JPH05266477A - Multiple recording method for optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a high quality reproduced signal output by setting the intensity of light for recording emitted from plural light sources to a value in which an non-linear component of cross talk developed on each signal multiply recorded becomes the minimum. CONSTITUTION:In a circuit provided with subtracters 603, 703, 604, 704, and a multiplier 800, output current from a photo detector 65 and 75 are converted by IV (601, 701), a DC component of output voltage is eliminated by passing through filters 602 and 702, and a linear component of cross talk is eliminated by subtracters 603 and 703. Next, the product of an output after reduction of the linear component, that is, a non-linear component is made by a multiplier 800, and subtraction of the non-linear component of cross talk is performed by subtracting the non-linear component of cross talk again from the signal from which the linear component is reduced by using subtracters 604 and 704. And a high quality reproduced signal is obtained by performing arithmetic processing for reducing cross talk in detected signals of these multiple signals in reproducing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of performing multiplex recording on a photon mode optical recording medium using a photochromic material capable of recording high density information.

[0002]

2. Description of the Related Art In recent years, research has been actively conducted to apply photochromic materials as rewritable optical recording materials.

When such a photochromic material is irradiated with light having a predetermined wavelength, the structure of molecules is changed by a photochemical reaction,
Depending on the molecular structure change, absorbance corresponding to light of a specific wavelength or change in optical characteristics such as refractive index occurs, and the changed molecular structure is restored by adding light or heat of another wavelength. It has the property of

Therefore, the recording of information on the optical recording medium using the photochromic material is carried out by the change of the molecular structure due to the irradiation of the light of the specific wavelength, and the reproduction is carried out by detecting the change of the optical characteristics accompanying the reproduction. To be done.

By the way, the photochromic materials have different absorption spectra depending on the difference in their molecular structures. However, wavelength multiplexing recording utilizing this degree of freedom of wavelength is disclosed in Japanese Patent Laid-Open No. 61-2.
It is proposed in Japanese Patent No. 03450 (G03C 1/733).

In the case of the above publication, wavelength multiplexing recording uses several kinds of photochromic compounds having different light absorption wavelengths,
A recording medium is prepared by laminating or mixing these materials, and recording and reproduction are independently performed by irradiating with light having a wavelength corresponding to each material. A photochromic material at a specific wavelength for recording and reproduction. Since the selectivity of the reaction of 1 is incomplete, there is a possibility that crosstalk may occur between the multiplexed channels. If the amount of this crosstalk is large, the quality of the reproduced signal deteriorates, and the error rate increases when recording and reproducing digital data, for example.

In order to solve the above-mentioned problems of the prior art, the inventors of the present invention have disclosed in Japanese Patent Application No. 3-291601 a linear crosstalk component corresponding to the superposition of multiplexed recording signals. In addition to the above, it is shown that there is a nonlinear crosstalk component corresponding to the product between multiplexed recording signals by intermodulation, and that such linear and nonlinear crosstalk components can be reduced, and a method therefor is disclosed. did.

However, in such a method, although it is possible in principle to reduce the linear crosstalk component by the crosstalk reduction processing, there is a limit to the nonlinear crosstalk component.

Particularly, when the output of the recording light is insufficient, or when the C / N of the reproduced signal is low, the existence of the non-linear crosstalk component greatly affects the reliability of the reproduced signal. Was there.

[0010]

SUMMARY OF THE INVENTION Therefore, the present invention simultaneously reduces linear and non-linear components of crosstalk generated between signals when performing multiplex recording of information on an optical recording medium using a photochromic material, thereby reproducing signals. The purpose is to improve the quality and reliability of.

[0011]

SUMMARY OF THE INVENTION Therefore, according to the present invention, an optical recording medium made of a plurality of types of photochromic materials having different absorption wavelengths is provided with light having a wavelength corresponding to the absorption wavelength of each type of photochromic material. In a multiplex recording method of an optical recording medium, wherein a plurality of light sources are emitted, and recording light whose intensity is independently modulated according to a multiplex signal to be recorded is irradiated, recording emitted from the plurality of light sources is performed. The intensity of the working light is set to a value that minimizes the non-linear component of crosstalk that appears between the multiplex-recorded signals.

[0012]

The strength of the non-linear component of crosstalk depends on the emission intensity of a plurality of light sources for performing multiplex recording, and the intensity of the non-linear component decreases with the increase of the emission intensity of the light source. Has the property of increasing.

The intensity of the linear component of one crosstalk is
It has the characteristic of decreasing with the increase of the emission intensity of the light source.

By using these two characteristics and setting the emission intensity of the light source to a value that minimizes the nonlinear component, a crosstalk component with reduced linearity and nonlinearity can be obtained.

[0015]

EXAMPLE As described above, the linear component of crosstalk in wavelength-multiplexed recording can be completely removed in principle, but the nonlinear component cannot be completely removed.

On the other hand, the intensity of the non-linear component depends on the irradiation intensity on the medium of a plurality of light sources for performing multiple recording.

Therefore, when recording, the emission intensity of the plurality of light sources is set to a value that minimizes the non-linear component of crosstalk, and recording is performed, and crosstalk is reduced between the detection signals of these multiple signals during reproduction. Therefore, it is possible to extract a high-quality reproduced signal with reduced crosstalk.

An embodiment for carrying out the multiplex recording method of the present invention based on the principle will be given below and will be described in detail with reference to the drawings.

First, FIGS. 1 and 2 show the molecular structures and absorption spectra of two diarylethene-based materials which are typical examples of the photochromic material used in this embodiment.

The material of FIG. 1, namely 2- (1,2-dimethyl-3-indolyl) -3- (2,3,5-trimethyl-3-thienyl) maleic anhydride (abbreviated as asymmetric indole-thiophene type). In the state A having the absorption spectrum shown by the solid line in the figure, the wavelength 400
When irradiated with light in the vicinity of ~ 490 nm, the state changes to the state B having the absorption spectrum shown by the broken line, and the wavelength of 500 ~
When it is irradiated with light in the vicinity of 700 nm, it has a characteristic of returning to the state A shown by the solid line by a reaction opposite to this.

Using this characteristic, an asymmetric indole
For the thiophene type recording material, the recording can be performed by setting the broken line state B in advance and irradiating it with light from a He-Ne laser having a wavelength of 633 nm as a light source with relatively strong power. Similarly 633 nm
It is possible to perform reproduction by irradiating the material with the laser as the light source with relatively weak power and detecting the change in the reflectance.

On the other hand, the material of FIG. 2, that is, 2,3-bis (2-methylbenzo [b] thiophen-3-yl) maleic anhydride (abbreviated as symmetrical benzothiophene type) has an absorption spectrum shown by a solid line. In state C which has, when light with a wavelength near 400 to 460 nm is irradiated, it changes to state D having an absorption spectrum shown by a broken line, and in state D, light with a wavelength near 500 to 600 nm is irradiated. Therefore, it has the characteristic of returning to the state C shown by the solid line by the opposite reaction.

Therefore, by using this characteristic, for example, the symmetrical benzothiophene type material is recorded in advance by setting the broken line state D and irradiating the light source of the Ar laser of 514.5 nm with relatively strong power. The reproduction can be performed by irradiating the material with the same 514.5 nm laser light source at a relatively low power and detecting the change in the reflectance.

FIG. 3 shows the structure of an optical recording medium using the materials disclosed in FIGS. 1 and 2. In the figure, 101 is a glass substrate, 102 is a recording layer, and 103 is a reflective layer.

The above materials were mixed with polyvinyl butyral resin in an amount of 5 wt%, dissolved with anone, spin-coated on a grooveless glass disk substrate 101 having a thickness of 1.2 mm and a diameter of 120 mmφ, and dried to form a film. The recording layer 102 of about 1 mm is formed.

Next, a multiplex recording / reproducing apparatus using such an optical recording medium will be described.

FIG. 4 is a block diagram showing a recording / reproducing optical system. 1 is the recording medium, 2 is an objective lens system, 3 is a dichroic mirror, 5 is a focus / tracking servo optical system, and 6 is a first optical system. Is a recording / reproducing beam system, 7 is a second recording / reproducing beam system, and 8 is a focus servo control circuit.

The first recording / reproducing beam system 6 and the second
The recording / reproducing beam system 7 includes the first and second λ / 4 plates 61, 7
1, first and second polarization beam splitters 62 and 72, first and second collimator lenses 63 and 73, first and second optical fiber output units 64 and 74, first and second optical fiber input units 65 and 75, and The first and second AO modulators 66 and 76, the first and second ND filters 67 and 77 are respectively provided, and an optical fiber-6 is provided between each of the emitting portions 64 and 74 to the incident portions 65 and 75.
Combined at 0 and 70.

A He--Ne laser 68 having a wavelength of 633 nm is used as a light source in the first recording / reproducing beam system 6, and a wavelength of 514.5 in the second recording / reproducing beam system 7.
A nm Ar laser 78 is used.

Further, the focus / tracking servo optical system 5 has a third λ / 4 plate 51, a third polarization beam splitter 52, a third collimator lens 53, and a focus servo optical system 59, and has a wavelength of 780 as a light source.
A semiconductor laser 58 of nm is used.

In such an optical system, the beam of wavelength 633 nm emitted from the He-Ne laser light source 68 is N
The power is adjusted by the D filter 67 and the AO modulator 6
It is incident on 6.

The AO modulator 66 intensity-modulates the light from the laser light source 68 at the modulation signal frequency f1 from the outside at the time of recording, and transmits the light from the laser light source 68 at a constant power at the time of reproducing. Have a function.

The light passing through the AO modulator 66 is incident on the optical fiber 60 by the optical fiber incident section 65 and is transmitted to the emission section 64. The light emitted from the emission unit 64 is collimated by the lens 63, and is incident / reflected by the polarization beam splitter 62 as an S wave,
It is converted into circularly polarized light by the / 4 plate 61.

After that, the light is reflected by the dichroic mirrors 4 and 3 and is condensed on the photochromic medium 1 by the objective lens system 2. Here, the dichroic mirror 4 is 6
It has a property of reflecting light of 33 nm and transmitting light of 514.5 nm, and the dichroic mirror 3 has a property of transmitting light of 780 nm and reflecting light of 700 nm or less.

Therefore, at the time of reproduction by the He-Ne laser light source 68, the reflected light from the medium 1 passes through the objective lens system 2 and the dichroic mirrors 3 and 4 again, and passes through the λ / 4 plate 6.
1 and the polarized beam splitter 62, and is detected by the photodetector 65.

The 514.5 nm light emitted from the Ar laser light source 78 operates in the same manner as the 633 nm light except that it passes through the dichroic mirror 4. The light of the Ar laser light source 78 is also focused on the same spot as the light of 633 nm.

Further, for the focus / tracking servo optical system 5, in this embodiment, the grooveless substrate 101 is used, and reproduction is performed immediately after recording. In particular, tracking servo is not performed. I chose

The light emitted from the semiconductor laser light source 58 passes through the polarization beam splitter 52, the λ / 4 plate 51 and the dichroic mirror 3 and is radiated to the medium 1 by the objective lens 2. One of the reflected light is again in the same optical path. It is reflected by the polarization beam splitter 52 through the beam and enters the focus servo optical system 59.

The focus servo optical system 59
The focus servo control circuit drives the objective lens system 2 to execute the focus servo by the focus error signal obtained via the.

FIG. 5 shows a circuit block diagram for reducing crosstalk from the reproduced signals detected by the photodetectors 65 and 75. 601 and 701 are IV converters, 602 and 702 are DC removal filters, and 603. , 7
Reference numerals 03, 604 and 704 are subtractors, and 800 is a multiplier.

In such a circuit, the photo detector 6
The output currents from 5, 75 are IV converters 601, 701.
After being converted into a voltage signal by means of a filter, the DC components are removed through the filters 602 and 702, subtraction of these two signals is performed by using subtractors 603 and 703, and a linear component of crosstalk is first removed.

Next, the product of the output after the crosstalk linear component reduction, that is, the non-linear component is created in the multiplier 800, and the non-linear component of the crosstalk created in this way is subtracted from the signal in which the linear component is reduced by the subtracter 604. Further subtraction using 704 can reduce the nonlinear component of crosstalk.

In the figure, (A1) to (A3) and (B1)
(B3) shows the output of each part.

Experiments for wavelength-multiplexed recording / reproduction with respect to the medium 1 were conducted using the above optical system, optical recording medium, and reproduction signal detection system. The disk rotation speed at this time is 300 rp
m, the relative speed is 1.4 m / s, and the emission intensity of the light source during reproduction is set to a constant power of 0.3 mW on the disk surface for both the He-Ne laser and the Ar laser, and the emission intensity during recording is changed variously. The intensity of the crosstalk component contained in the reproduced signal was measured.

The recording frequency was set to 100 kHz for the He-Ne laser system and 80 kHz for the Ar laser system, and the reproduction output was analyzed by a spectrum analyzer. The results are shown in FIG.

In FIG. 6, the reproduction output of the He-Ne laser system before the crosstalk reduction process (A1)
About, the Ar laser power for recording is constant (5 mW)
And the He-Ne laser power for recording is 1 to 10 mW.
The linear component of crosstalk (80kHz
z: indicated by X mark) and non-linear component (180 kHz: indicated by Δ mark) with reference to signal component (100 kHz) (0 dB)
Is plotted as.

According to FIG. 6, He-Ne is recorded at the time of recording.
It is clear that the linear component of crosstalk decreases monotonically as the laser emission intensity is increased.

On the other hand, in the case of the non-linear component, as the emission intensity is increased, it is reduced to around 5 mW, but it takes a minimum value here, and when it exceeds this value, it tends to increase conversely.

Therefore, if only the linear component of the crosstalk is to be reduced, it is sufficient to simply increase the emission intensity at the time of recording. In this case, the crosstalk reduction processing (by the circuit of FIG. 5) completely eliminates it. The disadvantage arises that the non-linear components of crosstalk that are difficult to remove increase.

By the way, Table 1 shows the crosstalk amount of the output (A1) and the output (A3) after the crosstalk reduction process when the emission intensity of the He-Ne laser is 10 mW, and He.
The same (A1) output and (A3) output when the emission intensity of the -Ne laser is 5 mW are compared.

[0051]

[Table 1]

It can be seen from Table 1 that, when the recording power is 10 mW, both components of the crosstalk are reduced to a lower level of -30 dB or less by the crosstalk reduction calculation processing when the recording power is 5 mW.

By setting the recording power so that the non-linear component of the crosstalk is minimized during the wavelength multiplex recording as described above, a smaller crosstalk, that is, a higher quality reproduction signal output is obtained by the crosstalk reduction calculation process. be able to.

Regarding the reproduction output of the Ar laser system, as shown in Table 2, even if the He-Ne laser power changes, the goodness of crosstalk is at a relatively low level, and the crosstalk reduction calculation process is performed. It was easy to reduce to -30 dB or less.

[0055]

[Table 2]

In this embodiment, two diarylethene-based photochromic materials were used, but the present invention can be applied to recording on a medium using various other spiropyran-based or fulgide-based materials.

Further, as a device for carrying out the present invention, various modifications other than the device shown in FIG. 4, for example, a device using a short wavelength semiconductor laser or an SHG element as a light source can be used. It goes without saying that it can be applied to multiple recording of.

[0058]

Since the present invention is configured as described above, it is expected that a high quality reproduction signal output with a small crosstalk can be obtained during wavelength multiplexing recording.

[Brief description of drawings]

FIG. 1 is a diagram showing a molecular structural formula and an absorption spectrum of a diarylethene-based material.

FIG. 2 is a diagram showing a molecular structural formula and an absorption spectrum of another diarylethene-based material.

FIG. 3 is a cross-sectional view showing the structure of an optical recording medium.

FIG. 4 is a block diagram showing a recording / reproducing optical system.

FIG. 5 is a block diagram showing a reproduction output crosstalk reduction circuit.

FIG. 6 is a characteristic diagram showing the relationship between the emission intensity of the recording light source and the linear and nonlinear components of crosstalk.

[Explanation of symbols]

 1 Medium 2 Objective Lens System 3, 4 Dichroic Mirror 5 Focusing / Tracking Optical System 51, 61, 71 λ / 4 Plate 52, 62, 72 Polarizing Beam Splitter 53, 63, 73 Collimator Lens 64, 74 Optical Fiber Emitting Unit 60 , 70 Optical fiber 65, 75 Optical fiber incident part 66, 76 AO modulator 67, 77 ND filter 58, 68, 78 Light source 69, 79 Photodetector

Claims (1)

[Claims] 1. An optical recording medium made of a plurality of types of photochromic materials having different absorption wavelengths is recorded from a plurality of light sources that emit light having wavelengths corresponding to the absorption wavelengths of the respective types of photochromic materials. In the multiplex recording method of an optical recording medium, which irradiates recording light whose intensity is independently modulated according to a multiplex signal to be recorded, the intensity of the recording light emitted from the plurality of light sources is Multiplex recording method for an optical recording medium, characterized in that the nonlinear component of the crosstalk appearing between the generated signals is set to a minimum value.