JPH02312018A - Optical recording and reproducing system - Google Patents

Abstract

PURPOSE:To maintain a reproducing signal to be stable, to maintain the quality thereof to be excellent and to improve recording density by positively using interference between codes at a reproducing time which occurs when the recording density becomes high. CONSTITUTION:In the process of recording, storage data encoded by passing original data through a modulation encoder 1 is converted into intermediate serial data through a modulo 2 addition circuit 2 being an equalizer on a recording side and information is recorded on a recording medium in the form of a recording bit with a recording and reproducing head whose light source is a semiconductor laser by an LD driving circuit 3. On the other hand, at the time of reproducing, data read out by a recording and reproducing analog system 4 passes through a read-out amplifier 5. Then, the intermediate serial data of binary level is discriminated from a signal of ternary level read out by a ternary level decision system 6 and the equivalent characteristic thereof is controlled to be optimum by an equalizer controller 7. The optimized demodulation signal is reproduced to an original data series through a modulo 2 addition circuit 8 and a demodulation encoder 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording/reproducing method related to a high recording density method in an optical disc device.

[Conventional technology]

In the optical recording and reproducing method of magneto-optical disks, which represent especially erasable disks among optical recording and reproducing, information is recorded by condensing a laser beam onto a recording medium made of a magnetic thin film, and detecting changes in magnetization on the recording medium. This is done by thermomagnetic recording, which records information.

That is, an external magnetic field is applied perpendicularly to the entire surface of the recording layer in advance so that the recording layer is magnetized upward.

After magnetizing the layer and writing "0", a laser beam is spot-wise irradiated onto the part where "l" is to be written to heat it. The coercive force H0 of the heated minute portion becomes small, and when a weak external bias magnetic field is applied in the direction of downward magnetization during laser beam irradiation, the magnetization is reversed and "l" is recorded. A method is used to form a magnetic recording pattern depending on whether or not a laser beam is irradiated, that is, whether or not the temperature of a minute spot irradiated onto a recording layer is raised or not.

On the other hand, the method of reading information uses the effect of rotating the plane of polarization of reflected or transmitted light (called magnetic Kerr effect and magnetic Faraday effect, respectively) when a magnetic recording pattern is irradiated with a linearly polarized laser beam, for example. For example, when using the magnetic Kerr effect, the reflected light is directed to a photodetector by utilizing the fact that the rotation angle θ of the polarization plane of the reflected light differs depending on the direction of recording magnetization. Before entering, it is passed through an analyzer and information corresponding to the direction of magnetization is read out as changes in the amount of light.

That is, in the conventional method of reading information in such a magneto-optical disk device, an area where magnetization has changed on the surface of a recording medium becomes a bright or dark area (hereinafter referred to as a recording bit). This is basically equivalent to a method in which a reproduced signal is read out by detecting a change in the amount of light reflected from a recording pit in a reflectance change type optical disk device. Such detection methods include those that use a single photodetector, and those that use two photodetectors to receive a beam split into two polarized beams by a polarizing beam splitter, and then calculate the difference between the outputs. There are motion detection methods, etc.

At this time, to identify the playback of digital information, a slice level is set near the midpoint of the read signal amplitude, and the recorded pit information is pulsed from the recorded pit string. Detect the peak value using
The pattern of "0" and "l" is determined from the timing relationship between the bit information and the reproduction clock determined by various modulation methods, and the information of the source data is reproduced.

(Problems to be Solved by the Invention) In the information recording and reproducing method in the conventional magneto-optical disk device described above, the intensity distribution of the reading laser spot focused on the recording medium surface has a spread (Gaussian beam). Therefore, as the recording density increases, the interference between recording pits (hereinafter referred to as code amount interference) increases, which causes a decrease in the S/N ratio. For example, as shown in the upper diagram of FIG.
When high-density recording is performed with the bits approaching each other to near the diameter of the laser spot 62 for reproduction, the read signal between the recorded bits changes from a solid line to a dotted line, as shown in the lower part of FIG. The reproduction resolution at this time is expressed as B/A. In order to actually identify information, information is reproduced by setting a slice level near the midpoint of the read signal amplitude in consideration of the phase margin, so if the reproduction resolution is less than 0.5, reproduction noise, reproduction optical power fluctuations, and recording This method has the disadvantage that information cannot be stably reproduced due to changes in the reflectance of the medium.

Furthermore, since the read waveform is distorted at the same time, the reproduction timing of recorded information is disturbed, the phase margin of the magneto-optical disk device is reduced, and the pit error rate is reduced.

On the other hand, due to the medium exchangeability that is a feature of magneto-optical disks, recording and reproducing conditions differ, such as individual variations in the characteristics of the head system and medium system and non-uniformity in the characteristics of the medium film. Therefore, it has drawbacks such as not being able to fully demonstrate the device performance.

Conventional optical recording and reproducing systems have the above-mentioned drawbacks, and therefore are severely restricted in increasing the recording density, which limits the applications of magneto-optical disk devices. This also applies to reflectance change type optical disc devices.

The purpose of the present invention is to improve the above-mentioned drawbacks and adaptively control the recording and reproducing conditions, thereby keeping the reproduced signal stable and of good quality, and increasing the recording density to more than twice that of the conventional one. The objective is to provide an optical recording and reproducing method.

[Means to solve the problem]

The present invention relates to an optical recording and reproducing system that uses a laser as a light source and performs recording and reproducing using a bit string, and in which the system including the recording system and reproducing system can be regarded as a partial response type digital transmission path. On the recording side, there is a modulation encoder that modulates source data into binary data, a recording side equalizer that creates binary intermediate series data to suppress error propagation in the recording/reproduction system, and a semiconductor laser drive circuit. The reproduction side includes a readout amplifier, a waveform equalizer that opposes the recording side equalizer and identifies the binary intermediate series data from the read multilevel signal, and the waveform equalizer. The present invention is characterized in that it includes a vase control device that adaptively controls the tap coefficients of the vase, and a demodulation encoder that reproduces the source data, and performs recording and reproducing of multilevel signals.

In the present invention, the recording side equalizer can be constructed from a modulo addition circuit.

Further, the waveform equalizer can be constructed from a multilevel level determination system having variable taps compatible with the equalizer control device and a modulo addition circuit.

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

[Effect]

According to the present invention, the recording density can be increased to more than twice that of the conventional method by actively utilizing the code amount interference during reproduction that occurs when the recording density is high.

In addition, it is possible to adaptively compensate for deterioration in reproduction characteristics due to variations in characteristics of the magneto-optical disk medium and head system, changes over time, etc., so stable and high-quality recording and reproduction is always possible.

On the other hand, it is also possible to suppress error propagation that occurs during recording and reproduction, and high density can be achieved without reducing the error rate.

〔Example〕

FIG. 1 is a block diagram showing a first embodiment of the present invention. In this example, the optical disc system uses a semiconductor laser as a light source and records and plays back using a pit train, and the system including the recording system and playback system is a duobinary transmission line, which is a type of partial response digital transmission line. Among the recording and reproducing systems that can be considered, a magneto-optical disk system, which is an erasable medium, will be explained as an example.

On the magneto-optical recording side, it is composed of, for example, a modulation encoder 1 that modulates source data into binary data, and a modulo-2 addition circuit 2 that creates binary intermediate series data to suppress error propagation in the recording/reproducing system. It includes a recording side equalizer and an LD (semiconductor laser) drive circuit 3. That is, in the recording process, the source data is passed through the modulation encoder l, and the encoded recording data is sent to the modulo 2 addition circuit 2, which is the recording side equalizer.
The information is converted into intermediate series data via the LD drive circuit 3, and the information is recorded on the recording medium in the form of a recording pit string by a recording/reproducing head using a semiconductor laser as a light source. Note that a system including a semiconductor laser, a recording/reproducing head, and a recording medium is shown as a recording/reproducing analog system 4.

FIG. 3(a) shows an example of data conversion without a recording equalizer, and FIG. 3(b) shows an example of data conversion with a recording equalizer. Third
As shown in Figure (a), if reproduced data is erroneously reproduced due to noise during recording and reproduction, error propagation of the data occurs after demodulation.

In contrast, as shown in Figure 3(b), by converting the information sequence, which is recorded data, into intermediate sequence data using the recording side equalizer, bit reading errors due to noise in the recording/reproducing system can be avoided. Propagation (referred to as error propagation) can be significantly improved. At this time, the recording pit string recorded on the surface of the recording medium is of course a binary digital information string, but during readout, as mentioned above, interference between symbols causes distortion of the readout signal waveform and a decrease in resolution. . In the present invention, a ternary recording and reproducing system is constructed by actively using this code amount interference.

On the other hand, on the playback side, there is a readout amplifier 5 attached to the recording/playback head in the recording/playback analog system 4, and a ternary amplifier that identifies the binary intermediate series data from the ternary signal read out by the readout amplifier. a waveform equalizer composed of a bell determination system 6 and a modulo-2 addition circuit 8; an equalizer control device 7 for adaptively controlling the tap coefficients of the waveform equalizer; It also includes a demodulation encoder 9 for reproducing the data sequence.

At this time, the ternary level discriminator 6 of the waveform equalizer is composed of a reproduced waveform equalization filter having variable taps and a ternary level discriminator. Here, a reproduced clock is simultaneously generated by a three-level level discriminator that identifies binary intermediate series data from a three-level signal.

At this time, the equalizer control device 7 adjusts the tap coefficients of the reproduced waveform equalization filter so that the square error of the average power between the intermediate data series demodulated by the mean square error method and the source information data series is minimized. This is a configuration that performs adaptive control. In this adaptive control, in addition to the method of equalizing the sequentially read data, for example, for code correspondence, there is a method of providing a preamble period in the beginning area of the sector part, or a method of providing a preset area of several tracks. This configuration optimizes the equalization characteristics depending on the method.

FIG. 4 is a diagram for explaining the principle of reading according to the present invention. Here, the recording pitch 1-
The column is ternarized by code amount interference and read out. Unlike the conventional method, the slice level is set to two levels, 31 and S2, as shown in FIG. 4(d), for information identification of the read signal. At this time, the identification at each slice level corresponds to "l", "0", and "1", respectively. At the same time, the readout waveform “1”, “0°゛”,
A peak value corresponding to "1" is detected, and the timing relationship between the bit information and the reproduced clock is determined. The information sequence pulsed at each slice level is shown in Fig. 4(e), (
As shown in f) and (g), the data is converted into a binary intermediate data series based on the timing with the sampling clock as a data identification window. 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 series and the source information data series. The intermediate data sequence, which is the demodulated signal optimized by adaptive control in this way, is
The demodulation encoder 9 reproduces the source data sequence.

As shown in FIG. 5, which shows the electric scum vector of the partial response method of this embodiment, this can be achieved with half the bandwidth compared to the conventional method of reading out data recorded in binary form as binary data. Therefore, twice as much information can be recorded and reproduced compared to conventional methods.

FIG. 2 shows a second embodiment of the optical recording and reproducing system of the present invention.The difference from the first embodiment of the present invention is that an equalizing filter 10 of the read analog level is provided on the reproduction side. This configuration has the role of correcting waveform distortion in the analog recording/reproduction system by inserting it into the duobinary transmission line.

This is a configuration that facilitates correction of waveform distortion due to recording power dependence in the recording/reproduction system and waveform distortion in the reproduction amplifier system, and realizes a partial response type equalization 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 method using adaptive control was shown using a duobinary code, but it is also possible to use a duobinary code. good. In this case, the recording side equalizer and the reproduction side equalizer can be handled by using an N-element modulo addition circuit. Note that in the recording-side equalizer, a compensation circuit may be additionally inserted to take into account the thermomagnetic characteristics of the recording bit shape in the recording/reproduction analog system and equalize the recording timing in advance.

Although the present invention has been described using magneto-optical recording as an example, it is of course possible to similarly utilize the partial response type system in an optical disk system using a variable reflectance type medium such as a write-once type.

〔Effect of the invention〕

As explained above, the optical recording and reproducing method of the present invention can increase the information recording density to more than twice that of the conventional method and improve the information transfer rate by actively utilizing code amount interference. This allows the range of applications of optical discs to be expanded. Furthermore, since the propagation of bit errors is suppressed, unstable factors such as bit dropouts that occur at the analog level of optical disc systems are eliminated, and the overall bit error rate can be reduced.

Further, according to the present invention, it is possible to adaptively compensate for deterioration in reproduction characteristics due to variations in characteristics of the optical disk medium and head system, changes over time, etc., so stable and high-quality recording and reproduction is always possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the optical recording/reproducing method of the present invention, FIG. 2 is a block diagram showing a second embodiment of the optical recording/reproducing method of the present invention, and FIG. 3 is a block diagram showing the second embodiment of the optical recording/reproducing method of the present invention. 4 is a diagram for explaining the principle of reading according to the present invention. FIG. 5 is a diagram for explaining an example of data conversion according to the optical recording and reproducing method according to the present invention. FIG. 6 is a diagram showing vectors for explaining code amount interference according to the present invention. l...Modulation encoder 2...Modulo 2 addition circuit 3...LD drive circuit 4...Recording/reproducing analog system 5...Reading amplifier 6... ...Ternary value judgment system 7...Vase control device 8...Modulo 2 addition circuit 9...Demodulation encoder 10...Equalization filter agent Patent attorney Yoshiyuki Iwasa record data 11010+1100 2 stories Gator
l 101011100 Middle surface series tool 101
000 Playback data 1211112210 Playback data
1101211100 demodulation 201001020
0 Double H data 0101011100(a)
(b) Fig. 3 (0) Recorded data + 10101 1 100 (
b) Intermediate series +001101000 Figure 4 Figure 5 Figure 6

Claims (4)

[Claims] (1) In an optical recording and reproducing system that uses a laser as a light source and performs recording and reproducing using a pit train, the system including the recording system and reproducing system can be regarded as a partial response type digital transmission path. On the recording side, there is a modulation encoder that modulates source data into binary data, a recording side equalizer that creates binary intermediate series data to suppress error propagation in the recording/reproduction system, and a semiconductor laser drive circuit. The reproduction side includes a readout amplifier, a waveform equalizer that opposes the recording side equalizer and identifies the binary intermediate series data from the read multilevel signal, and the waveform equalizer. 1. An optical recording and reproducing method, comprising: an equalizer control device that adaptively controls tap coefficients of an equalizer; and a demodulation encoder that reproduces the source data, and performs recording and reproducing of multilevel signals. (2) The optical recording and reproducing system according to claim 1, wherein the recording side equalizer is constituted by a modulo addition circuit. (3) The optical recording and reproducing system according to claim 1, wherein the waveform equalizer is comprised of a multilevel level determination system having variable taps corresponding to the equalizer control device and a modulo addition circuit. Optical recording and reproducing method. (4) In the optical recording and reproducing system according to claim 3, the multi-level determination system of the waveform equalizer is composed of a reproduced waveform equalization filter having variable taps and a multi-level discriminator. Optical recording and playback method.