JP2600905B2 - Optical recording / reproducing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing method according to a high recording density method in an optical disc device.

[Conventional technology]

In the optical recording / reproducing method of a magneto-optical disk, which represents an erasable disk in particular, the information recording method involves focusing and irradiating a recording medium made of a magnetic thin film with a laser beam, and as a change in magnetization on the recording medium. This is performed by thermomagnetic recording for recording information.

That is, an external magnetic field is applied vertically to the entire surface of the recording layer in advance to magnetize the recording layer so as to have an upward magnetization, write “0”, and then apply a laser beam to the portion where “1” is written. Irradiate and heat. Heated minute portion becomes small coercive force H _c, the previously applied in the direction facing downward magnetization weak external bias magnetic field when the laser beam irradiation, the magnetization reversal to "1" is recorded. A method of forming a magnetic recording pattern is adopted depending on whether or not the laser beam is irradiated, that is, whether or not the temperature of the minute spot irradiated on the recording layer is raised.

On the other hand, information is read out by, for example, irradiating a magnetic recording pattern with a linearly polarized laser beam by rotating the plane of polarization of the reflected light or transmitted light (called the magnetic Kerr effect and the magnetic Faraday effect, respectively). Since the recording layer has a recording layer, for example, when utilizing the magnetic Kerr effect, the reflected light is transmitted to the photodetector by utilizing that the rotation angle θ _k of the polarization plane of the reflected light varies depending on the direction of the recording magnetization. Before entering, the information corresponding to the direction of magnetization is read out as a change in the amount of light through an analyzer.

That is, in the conventional information reading method in such a magneto-optical disk device, the area on the recording medium surface changes to a light or dark area (hereinafter referred to as a recording pit) due to a change in magnetization. This is basically a method in which a reproduction signal is read out by detecting a change in the total amount of light reflected by recording pits in an optical disk device of a reflectance change type. Such detection methods include those using a single photodetector,
There is a differential detection method or the like in which light beams deflected by the deflection beam splitter into two light beams are received by two photodetectors, respectively, and the output difference is obtained.

At this time, for reproduction identification of digital information, a slice level is provided near the middle point of the read signal amplitude, and recording pit information is pulsed from the recording pit train. At the same time, the peak value is detected corresponding to “0” and “1” of the read waveform, and the pattern of “0” and “1” is determined based on the timing relationship between the bit information and the reproduction clock determined by various modulation methods. The data is being reproduced.

[Problems to be solved by the invention]

In the above-described information recording / reproducing method in the conventional magneto-optical disk device, the intensity distribution of the read laser spot focused on the recording medium surface has a broadness (Gaussian beam), so that the intensity change of the reflected light is steep. It does not become something. Therefore, when the recording density increases, the interference between recording pits (hereinafter, referred to as intersymbol interference) at the time of reading increases, causing a decrease in the SN ratio and an increase in the bit error rate. That is, for example, as shown in the upper part of FIG. 6, when the recording pits 61 recorded on the recording medium surface approach each other to the vicinity of the diameter of the reproducing laser spot 62 and are recorded at a high density, FIG. As shown in the lower diagram, the read signal between the recording pits changes from a solid line to a dotted line. The reproduction resolution at this time is represented by B / A. In order to actually identify the information, a slice level is provided near the midpoint of the read signal amplitude in consideration of the phase margin, and the information is reproduced. Therefore, when the reproduction resolution is smaller than 0.5, the reproduction noise, the reproduction light power fluctuation, the recording medium There is a drawback that information cannot be reproduced stably due to the influence of reflectance fluctuation and the like.

At the same time, the read waveform is distorted, which disturbs the reproduction timing of the recorded information, lowers the phase margin of the magneto-optical disk device, and lowers the bit error rate.

On the other hand, recording / reproducing conditions such as individual variations of the characteristics of the head system and the media system and non-uniformity of the characteristics of the medium film differ according to the medium interchangeability which is a characteristic of the magneto-optical disk. Therefore, it has a drawback that the device performance cannot be sufficiently exhibited.

Since the conventional optical recording / reproducing method has the above-mentioned drawbacks, there is a great limitation in increasing the recording density, which narrows the application of the magneto-optical disk device. This is the same for an optical disk device of a reflectance change type.

An object of the present invention is to improve the above-mentioned drawbacks and adaptively control recording / reproducing conditions, so that a reproduced signal can be kept stable and good in quality, and the recording density can be improved to twice or more the conventional one. An object of the present invention is to provide an optical recording / reproducing method.

[Means for solving the problem]

The present invention relates to an optical recording / reproducing system which uses a laser as a light source and records / reproduces data using a pit array, and in which a system including a recording system and a reproducing system can be regarded as a partial response digital transmission path. In the recording side, a modulation encoder for modulating source data into binary data, a recording-side equalizer for producing binary intermediate sequence data to suppress error propagation in a recording / reproducing system, and a semiconductor laser driving circuit A reproducing amplifier, a waveform equalizer for identifying the binary intermediate sequence data from the multi-valued signal read out against the recording side equalizer, and a waveform equalizer on the reproducing side. An equalizer controller that adaptively controls tap coefficients of a waveform equalizer so as to automatically set the characteristics of an equalizer to an optimal state; and the source data from the identified binary intermediate sequence data. Demodulation code to play And a vessel, and performing recording and reproduction of the multi-level signal.

In the present invention, the recording-side equalizer can be constituted by a modulo addition circuit.

Further, the waveform equalizer can be configured by a multi-level level determination system having variable taps corresponding to the equalizer control device and a modulo addition circuit.

Also, the multi-level decision system of the waveform equalizer can be composed of a reproduced waveform equalization filter having a variable tap system and a multi-level level discriminator.

[Action]

According to the present invention, the recording density can be improved to twice or more the conventional one by positively utilizing the intersymbol interference at the time of reproduction which occurs when the recording density becomes high.

In addition, since it is possible to adaptively compensate for the deterioration of the reproduction characteristics due to the characteristic variation of the magneto-optical disk medium or the head system or the change with time, stable and high-quality recording and reproduction can be always performed.

On the other hand, it is also possible to suppress error propagation that occurs at the time of recording and reproduction, and it is possible to realize high density without lowering the error rate.

〔Example〕

FIG. 1 is a block diagram showing a first embodiment of the present invention. In the present embodiment, a semiconductor laser is used as a light source, an optical disk system that performs recording and reproduction using a pit array, and a system including a recording system and a reproduction system is referred to as a duobinary transmission line, which is a kind of a partial response digital transmission line. A description will be given of a magneto-optical disk system as an erasable medium among recording / reproducing systems which can be regarded as an example.

On the magneto-optical recording side, for example, a modulation encoder 1 that modulates source data into binary data, and a modulo 2 that produces binary intermediate sequence data to suppress error propagation in a recording / reproducing system.
A recording equalizer including an adder circuit 2 and an LD (semiconductor laser) drive circuit 3 are provided. That is, in the recording process, the source data is passed through the modulation encoder 1 and the encoded recording data is converted into intermediate sequence data through the modulo-2 addition circuit 2 which is a recording-side equalizer, and the semiconductor laser is driven by the LD driving circuit 3. The information is recorded on a recording medium in the form of a recording pit row by a recording / reproducing head using the light source as a light source. Note that a system including a semiconductor laser, a recording / reproducing head, and a recording medium is indicated by a recording / reproducing analog system 4.

FIG. 3A shows an example of data conversion when there is no recording-side equalizer, and FIG. 3B shows an example of data conversion when there is a recording-side equalizer. As shown in FIG. 3 (a), if reproduced data is erroneously reproduced due to noise or the like during recording / reproducing, error propagation of data occurs after demodulation. On the other hand, as shown in FIG. 3 (b), by converting the information sequence, which is the recording data, into the intermediate sequence data by the recording-side equalizer, the bit reading error due to noise or the like in the recording / reproducing system is reduced. Propagation (referred to as error propagation) can be greatly improved. At this time, the recording pit sequence recorded on the recording medium surface is, of course, a binary digital information sequence. However, at the time of reading, as described above, interference between codes causes distortion of the readout signal waveform and a decrease in resolution. Let it. In the present invention, a ternary recording / reproducing system is configured by actively using this intersymbol interference.

On the reproducing side, a read amplifier 5 attached to the recording / reproducing head in the recording / reproducing analog system 4 and a ternary level for identifying the binary intermediate sequence data from the ternary signal read by the read amplifier. A waveform equalizer composed of a decision system 6 and a modulo-2 addition circuit 8, an equalizer control device 7 for adaptively controlling tap coefficients of the waveform equalizer, and a source data sequence from the binary intermediate sequence And a demodulation encoder 9 for reproducing.

At this time, the ternary level determination system 6 of the waveform equalizer includes a reproduced waveform equalization filter having variable taps and a ternary level discriminator. Here, a reproduction clock is simultaneously generated by a ternary level discriminator for discriminating binary intermediate sequence data from the ternary signal. At this time, the equalizer control device 7
For example, the tap coefficient of the reproduced waveform equalization filter is adaptively controlled so that the square error of the average power between the intermediate data sequence demodulated by the mean square error method and the source information data sequence is minimized. In this adaptive control, besides the method of performing equalization of the sequential read data, a method of providing a preamble period in the head area of the sector portion as a training period, for example, or a method of providing a preset area of several tracks as a training period. This is a configuration that optimizes the equalization characteristics.

FIG. 4 is a diagram for explaining the principle of reading according to the present invention. Here, a recording pit sequence recorded with binary information is ternarized by intersymbol interference and read. Unlike the conventional method, the slice level of the read signal is set to two levels, as shown in FIG. 4D, as shown in FIG. At this time, the identification at each slice level corresponds to “1”, “0”, and “1”, respectively. At the same time, a peak value is detected corresponding to "1", "0", and "1" of the read waveform, and the timing relationship between the bit information and the reproduction clock is obtained. As shown in FIGS. 4 (e), (f), and (g), the information sequence pulsed at each slice level is converted into an original binary intermediate data sequence by a timing with a sampling clock as a data identification window. Will be converted. At this time, the equalizer controller 7 controls the tap coefficients of the reproduced waveform equalization filter so as to minimize the mean square error between the demodulated intermediate data sequence and the source information data sequence. The intermediate data sequence, which is a demodulated signal optimized by the adaptive control in this manner, is reproduced through the demodulation encoder 9 into a source data sequence.

FIG. 5 shows a power spectrum of the partial response system of this embodiment. As shown in the figure, it can be achieved with half the bandwidth as compared with the conventional method of reading binary recorded data as binary data. Therefore, twice as much information can be recorded and reproduced as compared with the conventional method.

FIG. 2 shows a second embodiment according to the optical recording / reproducing method of the present invention. The difference from the first embodiment according to the present invention resides in that the read-out analog level equalizing filter 10 is inserted on the reproducing side, and has a role of correcting waveform distortion in a recording / reproducing analog system into a duobinary transmission path. It is a configuration that is performed.
This configuration facilitates correction of waveform distortion due to recording power dependence in the recording / reproducing system and waveform distortion in the reproducing amplifier system, and realizes a partial response type equalizing filter.

In each of the above embodiments, an example of a multilevel signal detection system in a basic magneto-optical disk using a partial response system by adaptive control is shown using a duobinary code, but various partial response codes may be used. Good.
In that case, the recording-side equalizer and the reproduction-side equalizer can be handled by using an N-element modulo addition circuit. In addition,
The recording-side equalizer may additionally include a compensation circuit for pre-equalizing the recording timing and the like in consideration of the thermomagnetic characteristics of the recording pit shape in the recording / reproducing analog system.

In the present invention, magneto-optical recording has been described as an example, but it is needless to say that a partial response type system can also be used in an optical disk system using a reflectance-change medium such as a write-once type.

〔The invention's effect〕

As described above, the optical recording / reproducing method of the present invention can increase the information recording density to twice or more of the conventional one and improve the information transfer rate by positively utilizing the intersymbol interference, It can expand the application range of the optical disk. In addition, since the propagation of bit errors is suppressed, there is an effect that unstable elements such as bit drops occurring at the analog level of the optical disk system are eliminated, and the overall bit error rate can be reduced.

Further, according to the present invention, it is possible to adaptively compensate for the deterioration of the reproduction characteristics due to the characteristic variation of the optical disk medium or the head system, the aging, etc., so that stable and high-quality recording and reproduction can be always performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the optical recording / reproducing system of the present invention, FIG. 2 is a block diagram showing a second embodiment of the optical recording / reproducing system of the present invention, and FIG. FIG. 4 is a diagram for explaining an example of data conversion according to the optical recording / reproducing method, FIG. 4 is a diagram for explaining the principle of reading according to the present invention, and FIG. 5 is a power spectrum of a partial response method according to the present invention FIG. 6 is a diagram for explaining the intersymbol interference according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Modulation encoder 2 ... Modulo 2 addition circuit 3 ... LD drive circuit 4 ... Recording / reproducing analog system 5 ... Read-out amplifier 6 ... Ternary level determination system 7 ... Equalizer control device 8 ... Modulo-2 addition circuit 9 Demodulation encoder 10 Equalization filter

Claims (4)

(57) [Claims] 1. An optical recording / reproducing system for recording / reproducing data using a pit array by using a laser as a light source, wherein the system including the recording system and the reproducing system can be regarded as a partial response type digital transmission path. In the system, the recording side includes a modulation encoder that modulates source data into binary data, a recording side equalizer that produces binary intermediate sequence data to suppress error propagation in a recording / reproducing system, and a semiconductor laser drive. A reproducing amplifier, a waveform equalizer for identifying the binary intermediate sequence data from the multi-valued signal read out against the recording-side equalizer, Controller for adaptively controlling the tap coefficients of the waveform equalizer so as to automatically set the characteristics of the equalizer to an optimum state, and the source data from the identified binary intermediate sequence data. Play demodulation A issue unit, the optical recording and reproducing system, characterized in that for recording and reproducing multi-valued signals. 2. An optical recording / reproducing method according to claim 1, wherein said recording-side equalizer comprises a modulo addition circuit. 3. The optical recording / reproducing method according to claim 1, wherein said waveform equalizer comprises a multi-value level determination system having a variable tap corresponding to said equalizer control device, and a modulo addition circuit. Characteristic optical recording / reproducing method. 4. The optical recording / reproducing method according to claim 3, wherein the multi-value level determination system of the waveform equalizer comprises a reproduced waveform equalizing filter having variable taps and a multi-value level discriminator. Optical recording / reproducing method.