JPH02236823A - Optical recording and reproducing system - Google Patents

Abstract

PURPOSE:To promote the recording density of information and to suppress the propagation of an error to be generated at the time of recording and reproducing by utilizing positively an intervention between codes at the time of reproducing as to be generated when the recording density is raised at a high level. CONSTITUTION:In a recording process, a recording data obtained by coding a source data through a modulation coder 1 is converted into an intermediate series data via a modulo-2 counter circuit 2 as an equivalent circuit of the recording side, and this record is recorded in a form of a recording pit train to a recording medium by a recording and reproducing head with a light source as of a semiconductor laser of a recording and reproducing analog system 4. On the other hand, in a reproducing system, the pit train recorded in binary information is ternarized by the intervention between the codes to be read out, and a demodulated data is outputted, via a read amplifier 5, a ternary level discriminator 6, a clock regenerating system 7, a modulo-2 counter circuit 8 and a demodulation coder 9. The propagation of a pit read error due to noise, etc., in the recording and reproducing system is improved by converting the information series as the recording data into the intermediate series data with the equivalent circuit 2 on the recording side.

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 particularly erasable disks among optical recording and reproducing, a recording medium made of a magnetic thin film is irradiated with focused laser light, and information is recorded as a change in magnetization on the recording medium. This is done by magnetic recording.

That is, in advance, an external magnetic field is applied perpendicularly to the entire film surface of the recording layer to magnetize the recording layer so that it is magnetized upward to write "0", and then a laser beam is spot-wise applied to the part where "1" is to be written. Irradiate and heat. The coercive force H, of the heated minute part becomes smaller, and if a weak external bias magnetic field is applied in the direction of downward magnetization during laser beam irradiation, the magnetization is reversed and "1°" is recorded. Laser beam A method is adopted in which a magnetic recording pattern is formed depending on whether or not to irradiate the recording layer, that is, whether or not to raise the temperature of the minute spot irradiated onto the recording layer.

On the other hand, the method of reading information is; for example, when a magnetic recording pattern is irradiated with a linearly polarized laser beam, the effect of rotating the plane of polarization of the reflected or transmitted light (called the magnetic Kerr effect and magnetic Faraday effect, respectively) is used. For example, when using the magnetic Kerr effect, the reflected light enters the photodetector by utilizing the fact that the rotation angle θ3 of the polarization plane of the reflected light differs depending on the direction of recording magnetization. Before passing it through an analyzer, information corresponding to the direction of magnetization is read out as changes in the amount of light.

That is, in the conventional method for reading information in such a magneto-optical disk device, the areas on the surface of the recording medium where the magnetization has changed become bright or dark areas (hereinafter referred to as recording pits). 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 a polarization beam splitter to split the beam into two, which are each received by two photodetectors, and the difference between the outputs is calculated. There are motion detection methods, etc.

At this time, to identify the reproduction of digital information, a slice level is provided near the midpoint of the read signal amplitude, and the recorded pit information is pulsed from the recorded pit string. At the same time, the peak values corresponding to ゜“0” 1 ゜゛1'' of the readout waveform are detected, and the pattern of “0” and “1” is determined from the timing relationship between the pit information and the reproduced clock determined by various modulation methods. The information of the source data is being reproduced.

[Problem to be solved by the invention]

In the information recording and reproducing method of 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), so the intensity change of the reflected light is steep. It doesn't become something. Therefore, as the recording density increases, interference between recorded pits (hereinafter referred to as inter-symbol interference) increases during reading, causing a decrease in the S/N ratio and worsening of the pit error rate. That is, for example, as shown in the upper diagram 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 laser spot 62 for reproduction and are recorded at high density, as shown in FIG. As shown in the lower figure, the read signal between recording pits changes from a solid line to a dotted line. 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.

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.

It is an object of the present invention to provide an optical recording and reproducing system that can improve the above-mentioned drawbacks, provide stable and good quality reproduced signals, and increase the recording density to more than twice that of the conventional method.

[Means for solving the problem]

The present invention relates to an optical disc system that uses a laser as a light source and performs recording and playback using a pit train, and is an optical recording and playback system for the recording and playback system in which the system including the recording system and playback 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 equalization circuit that creates binary intermediate series data to suppress error propagation in the recording/reproduction system, and a semiconductor laser drive circuit. and on the reproduction side, a readout amplifier, and a reproduction side equalization circuit that opposes the recording side equalization circuit and identifies the binary intermediate series data from the read multi-level signal;
The apparatus is characterized in that it includes a demodulation encoder that reproduces the source data from the identified intermediate sequence data, and performs recording and reproduction of multilevel signals.

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

Further, the reproduction side equalization circuit can be constructed from a multilevel level determination system and a modulo addition circuit.

Further, the multi-value level determination system of the reproduction-side equalization circuit can be composed of a read waveform equalization filter and a multi-value level discriminator.

[Effect]

According to the present invention, by actively utilizing the intersymbol interference during reproduction that occurs when recording density is high, it is not only possible to increase the recording density to more than twice that of the conventional method, but also to
It is also possible to suppress error propagation that occurs during recording and playback. [Embodiment] 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. An example of a recording/reproducing system will be explained.

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 equalization circuit and an LD (semiconductor laser) drive circuit 3. That is, in the recording process, source data is passed through a modulation encoder 1 and encoded recording data is converted to intermediate series data via a modulo 2 addition circuit 2, which is a recording side equalization circuit, and recording is performed using a semiconductor laser as a light source. A playback head records information on a recording medium in the form of a recording pit train. 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 the recording-side equalization circuit, and FIG. 3(b) shows an example of data conversion with the recording-side equalization circuit.

As shown in FIG. 3(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 series, which is recorded data, into intermediate series data in the recording side equalization circuit, errors in pit reading due to noise in the recording/reproducing system can be avoided. The transmission lm (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 intersymbol interference.

On the other hand, on the playback side, there is a readout amplifier 5, a ternary level discriminator 6 that opposes the recording side equalization circuit, and identifies the binary intermediate series data from the readout ternary signal, and a modulo-2 addition. It includes a reproduction side equalization circuit constituted by a circuit 8, a demodulation encoder 9 for reproducing the source data sequence, and a clock reproduction system 7.

FIG. 4 is a diagram for explaining the principle of reading according to the present invention. Here, the recorded pit string recorded as binary information is ternarized by intersymbol interference and read out. Unlike the conventional method, the information identification of the read signal is performed using the method shown in Fig. 4 (
As shown in d), the slice level is set to two levels, 81 and S2. At this time, the identification at each slice level corresponds to "1", "O", and "1", respectively. At the same time, the clock regeneration system 7 outputs "1" O of the read waveform.
The peak value corresponding to "1" is detected and the timing relationship between the pit information and the reproduced clock is determined.The information sequence pulsed at each slice level is shown in Fig. 4(e).
．． (f). As shown in (g), the data is converted into the original binary data series based on the timing with the sampling clock as the data identification window. A source data sequence is reproduced from this demodulated data sequence through a demodulation encoder 9.

FIG. 5 shows the power spectrum of the partial response method of this embodiment. As shown in the figure, this can be achieved with half the bandwidth compared to the conventional method of reading data recorded in binary format 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/reproducing system of the present invention. The difference from the first embodiment of the present invention is that an equalization filter 10 for the read analog level is inserted on the playback side, and has the role of correcting waveform distortion in the recording/playback analog system to the duobinary transmission line. The configuration is

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 basic multilevel signal detection system in a magneto-optical disk using a partial response method is shown using a duobinary code, but various partial response codes may be used. In this case, the recording side equalization circuit and the reproduction side equalization circuit can be handled by using an N-element modulo addition circuit. Note that in the recording-side equalization circuit, a compensation circuit may be additionally inserted to take into account the thermomagnetic characteristics of the recording pit 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 reflectance change type recording 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 recording density of information to more than twice that of the conventional method and improve the information transfer rate by actively utilizing intersymbol interference. This allows the range of applications of optical discs to be expanded. Furthermore, since the propagation of pit errors is suppressed, unstable factors such as dropped pits that occur at the analog level of optical disc systems are eliminated, and the overall pit error rate can be reduced.

[Brief explanation of drawings]

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. Figure 4 is a diagram for explaining the principle of readout according to the present invention. Figure 5 is a power spectrum of the partial response method according to the present invention. FIG. 6 is a diagram for explaining intersymbol interference according to the present invention. 1... Modulation encoder 2... Modulo 2 addition circuit 3... LD drive circuit 4... Recording/playback analog system 5... Readout amplifier 6... ... Three-level level discriminator 7 ... Clock recovery system 8 ... Modulo 2 addition circuit 9 ... Modulation encoder 10 ... Equalization filter Figure 2 +10 Recorded data +10 +00 Middle series 10α1101000 Reproduction data Reproduction data +00 Demodulated data Demodulated data (○) Recorded data (b) Intermediate series o 0 0 o O Peng Figure 8! darkness

Claims (1)

[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 equalization circuit 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 reproduction side equalization circuit that opposes the recording side equalization circuit and identifies the binary intermediate series data from the read multi-level signal, and an identified reproduction side equalization circuit. An optical recording and reproducing method, comprising: a demodulating encoder for reproducing the source data from intermediate sequence data, and recording and reproducing multilevel signals.