JP3081303B2 - Optical recording medium recording / reproducing method and recording / reproducing apparatus - Google Patents

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 a recording / reproducing apparatus for a photon mode optical recording medium capable of recording at a high density.

[0002]

2. Description of the Related Art In recent years, research on using a photochromic material as a material of a rewritable optical recording medium has been actively conducted.

[0003] When the photochromic material is irradiated with light having a predetermined wavelength, the structure of the molecule changes due to a photochemical reaction, and the absorbance, refractive index, and the like for light of a specific wavelength change according to the change in the molecular structure. It has such a property that a change occurs in optical characteristics or that the structure of a molecule changed by applying light or heat of another wavelength is restored.

Therefore, recording on an optical recording medium using such a photochromic material is performed by a structural change of constituent molecules caused by irradiation with light of a specific wavelength, and one type of reproduction detects an optical characteristic change accompanying the structural change. This is done by:

[0005] Optical characteristic changes frequently used for reproduction include a change in absorbance due to a photochromic reaction. This means that the laser as a light source for reproduction has a low power.
It has been put to practical use by irradiating an optical recording medium with the above method and detecting a change in absorbance accompanying the photochromic reaction as a change in reflectance.

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

[0007] The encoding and modulation method of the information signal used in the compact disc is EFM (Eight to Fourteen).
n Modulation), each sample point at the sampling frequency is quantized by 16 bits, and 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.
1-1102, Nikkei McGraw-Hill, s62 edition).

One of the features of such an EFM system is that there are at most ten 0s between channel bits 1 and 1, which makes it easy to detect a clock when performing digital reproduction. can give.

When a signal is recorded and reproduced digitally on a device other than a compact disk, an encoding modulation method in which a large number of 0s are not continuous in channel bits, that is, a low frequency component is small, in order to facilitate clock detection. (“OPTICAL RECORDING” pp235-242, ALAN B.
MARCHANT, Addison-Wesley Publishing Company, '90
Issue).

[0010] On the other hand, it is known that a data recording density is large in the case of a coding system that can also use a symbol system in which many 0s are continuous. The coding method is determined in consideration of the above.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a recording / reproducing method and a recording / reproducing apparatus for an optical recording medium capable of performing recording / reproducing at a higher density than the above-mentioned prior art. It is in.

[0012]

SUMMARY OF THE INVENTION The present invention is a method of recording an information signal component by a change in optical density and recording a clock signal component by a change in optical anisotropy. And irradiating a beam having a point-symmetric polarization state to an optical recording medium on which an information signal component and a clock signal component are respectively recorded by a change in optical anisotropy, and transmitting or reflecting the beam with respect to the medium. The light corresponds to the azimuth of the optical anisotropy of the optical recording medium.
In this method, the components are separated into orthogonally polarized light components, each component is independently detected, the sum of these detected 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 components for performing the recording / reproducing method.

[0014]

By using the above method or apparatus,
Because the clock signal is recorded with the degree of freedom of polarization,
There is no need to use a conventional digital encoding method that does not include a low-frequency component, and as a result, higher-density recording can be performed than in the related art.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a recording / reproducing method for an optical recording medium according to the present invention.

FIG. 1 is a diagram showing the principle of recording and reproduction using an optical recording medium. It is generally known that dichroism occurs when an optical recording medium made of a photochromic material is irradiated with linearly polarized light (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 in FIG. 1B corresponds to the channel bit 1 in FIG.

On the other hand, the clock signal is most desirably a signal which is inverted with a minimum symbol length of 1, 0 or the like as shown in FIG.

Next, a beam corresponding to the channel bit
When the power of the optical recording medium is modulated as shown in FIG. 1D and the polarization direction of the beam is modulated as shown in FIG. 1
(F) As shown in the reflectance RX in the X direction, when the beam power is high in the wavelength region of the recording beam, the reflectance is low,
When it is low, the reflectance is high.

At this time, dichroism is simultaneously induced by the irradiation of linearly polarized light. For example, for linearly polarized light having a plane of polarization in the X direction, the level of the clock signal in the high and low reflectance portions is reduced. Will exist.

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 the beam power is low, the reflectance is high. There is a level difference with respect to the clock signal.

Since the X and Y components of the level difference have opposite phases in the clock signal, when the difference signal ΔRX−RY is created, the original clock signal is reproduced as shown in FIG. Is done.

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

In FIG. 1F and FIG. 1G, the level difference due to the induced dichroism is smaller than the difference in the reflectance level corresponding to the beam power modulation in the optical recording medium. This is due to the incomplete selectivity of the photochromic molecules 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. Therefore, it is not necessary to use a digital encoding method that does not include a low-frequency component, and high-density recording becomes 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 transmitted from the light source 1 through the power modulator 2. Is a polarization state modulator, 4 is an objective lens system, 5 is an optical recording medium, 6 is a first drive circuit for driving the power modulator 2,
7 is a second drive circuit for driving the polarization state modulator 3;
Is a channel bit recording signal generating circuit for controlling these first and second driving circuits.

In FIG. 2, most of the photochromic materials used for the optical recording medium 5 absorb light even in a relatively short wavelength region.
A gas laser such as an Ar laser capable of outputting a beam is used.

The light source 1 emits a laser beam having a relatively high constant power, and the beam is intensity-modulated by a power modulator 2 such as an AO modulator.

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

FIGS. 1A to 1C output from the light source 1
The beam including the information (c) passes through the power modulator 2 and the modified state modulator 3 to become the beams shown in FIGS. 1D and 1E. The objective lens system 4
Is collected on the medium 5 and recorded.

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

In FIG. 3, a long-wavelength spiropyran-based material is used as a photochromic material as the optical recording medium 5. This material has an absorptivity especially in a semiconductor laser wavelength range (up to 0.8 μm). Therefore, a semiconductor laser having a wavelength λ = 780 μm is used for the two light sources 21 and 22, and the control is performed for this purpose. Drive circuits 9 and 10 were used.

Reference numerals 11 and 12 denote lenses interposed on the beam radiation sides of the light sources 21 and 22, respectively.

Numeral 13 denotes a deflecting beam splitter. The light emitted from the light source 21 enters the beam splitter 13 in P-polarized light, and the light emitted from one light source 22 enters in S-polarized light.

Further, each of the incident lights is converted into a beam splitter 13.
And 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. The clock signal and information signal output from the channel bit recording signal generating circuit 8 are synthesized as control signals. .

FIG. 4 shows laser output waveforms corresponding to the clock signal and the information signal. Each of the laser drive circuits 9 and 10 has the information signal of FIG.
The clock signal of (c) is obtained by a product using a logical operation.
A driving current is supplied, and the laser driving circuits 9 and 10 emit low-level and high-level powers as shown in FIGS.

At this time, the laser driving circuits 9 and 10 described above are used.
Is adjusted so that when one is on, the other is off.

Although the case where the beam power is not 0 when the beam power is low is shown in FIGS. 4D and 4E, the low level may be set to 0. In this case, the clock signal can be detected only in the portion recorded with the high level power, and the clock stability is halved.

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

As the reproducing light source 23, a light source capable of emitting a laser beam in a wavelength region where the change in the reflectance of the medium 5 and the occurrence of dichroism has occurred in the above-described recording apparatus is used, and the power is very weak. I do.

If the light emitted from the light source 23 is linearly polarized, the light is converted into circularly polarized light by using a λ / 4 plate as the optical polarizing element 16.
It is necessary to convert the light into a randomly polarized light using a depolarizing plate.
As 3, there is a gas laser of a type that emits randomly polarized light. If this gas laser is used, the optical polarizing element 16 becomes unnecessary.

The beam splitter 13 uses a so-called non-polarized beam splitter having the same transmittance and reflectance for the P-polarized wave and the S-polarized wave. When the light source 23 emits circularly polarized light or random polarized light, Even when the light passes through the beam splitter 13, the polarization state does not change, and the medium 5 is irradiated with circularly polarized light or random polarized light.

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

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. Undergo beam intensity modulation and polarization state modulation.

When circularly polarized light is used for the light source 23, a part of the reflected light is reflected by the beam splitter 13,
At this time, the dichroic direction of the medium 5 and the direction of the beam splitter 13 (for example, the direction of the P-polarized wave component) should be matched in order to prevent a change in the polarization state due to the generation of the phase difference of the light due to the reflection. Is desirable. However, such attention is not required when using random polarized light for the light source 23.

Numeral 17 designates the beam reflected by the beam splitter 13 as a polarized light component corresponding to the dichroic direction of the medium.
This is a polarizing beam splitter for separation . 18, 19
Is a photodetector that inputs each of the polarization components through lenses 31 and 32, 33 and 34 are an IV conversion system that converts 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 a clock signal and an information signal by IV conversion systems 33 and 34, respectively.
Outputs 3 and 34 correspond to RX and RY as shown in FIGS. 1F and 1G, and are input to a subtraction circuit 35 to become a reproduced clock signal, and are also input to a summing circuit 36. To become a reproduction information signal.

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

The main components of the reproducing apparatus shown in FIG. 6 are shared with the recording optical system shown in FIG. 3, and a recording mode and a reproducing mode are provided before the laser driving circuits 9 and 10. Are provided, and half mirrors 39, 40 are provided between the polarization beam splitter 13 and the lenses 11, 12, respectively. 19 and IV conversion systems 33, 3
4 are connected. Other components and connections are the same as those in FIG.

In the reproducing apparatus shown in FIG. 6 having such a configuration, the light emitted from the light source 22 is converted into linearly polarized light, and the emitted light is transmitted through the half mirror 39 to be polarized beam splitter 13.
The light is incident on the medium 5 through the objective lens system 4 and totally reflected therefrom.

The reflected light on the surface of the medium 5 is reflected by the polarizing beam splitter 13 after passing through the objective lens system 4 and re-enters the half mirror 39. At this time, a part of the incident beam is lost. The reflected power is detected by the photodetector 18 via the lens 31.

Similarly, the radiated light 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 power is detected by the photodetector 19.

The detected values of the two photodetectors 18 and 19 are obtained by the IV conversion systems 33 and 34 as in the case of FIG.
-V conversion is performed, and this voltage value is calculated by the subtraction circuit 35 and the addition circuit 36, respectively, to become a reproduction clock signal and a reproduction information signal.

The radiated light 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 matches the dichroic orientation of the medium 5.

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

Although this device requires two light sources as compared with the device shown in FIG. 5, it is excellent in that it can also have a recording function.
2, the modulation in a higher band becomes possible, a larger data transfer rate can be obtained, and the reproduction can be performed, as compared with the case where a laser power modulator is used with a single light source as shown in FIG. The device can be downsized.

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

In this case, the azimuth of the linearly polarized plane irradiated on the medium 5 is 45 ° with respect to the anisotropic axis generated on the medium 5 by recording.
Must be leaning. Therefore, in the example of FIG. 7, 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 for such azimuth adjustment.

[0061]

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

[Brief description of the drawings]

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

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

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

FIG. 4 is a waveform chart showing output signals of respective units of the recording apparatus of FIG. 3;

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

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

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

[Explanation of symbols]

 Reference numerals 1, 21, 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 Summation circuit

Claims (6)

(57) [Claims] 1. A method for recording an optical recording medium, comprising recording an information signal component by a change in optical density and recording a clock signal component by a change in optical anisotropy. 2. 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 is irradiated with a beam having a point-symmetric polarization state. The transmitted light or reflected light of the beam with respect to the medium is converted into the optical anisotropy of the optical recording medium.
An optical recording medium which separates polarization components orthogonal to each other corresponding to an azimuth, detects each component independently, extracts a sum of these detected components as a reproduction information signal, and extracts a difference as a reproduction clock signal. How to play. 3. A light source for emitting a recording beam having a wavelength in an absorption wavelength region of an optical recording medium, a modulating means for modulating the intensity of the beam emitted from the light source, and a light source for emitting a beam emitted from the light source. Modulation means for modulating the polarization state,
Supply means for supplying an information signal component to be recorded to the intensity modulation means and a clock signal component to the polarization state modulation means; and an optical element for condensing a beam modulated based on the supply means on the medium. Recording device for an optical recording medium, comprising: 4. A light source for emitting a recording beam having a wavelength in an absorption wavelength region of an optical recording medium as linearly polarized light, and a signal for synthesizing an information signal to be recorded and a clock signal.
Signal combining means, and a signal combined by the signal combining means.
The combined signal is supplied to each of the two light sources, and
Information signal component and clock signal component to be recorded in the signal
Radiation beam emitted from each of the two light sources on the basis of
Modulating means for modulating the intensity of the light from the two light sources;
Beam combining means for combining radiation beams on the same optical axis in orthogonal polarization states, the modulating means and the beam combining means
Optical means for condensing the beam modulated and combined by the means on the medium. 5. A change in optical density and a change in optical anisotropy.
Information signal component and clock signal component respectively
Optical recording media playback device that plays back recorded optical recording media
Oite, a light source for emitting linearly polarized light beam reproduction, modulating means for modulating the beam emitted from the light source to the point-symmetric polarization state, and optical means for focusing said beam onto an optical recording medium The reflected light or transmitted light from the medium
Separation means for separating into mutually orthogonal polarization components corresponding to the azimuth of the optical anisotropy of the optical recording medium, and detection means for independently detecting these separated polarization components, An apparatus for reproducing an optical recording medium, comprising: an information reproducing means for outputting a sum of outputs from respective detecting means as a reproduced information signal; and a clock reproducing means for outputting a difference between outputs from the detecting means as a reproduced clock signal. 6. A change in optical density and a change in optical anisotropy.
Information signal component and clock signal component respectively
Optical recording media playback device that plays back recorded optical recording media
In this case, two light sources for emitting a reproducing beam with linearly polarized light, and a beam emitted from the light source are arranged in front of the optical recording medium.
Combining means for combining on the same optical axis in linear polarization states orthogonal to each other corresponding to the orientation of the optical anisotropy, optical means for condensing the beam on an optical recording medium, and reflection from the medium Light or transmitted light to the optical recording medium
Means for separating polarization components orthogonal to each other corresponding to the direction of the spatial anisotropy, detection means for independently detecting these separated polarization components, and the sum of the outputs of the detection means is output as a reproduction information signal An optical recording medium reproducing apparatus, comprising: an information reproducing unit for performing the above operation;