JPH05109071A - Method and device for recording and reproducing information on and from optical recording medium - Google Patents

Abstract

PURPOSE:To record and reproduce information on and from an optical recording medium at a density higher than the conventional example by recording information signal components by utilizing changes in optical concentration and recording clock signal components by utilizing changes in optical anisotropy. CONSTITUTION:An AR laser, etc., which outputs a laser beam having a short wavelength is used as a light source 1 against an optical recording medium 5 made of a photochromic material. The laser beam of relatively high constant power emitted from the light source 1 is modulated in intensity by means of a power modulator, such as an AO modulator, etc. In addition, the polarized state of the beam is changed in accordance with clock signals by using a Faraday element or electrooptic element as a polarized-state modulator 3. The information-carrying beam from the light source 1 is modulated through the modulators 2 and 3 and condensed onto and recorded on the medium 5 through an objective lens system 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital recording / reproducing method and recording / reproducing apparatus for a photon mode optical recording medium capable of recording at high density.

[0002]

2. Description of the Related Art In recent years, researches for utilizing a photochromic material as a material for a rewritable optical recording medium have been actively pursued.

When the photochromic material is irradiated with light having a predetermined wavelength, the structure of the molecule is changed by a photochemical reaction, and the absorbance and the refractive index with respect to the light of a specific wavelength are changed according to the change of the molecular structure. It has the property that the optical properties change, or the changed molecular structure returns to its original state when light or heat of another wavelength is applied.

Therefore, the recording of the optical recording medium using such a photochromic material is performed by the structural change of the constituent molecules by irradiation with light of a specific wavelength, and the reproduction of one side detects the optical characteristic change due to this structural change. Done by.

By the way, as a change in optical characteristics often used for reproduction, there is a change in absorbance accompanying a photochromic reaction. This means that the laser as a reproducing light source has a low power.
It is put into practical use by irradiating the optical recording medium with the above and detecting a change in absorbance accompanying the photochromic reaction as a change in reflectance.

Further, there are an analog system and a digital system as a system for recording the information signal on the optical recording medium. A laser vision player is an example of an analog system, and a compact disc is a digital system.

The coded modulation method of the information signal used for the compact disc is EFM (Eight to Fourtee).
n Modulation), each sampling point depending on the sampling frequency is quantized with 16 bits, this is further divided into 8 bit data bits, and then the 8 bit data bits are converted into 14 bit channel bits. This is a modulation method in which NRZI recording is performed by adding a 3-bit margin bit ("Optical Disc Technology Handbook" pp10
1-102, Nikkei McGraw-Hill, s62 version).

One of the characteristics of the EFM system is that there are at most 10 0s between channel bits 1 and 1, which facilitates clock detection during digital reproduction. can give.

When a signal is digitally recorded / reproduced on a disc other than a compact disc, there is a coding / modulation system in which a large number of 0s are not consecutive in the channel bits, that is, a low frequency component is small in order to facilitate clock detection. Adopted ("OPTICAL RECORDING" pp235-242, ALAN B.
By MARCHANT, Addison-Wesley Publishing Company, '90
See Issue).

On the other hand, it is known that the data recording density is high in the case of a coding system capable of a symbol system in which a large number of 0s are continuous, and in an actual system, the features of each system are The encoding method is determined in consideration.

[0011]

SUMMARY OF THE INVENTION The problem to be solved by the present invention is to provide a recording / reproducing method and a recording / reproducing apparatus for an optical recording medium capable of recording / reproducing at a higher density than the conventional technique. Especially.

[0012]

The present invention is a method of recording an information signal component by a change in optical density and a clock signal component by a change in optical anisotropy, and also a change in optical density. And a beam having a point-symmetric polarization state is irradiated to an optical recording medium on which an information signal component and a clock signal component are recorded by a change in optical anisotropy, and the beam is directed to the medium. In this method, transmitted light or reflected light is separated into orthogonal polarization components, each component is independently detected, the sum of these detection components is extracted as a reproduction information signal, and the difference is extracted as a reproduction clock signal.

Further, the present invention is a recording apparatus and a reproducing apparatus including various constituent elements for performing the recording / reproducing method.

[0014]

By using the above method or device,
Since the clock signal is recorded with the degree of freedom of polarization,
It is not necessary to use a conventional digital encoding method that does not include a low frequency component, and as a result, it is possible to perform high-density recording as compared with the related art.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A recording / reproducing method and a recording / reproducing apparatus for an optical recording medium according to the present invention will be described in detail below with reference to an embodiment of the drawings.

FIG. 1 is a diagram showing the principle of recording / reproducing using an optical recording medium. It is generally known that when an optical recording medium made of a photochromic material is irradiated with linearly polarized light, dichroism occurs (for example, Polymer Preprint, Japan Vol.
38, No. 8 (1989) pp. 2716-2718).

For example, in the NRZI recording method described in the section of the prior art, the recording mark edge of the recording information signal of FIG. 1B corresponds to the channel bit 1 of FIG. 1A.

On the other hand, the clock signal is most preferably a signal which is inverted with a minimum symbol length such as 1, 0 as shown in FIG.

Next, a beam corresponding to the channel bit is transmitted.
When the power is modulated as shown in FIG. 1D and the polarization direction of the beam is modulated as shown in FIG. 1E in response to the clock signal, the optical characteristics of the optical recording medium are as shown in FIG. 1
When the beam power is high in the wavelength region of the recording beam, the reflectance is low as shown in (f) the reflectance RX in the X direction,
When it is low, the reflectance is high.

At this time, since dichroism is induced by irradiation of linearly polarized light at the same time, for linearly polarized light having a plane of polarization in the X direction, for example, the level is higher than that of the clock signal in the high reflectance and low reflectance portions. There will be a difference of.

Similarly in the Y direction, as shown by the reflectance RY in FIG. 1 (g), when the beam power is high in the wavelength region of the recording beam, the reflectance is low, and when it is low, the reflectance is high. There is a level difference with respect to the clock signal.

By the way, since the X component and the Y component of the level difference have opposite phases in the clock signal, when the difference signal ∝RX-RY is created, the original clock signal is reproduced as shown in FIG. 1 (j). To be done.

The sum signal ∝R of the reflectances RX and RY
When X + RY is created, the level of the clock signal is canceled and the recorded information is reproduced as a reproduced information signal as shown in FIG.

The optical recording medium has a smaller level difference due to the induced dichroism than the reflectance level difference corresponding to the beam power modulation in FIGS. 1 (f) and 1 (g). This is because the photochromic molecule does not have complete selectivity for polarized light.

However, it is clear from FIG. 1 that the information signal can be effectively reproduced even if the polarization selectivity is small, that is, the induced dichroism is small. Moreover, when this principle is used, the clock signal has a degree of freedom of polarization. Since it is recorded by, it is not necessary to use a digital encoding method that does not include a low frequency component, and high density recording is possible.

FIG. 2 schematically shows an optical system and a circuit system when the recording method described above is carried out.

In the figure, 1 is a light source, 2 is a power modulator for modulating the power of the output beam of the light source 1, and 3 is the polarization state of the beam from the light source 1 through the power modulator 2. A polarization state modulator for modulating the optical modulator, 4 an objective lens system, 5 an optical recording medium, 6 a first drive circuit for driving the power modulator 2,
7 is a second drive circuit for driving the polarization state modulator 3, 8
Is a channel bit recording signal generating circuit for controlling these first and second driving circuits.

Since many of the photochromic materials used for the optical recording medium 5 in FIG. 2 have absorption even in a relatively short wavelength region, the light source 1 has a short wavelength laser.
A gas laser such as an Ar laser capable of outputting a beam is used.

A relatively high constant power laser beam is emitted from the light source 1, and this beam is intensity-modulated by a power modulator 2 such as an AO modulator.

The polarization state modulator 3 is a Faraday
An element or an electro-optical element is used, and the polarization state of the beam is changed according to the clock signal.

FIG. 1A to FIG. 1A to be output from the light source 1.
The beam containing the information of (c) passes through the power modulator 2 and the change state modulator 3 to become the beam shown in FIGS. 1 (d) and (e), and this modulated beam is obtained. Objective lens system 4
Is focused on the medium 5 and recorded.

FIG. 3 shows an outline of another recording apparatus different from that of FIG. 2, and the same components as those of FIG. 2 are designated by the same reference numerals.

In FIG. 3, a long wavelength spiropyran material is used as the photochromic material as the optical recording medium 5. This material exhibits absorptivity particularly in the wavelength range of the semiconductor laser (up to 0.8 μm). Therefore, a semiconductor laser with a wavelength λ = 780 μm is used for the two light sources 21 and 22, and this control is performed. The drive circuits 9 and 10 were used.

Reference numerals 11 and 12 denote lenses inserted on the beam emitting side of the light sources 21 and 22.

Denoted at 13 is a deflecting beam splitter. The light emitted from the light source 21 enters the beam splitter 13 with P deflection, and the light emitted from one light source 22 enters with S deflection.

Furthermore, each of the incident lights is a beam splitter 13.
Are combined and are focused on the medium 5 via the objective lens system 4.

Reference numerals 14 and 15 denote clock signal information signal synthesizing circuits for controlling the respective semiconductor lasers, which synthesize the respective clock signals and information signals output from the channel bit recording signal generating circuit 8 into control signals. .

FIG. 4 shows the laser output waveforms corresponding to the clock signal and the information signal. The laser drive circuits 9 and 10 have the information signal of FIG.
A drive current in the form of a product of the clock signals of (c) is supplied, and the laser drive circuits 9 and 10 are supplied with the drive currents shown in FIG.
(D) Emit low-level and high-level power as shown in (e).

At this time, each of the above laser drive circuits 9 and 10 is
Are adjusted so that when one is on, the other is off.

4 (d) and 4 (e), the case where the beam power does not become 0 when the beam power is low is shown, but the low level may be set to 0. In this case, the clock signal can be detected only in the portion recorded with high level power, and the clock stability becomes half.

Next, a reproducing apparatus for the optical recording medium on which the information signal and the clock signal are recorded as described above will be described with reference to FIG. The same components as those of the above recording apparatus are designated by the same reference numerals.

As the reproducing light source 23, a light source capable of emitting a laser beam in the wavelength region in which the reflectance change of the medium 5 and the dichroism are generated in the recording device is used, and the power is weak. To do.

If the light emitted from the light source 23 is linearly polarized, it is necessary to use a λ / 4 plate as the optical polarization element 16 to polarize it into circularly polarized light, or to use a depolarizer to polarize it into random polarized light. Light source 2 that can be used here
There is a gas laser of the type that emits randomly polarized light as 3, and if this is used, the optical polarization element 16 becomes unnecessary.

The beam splitter 13 is a so-called non-polarization beam splitter whose transmittance and reflectance are equal to the P-polarized wave and the S-polarized wave, and when the light source 23 emits circularly polarized light or random polarized light, The polarization state does not change even when transmitted through the beam splitter 13, and the medium 5 is irradiated with circularly polarized light or random polarized light.

In particular, when the optical anisotropy, that is, the dichroism recorded on the medium 5 is to be detected by a single beam, it is preferable to use a beam having an isotropic polarization state as described above. desirable.

Since the medium 5 has a change in the total reflectance corresponding to the recording information signal and a dichroic azimuth corresponding to the recording clock signal, the reflected light from the medium 5 due to these optical characteristics. Undergoes beam intensity modulation and polarization state modulation.

When circularly polarized light is used for the light source 23, part of the reflected light is reflected by the beam splitter 13.
At this time, the dichroic azimuth of the medium 5 and the azimuth of the beam splitter 13 (for example, the azimuth of the P-polarized wave component) are made to coincide with each other in order to prevent the polarization state from changing due to the occurrence of a phase difference of light due to reflection. Is desirable. However, such precautions are not necessary when using randomly polarized light for the light source 23.

Reference numeral 17 denotes a polarization beam splitter for separating a polarization component corresponding to the information signal of the medium 5 and a polarization component corresponding to the dichroic azimuth from the beam reflected by the beam splitter 13. is there. 18 and 19 are lenses 31 and
Photodetectors for inputting the respective polarization components via 32, 33 and 34 are IV conversion systems for converting the output currents of the photodetectors 31 and 32 into voltages, 35 is a subtraction circuit, and 36 is a summing circuit.

The output currents of the photodetectors 18 and 19 are converted into voltages corresponding to the clock signal and the information signal by the IV conversion systems 33 and 34, respectively.
The outputs of 3, 34 correspond to RX and RY as shown in FIGS. 1 (f) and (g), and are input to the subtraction circuit 35 to become a reproduction clock signal, and are also input to the summing circuit 36. And becomes a reproduction information signal.

FIG. 6 is a further improvement of the reproducing apparatus of FIG. 5 and shows an example in which the light sources 21 and 22 which emit linearly polarized light are used.

The reproducing apparatus shown in FIG. 6 shares its main components with the recording optical system shown in FIG. 3, and a recording mode and a reproducing mode are provided in front of the laser driving circuits 9 and 10. Mode selectors 37 and 38 for switching between the two are provided, and half mirrors 39 and 40 are provided between the polarization beam splitter 13 and the lenses 11 and 12, respectively, and the photo detectors 18 and 39 are provided to the half mirrors 39 and 40, respectively. 19 and IV conversion system 33, 3
4 is connected. Other components and connection relationships are the same as in FIG.

In the reproducing apparatus of FIG. 6 having such a structure, the emitted light from the light source 22 is made into linearly polarized light, and this emitted light is transmitted by the half mirror 39 and is transmitted through the polarization beam splitter 13.
S-polarized light is incident on the medium 5, is totally reflected here, and is irradiated onto the medium 5 through the objective lens system 4.

The light reflected on the surface of the medium 5 is transmitted through the objective lens system 4 and then reflected by the polarization beam splitter 13 to enter the half mirror 39 again. At this time, a part of the incident beam is partially reflected. The reflected power is detected by the photodetector 18 via the lens 31.

Similarly, the light emitted from the light source 21 passes through the polarization beam splitter 13 as a P-polarized wave, is reflected by the medium 5, and the photodetector 19 detects the power.

The detected values of the photodetectors 18 and 19 are I and V conversion systems 33 and 34, as in the case of FIG.
The −V conversion is performed, and the voltage values are calculated by the subtraction circuit 35 and the summation circuit 36, respectively, and become a reproduction clock signal and a reproduction information signal.

The light emitted from each of the light sources 21 and 22 is applied to the medium 5 in a polarization state orthogonal to each other during recording and reproduction, so that the polarization plane direction coincides with the dichroic direction of the medium 5.

Therefore, RX and RY are obtained from the respective IV conversion systems 33 and 34, and the subtraction circuit 35 and the summing circuit 36 obtain the reproduction clock signal and the reproduction information signal.

This device requires two light sources as compared with the device of FIG. 5, but is excellent in that it can also have a recording function, and the semiconductor laser is used as both light sources 21 and 2.
When it is used for No. 2, it is possible to perform modulation in a higher band compared with the case where the laser power modulation element is used with a single light source as shown in FIG. The device can be downsized.

FIG. 7 shows a reproducing apparatus for irradiating the medium 5 with linearly polarized light for reproduction, and the main components are almost the same as those in FIG.

In this case, the azimuth of the plane of linear polarization irradiating the medium 5 is 45 ° with respect to the anisotropic axis generated on the medium 5 by recording.
Need to lean. Therefore, in the example of FIG. 7, in order to perform such azimuth adjustment, it is necessary to adjust the azimuth of the entire pickup optical system 41 or to provide a polarization azimuth adjusting element 42 such as a λ / 2 plate inside the optical system.

[0061]

As described above, the recording / reproducing method of the present invention and the recording / reproducing apparatus which realizes this method can simultaneously record information signals and clock signals at a high density on an optical recording medium, and The reproduced information signal and clock signal are faithful to the original signal.

[Brief description of drawings]

FIG. 1 is a waveform diagram illustrating the principle of a recording / reproducing method for an optical recording medium of the present invention.

FIG. 2 is a block diagram showing an embodiment of a recording apparatus for an optical recording medium of the present invention.

FIG. 3 is a block diagram showing another embodiment of another recording apparatus for the optical recording medium of the present invention.

FIG. 4 is a waveform diagram showing output signals of respective parts of the recording apparatus of FIG.

FIG. 5 is a block diagram showing an embodiment of a reproducing apparatus for an optical recording medium of the present invention.

FIG. 6 is a block diagram showing another embodiment of the reproducing apparatus for the optical recording medium of the present invention.

FIG. 7 is a block diagram showing still another embodiment of the reproducing apparatus for the optical recording medium of the present invention.

[Explanation of symbols]

 1,2,22 Light source 2 Laser power modulator 3 Polarization state modulator 4 Objective lens system 8 Channel bit recording signal generation circuit 13 Polarization beam splitter 18, 19 Photodetector 33, 34 IV conversion system 35 Subtraction circuit 36 Summing circuit

Claims (6)

[Claims] 1. A recording method for an optical recording medium, wherein an information signal component is recorded by a change in optical density and a clock signal component is recorded by a change in optical anisotropy. 2. A beam having a point-symmetrical polarization state is irradiated to an optical recording medium on which an information signal component and a clock signal component are respectively recorded by a change in optical density and a change in optical anisotropy. Then, the transmitted light or reflected light of the beam with respect to the medium is separated into polarization components orthogonal to each other, each component is independently detected, and the sum of these detected components is extracted as a reproduction information signal, and the difference is reproduced. A method for reproducing an optical recording medium, which is characterized in that it is taken out as a clock signal. 3. A light source that emits a recording beam having a wavelength in the absorption wavelength region of an optical recording medium, a modulation means that modulates the intensity of the beam emitted from the light source, and a radiation from the light source. Modulation means for modulating the polarization state of the beam,
Supplying means for supplying an information signal component to be recorded to the intensity modulating means and supplying a clock signal component to the polarization state modulating means, and a beam modulated based on the supplying means is condensed on the medium. A recording device for an optical recording medium, comprising: 4. Two light sources for radiating a recording beam having a wavelength in the absorption wavelength region of an optical recording medium as linearly polarized light, and light emitted from each of these light sources in a polarization state orthogonal to each other and having the same optical axis. Combining means for combining the above, and a modulating means for supplying the information signal component and the clock signal component to be recorded to the respective light sources and modulating the intensity of the radiation beam from the light sources based on these signal components A recording device for an optical recording medium, comprising: optical means for condensing the beam combined and modulated by the combining means and the modulating means on the medium. 5. A light source for emitting a reproducing beam as a linearly polarized light, a modulation means for modulating the beam emitted from the light source into a point-symmetrical polarization state, and the beam on an optical recording medium. An optical means for condensing the light into a polarized light component, and a separation means for separating the reflected light or the transmitted light from the medium into mutually orthogonal polarized components
Detection means for independently detecting these separated polarization components, information reproduction means for outputting the sum of the outputs of the detection means as a reproduction information signal, and a clock for outputting the difference between the outputs of the detection means as a reproduction clock signal A reproducing device for an optical recording medium, comprising a reproducing means. 6. A light source for radiating a reproducing beam as a linearly polarized light, a synthesizing means for synthesizing the beams emitted from the light source in a linearly polarized state orthogonal to each other on the same optical axis, Optical means for condensing the beam on the optical recording medium, separating means for separating the reflected light or transmitted light from the medium into polarized light components orthogonal to each other, and these separated polarized light components are independently detected. Detecting means, an information reproducing means for outputting a sum of outputs of the detecting means as a reproduction information signal, and a clock reproducing means for outputting a difference between outputs of the detecting means as a reproduction clock signal. Playback device.