JP2002352436A - Optical disk recording/reproducing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk recording/reproducing apparatus which can realize a high-density optical recording by suppressing an error rate to be low in reading out information, and which can stably realize the recording or the reproduction, in an optical disk recording/reproducing apparatus. SOLUTION: It includes an optical pickup 24, which has an optical spot forming means for forming on an optical disk a spot smaller than a diffraction limit of light and an information reproducing means for reproducing a record information series recorded on the optical disk using the optical spot, and a pre-code means 23, which receives an information series inputted from the outside, and which transforms, after adding an interference between codes to the information series at the time of recording, the information series into the record information series by calculating a remainder by a cardinal number of the information series, about each information unit of the information series to which the interference between codes at the time of recording is added.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk recording / reproducing apparatus for recording / reproducing data at a very high density using an optical or near-field optical effect.

[0002]

2. Description of the Related Art As one of data recording and reproducing methods, there is a method of recording and reproducing on a recording medium using light. As a typical example of such an optical recording method, one side of an optical disc having a diameter of 12 cm is recorded on one side of an MPEG2 (Moving Picture Expar).
DVD (Digital VersatileDivision)
sk) The system has been commercialized. According to the DVD standard, the storage capacity of a disc is 4.7 GB on one side, and the track density is
0.74 μm / track, linear density 0.267 μm / bit.
Hereinafter, a DVD based on this standard is referred to as a current DVD.

The principle of operation of this DVD will be described with reference to the block diagram of FIG. 1 includes an LD (laser diode) driver 110, an optical head 120, an optical disk 111, and a reproduction signal processing system 114. The optical head 120 includes an LD 121, a collimator lens 122, and a PBS (Polarized Beam Splitter).
r) 123, an objective lens 124, a condenser lens 125, and a light extractor (photodetector) 126.

[0004] Reproduction of information recorded on an optical disk such as a DVD is performed using an optical head 120. In the optical head 120, a light beam emitted from the LD 121 travels straight through the PBS 123 and is condensed by the objective lens 124 into a bit sequence on a track of the optical disc 111. The light beam reflected by the optical disk 111 is a PBS
The light is branched at 123, and the light is focused on a photodetector (light extractor) 126 by a condenser lens 125, and a reproduced signal is obtained. The reproduced signal from the photodetector 26 is input to the reproduced signal processing system 112, and the data is decoded by the equalizer 113 and the decoder 114. In the case of the DVD standard, the wavelength of the LD in the optical head is 0.65 μm, and the numerical aperture NA of the objective lens is 0.6.

[0005] In optical discs, higher densities are always required. For example, for the current DVD system,
Development of a high-definition DVD system capable of recording high-definition video on one side of a 12 cm-diameter disc for two hours or more is currently underway. The storage capacity required for a high-definition DVD is 15 GB / side, and it is necessary to increase the density by 3.19 (= 15 / 4.7) times compared to the current DVD. As a technique for increasing the density of an optical disc for realizing a high-definition DVD, reduction of a beam spot can be cited. The size of the beam spot is proportional to the wavelength of the laser and inversely proportional to the numerical aperture of the objective lens.

On an optical disk, laser light is condensed by a lens optical system and irradiated on a recording medium, and the spot diameter of the laser is an important parameter for determining the size of a recording mark. However, in such a method, it is impossible to make the light spot diameter smaller than the wavelength of the laser light source due to the diffraction limit of the light. For example, in a high-definition DVD system, an optical system having a blue laser (wavelength 0.41 μm) and an objective lens with a numerical aperture of 0.6 is considered promising. Is 0.397. In other words, the density increase of the optical disk achieved by reducing the beam spot is 2.52
(= 1 / 0.397), and in order to achieve the storage capacity of a high-definition DVD, it is necessary to increase the density by about 1.25 times (up to 3.2 / 0.397) in addition to reducing the beam spot. Next, three conventional examples considered to be related to the present invention will be described. (First Conventional Example) In recent years, optical recording using near-field light has attracted attention as a method for achieving a higher density optical disk device. For example, as a first conventional example, APPLIED PHYS
ICS LETTERS, Vol. 61, No. 2, pp. 142-144 (APPLIED
PHYSICS LETTERS, Vol.62, No.2, pp.142-144, 1992)
As described in, the tip of the optical fiber is processed into a cone shape, a probe whose tip is covered with a metal film other than the area of several tens nm is manufactured, and mounted on a precision actuator using a piezoelectric element. There has been reported an example of recording and reproducing a recording mark having a diameter of 60 nm on a platinum / cobalt multilayer film by controlling the position. In this conventional example, a probe is used in which the tip of an optical fiber is processed into a cone shape, and a region other than the region of several tens of nm at the tip is covered with a metal coating. (Second Conventional Example) Also, for example, as a second conventional example,
APPLIED PHYSICS LETTERS, Vol. 73, No. 15, page 2078 to 2
080 pages (APPLIED PHYSICS LETTERS, Vol. 73, No. 15,
pp. 2078-2080, 1998), a recording layer, a protective layer, and a non-linear optical material layer are provided on an optical disc substrate, and near-field light is generated by using the non-linear optical material layer as a mask for recording. A method for performing reproduction has been proposed. In this conventional example, a SiN protective layer, Ge2
There has been reported an example in which a recording layer of Sb2Te5 and a protective layer of Sb are stacked and vapor-deposited, and a recording mark having a diameter of 90 nm is recorded and reproduced by irradiating a laser beam from the substrate side. (Third conventional example) Also, for example, as a third conventional example,
A near-field fiber probe manufacturing method in which the tip of an optical fiber core is formed in a conical shape, and light propagating in the fiber interferes and condenses inside the cone to form a spot smaller than the light diffraction limit is disclosed in -271339. According to the technique described in this publication, when the opening diameter of the tip of the cone is changed from 1000 nm to 750 nm, the spot diameter becomes smaller than the diffraction limit with respect to the wavelength of 830 nm of the incident light. Hereinafter, a near-field probe that causes light inside the cone to form a spot smaller than the diffraction limit of the light is referred to as an internal interference type near-field probe.

[0007]

(Defects of the first conventional example) When near-field light is applied to optical recording as in the first conventional example, a probe with a sharpened optical fiber tip or a flat surface Near-field light generated by a minute aperture provided in a mold slider has been used. However, as the property of near-field light, if the distance between the minute aperture that generates the near-field and the recording layer increases, the light intensity rapidly decreases and the light diverges, so the spot diameter increases rapidly. There are drawbacks.
Therefore, the distance between the opening and the recording layer must always be kept at 10 nm or less, and an actuator for controlling the optical head very precisely and at high speed is required. When the optical disk is rotated at a high speed, the actuator cannot control the optical head and the light spot irradiated on the recording layer becomes large. In such a state, as shown in FIG. 2, the signal output from the signal detector for signal detection in the optical pickup is
Since the light spot (beam spot) is larger than the bit (mark), the read waveform of the adjacent bit is added to both sides of the read waveform. Therefore, the signal output from the optical pickup is subject to intersymbol interference from adjacent bits, making it difficult to independently detect only necessary bit information with high sensitivity. (Defects of the second conventional example) Further, a recording layer, a protective layer, and a nonlinear optical material layer are provided on an optical recording medium, and a near-field light is generated through a minute opening using the nonlinear optical material layer as a mask to perform recording and reproduction. In the method, the optical system can record and reproduce data by the same mechanism as that of a conventional optical disk. In this case, a land and a groove are provided on the optical disk substrate in the same manner as in the related art, and recording and reproduction are performed by generating a near-field with a laser beam which has been spatially propagated by an objective lens or the like through a minute aperture formed on an aperture mask.

In this method, when the diameter of the minute opening formed by the Sb mask layer is 50 nm, a light spot of about 50 nm can be formed on the recording layer of the surface recording type medium. The pitch of the bits recorded on the optical disc is 20nm
In this case, the signal output from the optical detector for signal detection in the optical pickup has a smaller aperture diameter than the bit diameter, so that the read waveforms of adjacent bits are added to both sides of the read waveform. In particular, when a small aperture is formed using the Sb layer as a mask, the aperture is formed so as to trail behind the traveling direction of the beam spot as shown in FIG. Becomes Therefore, the signal output from the optical pickup is subject to intersymbol interference from adjacent bits, and it is difficult to independently detect only necessary bit information with high sensitivity. (Disadvantage of Third Conventional Example 3) In the technology of the third conventional example, a main spot having a very narrow half width at a tip opening of 550 nm is observed. However, since the light intensity of the side lobe component is very large, about half the light intensity of the main spot, the detection signal component due to the side lobe light is added to the detection signal due to the main spot during data detection, and the S / N (Sign)
al to Noise ratio).

In order to record and reproduce data at a high density, it is necessary to improve the track density and the linear density in a well-balanced manner. In any case, the above-mentioned conventional technique requires a higher track density. On the other hand, the reproduced signal contains a large signal component called a crosstalk component mixed from an adjacent track, and contains many signal degradation components. On the other hand, when the linear density increases, the reproduced waveform becomes a duller waveform. Since the equalizer immediately after signal detection amplifies the high-frequency component of the reproduced signal, if the input reproduced waveform is more dull, it is necessary to amplify the high-frequency component more. As a result, the equalizer amplifies even such signal degradation components. As described above, in the reproduction signal processing method of the system, when the waveform slicing method in which a certain threshold value is set and binary data is used is used, the signal deterioration component increases regardless of the density. The data cannot be correctly decoded anymore.

[0010] The present invention has been made in view of the above-mentioned circumstances, and an optical disk capable of suppressing an error rate when reading information, enabling high-density optical recording, and enabling stable recording or reproduction. An object of the present invention is to provide a recording and reproducing device.

[0011]

In order to solve the above problems, the present invention employs means for solving the problems having the following features.

According to the first aspect of the present invention, there is provided a light spot forming means for forming a spot smaller than a diffraction limit of light on an optical disc, and an information reproducing apparatus for reproducing a recorded information sequence recorded on the optical disc by using the light spot. Means for receiving an information sequence input from the outside and adding inter-symbol interference during recording to the information sequence, and then adding each unit of the information sequence to which the inter-symbol interference during recording is added An optical disc recording / reproducing apparatus comprising: precoding means for converting the information sequence into the recording information sequence by calculating a remainder of the information sequence based on the radix of the information sequence; Is a configuration for compensating for intersymbol interference added when the recorded information sequence is reproduced.

According to the first aspect of the present invention, there is provided a precoding means for compensating for intersymbol interference during recording, and for reading information recorded on the optical disk, the information read by the side lobe of the light spot is read. Can be used positively. Therefore, it is not necessary to provide a slit, a condenser lens, and the like in the super-resolution optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified. The light spot forming means is used for recording and / or
Or, to read or record data at the time of reading,
This is a means for irradiating a light spot on the medium. For example, the optical pickup 24 shown in FIG. 5 has this means. As the precoding means, for example, the recording data generation unit 23 in FIG. 5 has the precoding means.

According to a second aspect of the present invention, in the optical disk recording / reproducing apparatus of the first aspect, a minute opening for generating the light spot is provided at a tip of a head, a slider or a probe close to the optical disk. An opening is used as the light spot forming means.

According to the second aspect of the present invention, there is provided a minute aperture for generating near-field light and a precode means for compensating for intersymbol interference during recording, and reads information recorded on an optical disk. Therefore, information read by the side lobe of the light spot can be positively utilized. Therefore, it is not necessary to provide a slit, a condenser lens, and the like in the super-resolution optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified.

According to a third aspect of the present invention, in the optical disk recording / reproducing apparatus according to the second aspect, an intersymbol interference added when the recorded information sequence is reproduced is added to the recorded information sequence. For each unit information of the reproduction information sequence to be obtained, a decoding means for calculating a remainder based on the radix of the input information sequence is further provided.

According to the third aspect of the present invention, a minute aperture for generating near-field light, a precoding means for compensating for intersymbol interference during recording, and a decoding means for calculating a remainder based on a radix are provided. Since the information recorded on the optical disk is read out, the information read out by the side lobe of the light spot can be positively utilized. Therefore, it is not necessary to provide a slit, a condenser lens, and the like in the super-resolution optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified.

According to a fourth aspect of the present invention, in the optical disk recording / reproducing apparatus according to the second aspect, an intersymbol interference added when the recording information sequence is reproduced is added to the recording information sequence. For each unit information of the reproduction information sequence to be obtained, a decoding unit based on the PRML system is further provided, and the decoding unit is configured to include a maximum likelihood decoder for decoding by the maximum likelihood decoding system.

According to the fourth aspect of the present invention, the optical disk includes a minute aperture for generating near-field light, a pre-code unit for compensating for inter-symbol interference during recording, and a decoding unit based on the PRML method. Therefore, the information read by the side lobe of the light spot can be positively utilized. Therefore, in order to exclude information read by the side lobe,
There is no need to provide a slit or a condenser lens in the super-resolution optical disk pickup, and the configuration of the optical pickup can be simplified.

According to a fifth aspect of the present invention, in the optical disk recording / reproducing apparatus according to the first aspect, a recording layer and a non-linear optical material layer are provided on the optical disc substrate, and the non-linear optical material layer is formed as a mask. The minute aperture for generating a light spot is used as the light spot forming means.

According to the fifth aspect of the present invention, a near-field light is generated by a nonlinear optical material layer for generating a minute aperture, and precoding means for compensating for intersymbol interference during recording is used. Since the information recorded on the optical disc is read, the information read by the side lobe of the light spot can be positively utilized. Therefore, it is not necessary to provide a slit, a condenser lens, and the like in the super-resolution optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified.

According to a sixth aspect of the present invention, in the optical disk recording / reproducing apparatus according to the fifth aspect, an intersymbol interference added when the recorded information sequence is reproduced is added to the recorded information sequence. For each unit information of the reproduction information sequence to be obtained, a decoding means for calculating a remainder based on the radix of the input information sequence is further provided.

According to the sixth aspect of the present invention, a near-field light is generated by a nonlinear optical material layer for generating a minute aperture, and precoding means for compensating for intersymbol interference at the time of recording is provided. Since the information recorded on the optical disk is read using the decoding means for calculating the remainder, the information read by the side lobe of the light spot can be positively utilized. Therefore, it is not necessary to provide a slit, a condenser lens, and the like in the super-resolution optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified.

According to a seventh aspect of the present invention, there is provided a light spot forming means for irradiating a light spot comprising a main spot smaller than a diffraction limit of light and a pair of side lobes formed on both sides of the main spot onto an optical disk, An optical pickup having information reproducing means for reproducing a recorded information sequence recorded on the optical disk using the light spot; receiving an information sequence inputted from the outside; and adding intersymbol interference during recording to the information sequence After that, for each unit information of the information sequence to which the intersymbol interference at the time of recording is added,
An optical disc recording / reproducing apparatus comprising: a precoding means for converting the information sequence into the recording information sequence by calculating a remainder based on the radix of the information sequence. In this configuration, inter-symbol interference added when a recorded information sequence is reproduced is compensated.

According to the seventh aspect of the present invention, there is provided a precoding means for compensating for intersymbol interference at the time of recording, and for reading information recorded on the optical disk, the information read by the side lobe of the light spot is read. Can be used positively. For this reason, it is not necessary to provide a slit or a condenser lens in the near-field optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified.

According to an eighth aspect of the present invention, in the optical disk recording / reproducing apparatus according to the seventh aspect, an internal interference type projection or opening for generating the light spot is provided at a tip of a head, a slider or a probe close to the optical disk. And
The projection or the opening is used as the light spot forming means.

According to the eighth aspect of the present invention, there is provided an internal interference type projection or aperture for generating near-field light, and a precode means for compensating for intersymbol interference during recording.
Since the information recorded on the optical disc is read, the information read by the side lobe of the light spot can be positively utilized. For this reason, it is not necessary to provide a slit or a condenser lens in the near-field optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified.

According to a ninth aspect of the present invention, in the optical disk recording / reproducing apparatus according to the eighth aspect, an intersymbol interference added when the recorded information sequence is reproduced is added to the recorded information sequence. For each unit information of the reproduction information sequence to be obtained, a decoding means for calculating a remainder based on the radix of the input information sequence is further provided.

According to the ninth aspect of the present invention, an internal interference type projection or opening for generating near-field light, a precoding means for compensating for intersymbol interference at the time of recording, and a remainder based on a radix are provided. Since information provided on the optical disk is read out by providing a decoding means for calculating, the information read out by the side lobe of the light spot can be positively utilized. For this reason, it is not necessary to provide a slit or a condenser lens in the near-field optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified.

According to a tenth aspect of the present invention, in the optical disk recording / reproducing apparatus according to the eighth aspect, an intersymbol interference added when the recording information sequence is reproduced is added to the recording information sequence. For each unit information of the reproduced information sequence to be obtained, a decoding unit based on the PRML system is further provided, and the decoding unit is configured to include a maximum likelihood decoder for decoding by the maximum likelihood decoding system.

According to the tenth aspect of the present invention, an internal interference type projection or aperture for generating near-field light, a precode means for compensating for intersymbol interference during recording,
Since information recorded on the optical disc is read out by providing the decoding means by the RML method, the information read out by the side lobe of the light spot can be positively utilized. Therefore, it is not necessary to provide a slit, a condenser lens, and the like in the near-field optical disk pickup in order to eliminate information read by the side lobe,
The configuration of the optical pickup can be simplified.

According to an eleventh aspect of the present invention, in the optical disk recording / reproducing apparatus according to the seventh aspect, a recording layer and a non-linear optical material layer are provided on the optical disc substrate, and the non-linear optical material layer is formed as a mask. A minute aperture for generating a light spot is used as the light spot forming means.

According to the eleventh aspect of the present invention, a near-field light is generated by a nonlinear optical material layer for generating a minute aperture, and precoding means for compensating for intersymbol interference during recording is used. Since the information recorded on the optical disc is read, the information read by the side lobe of the light spot can be positively utilized. For this reason,
In order to eliminate the information read by the side lobe, it is not necessary to provide a slit, a condenser lens or the like in the near-field optical disk pickup, and the configuration of the optical pickup can be simplified.

According to a twelfth aspect of the present invention, for each unit information of a reproduction information sequence obtained by adding intersymbol interference added when the recording information sequence is reproduced to the recording information sequence, This configuration is further provided with decoding means for calculating a remainder based on the radix of the input information sequence.

According to the twelfth aspect of the present invention, a near-field light is generated by a non-linear optical material layer for generating a minute aperture, and precoding means for compensating for intersymbol interference during recording, and a radix-based Since the information recorded on the optical disk is read using the decoding means for calculating the remainder, the information read by the side lobe of the light spot can be positively utilized. For this reason, it is not necessary to provide a slit or a condenser lens in the near-field optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified.

According to a thirteenth aspect of the present invention, in the optical disk recording / reproducing apparatus according to the eleventh aspect, an intersymbol interference added when the recorded information sequence is reproduced is added to the recorded information sequence. For each unit information of the reproduced information sequence to be obtained, a decoding unit based on the PRML system is further provided, and the decoding unit is configured to include a maximum likelihood decoder for decoding by the maximum likelihood decoding system.

According to the thirteenth aspect of the present invention, a near-field light is generated by a non-linear optical material layer for generating a minute aperture, and precoding means for compensating for intersymbol interference during recording, and a PRML system. Since the information recorded on the optical disk is read out by using the decoding means according to (1), the information read out by the side lobe of the light spot can be positively utilized. For this reason, it is not necessary to provide a slit or a condenser lens in the near-field optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified.

[0038]

Next, an embodiment of the present invention will be described with reference to the drawings. [First Embodiment] First, a first embodiment will be described with reference to FIGS.
An optical disk recording / reproducing apparatus according to the embodiment will be described.

In the optical disk recording / reproducing apparatus according to the first embodiment, as shown in FIG. 4, a data recording layer 13 is provided on an optical disk substrate 11 made of polycarbonate or the like as a recording medium, and optical recording is performed using a super-resolution optical head or the like. Recording and reproduction are performed by generating light of a spot smaller than the diffraction limit of Further, a magneto-optical recording medium may be used, and the present invention is also applicable to a recording / reproducing method using light only for recording or reproduction.

In this embodiment, the SiN protective layer 12 and the recording layer 13 are laminated on the polycarbonate optical disk substrate 11 and vapor-deposited. For example, the respective film thicknesses are such that the SiN protective layers 12 above and below the recording layer are laminated to 20 nm, and the data recording layer 13 is laminated to 15 nm. At the time of recording, in the case of the present embodiment, light of a small spot enters from the recording layer side. Light can be incident from either the substrate side or the recording layer side of the medium.
FIG. 3 is a diagram when light is incident from the recording layer side. Light emitted from the optical head enters the sample, and the light passes through the recording layer and is emitted toward the polycarbonate substrate.
Recording marks smaller than the diffraction limit of light can be formed on the data recording layer 13 according to the intensity of light. When reading a mark, the recording layer is irradiated with light to such an extent that it does not change, and the reflected light intensity or transmitted light intensity is read.

FIG. 5 is a block diagram showing an example of the configuration of an optical disk recording / reproducing apparatus. 5 includes a controller 21, a spindle motor 22, a recording data generation unit 23, an optical pickup 24, a clock extraction unit 25, an equalization circuit 26, an A / D (analog / digital) converter 27, a decoder 28, It is composed of a medium 29.

The recording data generation unit 23 includes the controller 2
The recording data to be actually written to the optical disk is generated by applying a pre-code by the partial response (PR) method to the write data sent from the first. This precode is for performing an operation of the following equation (1) on write data.

(1 / G (D)) mod 2... (1) D: delay operator G: transfer function of PR (partial response) transmission path Mod 2: modulo 2 expression (1) In the calculation of ()), after adding the inverse characteristic of the correlation characteristic of the intersymbol interference of the adjacent bit data when the bit data is read by the light spot generated by the optical pickup, the result is 2 (radix of the bit data). ) Is calculated.

When an isolated bit is recorded on the recording layer of the optical disk, the signal output from the signal detector for signal detection in the optical pickup has a larger spot than the bit, so that the adjacent bits are read on both sides of the read waveform. A waveform will be added. Therefore, the signal output by the optical pickup is subject to intersymbol interference from adjacent bits, and the intersymbol interference makes it possible to detect the partial response method as described above.

As shown in FIG. 5, an output signal from the optical pickup 24 is sent to an equalizing circuit 26 and a clock extracting unit 25. As shown in FIG. 6, the equalizing circuit 26 is a transversal filter including a delay element T (31), a weight coefficient multiplier 32, and an adder 33, and changes the gain of each weight coefficient multiplier 32. By doing so, the tap coefficient can be adjusted. The clock extracting unit 25 converts the signal output from the photodetector in the optical pickup 24 into a PLL.
(Phase Locked Loop) to extract the sampling clock signal.

The signal output from the equalizing circuit 26 is A /
The data is sent to the D converter 27. A / D converter 27
Is a circuit for converting an analog signal output from the equalizing circuit 26 into digital data.
Performs sampling based on the sampling clock signal extracted by. Each sampling value is quantized into multi-values according to the PR system to be digital data in order to detect the partial response system.

The digital data output from the A / D converter 27 is sent to a decoder 28. Decoder 2
Numeral 8 denotes a circuit for performing a remainder operation of 2 on each of multi-valued digital data, thereby detecting original write data. The data detected by the decoder is sent to the controller 21. Controller 2
1 controls the rotation of the spindle motor 22 for rotating the medium, the servo control of the optical pickup 24, and the like, in addition to the input and output of data as described above. [Second Embodiment] In an optical disk recording / reproducing apparatus according to a second embodiment, as shown in FIG. 7, a spot smaller than the diffraction limit of light is formed at the tip of a probe or a slider head. A minute opening is provided. Using this minute aperture, near-field light or internally converging near-field light is generated for recording and reproduction.

For example, when the diameter of the minute aperture is 50 nm, a light spot of about 50 nm can be formed on the recording layer of the surface recording type medium. Assuming that the pitch of the bits recorded on the optical disk is 20 nm, the signal output from the optical detector for signal detection in the optical pickup has a light spot diameter larger than the bit diameter as shown in FIG. The read waveform of the adjacent bit is added. Therefore, the signal output by the optical pickup is subject to intersymbol interference from adjacent bits, and the intersymbol interference makes it possible to detect the partial response method as described above. [Third Embodiment] The recording / reproducing operation of the optical disc recording / reproducing apparatus of the third embodiment will be described with reference to FIG. 8 includes a controller 21, a spindle motor 22, a recording data generating unit 23, an optical pickup 24, a clock extracting unit 25, an equalizing circuit 26, an A /
It comprises a D converter 27, a decoder 28, a medium 29 and a clock generator 30.

Next, the case of writing an input data sequence {am} will be described. This input data sequence {am} is usually one which has been appropriately modulated in advance.

First, the input data sequence {am} is sent from the controller 21 to the recording data generation unit 23, where it is pre-coded and converted into the recording data sequence {bm} by the operation of the above equation (1). The calculation of equation (1) adds the inverse characteristic of the correlation characteristic of intersymbol interference due to the spread of the spot,
Therefore, in order to convert the input data am, an operation for obtaining bm that satisfies the following expression (2) using the already converted recording data bm-n is performed. Become.

[0051]

(Equation 1) gn: Weight coefficient of each tap N: Data length Recording data sequence ｛b pre-coded in this way
m｝ is sent to the LD driver according to the clock signal from the clock generation unit 30 and is recorded on the recording layer of the optical disc in a form including the spread of the light spot in the optical pickup.

The recording data sequence {bm} recorded on the recording layer of the optical disk is read out by the optical pickup 24, the waveform is equalized by the equalizing circuit 26, and the digital data is reproduced by the A / D converter 27. It is converted to a data sequence {xm}. This reproduced data sequence {xm}
Is obtained by adding the intersymbol interference of the adjacent bits due to the spread of the spot, and is obtained by performing the operation of the following equation (3) on the recording data sequence {bm}.

[0053]

(Equation 2) The reproduced data sequence {xm} read as multi-valued digital data is sent to the decoder 28. This reproduced data sequence {xm} is obtained by taking the remainder of 2 and converted into a binary output data sequence {dm}. Record data series {bm}
Is obtained by adding the inverse characteristic of the correlation characteristic to the input data sequence {am} and then taking the remainder of 2, so that the output obtained by taking the 2 remainder of the reproduced data sequence {xm} in which this correlation characteristic has been canceled out The data series {dm} is the original input data series {a
m｝. Then, this output data series {dm}
Is sent to the controller.

As a result, the optical disk recording / reproducing apparatus of the present embodiment can be used to detect original data by positively utilizing intersymbol interference caused by adjacent bits due to the spread of the spot of the optical pickup. As a result, it is not necessary to provide an optical component such as sharpening of a spot for removing intersymbol interference, so that the structure of the optical pickup can be simplified and the labor for assembling and adjusting can be reduced. Fourth Embodiment In a reproduced signal processing system of the PRML (partial response / maximum likelihood decoding) method, a detector arranged after an equalizer is a representative one of the maximum likelihood decoders. Viterbi decoders are commonly used. Assuming that the reproduced waveform is equalized to the PR characteristic by the equalizer, the Viterbi decoder selects a sequence having the smallest error from the sample sequence of the equalized waveform from all the sequences satisfying the PR characteristic, and selects the sequence. It outputs binary data (decoded data) corresponding to the sequence.
In the PRML method, decoding is performed not from one sample value but from a plurality of sample values, so that the resistance to a signal deterioration component having no correlation between the sample values is strong.
The maximum likelihood decoding method using the Viterbi decoder according to the present embodiment will be described below.

FIGS. 9 and 10 show a fourth embodiment. FIG. 9 is a block diagram showing an example of the configuration of an optical disk recording / reproducing apparatus, and FIG. 10 is an example of the configuration of a Viterbi decoder. FIG.

The optical disk recording / reproducing apparatus shown in FIG. 9 is different from the optical disk recording / reproducing apparatus of the first embodiment shown in FIG. 5 in that a Viterbi decoder 34 is provided instead of the decoder 28. Therefore, the reproduced data sequence {xm} is sent to the Viterbi decoder 34. The Viterbi decoder 34 outputs the PR
One that performs Viterbi decoding (maximum likelihood decoding) corresponding to the channel is used.

As shown in FIG. 10, the Viterbi decoder 34 includes ACS units (addition / comparison / selection units) 42 _{0 to} 42N _s−1 that perform operations for each state of the trellis transition diagram, and these addition / comparison / selection units. Path memory circuits 50 each storing a path (path) selected by 42 _{0 to} 42N _s−1, and an MLD circuit (maximum likelihood path selection unit) 51 that selects one path from the paths stored by the path memory circuit 50 And is constituted by. Then, Ns-number of ACS units 42 ₀
A case of tracing the trellis transition diagram of the Ns state using .about.42Ns _-1 will be described. Moreover, ACS unit 42 ₀
From the state ~42N _s-1 is computed, it can only be a transition to its state or condition of the ACS unit ₄₂ 0 ~42N _s-1, the state of the ACS unit ₄₂ 0 ~42N _s-1 Is the status of the own device or a specific addition / comparison / selection unit 42
It is assumed that transition can be made only to the state of _{0 to} 42N _s-1 .

When decoding by the Viterbi decoding method, A
The / D converter 27 does not limit the data to the Ns value, and usually performs finer quantization. The quantized data output from the A / D converter 27 is ideally Ns value data, but has a value having a width due to the influence of waveform distortion and noise. The quantized data is input to the branch metric calculation circuit 41 of each addition / comparison / selection unit.
Each branch metric calculation circuit 41 calculates the likelihood (branch metric) for the state transition from the difference between the input quantized data and the value indicated by its own state. The branch metric ACS unit 42 ₀
The addition unit (not shown) of .about.42N _s-1 adds the likelihood (path metric) of the past state transition path. The path metric is obtained by integrating the branch metrics in each past state of the path, and has a smaller value as the path of the quantized data that is actually read is closer to the path. The path metric to be added here is the addition / comparison / selection unit 42 that can transition to the addition / comparison / selection unit 42 _{0 to} 42N _s−1.
The path metrics from _{0 to} 42N _s-1 are stored in the path metric memory up to the previous time.

[0059] In this way, one of the quantized data is input to the Viterbi decoder 34, the ACS unit 42 ₀
Since the path from two directions transitions to ４２42N _s−1 , the comparison unit compares the two path metrics calculated by these addition units at this time, and the selection unit changes according to the comparison result. The path metric with the smaller value (the more likely one) is stored in the path metric memory. Further, the path selection unit selects a path having a smaller path metric, that is, a path that is most likely, and stores quantized data indicating this path in the path memory. Therefore, the path whose state has changed is stored in the path memory.

When a specified number of quantized data is input, the maximum likelihood path selector 51 selects Ns stored in the path memory.
The path having the smallest path metric (the maximum likelihood path) is selected from the book paths. By selecting the maximum likelihood path, the path of the state transition is determined, and a bit data string that causes the state transition is output as a decoded data string. Therefore, even if an error is included in the reproduced data sequence {xm} due to the influence of noise or the like, it can be decoded into the most reliable data sequence.

The data decoded by the Viterbi decoder as described above becomes an output data sequence {dm} and is sent to the controller.

As a result, according to the optical disk recording / reproducing apparatus of the present embodiment, the data recorded on the optical disk
Since the data can be reproduced by the RML method, that is, the method combining the partial response method and the maximum likelihood decoding method (Viterbi decoding method), S / N is corrected by error correction.
Can be improved. Fifth Embodiment In an optical disk recording / reproducing apparatus according to a fifth embodiment, as shown in FIG. 11, a recording layer, a protective layer,
Using the non-linear optical material layer provided with the non-linear optical material layer as a mask, a light spot smaller than the diffraction limit of light is generated on the recording layer to perform recording and reproduction. The generated light is near-field light,
It is an internal condensing type near-field light or the like. In the present embodiment, the SiN protective layer 12, the recording layer 13, and the mask layer 15 of Sb are laminated on the polycarbonate optical disk substrate 11 and deposited. Each film thickness is 20 nm for the SiN protective layers 12 above and below the recording layer,
The recording layer 13 was laminated so as to have a thickness of 15 nm, the Sb mask layer 15 having a thickness of 15 nm, and the SiN protective layer 12 between the Sb layer and the polycarbonate substrate having a thickness of 170 nm. The recording layer 13 may be made of any material that generates a contrast in transmitted light or reflected light when irradiated with light, so that not only a phase change material but also a magneto-optical material or a material exhibiting an electro-optical effect can be considered. . This contrast includes not only differences in light intensity due to changes in absorbance and reflectance, but also contrasts caused by changes in optical constants, such as rotation of the polarization plane and changes in birefringence.

At the time of recording, a laser beam condensed so as to focus on the Sb mask layer 15 from the substrate side as in a normal optical disk. At this time, the Sb mask layer 15 in a region corresponding to the incident laser power becomes transparent, and a minute opening is formed. At this time, near-field light seeps into the recording layer from the formed minute opening, and a recording mark smaller than the diffraction limit of light can be formed.

For example, if the minute aperture diameter formed by the Sb mask layer 15 is 50 nm, a light spot of about 50 nm can be formed on the recording layer of the surface recording type medium. Assuming that the pitch of the bits recorded on the optical disc is 20 nm, the signal output by the photodetector for signal detection in the optical pickup has a smaller aperture diameter than the bit diameter, so that the read waveform of the bit adjacent to both sides of the read waveform is Will be added. In particular, when a small aperture is formed using the Sb layer as a mask, the aperture is formed so as to trail behind the traveling direction of the beam spot as shown in FIG. Becomes Therefore, the signal output by the optical pickup is subject to intersymbol interference from adjacent bits, and the intersymbol interference makes it possible to detect the partial response method as described above. [Sixth Embodiment] An optical disk recording / reproducing apparatus according to a sixth embodiment has a recording layer on an optical disk substrate 11 made of polycarbonate or the like as shown in FIG. 13, a non-linear optical material layer provided with a protective layer 12, and a non-linear optical material layer is used as a mask layer 15, and a light spot smaller than the diffraction limit of light is generated on a recording layer to perform recording and reproduction.

For example, if the minute opening diameter formed by the Sb mask layer is 50 nm, a light spot of about 50 nm can be formed on the recording layer of the surface recording type medium. Assuming that the pitch of the bits recorded on the optical disc is 20 nm, the signal output by the photodetector for signal detection in the optical pickup has a smaller aperture diameter than the bit diameter, so that the read waveform of the bit adjacent to both sides of the read waveform is Will be added. In particular, when a small aperture is formed using the Sb layer as a mask, the aperture is formed so as to trail behind the traveling direction of the beam spot as shown in FIG. Becomes Therefore, the signal output from this optical pickup is
This causes intersymbol interference from adjacent bits, and this intersymbol interference enables detection of the partial response method as described above.

A description will be given based on the block diagram shown in FIG. As described above, the recording data sequence {bm} recorded by the partial response method is read out by the optical pickup 24, and after the waveform is equalized by the equalization circuit 26,
A / D converter 27 converts the digital data into a reproduced data sequence {xm}. This reproduced data sequence {xm} is obtained by adding intersymbol interference of adjacent bits due to the spread of the spot.

The reproduced data sequence {xm} read as multi-valued digital data is sent to the decoder. This reproduced data sequence {xm} is obtained by taking the remainder of 2 and converted into a binary output data sequence {dm}. Since the recording data sequence {bm} is obtained by adding the inverse characteristic of the correlation characteristic to the input data sequence {am} and then taking the remainder of 2, the reproduced data sequence {xm} of which the correlation characteristic has been canceled is 2 The output data series {dm} obtained by taking the remainder matches the original input data series {am}. Then, the output data series {dm} is sent to the controller 21.

As a result, the optical disk recording / reproducing apparatus of the present embodiment can utilize the intersymbol interference caused by adjacent bits due to the spread of the spot of the optical pickup to detect the original data. As a result, it is not necessary to provide an optical component such as sharpening of a spot for removing intersymbol interference, so that the structure of the optical pickup can be simplified and the labor for assembling and adjusting can be reduced. [Seventh Embodiment] A seventh embodiment is a modification of the optical disk recording / reproducing apparatus of the fifth embodiment, and is added to the recorded information sequence when the recorded information sequence is reproduced. An optical disc further comprising decoding means based on a PRML method for each unit information of a reproduction information sequence obtained by adding intersymbol interference, the decoding means being provided with a maximum likelihood decoder performing decoding by a maximum likelihood decoding method It is a recording and reproducing device.

In the optical disk recording / reproducing apparatus of the seventh embodiment, as in the fifth embodiment, as shown in FIG. 11, an optical disk substrate 11 made of polycarbonate or the like is used.
Using the non-linear optical material layer provided with the recording layer 13, the protective layer 12, and the non-linear optical material layer thereon as a mask layer 15, a light spot smaller than the diffraction limit of light is generated on the recording layer to perform recording and reproduction. .

For example, if the diameter of the minute opening formed by the Sb mask layer is 50 nm, a light spot of about 50 nm can be formed on the recording layer of the surface recording type medium. Assuming that the pitch of the bits recorded on the optical disc is 20 nm, the signal output by the photodetector for signal detection in the optical pickup has a smaller aperture diameter than the bit diameter, so that the read waveform of the bit adjacent to both sides of the read waveform is Will be added. In particular, when a small aperture is formed using the Sb layer as a mask, the aperture is formed so as to trail behind the traveling direction of the beam spot as shown in FIG. Becomes Therefore, the signal output from this optical pickup is
This causes intersymbol interference from adjacent bits, and this intersymbol interference enables detection of the partial response method as described above.

FIG. 9 is a block diagram showing an example of the configuration of an optical disk recording / reproducing apparatus according to the seventh embodiment, and FIG. 10 is a block diagram showing an example of the configuration of a Viterbi decoder. As shown in FIG. 9, the optical disc recording / reproducing apparatus according to the present embodiment is provided with a Viterbi decoder in place of the decoder in the optical disc recording / reproducing apparatus according to the first embodiment in FIG.
The Viterbi decoder can perform Viterbi decoding (maximum likelihood decoding) corresponding to a PR channel.

As a result, according to the optical disk recording / reproducing apparatus of the present embodiment, the data recorded on the optical disk
Since the data can be reproduced by the RML method, that is, the method combining the partial response method and the maximum likelihood decoding method (Viterbi decoding method), S / N is corrected by error correction.
Can be improved.

As is clear from the above description, according to the seventh embodiment, near-field light is generated by a nonlinear optical material layer for generating a minute aperture to compensate for intersymbol interference during recording. The information recorded on the optical disk is read using the precoding means for decoding and the decoding means based on the PRML method, so that the information read by the side lobe of the light spot can be positively utilized. Therefore, it is not necessary to provide a slit, a condenser lens, and the like in the super-resolution optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified. [Eighth Embodiment] An eighth embodiment is an optical disk recording / reproducing apparatus according to the second embodiment, in which the information recording layer of the optical disk is made of a phase change material.

In the optical disk recording / reproducing apparatus of the eighth embodiment, as shown in FIG. 12, a phase-change material and a protective layer are provided on an optical disk substrate made of polycarbonate or the like as an optical recording medium, and a near-field probe or Recording and reproduction are performed by generating near-field light using a near-field slider head. In the present embodiment, the SiN protective layer 12 and the phase change material 13 are stacked and evaporated on the polycarbonate optical disk substrate 11. For example, each film thickness is
The N protective layer was laminated to a thickness of 20 nm, and the phase change material was laminated to a thickness of 15 nm. A phase change material is a material that undergoes a phase change (a crystalline phase, an amorphous phase, or the like) by irradiating strong writing light. If multiple stable phases can be changed reversibly, Ram
When the recording medium changes irreversibly, it can be used as a write-once recording medium. Further, any material may be used as long as contrast is generated in a plurality of phases in the transmitted light or the reflected light when irradiated with weak reading light. The contrast includes not only a difference in light intensity due to a change in absorbance or reflectance but also a contrast caused by a change in an optical constant such as rotation of a polarization plane or a change in birefringence. During recording, in the case of the present embodiment, near-field light or internally converging near-field light is incident from the recording layer side by a near-field probe or the like.
Light can be incident from either the substrate side or the recording layer side of the medium, but FIG. 12 is a diagram when near-field light is incident from the recording layer side. Light emitted from the tip of the near-field probe temporarily becomes near-field light and enters the sample. The light passes through the recording layer and is emitted as propagation light to the polycarbonate substrate side. Recording marks smaller than the diffraction limit of light can be formed on the data recording layer.

For example, if the diameter of the minute aperture is 50 nm, a light spot of about 50 nm can be formed on the recording layer of the surface recording medium. Assuming that the pitch of the bits recorded on the optical disk is 20 nm, the signal output from the photodetector for signal detection in the optical pickup has a light spot diameter larger than the bit diameter as shown in FIG. The read waveform of the corresponding bit is added. Therefore, the signal output by the optical pickup is subject to intersymbol interference from adjacent bits, and the intersymbol interference makes it possible to detect the partial response method as described above.

As apparent from the above description, according to the eighth embodiment, a micro aperture for generating near-field light and a pre-code means for compensating for intersymbol interference during recording are provided. Since the information recorded on the phase change material layer of the optical disc is read, the information read by the side lobe of the light spot can be positively utilized. Therefore, it is not necessary to provide a slit, a condenser lens, and the like in the super-resolution optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified. [Ninth Embodiment] A ninth embodiment is the same as the second embodiment, except that the information recording layer of the optical disk is Ge2Sb2Te5.
This is an optical disk recording / reproducing device having a thin film.

The optical disk recording / reproducing apparatus according to the ninth embodiment has a recording layer and a protective layer provided on an optical disk substrate made of polycarbonate or the like as an optical recording medium, as shown in FIG. Recording and reproduction are performed by generating near-field light using a field slider head. In the present embodiment, the polycarbonate optical disc substrate 11
The N protective layer 12 and the recording layer 13 were stacked and vapor-deposited. In this embodiment, Ge2Sb2Te5, which is a phase change material, is used for the recording layer 13. This material has two states (crystal and amorphous) having different reflectivities at room temperature. By changing the condition of the light to be irradiated, the state can be freely changed, such as crystallization or amorphous state. Using this principle, it is possible to configure an optical memory that records data and reads out data based on the difference in reflectance. By using this material, a reproduction signal with high contrast and good S / N can be obtained, and an optical disk recording / reproducing apparatus having high recording / holding ability can be obtained. The thickness of each layer is above and below the recording layer.
The N protective layer was laminated to 20 nm, and the recording layer was laminated to 15 nm. At the time of recording,
In the case of the present embodiment, near-field light, internally converging near-field light, or normal propagation light is incident from the recording layer side by a near-field probe or the like. Although light can enter from the substrate side of the medium or from the recording layer side, FIG. 13 shows a case where near-field light enters from the recording layer side. Light emitted from the tip of the near-field probe temporarily becomes near-field light and enters the sample. The light passes through the recording layer and is emitted as propagation light to the polycarbonate substrate side. Recording marks smaller than the diffraction limit of light can be formed on the data recording layer.
The address information is formed in advance by a mark larger than the diffraction limit.

For example, if the diameter of the minute aperture is 50 nm, a light spot of about 50 nm can be formed on the recording layer of the surface recording medium. Assuming that the pitch of the bits recorded on the optical disk is 20 nm, the signal output from the photodetector for signal detection in the optical pickup has a light spot diameter larger than the bit diameter as shown in FIG. The read waveform of the corresponding bit is added. Therefore, the signal output by the optical pickup is subject to intersymbol interference from adjacent bits, and the intersymbol interference makes it possible to detect the partial response method as described above. As is clear from the above description, according to the ninth embodiment, the optical disc is provided with a micro aperture for generating near-field light and a precoding means for compensating for intersymbol interference during recording. Ge2Sb2
Since the information recorded on the Te5 recording layer is read, the information read by the side lobe of the light spot can be positively utilized. Therefore, it is not necessary to provide a slit, a condenser lens, and the like in the super-resolution optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified. [Tenth Embodiment] A tenth embodiment is the same as the second embodiment, except that the information recording layer of the optical disk is
This is an optical disk recording / reproducing device using an AgInSbTe thin film.

As shown in FIG. 14, the optical disc recording / reproducing apparatus of the tenth embodiment uses an AgInSbTe layer as a phase change material for the recording layer of the optical recording medium of the second embodiment. In this case, for example, the layer configuration of the disc is such that the SiN protective layer 12 is 10 nm above and below the recording layer, and the recording layer 13 is AgIn.
SbTe has a configuration of 15 nm and a polycarbonate substrate 11. This material has two states (crystal and amorphous) having different reflectivities at room temperature. By changing the condition of the light to be irradiated, the state can be freely changed, such as crystallization or amorphous state. Using this principle, it is possible to configure an optical memory that records data and reads out data based on the difference in reflectance. By using this material, a reproduced signal with high contrast and good S / N can be obtained, and an optical disk recording / reproducing apparatus capable of stably storing recorded information for a long time can be obtained. Further, since silver is used for the recording layer, it has good adhesion to the substrate and is excellent in abrasion resistance.
As the recording layer, it is possible to use a generally known optical recording material other than the above two examples.

At the time of recording, in the case of the present embodiment, near-field light or internally converging near-field light is incident from the recording layer side by a near-field probe or the like. Although light can be incident from the substrate side of the medium or from the recording layer side, FIG. 14 is a diagram when near-field light is incident from the recording layer side. Light emitted from the tip of the near-field probe temporarily becomes near-field light and enters the sample. The light passes through the recording layer and is emitted as propagation light to the polycarbonate substrate side. Recording marks smaller than the diffraction limit of light can be formed on the data recording layer.

For example, if the diameter of the minute aperture is 50 nm, a light spot of about 50 nm can be formed on the recording layer of the surface recording medium. Assuming that the pitch of the bits recorded on the optical disk is 20 nm, the signal output from the photodetector for signal detection in the optical pickup has a light spot diameter larger than the bit diameter as shown in FIG. The read waveform of the corresponding bit is added. Therefore, the signal output by the optical pickup is subject to intersymbol interference from adjacent bits, and the intersymbol interference makes it possible to detect the partial response method as described above.

As is clear from the above description, according to the tenth embodiment, a micro aperture for generating near-field light and a pre-code means for compensating for intersymbol interference during recording are provided. Since the information recorded on the AgInSbTe recording layer of the optical disc is read, the information read by the side lobe of the light spot can be positively utilized. Therefore, it is not necessary to provide a slit or a condenser lens in the super-resolution optical disk pickup in order to eliminate information read by the side lobe,
The configuration of the optical pickup can be simplified. [Eleventh Embodiment] An eleventh embodiment is an optical disk recording / reproducing apparatus according to the fifth embodiment, wherein the information recording layer of the optical disk is made of a phase change material.

In the optical disk recording / reproducing apparatus of the eleventh embodiment, as shown in FIG. 15, a phase change material, a protective layer, and a nonlinear optical material layer are provided on an optical disk substrate made of polycarbonate or the like as an optical recording medium. Recording and reproduction are performed by generating light using the nonlinear optical material layer as a mask. The generated light is near-field light, internally converging near-field light, or the like. In the present embodiment, the polycarbonate optical disc substrate 11
The SiN protective layer 12, the phase change material 13, and the mask layer 15 of Sb were stacked and deposited. For example, each film thickness is 20 nm for the SiN protective layer above and below the recording layer, 15 nm for the phase change material, 15 nm for the Sb mask layer, and SiN between the Sb layer and the polycarbonate substrate.
A protective layer having a thickness of 170 nm was laminated. A phase change material is a material that undergoes a phase change (a crystalline phase, an amorphous phase, or the like) by irradiating strong writing light. If a plurality of stable phases can be changed reversibly, it can be used as Ram, and if it changes irreversibly, it can be used as a write-once recording medium. Further, any material may be used as long as contrast is generated in a plurality of phases in the transmitted light or the reflected light when irradiated with weak reading light. The contrast includes not only a difference in light intensity due to a change in absorbance or reflectance but also a contrast caused by a change in an optical constant such as rotation of a polarization plane or a change in birefringence. At the time of recording, a laser beam condensed so as to focus on the Sb mask layer is incident from the substrate side similarly to a normal optical disc. At this time, the Sb mask layer in a region corresponding to the incident laser power becomes transparent, and a minute opening is formed. At this time, near-field light seeps into the recording layer from the formed minute opening, and a recording mark smaller than the diffraction limit of light can be formed.

For example, if the minute aperture diameter formed by the Sb mask layer is 50 nm, a light spot of about 50 nm can be formed on the recording layer of the surface recording type medium. Assuming that the pitch of the bits recorded on the optical disc is 20 nm, the signal output by the photodetector for signal detection in the optical pickup has a smaller aperture diameter than the bit diameter, so that the read waveform of the bit adjacent to both sides of the read waveform is Will be added. In particular, when a small aperture is formed using the Sb layer as a mask, the aperture is formed so as to trail behind the traveling direction of the beam spot as shown in FIG. Becomes Therefore, the signal output from this optical pickup is
This causes intersymbol interference from adjacent bits, and this intersymbol interference enables detection of the partial response method as described above.

As is clear from the above description, according to the eleventh embodiment, the near-field light is generated by the nonlinear optical material layer for generating the minute aperture, and the intersymbol interference at the time of recording is compensated. The information recorded on the phase change material layer of the optical disk is read out using the precoding means for the purpose, so that the information read out by the side lobe of the light spot can be positively utilized. Therefore, it is not necessary to provide a slit, a condenser lens, and the like in the super-resolution optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified. [Twelfth Embodiment] A twelfth embodiment is different from the fifth embodiment in that Ge is used as the information recording layer of the optical disc.
This is an optical disk recording / reproducing device using a 2Sb2Te5 thin film.

In the optical disk recording / reproducing apparatus according to the twelfth embodiment, as shown in FIG. 16, a non-linear optical disk having a recording layer, a protective layer and a non-linear optical material layer provided on an optical disk substrate made of polycarbonate or the like as an optical recording medium. Recording and reproduction are performed by generating light using the optical material layer as a mask. The generated light is near-field light, internally converging near-field light, or the like.
Ge2Sb2Te5 which is a phase change material is used for the recording layer. This material has two states (crystal and amorphous) having different reflectivities at room temperature. By changing the condition of the light to be irradiated, the state can be freely changed, such as crystallization or amorphous state. Using this principle, it is possible to configure an optical memory that records data and reads out data based on the difference in reflectance. By using this material, a reproduction signal with high contrast and good S / N can be obtained, and an optical disk recording / reproducing apparatus having high recording / holding ability can be obtained. In the present embodiment, the SiN protective layer 12, the recording layer 13, and the mask layer 15 of Sb are laminated on the polycarbonate optical disk substrate 11 and deposited. For example, each film thickness is 20 nm for the SiN protective layer above and below the recording layer, 15 nm for the recording layer, 15 nm for the Sb mask layer, and Si between the Sb layer and the polycarbonate substrate.
The N protective layer was stacked at 170 nm.

At the time of recording, a laser beam condensed so as to focus on the Sb mask layer from the substrate side as in a normal optical disk. At this time, the Sb mask layer in a region corresponding to the incident laser power becomes transparent, and a minute opening is formed. At this time, near-field light seeps into the recording layer from the formed minute opening, and a recording mark smaller than the diffraction limit of light can be formed.

For example, if the diameter of the minute opening formed by the Sb mask layer is 50 nm, a light spot of about 50 nm can be formed on the recording layer of the surface recording type medium. Assuming that the pitch of the bits recorded on the optical disc is 20 nm, the signal output by the photodetector for signal detection in the optical pickup has a smaller aperture diameter than the bit diameter, so that the read waveform of the bit adjacent to both sides of the read waveform is Will be added. In particular, when a small aperture is formed using the Sb layer as a mask, the aperture is formed so as to trail behind the traveling direction of the beam spot as shown in FIG. Becomes Therefore, the signal output from this optical pickup is
This causes intersymbol interference from adjacent bits, and this intersymbol interference enables detection of the partial response method as described above.

As is clear from the above description, according to the twelfth embodiment, near-field light is generated by a nonlinear optical material layer for generating a minute aperture to compensate for intersymbol interference during recording. The information recorded on the Ge2Sb2Te5 recording layer of the optical disc by using the precoding means for the optical disc, the information read by the side lobe of the light spot can be positively utilized. Therefore, it is not necessary to provide a slit, a condenser lens, and the like in the super-resolution optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified. [Thirteenth Embodiment] A thirteenth embodiment is the same as the fifth embodiment, except that the information recording layer of the optical disc is made of Ag.
This is an optical disk recording / reproducing device using an InSbTe thin film.

In the optical disk recording / reproducing apparatus of the thirteenth embodiment, as shown in FIG. 17, a non-linear optical disk having a recording layer, a protective layer, and a non-linear optical material layer provided on an optical disk substrate made of polycarbonate or the like as an optical recording medium. Recording and reproduction are performed by generating light using the optical material layer as a mask. The generated light is near-field light, internally converging near-field light, or the like.
Further, AgInSbTe which is a phase change material is used for the recording layer. This material has two states (crystal and amorphous) having different reflectivities at room temperature. By changing the condition of the light to be irradiated, the state can be freely changed, such as crystallization or amorphous state. Using this principle, it is possible to configure an optical memory that records data and reads out data based on the difference in reflectance. By using this material, a reproduced signal with high contrast and good S / N can be obtained, and an optical disk recording / reproducing apparatus capable of stably storing recorded information for a long time can be obtained. Further, since silver is used for the recording layer, it has good adhesion to the substrate and is excellent in abrasion resistance.
As the recording layer, it is possible to use a generally known optical recording material other than the above two examples.

In the present embodiment, a SiN protective layer 12, an AgInSbTe recording layer 13, a S
The mask layer 15 of b was deposited and deposited. For example, the thickness of each of the ZnS-SiO2 protective layers above and below the recording layer is 10 nm, the recording layer is 15 nm, the Sb mask layer is 15 nm, and the ZnS-SiO2 protective layer 120 nm is laminated between the Sb layer and the polycarbonate substrate. .

At the time of recording, a laser beam condensed so as to focus on the Sb mask layer is incident from the substrate side as in a normal optical disk. At this time, the Sb mask layer in a region corresponding to the incident laser power becomes transparent, and a minute opening is formed. At this time, near-field light seeps into the recording layer from the formed minute opening, and a recording mark smaller than the diffraction limit of light can be formed.

For example, if the minute aperture diameter formed by the Sb mask layer is 50 nm, a light spot of about 50 nm can be formed on the recording layer of the surface recording type medium. Assuming that the pitch of the bits recorded on the optical disc is 20 nm, the signal output by the photodetector for signal detection in the optical pickup has a smaller aperture diameter than the bit diameter, so that the read waveform of the bit adjacent to both sides of the read waveform is Will be added. In particular, when a small aperture is formed using the Sb layer as a mask, the aperture is formed so as to trail behind the traveling direction of the beam spot as shown in FIG. Becomes Therefore, the signal output from this optical pickup is
This causes intersymbol interference from adjacent bits, and this intersymbol interference enables detection of the partial response method as described above.

As is apparent from the above description, according to the thirteenth embodiment, near-field light is generated by a nonlinear optical material layer for generating a minute aperture to compensate for intersymbol interference during recording. The information recorded on the AgInSbTe recording layer of the optical disc by using the precoding means for the optical disc, the information read by the side lobe of the light spot can be positively utilized. Therefore, in order to exclude information read by the side lobe,
There is no need to provide a slit or a condenser lens in the super-resolution optical disk pickup, and the configuration of the optical pickup can be simplified. Fourteenth Embodiment In an optical disk recording / reproducing apparatus according to a fourteenth embodiment, as shown in FIG. 4, a recording layer is provided on an optical disk substrate made of polycarbonate or the like as a recording medium, and a super-resolution optical head or the like is used. Recording and reproduction by generating light of a spot smaller than the light diffraction limit.
Further, a magneto-optical recording medium may be used, and the present invention is also applicable to a recording / reproducing method using light only for recording or reproduction.

In the present embodiment, a SiN protective layer 12 and a recording layer 13 are stacked on a polycarbonate optical disk substrate 11 and vapor-deposited. For example, each film thickness is above and below the recording layer
A 20 nm SiN protective layer and a 15 nm data recording layer were stacked. At the time of recording, in the case of the present embodiment, light of a small spot enters from the recording layer side. Although light can enter from the substrate side or the recording layer side of the medium, FIG. 4 shows a case where light enters from the recording layer side. Light emitted from the optical head enters the sample, and the light passes through the recording layer and is emitted toward the polycarbonate substrate. Recording marks smaller than the diffraction limit of light can be formed in the data recording layer according to the intensity of light. Also, when reading the mark,
Light is irradiated to such an extent that the recording layer does not change, and the reflected light intensity or transmitted light intensity is read.

In the optical head used in the present embodiment, an optical fiber probe for generating near-field light or the like is installed at the tip in order to form a spot smaller than the diffraction limit of light. For example, when the probe is made of an optical fiber, the optical fiber probe according to the present embodiment includes a core 60, a clad 61 formed around the core 60, and a periphery of the clad 61, as shown in FIG. And a light-shielding coating layer 42 formed on the substrate. Core 60
Has a predetermined refractive index n, and the cladding 61 has a refractive index smaller than the refractive index n of the core 60. By forming the core 60 and the clad 61 in this manner, the laser light incident on the optical fiber probe travels while being totally reflected at the interface between the core 60 and the clad 61.

This optical fiber probe is compatible with the core 6
The light-transmitting portion includes a cladding 61, a light-shielding abdominal layer 62, and a sharp portion in which the diameter of the light-shielding coating layer gradually decreases from the light-transmitting portion toward the tip. The light propagation unit includes a core 60 having a predetermined refractive index n,
The cladding 61 has a lower refractive index. With such a configuration, the light propagation unit propagates the laser light into the core 60 and guides the laser light to the sharp part. The sharp portion includes a light-shielding abdominal layer 62 and a core 60 formed on the inner peripheral side of the light-shielding abdominal layer 62, and is sharpened so as to narrow an opening for emitting light. The sharp portion forms the inclined surface 63 by forming the inner wall of the light-shielding coating layer at an angle θ between the inner wall of the cladding of the light propagation portion and the inner wall of the light-shielding coating layer.
By forming the light-shielding abdomen layer 62 in this manner, the diameter of the sharpened portion of the sharpened portion is gradually reduced from the light propagation portion toward the emission opening. Here, θ may be 90 ° or less, and it is more desirable to form the inclined surface so as to be in the range of 10 ° to 90 °.

In this optical fiber probe, α is
Assuming a constant having a value in the range of 1.0 to 2.2 and λ being the wavelength of the emitted light, D = αλ / n (4) D is formed.

As described above, the optical fiber probe having the emission aperture satisfying the above equation (4) reflects the laser beam propagated from the light propagation section on the inclined surface which is the inner wall of the sharp section. As a result, the light is condensed and emitted to the outside through the emission aperture.

In such an optical fiber probe,
FIG. 19 shows the result of measuring the light intensity distribution in the near field when laser light is emitted from the emission aperture. In this optical fiber probe, the wavelength λ of the laser light incident on the light propagation section is 830 nm, the tip angle θ is 20 °, and the refractive index of the core is
When it is set to 1.53, the light intensity is high when the diameter of the exit aperture is in the range from 600 nm to 1200 nm. At this time, the constant α is calculated from 1.0 to 2.2 from 1.0.
FIG. 19 is a diagram showing the relationship between the light intensity and the distance from the focal position when the diameter D of the exit aperture is 1000, 750, and 550 nm. According to FIG. 19, when the diameter D of the exit aperture shown by the curve a and the curve b is 1000 nm and 750 nm, there is a relatively wide single peak at the focal position. The half widths are 600 nm and 400 nm. Further, when the diameter D of the emission aperture shown by the curve c is 550 nm, it is understood that a spot having a width much smaller than the peaks shown by the curves a and b is formed. The half width is 200 nm. However, curve c has a distance of 300 nm from the focal point as shown in the figure.
A second peak serving as a side lobe is formed symmetrically to the left and right. From these results, it can be seen that when the diameter D of the exit aperture is 550 nm, the laser light is focused on the focusing position beyond the diffraction limit at a wavelength of 830 nm.

Conventionally, in an optical disk recording / reproducing apparatus using an internal focusing type near-field head, when the half width of the main spot is increased in order to increase the writing density on the medium,
A side lobe like the curve c is generated, and the detection signal based on the side lobe is added to the detection signal based on the main spot, resulting in a defect that a read signal having a poor S / N is obtained.

The optical disk recording / reproducing apparatus according to the present embodiment converts a side lobe read signal generated when the width of the main spot of the internal focusing type near-field optical pickup is reduced to enable reading of high-density recorded data. It can be actively used to detect the original data. This eliminates the need to provide a slit or the like for removing a side lobe readout signal, thereby simplifying the structure of the super-resolution optical pickup and reducing the labor for assembly adjustment.

As in the present embodiment, as a means for forming a spot below the diffraction limit of light, an internally converging near-field light using an optical fiber probe is used. However, the present invention is not limited to this method. And spot forming by internal condensing with a planar slider, and various spot forming means.

In the optical disk recording / reproducing apparatus of this embodiment, for example, in the case of binary information, the bit interval (interval of each unit information) is different from the main spot in the light spot of the internal focusing type near-field optical pickup for reading. An information sequence is recorded on the optical disk so as to be 1 / N (N is an integer) of the peak interval of the side lobe. For this reason, at the time of reproduction, the preceding and succeeding bit information is simultaneously read by the side lobe in synchronization with the reading of the bit information by the main spot. However, in this case,
The bit information read by the side lobe is always the bit information before and after N bits, and the bit information read by the side lobe is determined by the ratio of the light intensity between the main spot and the side lobe. It becomes possible to reproduce recorded information by actively utilizing it instead of using information.

FIG. 5 is a block diagram showing an example of the configuration of an optical disk recording / reproducing apparatus to which the fourteenth embodiment is applied. The recording data generation unit 23 generates recording data to be actually written on the optical disk by applying a pre-code by a partial response method to the writing data sent from the controller 21. This precode is for performing the above-described operation of the equation (1) on write data.

Here, assuming that the PR (1, 0, 2, 0, 1) method is used as the partial response method, P
The transfer function G (D) of the R transmission path is as shown in Expression (5).

G (D) = 1 + 2D ² + D ⁴ (5) Therefore, the actual precode is obtained by performing the operation of the following expression (6) on the write data. Become. (1 / (1 + 2D ² + D ⁴ )) mod 2... (6) The calculation of equation (6) is based on the fact that the optical pickup 24 calculates the bit data After adding the inverse characteristic 1 / G (D) of the correlation characteristic G (D) of intersymbol interference when data recorded two bits before and after is read at a ratio of 2: 1, the result is 2 Indicates that the remainder of (radix of bit data) is to be calculated. When the bit interval is set to one third of the peak interval and the PR (1, 0, 0, 2, 0, 0, 1) is detected by the partial response method, the transfer function G
(D) is as shown in equation (7).

G (D) = 1 + 2D ³ + D ⁶ (7) When an isolated bit is recorded on the recording layer of the optical disc, a signal output by the photodetector for signal detection Since the spot is larger than the bit, the read waveform of the adjacent bit is added to both sides of the read waveform. Therefore, the signal output from the optical pickup 24 is subjected to intersymbol interference from adjacent bits, and the intersymbol interference enables detection of the partial response method as described above.

As shown in FIG. 5, the output signal of the optical pickup is sent to an equalizing circuit and a clock extracting unit. As shown in FIG. 6, the equalizer 26 is a transversal filter including a delay element T (31), a weight coefficient multiplier 32, and an adder 33, and changes the gain of each weight coefficient multiplier. Thus, the tap coefficient can be adjusted.
The clock extraction unit converts the signal output from the photodetector into a PLL.
Is a circuit for extracting a sampling clock signal by using.

The signal output from the equalizing circuit 26 is A / D
It is sent to converter 27. The A / D converter 27
This is a circuit for converting an analog signal output from the equalizing circuit 26 into digital data, and performs sampling based on a sampling clock signal extracted by a clock extracting unit. Each sampling value is quantized into multi-values according to the PR system to be digital data in order to detect the partial response system.

The digital data output from the A / D converter 27 is sent to a decoder 28. Decoder 2
Numeral 8 denotes a circuit for performing a remainder operation of 2 on each of multi-valued digital data, thereby detecting original write data. The data detected by the decoder is sent to the controller 21. Controller 2
1 controls the rotation of the spindle motor 22 for rotating the medium, the servo control of the optical pickup 24, and the like, in addition to the input and output of data as described above. [Fifteenth Embodiment] In the optical disk recording / reproducing apparatus of the fifteenth embodiment, as shown in FIG. An internal interference type projection or opening is provided. Using this projection or opening, three-beam type near-field light or internally converging near-field light is generated to perform recording and reproduction.

For example, if the minute aperture diameter is 50 nm, the recording layer of the surface recording medium can be irradiated with a main spot of light of about 50 nm. Assuming that the pitch of the bits recorded on the optical disk is 20 nm, the signal output from the signal detector for signal detection in the optical pickup is, as shown in FIG. A waveform will be added. Therefore, the signal output from this optical pickup is subject to intersymbol interference from the adjacent bits.
This intersymbol interference enables detection of the partial response method as described above.

Here, assuming that the PR (1, 0, 2, 0, 1) method is used as the partial response method, P
The transfer function G (D) of the R transmission path is as shown in the above equation (5).

Therefore, in the actual precode, the operation of the above equation (6) is performed on the write data.

The calculation of equation (6) is based on the code when the optical pickup reads out the bit data and the data recorded two bits before and after the bit data at a ratio of 2: 1 due to the spread of the main spot of the light spot. After adding the inverse characteristic 1 / G (D) of the correlation characteristic G (D) of the interfering interference, the remainder of this operation is calculated.

When an isolated bit is recorded on the recording layer of the optical disk, the signal output from the signal detection photodetector has a side lobe added to the spot of the detection light, so that a signal of the adjacent bit due to the spot spread is added. A readout waveform will be added. Therefore, the signal output from the optical pickup is subject to intersymbol interference from the adjacent bits, and the intersymbol interference makes it possible to detect the partial response method as described above. [Sixteenth Embodiment] The recording / reproducing operation of the optical disc recording / reproducing apparatus of the sixteenth embodiment will be described with reference to FIG. For example, as shown in FIG.
The case of writing m｝ will be described. This input data sequence {am} is usually one which has been appropriately modulated in advance.

First, the input data sequence {am} is sent from the controller 21 to the recording data generation unit 23, where it is pre-coded and converted into the recording data sequence {bm} by the above-described equation (6). Since the operation of equation (6) adds the inverse characteristic of the correlation characteristic G (D) of the intersymbol interference due to the side lobe and takes the remainder of 2, the input data am is already converted in order to convert the input data am. Recording data bm-4, bm-2
Is used to calculate bm that satisfies the following equation (8). bm = (am−2bm−2−bm−4) mod 2 (8) For example, when the input data a14 in FIG. 21 is converted, the value of a14 is 1,
The calculation of the remainder of 2 (1-2 × 1-0) to which the value of 1 is applied may be performed. Therefore, the recording data b14 becomes 1.

The pre-recorded recording data sequence {bm} is sent to the writing LD driver in accordance with the clock signal from the clock generation unit, and the peak interval between the main spot of the light spot and the side lobe in the optical pickup. Is recorded on the recording layer of the optical disk at a half bit interval of the above.

The recording layer is a phase-change material, and can change the phase state of the recording layer by heat due to light irradiation to form an amorphous state and a crystalline state. At the time of data writing, since writing is performed using only the portion of the center of the main spot of the LD light where the temperature rises most, even if there is a side lobe, it does not contribute to writing. Therefore, it is possible to switch between writing and reading by changing the optical power with the same head, so that it is not necessary to prepare two heads for writing and reading.

The recording data sequence {bm} recorded on the recording layer of the optical disk is read by the optical pickup 24, the waveform is equalized by the equalizing circuit 26, and the digital data is reproduced by the A / D converter 27. It is converted to a data sequence {xm}. This reproduced data sequence {xm}
Is a signal obtained by adding the side lobe read signal to the main spot read signal at a rate of 1/2, and performing the arithmetic operation of equation 9 on the recording data sequence {bm}.

Xm = bm−4 + 2bm−2 + bm (9) For example, the reproduced data x14 in FIG.
Since b12 and b14 are 0, 1, and 1, respectively, 3
(= 0 + 2 × 1 + 1). That is, here, the reproduced data sequence {xm} is quinary digital data having values of 0 to 4.

The reproduced data sequence {xm} read out as quinary digital data is sent to the decoder. This reproduced data sequence {xm} is obtained by taking the remainder of 2 and converted into a binary output data sequence {dm}. Therefore, the output data d14 is 3 mod 2 = 1. The recording data sequence {bm} is obtained by adding the inverse characteristic of the correlation characteristic G (D) to the input data sequence {am} and then taking the remainder of 2, so that the reproduction data sequence { The output data series {dm} obtained by taking the remainder of 2 of xm} matches the original input data series {am}. And this output data series ｛d
m｝ is sent to the controller 21.

As a result, the optical disk recording / reproducing apparatus of the present embodiment positively outputs a side lobe read signal generated when the width of the main spot of the optical pickup is reduced to enable reading of high-density recorded data. It can be used to detect the original data. This allows
It is not necessary to provide a slit or the like for removing a read signal of the side lobe, so that the structure of the near-field optical pickup can be simplified and the labor for assembling and adjusting can be reduced. [Seventeenth Embodiment] In a reproduction signal processing system of the PRML system, a Viterbi decoder, which is a representative of the maximum likelihood decoder, is generally used as a detector arranged after an equalizer. Assuming that the reproduced waveform is equalized to the PR characteristic by the equalizer, the Viterbi decoder selects a sequence having the smallest error from the sample sequence of the equalized waveform from all the sequences satisfying the PR characteristic, and selects the sequence. It outputs binary data (decoded data) corresponding to the sequence. In the PRML method, decoding is performed not from one sample value but from a plurality of sample values, so that the resistance to a signal deterioration component having no correlation between the sample values is strong. The maximum likelihood decoding method using the Viterbi decoder according to the present embodiment will be described below.

A seventeenth embodiment will be described with reference to FIGS. FIG. 9 is a block diagram showing an example of the configuration of an optical disk recording / reproducing apparatus, and FIG. 10 is a block diagram showing an example of the configuration of a Viterbi decoder.

As shown in FIG. 9, the optical disk recording / reproducing apparatus of the present embodiment has a Viterbi decoder instead of the decoder in the optical disk recording / reproducing apparatus of the fourteenth embodiment of FIG.

In this embodiment, the PR (1, 0, 2, 0, 1) partial response method is detected.
Since the weight coefficients g1 = 0 and g3 = 0 of the weight coefficient multiplier of No. 6
In the reproduced data sequence {xm}, no intersymbol interference occurs between the reproduced data sequence {x2m} composed of even-numbered data and the reproduced data sequence {x2m + 1} composed of odd-numbered data. Therefore, when performing decoding using the Viterbi decoding method, the maximum likelihood value must be calculated for every step of the reproduced data, which complicates the circuit. Therefore, two Viterbi decoders for even-numbered data and odd-numbered data are provided, and the digital data output from the A / D converter is switched by the switching circuit at each sampling interval before the reproduced data is input. You may make it distribute to a decoder alternately. In this case, the decoding system in each Viterbi decoder is equivalent to the PR (1, 2, 1) partial response system, and each Viterbi decoder uses this PR (1, 2, 1)
And a circuit that performs Viterbi decoding (maximum likelihood decoding) corresponding to the above can be used, and the circuit is simplified. Further, for example, PR (1, 0,
When detecting the partial response method of (0, 2, 0, 0, 1), three Viterbi decoders corresponding to PR (1, 2, 1) may be similarly used.

Here, a reproduced data sequence {x2m} composed of even-numbered data in the reproduced data sequence {xm} shown in FIG. 21 will be considered. The reproduced data sequence {x2m} is composed of a sequence of five-value data of 3, 3, 2, 2, 1, 1, 3, 4, 3,..., And each sample value can take a value from 0 to 4. However, since each sample value has a PR (1,2,1) correlation with the previously read sample value, when a certain sample value is determined, the next sample value becomes 0.
Cannot be changed to all the values of 4. This will be described with reference to the state transition diagram of PR (1, 2, 1) (PR2) in FIG. The eight ellipses in FIG. 22 indicate the data state with the number of states of 8, and the three-digit numerical value inside the ellipse indicates the recording data sequence {bm}
Represents three bits. The arrow represents a path that transitions from one state to the next, and cannot transition to a state without an arrow. The numerical values from 0 to 4 shown beside the arrow indicate the detected sample value x2m. For example, when the detected sample value X0 is 3, the pattern of the recording data sequence {bm} is either (0, 1, 1) or (1, 1, 0). Therefore, the pattern of the recording data sequence {bm} corresponding to the next sample value is (1, 1, 0), (1, 1,
1), (1, 0, 0) or (1, 0, 1), and the next sample value cannot transition to 0. The next sample value X2 is 3, and the transition from sample value 3 to 3 can only have data state (0,1,1) to (1,1,0), so
The recording data b2 is uniquely determined to be 0. The next X4 is 2,
The next data state will be (1, 0, 1) and b4 will be 1. By performing such decoding sequentially, the decoding result becomes “1, 0, 1, 0, 0, 1, 1, 1, 0”, which indicates that it matches the recording data sequence {bm}. . Therefore, such a reproduced data sequence {x2m} is
Detection by the Viterbi decoding method is possible.

As shown in FIG. 10, the Viterbi decoder 34 includes ACS units (addition / comparison / selection units) 42 _{0 to} 42N _s−1 for performing operations for each state of the trellis transition diagram, and these addition / comparison / selection units. Path memory circuits 50 each storing a path (path) selected by 42 _{0 to} 42N _s−1, and an MLD circuit (maximum likelihood path selection unit) 51 for selecting one path from the paths stored by the path memory circuit 50 And is constituted by. Then, Ns-number of ACS units 42 ₀
A case of tracing the trellis transition diagram of the Ns state using .about.42Ns _-1 will be described. Moreover, ACS unit 42 ₀
From the state ~42N _s-1 is computed, it can only be a transition to its state or condition of the ACS unit ₄₂ 0 ~42N _s-1, the state of the ACS unit ₄₂ 0 ~42N _s-1 Is the status of the own device or a specific addition / comparison / selection unit 42
It is assumed that transition can be made only to the state of _{0 to} 42N _s-1 .

When decoding by the Viterbi decoding method, A
The / D converter 27 does not limit the data to the Ns value, and usually performs finer quantization. The quantized data output from the A / D converter 27 is ideally Ns value data, but has a value having a width due to the influence of waveform distortion and noise. The quantized data is input to the branch metric calculation circuit 41 of each addition / comparison / selection unit.
Each branch metric calculation circuit 41 calculates the likelihood (branch metric) for the state transition from the difference between the input quantized data and the value indicated by its own state. The branch metric ACS unit 42 ₀
The addition unit (not shown) of .about.42N _s-1 adds the likelihood (path metric) of the past state transition path. The path metric is obtained by integrating the branch metrics in each past state of the path, and has a smaller value as the path of the quantized data that is actually read is closer to the path. The path metric to be added here is the addition / comparison / selection unit 42 that can transition to the addition / comparison / selection unit 42 _{0 to} 42N _s−1.
The path metrics from _{0 to} 42N _s-1 are stored in the path metric memory up to the previous time.

[0130] In this way, one of the quantized data is input to the Viterbi decoder 34, the ACS unit 42 ₀
Since the path from two directions transitions to ４２42N _s−1 , the comparison unit compares the two path metrics calculated by these addition units at this time, and the selection unit changes according to the comparison result. The path metric with the smaller value (the more likely one) is stored in the path metric memory. Further, the path selection unit selects a path having a smaller path metric, that is, a path that is most likely, and stores quantized data indicating this path in the path memory. Therefore, the path whose state has changed is stored in the path memory.

When a specified number of quantized data are input, the path with the smallest path metric (the maximum likelihood path) is selected from the four paths stored in the path memory by the maximum likelihood path selection unit. By selecting the maximum likelihood path, the path of the state transition is determined, and a bit data string that causes the state transition is output as a decoded data string. Therefore,
Even if an error is included in the reproduced data sequence {xm} due to the influence of noise or the like, it can be decoded into the most reliable data sequence.

The data decoded by the Viterbi decoder as described above becomes an output data sequence {DM} and is sent to the controller.

As a result, according to the optical disk recording / reproducing apparatus of the present embodiment, the data recorded on the optical disk
Since the data can be reproduced by the RML method, that is, the method combining the partial response method and the maximum likelihood decoding method (Viterbi decoding method), S / N is corrected by error correction.
Can be improved. [Eighteenth Embodiment] In an optical disk recording / reproducing apparatus according to an eighteenth embodiment, as shown in FIG. 11, a recording layer, a protective layer, and a nonlinear optical material layer are provided on an optical disk substrate made of polycarbonate or the like. Using the non-linear optical material layer as a mask, a light spot smaller than the light diffraction limit is generated on the recording layer to perform recording and reproduction. The generated light is near-field light, internally converging near-field light, or the like. In the present embodiment, a SiN protective layer 12 is
The recording layer 13 and the mask layer 15 of Sb were stacked and deposited. The respective film thicknesses are such that the SiN protective layers 12 above and below the recording layer have a thickness of 20 n.
m, the recording layer 13 was 15 nm, the Sb mask layer 15 was 15 nm, and the SiN protective layer 12 between the Sb layer and the polycarbonate substrate was 170 nm. When the recording layer 13 is irradiated with light,
Any material can be used as long as a contrast is generated in the transmitted light or the reflected light. Therefore, not only a phase change material but also a magneto-optical material or a material exhibiting an electro-optical effect can be considered. This contrast includes not only differences in light intensity due to changes in absorbance and reflectance, but also contrasts caused by changes in optical constants, such as rotation of the polarization plane and changes in birefringence.

At the time of recording, a laser beam focused so as to focus on the Sb mask layer 15 from the substrate side is incident as in a normal optical disk. At this time, the Sb mask layer 15 in a region corresponding to the incident laser power becomes transparent, and a minute opening is formed. At this time, near-field light seeps into the recording layer from the formed minute opening, and a recording mark smaller than the diffraction limit of light can be formed.

For example, if the minute aperture diameter formed by the Sb mask layer 15 is 50 nm, a light spot of about 50 nm can be formed on the recording layer of the surface recording type medium. Assuming that the pitch of the bits recorded on the optical disc is 20 nm, the signal output by the photodetector for signal detection in the optical pickup has a smaller aperture diameter than the bit diameter, so that the read waveform of the bit adjacent to both sides of the read waveform is Will be added. In particular, when a small opening is formed using the Sb layer as a mask, the opening is formed so as to trail behind the traveling direction of the beam spot as shown in FIG. It will be. Therefore, the signal output by the optical pickup is subject to intersymbol interference from adjacent bits, and the intersymbol interference makes it possible to detect the partial response method as described above.

Here, assuming that the PR (1, 2, 1) system is used as the partial response system, the transfer function G (D) of the PR transmission line is as shown in equation (10).

G (D) = 1 + 2D + D ² (10) Accordingly, in the actual precode, the operation of Expression (14) is performed on the write data.

(1 / (1 + 2D + D ² )) mod 2... (11) In the calculation of the expression (11), the optical pickup determines the bit data and the After adding the inverse characteristic 1 / G (D) of the correlation characteristic G (D) of intersymbol interference when data recorded one bit before and after is read out at a ratio of 2: 1, the result is 2
(Remainder of bit data) is calculated.

When an isolated bit is recorded on the recording layer of the optical disk, the signal output from the photodetector for signal detection has a spot larger than the bit, so that a read waveform of an adjacent bit due to the spread of the spot is added. Become. Therefore, the signal output by the optical pickup is subject to intersymbol interference from adjacent bits, and the intersymbol interference makes it possible to detect the partial response method as described above. [Nineteenth Embodiment] In the optical disk recording / reproducing apparatus of the nineteenth embodiment, as shown in FIG. 11, a recording layer is formed on an optical disk substrate 11 made of polycarbonate or the like, as shown in FIG. 13, a non-linear optical material layer provided with a protective layer 12, and a non-linear optical material layer is used as a mask layer 15, and a light spot smaller than the diffraction limit of light is generated on a recording layer to perform recording and reproduction.

For example, assuming that the fine opening diameter formed by the Sb mask layer is 50 nm, the recording layer of the surface recording medium can be irradiated with a light spot of about 50 nm. Assuming that the pitch of the bits recorded on the optical disc is 20 nm, the signal output by the photodetector for signal detection in the optical pickup has a smaller aperture diameter than the bit diameter, so that the read waveforms of the bits adjacent to both sides of the read waveform respectively. Will be added. In particular, when a small aperture is formed using the Sb layer as a mask, the aperture is formed so as to trail behind the traveling direction of the beam spot as shown in FIG. Becomes Therefore, the signal output from this optical pickup is
This causes intersymbol interference from adjacent bits, and this intersymbol interference enables detection of the partial response method as described above.

The recording / reproducing operation of the optical disk recording / reproducing apparatus having the above configuration will be described.

For example, a case where an input data sequence {am} is written will be described. This input data series {am}
Are usually those which have been appropriately modulated in advance.

First, this input data sequence {am} is sent from the controller to the recording data generation unit, and the above equation (11)
And the recording data sequence ｛b
m｝. The calculation of equation (11) adds the inverse characteristic of the correlation characteristic G (D) of the intersymbol interference due to the side lobe, and adds 2
Therefore, in order to convert the input data am, an operation for obtaining bm that satisfies the following expression (12) using the already converted recording data bm-4 and bm-2 is performed. Will do.

Bm = (am−2bm−1−bm−2) mod 2 (12) The precoded recording data sequence {bm} is output from the clock generation unit. Write LD according to clock signal
It is sent to the driver and recorded on the recording layer of the optical disk.

The recorded data sequence {bm} recorded on the recording layer of the optical disk is read out by the optical pickup, and after the waveform is equalized by the equalizing circuit, the reproduced data sequence of the digital data by the A / D converter. xm}. Since the read data sequence {xm} is obtained by adding read signals of bits adjacent to the read signal at the beam center at a rate of 1/2, the recorded data sequence {bm} is obtained by adding the expression (13) This is the result of the calculation.

Xm = bm−2 + 2bm−1 + bm (13) The reproduced data sequence {xm} read out as quinary digital data is sent to the decoder. This reproduced data sequence {xm} is obtained by taking the remainder of 2 and converted into a binary output data sequence {dm}. The recording data sequence {bm} is obtained by adding the inverse characteristic of the correlation characteristic G (D) to the input data sequence {am} and then taking the remainder of 2, so that the reproduction data sequence { The output data series {dm} obtained by taking the remainder of 2 of xm} matches the original input data series {am}. And this output data series ｛d
m｝ is sent to the controller.

As a result, the optical disk recording / reproducing apparatus of the present embodiment can utilize the intersymbol interference caused by adjacent bits due to the spread of the spot of the optical pickup to detect the original data. As a result, it is not necessary to provide a slit or the like for removing a read signal of a side lobe, so that the structure of the near-field optical pickup can be simplified and the labor for assembling and adjusting can be reduced. [Twentieth Embodiment] In the optical disc recording / reproducing apparatus of the twentieth embodiment, as shown in FIG. 11, as shown in FIG. 11, a recording layer is formed on an optical disc substrate 11 made of polycarbonate or the like. 13, a non-linear optical material layer provided with a protective layer 12, and a non-linear optical material layer is used as a mask layer 15, and a light spot smaller than the diffraction limit of light is generated on a recording layer to perform recording and reproduction.

For example, assuming that the minute opening diameter formed by the Sb mask layer is 50 nm, the recording layer of the surface recording type medium can be irradiated with a light spot of about 50 nm. Assuming that the pitch of the bits recorded on the optical disc is 20 nm, the signal output by the photodetector for signal detection in the optical pickup has a smaller aperture diameter than the bit diameter, so that the read waveforms of the bits adjacent to both sides of the read waveform respectively. Will be added. In particular, when a small aperture is formed using the Sb layer as a mask, the aperture is formed so as to trail behind the traveling direction of the beam spot as shown in FIG. Becomes Therefore, the signal output from this optical pickup is
This causes intersymbol interference from adjacent bits, and this intersymbol interference enables detection of the partial response method as described above.

A twentieth embodiment will be described with reference to FIGS. FIG. 9 is a block diagram showing an example of the configuration of an optical disk recording / reproducing apparatus, and FIG. 10 is a block diagram showing an example of the configuration of a Viterbi decoder. As shown in FIG. 9, the optical disc recording / reproducing apparatus of the present embodiment is provided with a Viterbi decoder instead of the decoder in the optical disc recording / reproducing apparatus of the fourteenth embodiment of FIG.

If the PR (1, 2, 1) system is used as the partial response system, the Viterbi decoder performs Viterbi decoding (maximum likelihood decoding) corresponding to the PR (1, 2, 1). Use what does.

Here, the reproduced data sequence {xm} will be considered. This reproduction data sequence {xm} is composed of a sequence of quinary data, and each sample value can take a value from 0 to 4. However, since each sample value has a PR (1,2,1) correlation with the previously read sample value,
Once a certain sample value is determined, the next sample value is 0 to 4
Cannot transition to all the values of Fig. 22 shows the situation.
This will be described with reference to the state transition diagram of PR (1, 2, 1) (PR2). The eight ellipses in FIG. 22 indicate a data state having eight states, and the three-digit numerical value inside the ellipse represents three bits of the recording data sequence {bm}. The arrow represents a path that transitions from one state to the next, and cannot transition to a state without an arrow. Numerical values from 0 to 4 shown beside the arrow indicate the detected sample value xm. For example, when the detected sample value X0 is 3, the pattern of the recording data sequence {bm} is either (0, 1, 1) or (1, 1, 0). Therefore, the pattern of the recording data sequence {bm} corresponding to the next sample value is (1, 1, 0), (1, 1,
1), (1, 0, 0) or (1, 0, 1), and the next sample value cannot transition to 0. The next sample value X2 is 3, and the transition from sample value 3 to 3 is only possible when the data state is from (0, 1, 1) to (1, 1, 0), so the recording data b2 is 0. Uniquely determined. The next X4 is 2, the next data state will be (1, 0, 1), and b
4 will be 1. By sequentially performing such decoding, the recording data sequence {b
m｝ is obtained. Therefore, such a reproduced data sequence {xm} can be detected by the Viterbi decoding method.

As shown in FIG. 10, the Viterbi decoder 34 includes ACS units (addition / comparison / selection units) 42 _{0 to} 42N _s−1 for performing operations for each state of the trellis transition diagram, and these addition / comparison / selection units. Path memory circuits 50 each storing a path (path) selected by 42 _{0 to} 42N _s−1, and an MLD circuit (maximum likelihood path selection unit) 51 for selecting one path from the paths stored by the path memory circuit 50 And is constituted by. Here, a case will be described in which a four-state trellis transition diagram is traced using four addition / comparison / selection units. Also, it is possible to transition only from the state calculated by the addition / comparison / selection unit to its own state or the state of the addition / comparison / selection unit. It is assumed that transition is possible only to

When decoding by the Viterbi decoding method, A
The / D converter 27 normally quantizes the data not only to five values but also more finely. A / D converter 27
Is ideally quinary data, but it has a width due to the influence of waveform distortion and noise. The quantized data is input to the branch metric calculation circuit 41 of each addition / comparison / selection unit. Each branch metric calculation circuit 41 calculates the likelihood (branch metric) for the state transition from the difference between the input quantized data and the value indicated by its own state. This branch metric is added to the likelihood (path metric) of the past state transition path by the adding unit 42. The path metric is obtained by integrating the branch metrics in each past state of the path, and has a smaller value as the path of the quantized data that is actually read is closer to the path. The path metric added here is the path metric up to the previous time stored in the path metric memory of the addition / comparison / selection unit that can transition to the addition / comparison / selection unit 42.

When one piece of quantized data is input to the Viterbi decoder in this way, each addition / comparison / selection unit 42
Since the path from the direction changes, the comparing unit 42 compares the two path metrics calculated by the adding unit this time, and according to the comparison result, the selecting unit selects the smaller one (the more reliable). Is stored in the path metric memory. Further, the path selection unit selects a path having a smaller path metric, that is, a path that is most likely, and stores quantized data indicating this path in the path memory. Therefore, the path whose state has changed is stored in the path memory.

When a specified number of quantized data is input, the path with the smallest path metric (the maximum likelihood path) is selected by the maximum likelihood path selection unit 51 from the four paths stored in the path memory. By selecting the maximum likelihood path, the path of the state transition is determined, and a bit data string that causes the state transition is output as a decoded data string. Therefore, even if an error is included in the reproduced data sequence {xm} due to the influence of noise or the like, it can be decoded into the most reliable data sequence.

The data decoded by the Viterbi decoder as described above is output to the controller 21 as an output data sequence {dm}.

As a result, according to the optical disk recording / reproducing apparatus of the present embodiment, the data recorded on the optical disk
Since the data can be reproduced by the RML method, that is, the method combining the partial response method and the maximum likelihood decoding method (Viterbi decoding method), S / N is corrected by error correction.
Can be improved. [Twenty-first Embodiment] In an optical disk recording / reproducing apparatus according to a twenty-first embodiment, as shown in FIG. 12, a phase change material and a protective layer are provided on an optical disk substrate made of polycarbonate or the like as an optical recording medium. Recording and reproduction are performed by generating near-field light using a near-field probe or a near-field slider head. In the present embodiment, the SiN protective layer 12 and the phase change material 13 are stacked and evaporated on the polycarbonate optical disk substrate 11. For example, the respective film thicknesses are such that the SiN protective layers above and below the recording layer are laminated to 20 nm, and the phase change material is laminated to 15 nm. A phase change material is a material that undergoes a phase change (a crystalline phase, an amorphous phase, or the like) by irradiating strong writing light. When stable multiple phases can change reversibly
It can be used as a Ram, or when it changes irreversibly, as a write-once recording medium. Further, any material may be used as long as contrast is generated in a plurality of phases in the transmitted light or the reflected light when irradiated with weak reading light. The contrast includes not only a difference in light intensity due to a change in absorbance or reflectance but also a contrast caused by a change in an optical constant such as rotation of a polarization plane or a change in birefringence. During recording, in the case of the present embodiment, near-field light or internally converging near-field light is incident from the recording layer side by a near-field probe or the like. Light can be incident from either the substrate side or the recording layer side of the medium, but FIG. 12 is a diagram when near-field light is incident from the recording layer side. Light emitted from the tip of the near-field probe temporarily becomes near-field light and enters the sample.
The light passes through the recording layer and is emitted as propagation light to the polycarbonate substrate side. Recording marks smaller than the diffraction limit of light can be formed on the data recording layer.

When an isolated bit is recorded on the recording layer of the optical disk, the signal output from the signal detection photodetector has a side lobe added to the spot of the detection light, so that a signal of the adjacent bit due to the spread of the spot is added. A readout waveform will be added. Therefore, the signal output from the optical pickup is subject to intersymbol interference from the adjacent bits, and the intersymbol interference makes it possible to detect the partial response method as described above.

As is clear from the above description, according to the twenty-first embodiment, an internal interference type projection or aperture for generating near-field light and a component for compensating for intersymbol interference during recording are provided. Since information provided on the phase change material layer of the optical disk is read out by providing the precoding means, the information read out by the side lobe of the light spot can be positively utilized. For this reason, it is not necessary to provide a slit or a condenser lens in the near-field optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified. [Twenty-second Embodiment] In an optical disk recording / reproducing apparatus according to a twenty-second embodiment, as shown in FIG. 13, a recording layer and a protective layer are provided on an optical disk substrate made of polycarbonate or the like as an optical recording medium. Recording and reproduction are performed by generating near-field light using a field probe or a near-field slider head. In the present embodiment, the SiN protective layer 12 and the recording layer 13 are stacked and evaporated on the polycarbonate optical disk substrate 11. In this embodiment, Ge2Sb2Te5, which is a phase change material, is used for the recording layer 13. This material has two states (crystal and amorphous) having different reflectivities at room temperature. By changing the condition of the light to be irradiated, the state can be freely changed, such as crystallization or amorphous state. Using this principle, it is possible to configure an optical memory that records data and reads out data based on the difference in reflectance. By using this material, high contrast S /
It is possible to obtain an optical disk recording / reproducing apparatus that can obtain a reproduction signal with a good N and has a high recording and holding capability. The thickness of each layer was 20 nm for the SiN protective layer above and below the recording layer, and 15 nm for the recording layer. At the time of recording, in the case of the present embodiment, near-field light, internally converging near-field light, or normal propagation light is incident from the recording layer side by a near-field probe or the like. Although light can enter from the substrate side of the medium or from the recording layer side, FIG. 13 shows a case where near-field light enters from the recording layer side. Light emitted from the tip of the near-field probe temporarily becomes near-field light and enters the sample. The light passes through the recording layer and is emitted as propagation light to the polycarbonate substrate side. Recording marks smaller than the diffraction limit of light can be formed on the data recording layer. The address information is formed in advance by a mark larger than the diffraction limit.

When an isolated bit is recorded on the recording layer of the optical disk, the signal output from the photodetector for signal detection has a side lobe added to the spot of the detection light, so that the signal of the adjacent bit due to the spread of the spot is added. A readout waveform will be added. Therefore, the signal output from the optical pickup is subject to intersymbol interference from the adjacent bits, and the intersymbol interference makes it possible to detect the partial response method as described above.

As is clear from the above description, according to the twenty-second embodiment, an internal interference type projection or aperture for generating near-field light and a component for compensating for intersymbol interference during recording are provided. Ge2Sb2Te on optical disc with precoding means
Since the information recorded in the recording layer 5 is read, the information read by the side lobe of the light spot can be positively utilized. For this reason, it is not necessary to provide a slit or a condenser lens in the near-field optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified. [Twenty-third Embodiment] In an optical disk recording / reproducing apparatus according to a twenty-third embodiment, as shown in FIG. 14, the recording layer of the optical recording medium according to the fifteenth embodiment has a phase change material of AgIn.
An SbTe layer is used. In this case, for example, the layer configuration of the disc is such that the SiN protective layer 12 is 10 nm above and below the recording layer,
Third, AgInSbTe has a configuration of 15 nm and a polycarbonate substrate. This material has two states (crystal and amorphous) having different reflectivities at room temperature. By changing the condition of the light to be irradiated, the state can be freely changed, such as crystallization or amorphous state. Using this principle, it is possible to configure an optical memory that records data and reads out data based on the difference in reflectance. By using this material, a reproduced signal with high contrast and good S / N can be obtained, and an optical disk recording / reproducing apparatus capable of stably storing recorded information for a long time can be obtained. Further, since silver is used for the recording layer, it has good adhesion to the substrate and is excellent in abrasion resistance. As the recording layer, a generally known optical recording material other than the above two examples can be used.

At the time of recording, in the case of the present embodiment, near-field light or internally converging near-field light is incident from the recording layer side by a near-field probe or the like. Although light can be incident from the substrate side of the medium or from the recording layer side, FIG. 14 is a diagram when near-field light is incident from the recording layer side. Light emitted from the tip of the near-field probe temporarily becomes near-field light and enters the sample. The light passes through the recording layer and is emitted as propagation light to the polycarbonate substrate side. Recording marks smaller than the diffraction limit of light can be formed on the data recording layer.

When an isolated bit is recorded on the recording layer of the optical disk, the signal output from the signal detection photodetector has a side lobe added to the spot of the detection light. A readout waveform will be added. Therefore, the signal output from the optical pickup is subject to intersymbol interference from the adjacent bits, and the intersymbol interference makes it possible to detect the partial response method as described above.

As is clear from the above description, according to the twenty-third embodiment, the internal interference type projection or aperture for generating near-field light and the inter-symbol interference for recording are compensated. AgInSbTe on optical disc with precoding means
Since the information recorded on the recording layer is read, the information read by the side lobe of the light spot can be positively utilized. For this reason, it is not necessary to provide a slit or a condenser lens in the near-field optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified. Twenty-fourth Embodiment In an optical disc recording / reproducing apparatus according to a twenty-fourth embodiment, as shown in FIG. 15, a phase-change material, a protective layer, and a non-linear optical disc are formed on an optical disc substrate made of polycarbonate or the like as an optical recording medium. Recording and reproduction are performed by generating light using the nonlinear optical material layer provided with the material layer as a mask. The generated light is near-field light, internally converging near-field light, or the like. In the present embodiment, the SiN protective layer 12, the phase change material 13, and the mask layer 15 of Sb are stacked and vapor-deposited on the polycarbonate optical disk substrate 11. For example, each film thickness is 20 nm for the SiN protective layer above and below the recording layer, and 15 nm for the phase change material.
A mask layer of m and Sb was 15 nm, and a 170 nm SiN protective layer was laminated between the Sb layer and the polycarbonate substrate. A phase change material is a material that undergoes a phase change (a crystalline phase, an amorphous phase, or the like) by irradiating strong writing light. If a plurality of stable phases can be changed reversibly, it can be used as Ram, and if it changes irreversibly, it can be used as a write-once recording medium. Further, any material may be used as long as contrast is generated in a plurality of phases in the transmitted light or the reflected light when irradiated with weak reading light. The contrast includes not only a difference in light intensity due to a change in absorbance or reflectance but also a contrast caused by a change in an optical constant such as rotation of a polarization plane or a change in birefringence.

At the time of recording, a laser beam condensed so as to focus on the Sb mask layer is incident from the substrate side as in a normal optical disk. At this time, the Sb mask layer in a region corresponding to the incident laser power becomes transparent, and a minute opening is formed. At this time, near-field light seeps into the recording layer from the formed minute opening, and a recording mark smaller than the diffraction limit of light can be formed.

For example, assuming that the minute opening diameter formed by the Sb mask layer is 50 nm, the recording layer of the surface recording type medium can be irradiated with a light spot of about 50 nm. Assuming that the pitch of the bits recorded on the optical disc is 20 nm, the signal output by the photodetector for signal detection in the optical pickup has a smaller aperture diameter than the bit diameter, so that the read waveforms of the bits adjacent to both sides of the read waveform respectively. Will be added. In particular, when a small aperture is formed using the Sb layer as a mask, the aperture is formed so as to trail behind the traveling direction of the beam spot as shown in FIG. Becomes Therefore, the signal output from this optical pickup is
This causes intersymbol interference from adjacent bits, and this intersymbol interference enables detection of the partial response method as described above.

As is clear from the above description, according to the twenty-fourth embodiment, near-field light is generated by a nonlinear optical material layer for generating a minute aperture, and intersymbol interference during recording is compensated. The information recorded on the phase change material layer of the optical disk is read using the precoding means for the optical disk, so that the information read by the side lobe of the light spot can be positively utilized. For this reason, it is not necessary to provide a slit or a condenser lens in the near-field optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified. [Twenty-fifth Embodiment] In an optical disc recording / reproducing apparatus according to a twenty-fifth embodiment, as shown in FIG. 16, an optical disc substrate 1 made of polycarbonate or the like is used as an optical recording medium.
A recording layer 13, a protective layer 12, and a non-linear optical material layer having a non-linear optical material layer provided thereon are used as a mask layer 13 to generate light to perform recording and reproduction. The generated light is near-field light, internally converging near-field light, or the like. Ge2Sb2Te5 which is a phase change material is used for the recording layer. This material has two states (crystal and amorphous) having different reflectivities at room temperature. By changing the condition of the light to be irradiated, the state can be freely changed, such as crystallization or amorphous state. Using this principle, it is possible to configure an optical memory that records data and reads out data based on the difference in reflectance. By using this material, a reproduction signal with high contrast and good S / N can be obtained, and an optical disk recording / reproducing apparatus having high recording / holding ability can be obtained. In the present embodiment, a SiN protective layer, a recording layer, and a mask layer of Sb are stacked and evaporated on a polycarbonate optical disk substrate. For example, the film thickness of each of the SiN protective layers above and below the recording layer was 20 nm, the recording layer was 15 nm, the Sb mask layer was 15 nm, and the SiN protective layer was 170 nm between the Sb layer and the polycarbonate substrate.

At the time of recording, a laser beam condensed so as to focus on the Sb mask layer from the substrate side is incident as in a normal optical disk. At this time, the Sb mask layer in a region corresponding to the incident laser power becomes transparent, and a minute opening is formed. At this time, near-field light seeps into the recording layer from the formed minute opening, and a recording mark smaller than the diffraction limit of light can be formed.

For example, assuming that the fine opening diameter formed by the Sb mask layer is 50 nm, the recording layer of the surface recording type medium can be irradiated with a light spot of about 50 nm. Assuming that the pitch of the bits recorded on the optical disc is 20 nm, the signal output by the photodetector for signal detection in the optical pickup has a smaller aperture diameter than the bit diameter, so that the read waveforms of the bits adjacent to both sides of the read waveform respectively. Will be added. In particular, when a small aperture is formed using the Sb layer as a mask, the aperture is formed so as to trail behind the traveling direction of the beam spot as shown in FIG. Becomes Therefore, the signal output from this optical pickup is
This causes intersymbol interference from adjacent bits, and this intersymbol interference enables detection of the partial response method as described above.

As is clear from the above description, according to the twenty-fifth embodiment, near-field light is generated by a nonlinear optical material layer for generating a minute aperture, and intersymbol interference during recording is compensated. The information recorded on the Ge2Sb2Te5 recording layer of the optical disk is read using the precoding means for reading the information, so that the information read by the side lobe of the light spot can be positively utilized. For this reason, it is not necessary to provide a slit or a condenser lens in the near-field optical disk pickup in order to exclude information read by the side lobe, and the configuration of the optical pickup can be simplified. [Twenty-Sixth Embodiment] In an optical disc recording / reproducing apparatus according to a twenty-sixth embodiment, as shown in FIG. 17, an optical disc substrate 1 made of polycarbonate or the like is used as an optical recording medium.
A recording layer 13, a protective layer 12, and a nonlinear optical material layer having a nonlinear optical material layer provided thereon are used as a mask layer 13 to generate light and perform recording and reproduction. The generated light is near-field light, internally converging near-field light, or the like. Further, AgInSbTe which is a phase change material is used for the recording layer. This material has two states (crystal and amorphous) having different reflectivities at room temperature.
By changing the condition of the light to be irradiated, the state can be freely changed, such as crystallization or amorphous state. Using this principle, it is possible to configure an optical memory that records data and reads out data based on the difference in reflectance. By using this material, high contrast S
An optical disk recording / reproducing apparatus which can obtain a reproduced signal having a good / N and can stably store recorded information for a long time can be obtained. Further, since silver is used for the recording layer, it has good adhesion to the substrate and is excellent in abrasion resistance. As the recording layer, a generally known optical recording material other than the above two examples can be used.

In the present embodiment, a SiN protective layer, an AgInSbTe recording layer, and a mask layer of Sb are stacked and evaporated on a polycarbonate optical disk substrate. For example, each film thickness is 10 nm for the ZnS-SiO2 protective layer above and below the recording layer, 15 nm for the recording layer, 15 nm for the Sb mask layer, and Si between the Sb layer and the polycarbonate substrate.
An N protective layer of 120 nm was laminated.

At the time of recording, a laser beam condensed so as to focus on the Sb mask layer is incident from the substrate side as in a normal optical disk. At this time, the Sb mask layer in a region corresponding to the incident laser power becomes transparent, and a minute opening is formed. At this time, near-field light seeps into the recording layer from the formed minute opening, and a recording mark smaller than the diffraction limit of light can be formed.

For example, assuming that the minute opening diameter formed by the Sb mask layer is 50 nm, the recording layer of the surface recording type medium can be irradiated with a light spot of about 50 nm. Assuming that the pitch of the bits recorded on the optical disk is 20 nm, the signal output from the photodetector for signal detection in the optical pickup has a smaller aperture diameter than the bit diameter, so that the read waveforms of the bits adjacent to both sides of the read waveform respectively. Will be added. In particular, when a small aperture is formed using the Sb layer as a mask, the aperture is formed so as to trail behind the traveling direction of the beam spot as shown in FIG. Becomes Therefore, the signal output from this optical pickup is
This causes intersymbol interference from adjacent bits, and this intersymbol interference enables detection of the partial response method as described above.

As is clear from the above description, according to the twenty-sixth embodiment, near-field light is generated by a nonlinear optical material layer for generating a minute aperture to compensate for intersymbol interference during recording. The information recorded on the AgInSbTe recording layer of the optical disc by using the precoding means for the optical disc, the information read by the side lobe of the light spot can be positively utilized. Therefore, in order to exclude information read by the side lobe,
There is no need to provide a slit, a condenser lens, or the like in the near-field optical disk pickup, and the configuration of the optical pickup can be simplified.

In the above embodiment, the case where the SiN protective layer is used as the protective layer has been described. However, the present invention is not limited to this. For example, the present invention can be applied to the case of a ZnS-SiO2 protective layer.

In the above embodiment, the phase change type optical recording system has been mainly described. However, the present invention is similarly applicable to other rewritable or write-once optical disks or read-only optical disks. Can be. In a rewritable or write-once optical disc recording / reproducing apparatus, the same type of recording can be performed by controlling the laser beam intensity of a semiconductor laser as in the phase change type. Furthermore, in the case of a read-only optical disk, recording in a similar format is performed when a master for forming pits and the like is created.

In the above embodiment, a phase-change type optical disk has been described. However, the present invention can be similarly applied to an optical modulation type or magnetic field modulation type magneto-optical recording / reproducing apparatus. In a light modulation type magneto-optical recording / reproducing device,
As in the case of the phase change type optical disk recording method, the same type of recording can be performed by controlling the laser beam intensity of the semiconductor laser for writing. In the case of the magnetic field modulation type, the same type of recording can be performed by controlling the magnetic field of the electromagnet while the semiconductor laser irradiates the vertical straight film with strong light.

[0178]

As described above, according to the present invention,
It is possible to provide an optical disk recording / reproducing apparatus which enables optical recording at a high density while suppressing an error rate at the time of reading information and enables stable recording or reproduction.

[Brief description of the drawings]

FIG. 1 is a block diagram of the operation principle of a DVD.

FIG. 2 is an example of a diagram showing a relationship between bit spots and marks.

FIG. 3 is an example of a diagram showing a relationship between a micro aperture and a bit in a beam spot.

FIG. 4 is an example of a diagram when light is incident from the recording layer side.

FIG. 5 is an example of a block diagram of an optical disc recording / reproducing apparatus according to the first and fourteenth embodiments.

FIG. 6 is an example of a circuit of a transversal filter.

FIG. 7 is an example of a diagram showing a slider head portion of the optical disc recording and reproducing apparatus according to the second and fifteenth embodiments.

FIG. 8 is an example of a block diagram of an optical disc recording / reproducing apparatus according to the third and sixteenth embodiments.

FIG. 9 is an example of a block diagram of an optical disk recording / reproducing device according to a fourth or a 17th embodiment;

FIG. 10 is an example of a block diagram of a Viterbi decoder.

FIG. 11 shows fifth, sixth, seventh, eighteenth, nineteenth, and twentieth.
FIG. 3 is an example of a diagram for explaining recording and reproduction of the optical disk recording / reproduction device according to the embodiment.

FIG. 12 is an example of a diagram for explaining recording and reproduction by the optical disk recording and reproduction devices according to the eighth and twenty-first embodiments.

FIG. 13 is an example of a diagram for explaining recording and reproduction by the optical disk recording and reproduction devices according to the ninth and twenty-second embodiments.

FIG. 14 is an example of a diagram for explaining recording and reproduction by the optical disk recording and reproduction devices according to the tenth and twenty-third embodiments.

FIG. 15 is an example of a diagram for explaining recording and reproduction by the optical disk recording and reproduction devices according to the eleventh and twenty-fourth embodiments.

FIG. 16 is an example of a diagram for explaining recording and reproduction of the optical disk recording and reproduction devices according to the twelfth and twenty-fifth embodiments.

FIG. 17 is an example of a diagram for explaining recording and reproduction by the optical disc recording and reproducing device according to the thirteenth and twenty-sixth embodiments.

FIG. 18 is a diagram illustrating an example of an optical fiber probe according to a fourteenth embodiment.

FIG. 19 is a diagram for explaining a relationship between light intensity and a distance from a focal position.

FIG. 20 is a diagram for explaining that read waveforms of bits adjacent to each other are added to both sides of the read waveform of the main spot.

FIG. 21 is a diagram for describing a case where an input data sequence {am} is written.

FIG. 22 is a state transition diagram of PR (1, 2, 1) (PR2).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Base plate 12 Protective layer 13 Data recording layer 15 Mask layer 21 Controller 22 Spindle motor 23 Recording data generation unit 24 Optical pickup 25 Clock 26 Equalization circuit 27 A / D converter 28 Decoder 29 Media 30 Clock generation unit 31 Delay element T32 Weight coefficient multiplier 33 Adder 34 Viterbi decoder 40 ACS unit 41 Branch metric calculation circuit 42 Addition / comparison / selection unit 50 Path memory circuit 51 MLD circuit (most likely path selection unit) 60 Core 61 Clad 62 Light-shielding covering layer 63 Slope 110 LD (Laser Diode) Driver 111 Optical Disk 114 Reproduction Signal Processing System 120 Optical Head 121 LD 122 Collimator Lens 123 PBS 124 Objective Lens 125 Condensing Lens 126 Light Extractor (Photo Detector) 126

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G11B 20/10 301 G11B 20/10 301Z 341 341B 341Z 20/18 534 20/18 534A 570 570F 572 572C 574 574A

Claims (13)

[Claims] 1. An optical pickup comprising: a light spot forming means for forming a spot smaller than a diffraction limit of light on an optical disc; and an information reproducing means for reproducing a recorded information sequence recorded on the optical disc by using the light spot. And receiving an information sequence input from the outside, adding inter-symbol interference at the time of recording to the information sequence, and then, for each unit information of the information sequence to which the inter-symbol interference at the time of recording is added, the information sequence An optical disc recording / reproducing apparatus comprising: a precoding means for converting the information sequence into the recording information sequence by calculating a remainder according to the radix of the recording information sequence. An optical disc recording / reproducing apparatus characterized in that it is configured to compensate for intersymbol interference added when a is reproduced. 2. The light spot forming means according to claim 1, wherein a minute opening for generating said light spot is provided at a tip of a head, a slider or a probe close to said optical disk, and said minute opening is used as said light spot forming means. An optical disk recording / reproducing apparatus according to claim 1. 3. A unit information of a reproduction information sequence obtained by adding intersymbol interference added when the recording information sequence is reproduced to the recording information sequence, according to a radix of the input information sequence. 3. The optical disk recording / reproducing apparatus according to claim 2, further comprising decoding means for calculating a remainder. 4. A unit information of a reproduction information sequence obtained by adding intersymbol interference added when the recording information sequence is reproduced to the recording information sequence,
3. The optical disk recording / reproducing apparatus according to claim 2, further comprising a decoding unit using an RML system, wherein the decoding unit includes a maximum likelihood decoder that performs decoding using a maximum likelihood decoding system. 5. A light spot forming means, wherein a recording layer and a non-linear optical material layer are provided on the optical disc substrate, and a minute aperture for generating the light spot formed using the non-linear optical material layer as a mask is used as the light spot forming means. 2. The method according to claim 1, wherein
An optical disk recording / reproducing apparatus according to the above. 6. A unit information of a reproduction information sequence obtained by adding intersymbol interference added when the recording information sequence is reproduced to the recording information sequence, based on a radix of the input information sequence. 6. The optical disk recording / reproducing apparatus according to claim 5, further comprising decoding means for calculating a remainder. 7. A light spot forming means for irradiating an optical disk with a light spot composed of a main spot smaller than a diffraction limit of light and a pair of side lobes formed on both sides of the main spot, and using the light spot. An optical pickup having information reproducing means for reproducing a recorded information sequence recorded on the optical disc; receiving an information sequence inputted from the outside; adding intersymbol interference during recording to the information sequence; For each unit information of the information sequence to which the intersymbol interference has been added, a precoding means for converting the information sequence into the recording information sequence by calculating a remainder based on the radix of the information sequence. An optical disc recording / reproducing apparatus, wherein the intersymbol interference at the time of recording compensates for intersymbol interference added when the recording information sequence is reproduced. Optical disk recording and reproducing apparatus. 8. An internal interference type projection or opening for generating said light spot is provided at the tip of a head, slider or probe close to said optical disk, and said projection or opening is used as said light spot forming means. The optical disk recording / reproducing apparatus according to claim 7, wherein: 9. The unit information of a reproduction information sequence obtained by adding intersymbol interference added when the recording information sequence is reproduced to the recording information sequence, according to a radix of the input information sequence 9. The optical disk recording / reproducing apparatus according to claim 8, further comprising decoding means for calculating a remainder. 10. Each unit information of a reproduction information sequence obtained by adding intersymbol interference added when the recording information sequence is reproduced to the recording information sequence,
9. The optical disk recording / reproducing apparatus according to claim 8, further comprising a decoding unit based on the PRML system, wherein the decoding unit includes a maximum likelihood decoder for performing decoding using a maximum likelihood decoding system. 11. A light spot forming means, wherein a recording layer and a non-linear optical material layer are provided on the optical disk substrate, and a minute aperture for generating the light spot is formed using the non-linear optical material layer as a mask. 8. The method according to claim 7, wherein
An optical disk recording / reproducing apparatus according to the above. 12. The unit information of a reproduced information sequence obtained by adding intersymbol interference added when the recorded information sequence is reproduced to the recorded information sequence, according to a radix of the input information sequence. 12. The optical disk recording / reproducing apparatus according to claim 11, further comprising decoding means for calculating a remainder. 13. The unit information of a reproduction information sequence obtained by adding intersymbol interference added when the recording information sequence is reproduced to the recording information sequence,
12. The optical disk recording / reproducing apparatus according to claim 11, further comprising a decoding unit based on a PRML system, wherein the decoding unit includes a maximum likelihood decoder performing decoding using a maximum likelihood decoding system.