalization. Sufficient eye opening 43 compared to FIG.
Since 00 is obtained, it can be seen that the three values can be reliably determined at the signal detection point 4302 using the two slice levels 413a and 413b. The recording position is a grid point compared to NRZ,
The signal detection point is an intermediate point of the grid points. Also, the simulation showed the waveform processing in a form close to a continuous waveform,
In the present invention, all signal processing is digital processing synchronized with the clock. Therefore, the grid point interval T corresponds to the slot interval, and the time slot is set to the middle point of each grid point. Therefore, in the above-described embodiment, the signal is sampled and held at each lattice point, but in this embodiment, each reproduction detection signal is sampled and held for each time slot, and the signal processing is performed. Note that 4301 corresponds to the amplitude of the reproduction signal of the isolated mark. Although the optical super-resolution effect has been used in the track radial direction in the above-described embodiments, the magnetic transfer structure shown in FIG. 9 as a medium is difficult to be magnetically super-resolved. I have no choice. However, with higher densities, and with a margin, 10 Gb / in2
In order to realize the above, it is possible to perform optical super-resolution in the circumferential direction according to the present invention. That is, the optical super-resolution effect can be achieved isotropically by using a circular shield plate or a circular phase plate as the optical filter. Also,
By adopting an elliptical shape, it is possible to cope with changes in track pitch and lattice point spacing. For detection, the influence of side lobes can be eliminated by applying a non-linear transmission material on the detector surface as described above.

Next, an embodiment for further performing high SN reproduction will be shown below.

FIG. 44 shows a principle diagram of high SN detection. Figure 44a
Is on the medium, Fig. 44b is the intensity of the irradiated laser, Fig. 4
4c shows the temperature distribution on the medium. The playback spot 4401 is
In the sample area 500 provided with the pre-pit mark 4400 for extracting the tracking signal and the clock, the normal direct-current light 441 is irradiated to reproduce. In the data area 501, the peak power level 503 larger than the reproduction level 502 is synchronized with the grid point.
The pulsed light 442 is emitted, and the reflected light is detected at the timing 504 synchronized with the lattice points. A gap area 505 was provided between the sample area 500 and the data area 501.

The reasons why high SN reproduction is possible are shown below.

FIG. 45 shows a reproduction system having a wavelength λ532 nm and a numerical aperture NA of 0.6 for a focusing lens, a linear velocity V = 10 m / s, a DC irradiation reproduction power of 1 mW, and a maximum repetition frequency of 12.5 [MHz], that is, 0.4 μm mark. The spectrum of the frequency measured by the spectrum analyzer when a repeating pattern is reproduced is shown. Here, the double period of the interval of the lattice points corresponds to the highest repetition frequency. Signal corresponding to the mark repetition period
The 4500 corresponds to the signal component C, and the base level signal 4501 corresponds to the total noise N.

FIG. 46 shows the noise level 4501 shown in FIG.
The measured values of various noise spectra included in are shown. The reproduction light power was set to 1 mW. The noise component 4501 is composed of system noise 506 including amplifier noise, shot noise 507 generated by a photodetector, and disk noise 508 including modulation noise caused by mark variations during recording. Here, the noise of the laser itself is at a level that can be sufficiently ignored because the SHG laser is used. As a result of the actual measurement, at the frequency fmin = 11 [MHz], the disk noise 508 dominates the noise in the low frequency range, and the shot noise 507 dominates in the high frequency range.

FIG. 47 shows the relationship between the signal level Sp-p, the noise amount N of each type, and the power of the reproducing light focused on the medium surface. The signal level Sp-p is the peak value of the signal 4500 in Fig. 45.
It corresponds to a value obtained by multiplying by 2√2, and the noise N corresponds to the noise amount integrated in the band from the frequency 0 to the cutoff frequency shown in FIG. The horizontal axis is standardized on a logarithmic scale with the reproduction power P0 being 1. 509 is a theoretical curve of shot noise indicated by 10Log (P / P0), 510 is a theoretical curve of signal level indicated by 20Log (P / P0), 511 is a theoretical curve of disk noise indicated by 20Log (P / P0) , 500 is a theoretical curve of 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 shot noise has a theoretical curve 509 proportional to the power P of the reproduction light. The signal level and the disk noise are proportional to the square of the power of the reproduction light, and the theoretical curve 510,
And 511. Here, by increasing the reproduction power, it is possible to reduce the shot noise that dominates the high frequency band of the signal band with respect to the disk noise, and it is possible to reduce the amount of noise obtained by integration within the band.

FIG. 48 shows the relationship between the reproduction power, the reproduction signal Sp-p and the total noise Nrms. 512 is a theoretical curve of the relationship with the reproducing power when reproducing light DC is irradiated, and 517 is a linear velocity of 20 m / sec.
Measured value when reproducing light is irradiated by DC at 518, linear velocity is 10 m / s
It is the actual measurement value when the reproduction light is pulsed with ec. The signal band at this time is the optical cutoff frequency fmax = V /
(Λ / 2NA) [MHz] = 22.5 MHz.

As can be seen from the theoretical curve 512, 1.8 dB when the reproducing power is changed from 1 mW to 2 mW and 2.8 when the reproducing power is changed to 4 mW.
It can be seen that dB and SN are improved. However, in an actual system, the following problems occur when the reproducing power is increased.

Returning to FIG. 47, the problem will be described. Figure 47
The curve 513 is the measured value of the signal level when the light is DC-irradiated at a linear velocity of 10 m / sec, and the curve 514 is the measured value of the disk noise level when the light is DC-irradiated at the linear velocity 10 m / sec.

First, the signal level is lower than the theoretical curve 510 as shown by the actual measurement curve 513. This is shown in Figure 4.
As shown in FIG. 9, the Kerr rotation angle of the magnetic film that governs the signal level has the property of decreasing with temperature, so that the temperature of the film surface rises and the signal level decreases as the reproducing power increases.

Secondly, as indicated by the actual measurement curve 514, the disk noise level increases more than the theoretical curve 511 as the reproducing power increases. This is because the magnetization of the magnetic film becomes unstable and the disk noise increases when the film surface temperature rises.

In order to solve the above problem, it can be considered that the temperature of the film surface does not rise even if the linear velocity is increased to increase the reproducing power.

Referring to FIG. 47, a curve 515 is a measured value of the signal level when the linear velocity is doubled to 20 m / s and the reproducing light is irradiated with DC, and a curve 516 is a measured value of the disk noise level. Is. Curves 515 and 516 show that the reproduction power can be increased up to about 3 mW. However, the actually measured SN with respect to the reproduction power can only be improved by about 0.5 dB as shown by the actually measured curve 517 in FIG.
The reason for this is that as the linear velocity increases, the signal band must be proportionally increased, and as can be seen in FIG. 46, the amount of noise in the band of shot noise that dominates high-frequency noise increases, As a result, the SN decreases. This phenomenon will be described below.

FIG. 50 shows the result of obtaining the SN5001 for the linear velocity by obtaining the reproducing power 5000 for keeping the peak temperature of the film surface for each linear velocity and obtaining the SN for the obtained reproducing power. As can be seen from these results, even if the linear velocity is increased from 10 m / s, the SN improvement is hardly obtained.

From the above consideration, in the present embodiment, in order to increase the reproduction power without increasing the signal band, a pulse is emitted at the data detection point during reproduction, and the signal is reproduced while preventing the film surface temperature from rising. To do. As for the intensity level of the reproduction light, as shown in FIG. 44 (C), light having a third intensity level Pp503 larger than the reproduction level Pdc502 normally emitted from the light source is emitted at the lattice points.

FIG. 51 shows measured values of temperature distribution on the recording film surface at various pulse widths under direct-current light reproduction under the above recording / reproduction conditions. The peak value of the irradiation power was 2 mW, the linear velocity of the light spot was 10 m / sec, and the pulse width was changed to 10 ns, 20 ns, 30 ns, and DC irradiation. Curve 511 has a pulse width of 10 ns, 512 has a pulse width
20ns and 513 are pulse widths of 30ns, and 514 is the reached temperature in the case of DC irradiation. It can be seen that when the pulse width is 10 ns, the peak temperature is half that of DC light irradiation, and 2 mW of reproducing power can be irradiated at 10 m / s.

In FIG. 47, a curve 4700 indicates a linear velocity of 10 m / s.
The measured value of the reproduced signal when the reproducing light is emitted in pulse form at, and the measured value of the disk noise is also shown in the curve 4701.
Similarly, reference numeral 517 in FIG. 48 shows an actual measurement curve of SN with respect to reproducing power. As can be seen from these, the SN could be increased by 2.3 dB at the linear velocity of 10 m / s and the reproducing power of 3 mW.

Here, the following problems occur during the irradiation of FIG. 44 (C). As shown in FIG. 44 (d), when the sample area 500 radiating light with DC is shifted to pulse irradiation,
The temperature level rises due to the residual heat at the grid points due to direct current irradiation (4400). However, at the time of the next pulse irradiation, the residual heat becomes small and the temperature level drops (4401). And
The temperature level after irradiation of several pulses becomes a steady value. In order to eliminate this temperature level fluctuation, a gap area 505 is provided between the sample area and the data area.

FIG. 52 shows a method of keeping the temperature level constant without providing a gap region. A third intensity level 503, which is greater than the reproduction level 502 of direct light irradiation from a light source.
Pulse is applied to the lattice points in a pulsed manner, and a pulse for residual heat having a second intensity level 519 larger than the reproduction level 502 is given between the lattice points with a period of zero intensity interposed.
By performing intensity modulation as shown in FIG. 52C, even if a light spot directly enters the data area 501 from the sample area 500,
The temperature level by pulse irradiation can be made constant as shown in FIG. 52 (d).

The specific operation during reproduction will be described below.

During reproduction, the sample area 500 for extracting the tracking signal and the clock is irradiated with direct current light for reproduction, and the data area 501 is read as shown in FIG.
The recording circuit shown in FIGS. 4 and 25 and FIG.
The recording strobe pulse 221 causes the AO drive circuit 3 shown in FIG. 15 at a timing synchronized with a lattice point during reproduction.
77 is driven to modulate the reproduction light. Here, since the reproduction spot 4400 is composed of three spots by the diffraction grating, the pulses from the recording strobes 221 are mixed so that each spot can generate a pulse at the lattice point.
The AO drive circuit 377 is modulated.

However, if one spot is pulse-irradiated at a grid point, the other spots are pulse-irradiated at a position other than the grid point, and the temperature rises. In practice, the pulse width is set to about 1/3 so that the temperature does not rise even if pulse irradiation by the other two spots occurs. Alternatively, the diffraction grating 311 shown in FIG. 15 may be rotationally controlled so that the three spots are always positioned at the grid point intervals in the spot scanning direction at the same time. As a result, one recording strobe pulse 221 causes 3
Since the pulse is emitted at each grid point of the spot, the reproduction pulse condition can be satisfied with one spot condition. On the other hand, instead of using the diffraction grating, three light sources and three AO drive circuits may be used as reproduction light sources to independently modulate.

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

In the embodiment, the reproduction pulse condition for pulse reproduction is defined by the peak temperature of the film surface. However, in practice, the mark has a finite width, so considering the temperature distribution in the mark width. Further optimization is possible. Further, in the case of performing partial response signal processing, pulse irradiation may be performed at the detection points in that class. Also for the optical super-resolution spot, if the pulse conditions are optimized with respect to the effective spot diameter, that is, (λ / NA × (spot miniaturization rate by optical super-resolution, 0.8 in the example)), Can be combined.

[0151]

According to the present invention, the recording density of the current optical disk device is about 1 Gbit / in2, while the presently available light source, optical element, and recording / reproducing technology are used for about one digit or more. Higher density can be realized.

[Brief description of drawings]

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

FIG. 2 is a block diagram of an optical system for optical super-resolution according to the present invention.

FIG. 3 is an explanatory diagram of an optical filter configuration of optical super-resolution according to the present invention.

FIG. 4 is a graph explaining the effect of the optical super-resolution of the present invention.

FIG. 5 is a graph explaining the relationship between coercive force and temperature on a recording film.

FIG. 6 is an explanatory diagram of a recording process of a magnetic mark.

FIG. 7 is an explanatory diagram of a configuration of one example of a medium of the present invention and measurement results.

FIG. 8 is an explanatory diagram of the configuration and measurement results of another embodiment of the medium of the present invention.

FIG. 9 is an explanatory view of the configuration of another embodiment of the medium of the present invention and the measurement results.

FIG. 10 is a graph of control performance of a magnetization mark having a TbFeCo composition.

FIG. 11 is a graph showing a temperature distribution by light spot irradiation.

FIG. 12 is a graph showing coercive force and recording temperature.

FIG. 13 is a graph showing fluctuations in mark diameter due to fluctuations in recording power of RE-rich composition.

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

FIG. 15 is a configuration block diagram of a recording / reproducing system of the present invention.

FIG. 16 is a plan view of spot arrangement of the recording / reproducing system of the present invention.

FIG. 17 is an explanatory diagram of a track shift signal detection process of the present invention.

FIG. 18 is a block diagram of an arithmetic circuit for detecting a track deviation signal according to the present invention.

FIG. 19 is an explanatory graph diagram of a track deviation signal detected by the present invention.

FIG. 20 is a circuit diagram of a control circuit using a track deviation signal detected by the present invention.

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

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

FIG. 23 is a plan view for explaining learning of an interference coefficient for reproducing the present invention.

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

FIG. 25 is an explanatory block diagram of a data detection unit of the present invention.

FIG. 26 is an explanatory block diagram of a data selection unit of the present invention.

FIG. 27 is an explanatory block diagram of an embodiment of the data recording unit of the present invention.

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

FIG. 29 is an explanatory block diagram of a detection unit in the data reproduction of the present invention.

FIG. 30 is an explanatory block diagram of a synchronization correction unit for recording / reproducing according to the present invention.

FIG. 31 is an explanatory block diagram of reproduced signal processing according to the present invention.

FIG. 32 is an explanatory diagram of a region recognition circuit of the present invention.

FIG. 33 is an explanatory diagram of an interference coefficient.

FIG. 34 is a spectrum characteristic graph of a diarylethene derivative.

FIG. 35 is a block diagram of a photodetector of the present invention.

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

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

FIG. 38 is a principle diagram of magnetic super-resolution.

FIG. 39 is an explanatory diagram of mark arrangement and signal processing in the recording / reproducing system of the present invention.

FIG. 40 is an explanatory diagram of signals and processing areas detected from marks existing at lattice point intervals according to the present invention.

FIG. 41 is an explanatory diagram of a partial response (1, 1) in the optical disc.

FIG. 42 is an explanatory diagram of a partial response process in which interference from an adjacent track of the present invention is eliminated.

FIG. 43 is an explanatory diagram of partial response waveforms when interference from an adjacent track of the present invention is removed and when interference is not removed.

FIG. 44 is an explanatory view of the principle of the pulse reproduction method.

FIG. 45 is a frequency spectrum graph diagram of a signal level and a noise level.

FIG. 46 is a frequency spectrum graph diagram of individual noise levels.

FIG. 47 is a reproduction power dependence characteristic graph of signal level and noise level.

FIG. 48 is a reproduction power dependence characteristic graph of SN.

FIG. 49 is a graph of temperature dependence characteristics of the Kerr rotation angle.

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

FIG. 51 is a temperature distribution graph diagram during direct current irradiation and during pulse irradiation.

52 is an explanatory diagram of a second pulse reproduction method. FIG.

[Explanation of symbols]

500: sample area, 501: data area, 502:
Playback level, 503: third intensity level, 504: timing, 505: gap.

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[Procedure amendment]

[Submission date] April 13, 1995

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

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Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location G11B 7/09 C 9368-5D (72) Inventor Koichiro Wakabayashi 1-280 Higashi Koikeku, Kokubunji, Tokyo Hitachi, Ltd. Central Research Institute (72) Hideki Saga Hideki Saga 1-280 Higashi Koikeku, Kokubunji, Tokyo Hitachi Central Research Institute (72) Inventor Ken Shimano 1-280 Higashi Koikeku, Kokubunji, Tokyo Hitachi Central Research Center ( 72) Inventor Atsushi Saito 1-280, Higashi Koigokubo, Kokubunji, Tokyo, Central Research Laboratory, Hitachi, Ltd. (72) Hiroyuki Awano 1-280, Higashi Koikeku, Kokubunji, Tokyo (72) Inventor, Central Research Laboratory, Hitachi, Ltd. (72) Keikichi Ando 1-280, Higashi Koikekubo, Kokubunji, Tokyo, Central Research Laboratory, Hitachi, Ltd. (72) Inventor Junko Ushiyama 1-280, Higashi Koikekubo, Kokubunji, Tokyo Hitachi, Ltd. The laboratory (72) inventor Komota ▲ Taku ▼ Tokyo Kokubunji Higashikoigakubo 1-chome 280 address Hitachi, Ltd. center within the Institute

Claims (12)

[Claims] 1. A high-density information recording / reproducing method, wherein an area density of 10 gigabits / square inch or more is realized in a method of optically recording and reproducing information. 2. A recording laser beam having a wavelength of 680 nm is used as the recording beam, and the recording laser beam is irradiated onto the medium as a recording spot by a super-resolution optical system, and the recording spot is divided into four quarters by the thermal energy of the recording spot. A high density information recording / reproducing method of forming marks of 1 or less and reproducing the marks by using a reproducing laser beam having a wavelength of 530 nm as reproducing light. 3. The high-density information recording / reproducing method according to claim 2, wherein two-dimensional recording is performed by arranging marks having the same circular shape on lattice points of a two-dimensional lattice extending in the track direction and the track radius direction on the medium. 4. A high density information recording / reproducing method according to claim 3, wherein the reproduced signal from the mark is detected, and the reproduced signal from each mark is used for signal processing to detect information. 5. A high density information recording / reproducing method according to claim 4, wherein a recording and reproducing clock is generated from clock marks discretely provided on the medium, and a track deviation signal is detected from the wobble mark. 6. The medium is provided with an embedded mark layer in which minute marks having a predetermined shape are recorded in advance, a recording spot is positioned on this layer, and information is recorded depending on whether or not the embedded mark is magnetically transferred by the recording spot. 3. The high density information recording / reproducing method according to claim 2, wherein the mark is recorded on the reproducing layer. 7. A recording film is irradiated with a powerful laser beam in advance in order to locally change the recording sensitivity characteristic of the medium in a minute region to form a minute mark independent of the recording spot shape, 4. The high density information recording / reproducing method according to claim 3, wherein structural relaxation is locally generated to weaken the coercive force. 8. In order to locally change the recording sensitivity characteristic of the medium in a minute area to form a minute mark which does not depend on the recording spot, a fine concavo-convex pattern is previously provided on the substrate of the optical disk by injection. The core of the formation of the magnetic mark facilitates the local formation of the recording mark. 4. The high density information recording / reproducing method according to claim 3, wherein a minute mark that does not depend on the shape of the recording spot is created. 9. A plurality of or singular spots are positioned on the formed mark by using a sample servo, and a detection signal when a light spot is positioned on a two-dimensional lattice point according to a clock generated from the embedded mark is provided. Claim to detect the presence or absence of a mark recorded at a grid point by performing sample-holding and obtaining the amount of interference from adjacent grid points in advance in the learning area, and then performing the process of removing the amount of interference from the detection signal after sample-holding. Item 1. A high-density information recording / reproducing method according to item 1. 10. A recording laser having a first output and a wavelength, and a reproducing laser having a second output lower than the first output and a second wavelength shorter than the first wavelength are used.
The recording and reproducing laser is irradiated onto a disc-shaped recording medium by using an objective lens having an NA of about 0.55, and the recording characteristics of the disc-shaped recording medium and shielding in an optical system for irradiating the laser. Compared to the spot size optically determined from the wavelength of the recording laser and the NA of the objective lens by the plate, it is about 1
Two-dimensional recording is performed in which minute marks of / 4 or less are formed on the recording medium, and the marks are arranged at lattice points of a two-dimensional lattice extending in the track direction and the track radius direction.
The reproducing method is an optical recording / reproducing method in which a reproduced signal from the mark on the two-dimensional lattice point is detected, and the reproduced signal from each mark is used for signal processing to detect information. 11. A magneto-optical recording / reproducing method for forming a channel clock in synchronization with a clock extracted from a disk and irradiating a reproducing beam in pulses in synchronization with the channel clock when reproducing information. Wavelength λ
[μm] and a reproducing spot of diameter λ / NA obtained through a numerical aperture NA focusing lens were used, and the reproducing spot was scanned at a predetermined linear velocity V [m / s] and a predetermined DC level film surface reproducing power Pdc. The characteristics of the noise spectrum N (f) of the reproduced signal obtained at this time are the frequency fmin [MHz] at which the shot noise Ns becomes larger than the disk noise Nd and the optical cutoff frequency fmax = V / (λ / 2NA) [MHz] In between, there is the highest repetition frequency of recording and reproduction, and high-density information reproduction characterized by irradiating and reproducing a pulse with a peak value Pp higher than the film surface reproduction power Pdc of the above constant DC level Method. 12. The information is detected by detecting a reproduction signal from a mark on a two-dimensional lattice point on the disk and performing signal processing by using the reproduction signals from the respective marks with each other. High-density information recording / reproducing method described in.