JPH0432040A - Optical information recording medium, information recording method using this medium, as well as information reproducing method and information reproducing device - Google Patents

Abstract

PURPOSE:To allow many valuing with high SNR (S/N) by providing 1st and 2nd reflecting layers which are disposed in parallel with each other and providing medium layers which vary in the refractive index thereof when irradiated with light between these layers. CONSTITUTION:The 1st and 2nd reflecting layers 12a, 12b, 14a, 14b which are disposed in parallel with each other and the medium layers 13a, 13b which vary in the refractive index thereof when irradiated with light are provided. Inorg. media consisting of TeOx, InSeTlCo, GeTeSbTl, GeTeSe, etc., and org. media consisting of an anthraquinone deriv., dioquiquedine compd., triphenodithiazine compd., etc., are adequate as the medium layers 13a, 13b. The multilayered reflecting layers 12a, 12b and 14a, 14b are formed by alternately laminating the layers having a high refractive index and the layers having a low refractive index at the optical path length thickness corresponding to 1/4 the wavelength. The phases of an optical multiple interference effect are varied in this way and, therefore, the many valued information is obtd. and the recording density is additionally increased in spite of high SNR.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a recording medium having an optical multiple interference effect, an information recording method using the medium, an information reproducing method, and an information reproducing apparatus.

[Background Art] In recent years, optical information recording media called optical memories, such as optical disks, optical cards, and optical tapes, and recording and reproducing devices using them have made remarkable progress. Such a recording/reproducing device has the advantage that the cost per bit is lower than that of a magnetic disk, etc., and a high transfer rate can be obtained because the optical memory has the feature of high-density recording.

Therefore, research and development is actively being conducted to further increase the density of optical memory.

In order to increase the density of optical memories, various methods have been proposed, such as miniaturization of the minimum bit size, multi-level recording of information, and multiple recording of information. Of these, most of the conventionally known multilevel techniques have been proposed using continuous reflectance changes of dye media or phase change media. These proposals basically involve further subdividing the intermediate value between two different reflectance levels with good contrast, which corresponded to conventional binary information. Therefore, in principle, multileveling is performed at the expense of SNR, which leads to deterioration of error rate.

In the method using this reflectance change, in the simplest form, if the complex refractive index N1 of the substrate and the complex refractive index N1 of the medium are:
The reflectance R is expressed by the following formula.

However, nm (m= 1.2) is the refractive index, K, (I
11=1.2) is the damping coefficient N m”ns −iK
It is @. For example, in the case of a TeOx-based phase change medium,
When in amorphous state, N*: 3.5-0.8i-
Since N1=3.9-1.3i in the crystal state, N,
=1.6, the change in reflectance ΔR is as small as 6%. Further, this ΔR is divided into smaller parts, but since the change in ΔR with respect to the optical energy required for recording is non-linear, it is difficult to divide it into equal parts, and it is also not easy to control the optical energy required for recording.

On the other hand, S
As a method to increase the NR, as shown in Japanese Patent Publication No. 63-26463, a metal mirror with high reflectance is provided on the back surface of the medium, and the difference in reflectance between the two states is widened by the multiple interference effect of the thin film. , a method for improving the contrast has been proposed.This Japanese Patent Publication No. 63-26463 proposes an increase in reflectance change due to a change in absorption coefficient, but this method solves the above-mentioned problem of multileveling. However, the nonlinearity and the difficulty of optical energy control cannot be solved.In fact, if we try to apply it to multi-leveling, the nonlinearity of the change in reflectance increases by combining the change in the absorption spectrum and the multiple interference effect. In other words, it is possible to increase the difference between the two reflectances corresponding to such binary values, improve the contrast, and improve the SNR as binary data.
Even if the characteristics can be improved, it does not necessarily mean that characteristics suitable for multilevel processing can be obtained.

In a digital memory, if the number of multivalue levels at the medium level is L, information is recorded bitv! when binary data is recorded. iM is expressed by the following formula.

M = 1ogzL For example, in the case of multi-value conversion using reflectance change, even if the medium achieves 8 levels of multi-value (L = 8), the amount of information that can be recorded is 3 bits (M = 3), so the recording density is 3. It only doubles. When considering the signal processing of devices such as computers that receive data from digital memory, and the processing systems such as modulation and demodulation within the memory, the effect of multilevel conversion becomes noticeable from 8-bit multilevel conversion. , it is necessary to ensure 256 levels of multi-value for the medium.

When performing multi-value conversion using reflectance for such light intensity, even if the total (ideally, 0 to 100% reflectance changes linearly) and is divided into equal parts, 256 levels of multi-value processing are required. If this is done, the change will be 0.391% per rubel, which means that it will be extremely difficult to put it into practical use considering the medium manufacturing technology, light source intensity stabilization technology, detection technology, etc.

Furthermore, a multiplex recording system using a photochemical hole burning (hereinafter referred to as PHB) effect using a light absorption spectrum has also been proposed, as in Japanese Patent Publication No. 63-26463. In principle, this multiplex recording method should enable multilevel recording by multiplex recording. However, PHB
At present, experiments to confirm the principle of this method at extremely low temperatures have been completed, and it is technically difficult to stably realize a medium with many narrow-band absorption spectra at room temperature. Furthermore, when performing a series of basic operations as a memory such as recording, reproducing, and erasing information, the light source needs to have a spectral width sufficiently narrower than each of the narrow absorption spectral widths. In addition, there are currently many issues that need to be resolved in addition to the instability of the medium itself, such as the need to simultaneously sweep the wavelength and the need to control the absolute value of the wavelength.

[Problems to be solved by the invention] As mentioned above, many problems remain with the conventional multilevel technology, especially problems such as low SNR and low degree of multilevel conversion. was there. In addition, although proposals have been made to increase the degree of multi-leveling, the reality is that many technical issues remain.

The present invention was made in view of the above circumstances, and its purpose is to provide an optical information recording medium that simultaneously realizes high SNR and high multilevel dust, thereby enabling high reliability and high density recording, and the medium. An object of the present invention is to provide an information recording method, an information reproducing method, and an information reproducing device using the above.

[Means for Solving the Problem] The above object is to provide first and second light beams that are arranged parallel to each other at a predetermined interval so that the light reflected by each light beam causes multiple interference.
This is achieved by an optical information recording medium consisting of a reflective layer and a medium layer provided between these reflective layers and whose refractive index changes when irradiated with light.

Also, an optical system comprising first and second reflective layers arranged parallel to each other at a predetermined interval so that light reflected from each layer causes multiple interference, and a medium layer provided between these reflective layers. By irradiating the medium layer with a light flux whose intensity is modulated according to the information to be recorded using an information recording medium,
This is achieved by an information recording method characterized by changing the refractive index of the medium layer according to the intensity of the irradiated light beam.

Furthermore, first and second reflective layers are arranged parallel to each other at a predetermined interval so that the light reflected from each causes multiple interference, and a change in the refractive index is provided between these reflective layers. A process of irradiating a reproducing light beam onto an optical information recording medium comprising a medium layer on which information is recorded, a process of sweeping the wavelength of the light beam within a predetermined range, and a process of receiving reflected light or transmitted light of the light beam by the medium. However, this is achieved by an information reproducing method comprising a process of detecting wavelengths that cause multiple interference, and a process of determining information recorded on a medium from the detected wavelengths.

Further, in a device that reproduces information recorded on an optical information recording medium by irradiating a light beam onto the medium and detecting reflected light or transmitted light of the light beam by the medium, the medium is Just as light causes multiple interference,
It consists of first and second reflective layers arranged in parallel with each other at a predetermined interval, and a medium layer provided between these reflective layers, on which information is recorded as a change in the refractive index, and the wavelength of the light beam is means for sweeping the wavelength within a predetermined range, means for detecting a wavelength that causes multiple interference by receiving the reflected light or transmitted light, and means for determining information recorded on the medium from the detected wavelength. This is achieved by an information reproducing device characterized by the following.

[Operation] According to the present invention, multilevel information is recorded on a recording medium having an optical multiple interference effect as a change in the optical parameter of the phase of the interference effect, and the spectral characteristics of the interference effect are used to record multiple information. By reproducing value information in correspondence with the wavelength of light, a high SNR and a high degree of multi-value can be achieved, and high-density recording can be performed with high reliability.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a configuration diagram that best represents the features of the present invention.

In FIG. 1, reference numeral 1 denotes a recording medium that records multilevel information using optical multiple interference effects. The specific configuration of this recording medium 1 will be described in detail later. 2 is a semiconductor laser which is a first light source for information recording, and 3 is a collimator lens that converts the laser beam of the semiconductor laser 2 into parallel light. 4 is a semiconductor laser which is a second light source for information reproduction; 5
is a collimator lens that converts the laser beam of the semiconductor laser 4 into parallel light. Also, 6.7 is a beam splitter,
8 is a pickup lens, 9 is a sensor lens, and 10 is a light detector.

The light converted into parallel light by each collimator lens 3, 5 is
They are combined by a beam splitter 6. The medium 1 is driven by a motor (not shown), and is configured to be scanned by the light beam emitted from the light source.

The recording semiconductor laser 2 is a relatively high-output laser, and is driven by a recording laser drive circuit 31. From the terminal 30, words expressed as binary signals of a large number of bits (for example, 8 bits) are input one after another. The input word is converted into a corresponding signal level in the modulation circuit 32 according to a predetermined table. for example,
If one word consists of 8 bits, there are 256 words, and 2 words corresponding to each word.
A recording signal modulated into 56 levels is output from the modulation circuit. This recording signal is transmitted to the recording laser drive circuit 31
The semiconductor laser 2 emits a recording light beam having an intensity corresponding to the signal level.

The recording light beam is collimated by a collimator lens 3,
The light passes through the beam splitters 6 and 7 and is imaged as a minute spot on the medium layer of the medium 1 by the pickup lens 8. The medium layer is heated by the irradiation of the recording light flux, and signals are recorded as a series of minute recording areas with varying refractive indexes. Here, each minute recording area exhibits a refractive index corresponding to the intensity of the irradiated light beam. That is, one word is recorded in one recording area. The signal output from the modulation circuit 32 is performed at regular intervals based on the clock signal output from the clock signal generation circuit 33. Therefore, minute recording areas are formed on the recording medium 1 at a constant pitch in the scanning direction of the light beam.

On the other hand, as the semiconductor laser 4 for reproduction, a relatively low output laser is used. This semiconductor laser 4 is driven by a reproduction laser drive circuit 34. The reproducing laser drive circuit 34 sweeps the wavelength of the reproducing light flux emitted from the semiconductor laser 4 at a constant cycle in synchronization with the clock signal input from the clock signal generating circuit 33. Such wavelength sweeping can be performed, for example, by using a normal DH laser and changing the amount of current injected into the laser. Further, if a tandem electrode type wavelength tunable semiconductor laser proposed in Japanese Patent Application Laid-Open No. 63-32985 is used, it is possible to sweep an even wider range and at higher speed. The clock signal generation circuit 33 synchronizes the minute recording area on the medium with the clock signal, for example, by detecting a synchronization mark recorded in advance on the medium. Based on this clock signal, the semiconductor laser 4 is controlled to perform a wavelength sweep of a small number of degrees within the minute recording area.

The reproducing light beam emitted from the semiconductor laser 4 is reflected by the beam splitter 6, transmitted through the beam splitter 7, and imaged as a minute spot on the medium layer of the medium 1 by the pickup lens 8. The light reflected by the medium 1 and modulated according to the recorded information is separated from the incident light from the laser by the beam splitter 7, focused by the sensor lens 9, and received by the optical detector 10.

The output of the optical detector 1o is input to a peak detection circuit 35, where the peak of the detection signal is detected. Based on the clock signal inputted from the clock signal generation circuit 33, the timer circuit 36 counts the time from the start of the wavelength sweep of the reproducing light beam to the time when the peak is detected. As will be described later, the present invention detects information recorded as a change in the refractive index of the medium layer of the medium 1 by converting it into a change in the wavelength at which interference occurs using optical multiple interference effects. . In the apparatus shown in FIG. 1, the wavelength is swept at a constant rate, so the change in wavelength appears as the time from the start of the sweep. Therefore, the information reproducing circuit 37
The information recorded on the medium 1 is reproduced from the time measured by the clock circuit 36 and output from the terminal 38.

Although not shown in the drawings, the focal position of the light spot of the recording light beam and the reproduction light beam is three-dimensionally controlled by autofocus and autotracking control. Further, in both of the semiconductor lasers described above, it is also possible to convert the optical output having an elliptical distribution into one having an approximately perfect circular distribution using a beam shaping prism or the like, if necessary.

Next, the specific configuration of the recording medium 1 will be explained. Second
The figure shows a cross-sectional structure of the recording medium 1.

The recording medium 1 is a double-sided medium that allows recording and reproduction on both the front and back sides. Reference numeral 11aJlb is a transparent polycarbonate substrate, and reflective layers and medium layers are alternately formed on each substrate. First, first reflective layers 12a and 12b are formed on substrates 11a and llb, respectively, and a medium layer 13a whose refractive index changes with heat is formed on the surface thereof.

13b is formed. In addition, each medium layer 13a, ]3
Second reflective layers 14a and 14b are formed on the second reflective layer 14a and 14b, and these are adhered by an adhesive layer 15. The layers are formed parallel to each other at predetermined intervals, and are designed to cause multiple interference as will be described later.

As the medium layers 13a and 13b, TeOx, TnSe
T(l Co.

Inorganic media such as GeTe5+, TJ2, GeTeSe, anthraquinone dielectrics, sioquikedine compounds,
Organic media such as triphuedithiazine compounds are preferred. In addition, multilayer reflective layers 12a, 12b and 14a,
14b, a layer with a high refractive index and a layer with a low refractive index are alternately formed,
The films are formed by stacking them with an optical path length and thickness corresponding to 174 wavelengths. The material of each reflective layer is SiOx
, 5isN4. MgF4. A dielectric material such as Al2O5 is used.

To manufacture such a recording medium 1, first, a first reflective layer, a medium layer, and a second reflective layer are sequentially formed on each of the substrates 11a and llb on both sides by sputtering or coating, respectively. Then, a recording medium for double-sided recording is completed by bonding each substrate 11a, llb with an adhesive (adhesive layer 15) with the second reflective layers facing each other.

Further, in the recording medium 1 of this embodiment, the first reflective layer and the second reflective layer
The structure of a medium layer sandwiched between reflective layers realizes a so-called Fapley bellows etalon. That is, as will be described later, the incident light is repeatedly reflected between the two reflective layers, resulting in a multiple interference effect. The present invention effectively utilizes this multiple interference effect to perform multilevel recording of information as will be described in detail later.

Therefore, the recording and reproducing operation of multivalued information on the recording medium 1 will be explained. First, the principle of recording and reproducing according to the present invention will be explained with reference to FIG.

In FIG. 3, 16 is a medium layer, which corresponds to the medium layers 13a and 13b shown in FIG. Further, 17 is a first reflective surface, which is the first reflective layer 12a shown in FIG.

12b is equivalently replaced with a reflective surface. Similarly, the second reflective surface 18 is equivalently replaced with the second reflective layers 14a and 14b as a reflective surface. Reference numeral 19 indicates a laser beam, and the medium layer 16 is shown from the top of the drawing as in FIG.
incident on . The beam waist of the laser is controlled to be located near the center of the medium layer 16 by the aforementioned autofocus mechanism. Therefore, within the medium layer 16, the laser light can be considered to be substantially parallel light.

Here, for the sake of simplicity, assuming that both the upper and lower sides of the medium layer 16 in FIG. It can be treated as if the

Therefore, the intensity reflectance of the first and second reflective surfaces is R, and the refractive index of the medium layer 16 is n. , where the thickness is d, the reflectance Rt of this etalon can be expressed by the following equation (1) as a result of the multiple interference effect due to repeated reflections.

ψ F sin” R, = ... (1)
ψ 1 + F sin'' Here, F is expressed by equation (2), and ψ is a phase difference expressed by equation (3) when the wavelength of the incident light is taken first.

4πnvd ψ=□ ... (3) λ F corresponds to finesse and is a parameter indicating the sharpness of interference fringes.
As shown in the figure, as a result of multiple interference of reflected light, the change in reflectance corresponding to the change in phase difference becomes sharper and the amount of change becomes larger. In other words, the degree of multi-level recording that can be recorded can be improved. The reason why the reflectance decreases is that from equation (1), where m is an integer, (4
) when the expression.

ψ=2πm (4) Therefore, the reflectance becomes low when the condition of equation (5) is satisfied.

nvd = m (5) λ FIG. 4 is a schematic diagram showing this situation, where the horizontal axis is the phase difference ψ, and the vertical axis is the reflected light intensity. The dotted line 21 in the figure is the reflectance R
is small, the solid line 20 is large. When the reflectance is set to high, the half-width of the reflection intensity change with respect to the phase difference,
In other words, WH in the same figure.

It can be seen that the width indicated by WHz becomes sharper.

The recording of multilevel information according to the present invention essentially utilizes the above-mentioned multiple interference effect characteristics. That is, when the medium layer 16 is heated by the light from the recording semiconductor laser 2 shown in FIG. 1, its refractive index n changes. Conventionally, the principle of recording has been the change in reflectance Rt due to the change in refractive index. However, in the present invention, unlike the conventional principle, changes in the refractive index are recorded by making them correspond to changes in the phase difference of the etalon, and reproduction is performed using the changes in the phase as changes in the wavelength showing the peak of the low reflection area. It was decided to detect it as a minute. To explain in detail using equation (3), the change Δnv in the refractive index due to laser heating is calculated by the following equation (6) from equation (3).
It is recorded on the etalon medium as a phase difference change Δψ expressed by the equation.

In other words, after recording, equation (7) is obtained.

That is, before recording, the condition of formula (5) was satisfied at wavelength λ, that is, the reflectance was low, but after recording, △ψ
This means that the reflectance has changed to a higher reflectance.

In order to reproduce this recorded information, in the present invention,
Rather than detecting a change in reflectance for a single wavelength as in the conventional method (such a conventional method cannot increase the degree of multivalue), the shift amount Δψ of the peak of low reflectance is detected. It is detected by converting the amount of shift in the peak into the amount of change in wavelength. In other words, in the state of equation (7), (6
) Since it is sufficient to find a wavelength that cancels Δψ expressed by the equation (7), Δψ° is expressed by the equation (8) from the equation (7).

Therefore, from equations (6) and (8), if △ψ=Δψ°, then
The following relationship (9) holds true.

Δ λ Δn e n2 (9) That is, by shifting the wavelength by eight, it becomes possible to detect the peak of low reflectance with a detector.

FIG. 5 is a time chart for explaining the specific reproduction operation of this embodiment.

FIG. 5(a) shows a wavelength sweep waveform of the reproducing semiconductor laser 4. FIG. In the case of the present invention, the minute recording area (hereinafter referred to as a cell) in the track direction of the recording medium 1 corresponds to a bit in a compact disk or a domain in a magneto-optical disk.
They are arranged at equal pitches in space or time.

Therefore, it is fundamentally different from mark-to-mark recording or mark-length recording used for compact discs and magneto-optical discs, in which multi-valued information is recorded at unique positions, and the spacing and length of each cell is , independent of the information recorded. Therefore, in terms of high-density recording, in addition to the main high-density recording means of multilevel recording, each cell can be arranged closely and consecutively, making it possible to use the recording area without wasting it. Density recording is possible. In terms of efficient use of the recording area, compared to, for example, the conventional mark-to-mark recording method, it is possible to increase the density by more than twice as much.

FIG. 5(a) shows an example of such a case, and time t0 is the reading time per cell. CI to Cs are cells in the aforementioned minute recording area in the track direction, and the information in the cells is successively and sequentially read. To play the information,
Information is reproduced in the rising region of the sawtooth wave 22 in FIG. 5(a). By sweeping the wavelength with a sawtooth wave in this way to make the relationship between time and wavelength linear, and measuring time in this state, wavelength conversion becomes easy. Furthermore, in addition to the process of converting recorded phase difference information into wavelength, which is a feature of the reproduction of the present invention, the reproduction system can be further simplified by converting wavelength information into time. It becomes possible.

The waveform shown as 23 in FIG. 5(b) is an example of the waveform of the reflected light intensity from the etalon when each cell is read out using the wavelength sweep waveform of FIG. 5(a). That is, this is an example of the output waveform of the optical detector 10. first cell C1
, a pulse P corresponding to a low reflectance, that is, a sharp dark stripe of the etalon, appears at the initial wavelength λ in the initial state, that is, in a state satisfying equation (5). In this case, the time from the start time of the rise of the sawtooth wave of the wavelength sweep until the peak of the pulse appears is Osee, so
By measuring it, the wavelength is λ, that is, the wavelength change Δχ=0, the phase difference change Δψ=0, and the refractive index change ΔnM
=o can be detected.

Next, when reading the second cell C2, the time when the peak of the pulse P appears is delayed by t from the rise start time of the sawtooth wave. The wavelength λ1 of the reproducing laser at this time t1 can be easily determined because its sweep is linear, so the change in phase difference Δψ° is determined from equation (8), where Δλ: λ1 - λ, and ( 7) Correspondence with the change in refractive index Δn2 is taken using equation (6). In the third cell C8, a different time t2 is determined until the pulse P appears, and the corresponding wavelength, phase, and refractive index are similarly determined. Therefore, by giving the medium layer a refractive index change that corresponds to the multi-value information, the multi-value information is recorded as a phase difference, and the multi-value information is reproduced by converting the phase difference into a wavelength change, thereby achieving good contrast. Furthermore, by converting wavelength detection to pulse detection on the time axis, the apparatus can be simplified.

The relationship between the refractive index change given to the recording medium and the final wavelength change was given by equation (9). Furthermore, if the slope of the rising portion of the sawtooth wave 22 shown in FIG. 5(a) is given by the equation (lO), then the equation (9) can be expressed by the following equation (11).

Therefore, the relationship between the refractive index change given as multi-value information and the time interval obtained as multi-value information can be obtained. For example, 1
In order to perform 8-bit multi-value conversion on a cell, 256 multi-value information must be recorded on the recording medium as described above, so the required resolution is 1/256 or more. The refractive index is 4, the resolution is 10-4, and the range is 3X10-"
Then, the 9 resolution and range of the corresponding wavelength is (11)
From the formula, assuming that λ=830, it is approximately 0.2 nm and 5 nm. If the electrical time resolution is 10 n5ec, the range is 2.56μ5ee (approximately 400k) + 2>, and the wavelength sweep rate is 2 nm/μse from equation (10).
It will be about c. If the cell size is 1 μm, the relative velocity between the spot and the medium will be approximately 0.4 m/see. This is an order of magnitude slower than a normal optical disc, but since 8 bits of information are recorded in one cell, the transfer rate is approximately 3 Mbps. Since the relative speed is low, the optical power required for recording is small. Of course, the temporal resolution,
If the wavelength sweep speed is improved, higher multilevel values and higher transfer rates can be realized.

In addition, in FIG. 5(b), the pulse P4 generated at each falling portion of the sawtooth wave in FIG. 5(a) is a pulse that appears because the same cell is read out in a round trip of the wavelength sweep. If this pulse is removed by providing a gate circuit or the like, no problem will occur. Also, in Figure 5,
Although the cells are arranged adjacent to each other, in reality, it is better to arrange them with a margin in order to reduce crosstalk between cells.

[Other Embodiments] FIG. 6 is a time chart for explaining the reproduction operation of another embodiment.

In this embodiment, in order to solve the above-described reduction in crosstalk between cells and to obtain a standard for multilevel information, a certain interval is provided between each cell, and this is used as an unrecorded area, that is, an initial refraction area. This is an area where the ratio is maintained. In Figure 6,
The unrecorded area is shown as R+ ""' R-. In this example, when reproducing information, the information cells are read out at the rising edge t of each sawtooth wave 24 in FIG. 6(a), and the reference cells provided between the cells are read out at the falling edge t0°. . Therefore, as shown in waveform 25 shown in FIG. 6(b), at the end wavelength of each sawtooth wave, the initial (eg, 0
A reference pulse P corresponding to the information (meaning ) is obtained. By detecting the time t+, tx from this pulse to the information pulse Pa, uncertainties such as variations between each medium, spatial variations within the medium, changes over time, and variations in the wavelength of the reproducing semiconductor laser 4 are detected. elements can be corrected. In this case, although the recording density is somewhat reduced, data reliability can be significantly improved.

2, according to the present invention, instead of simply recording and reproducing multilevel information based on differences in reflectance, the phase is recorded using optical interference, and the reproduction always uses the multiple interference effect to achieve high contrast. Because it detects the peak of the converted fringe, it is possible to record and reproduce highly reliable multi-value information without reducing the SNR due to multi-value conversion as in the conventional method. Therefore, the laser spectrum during wavelength sweeping only needs to be in a single mode, and does not need to have a narrow spectrum width like PHB, making wavelength sweeping easy.Furthermore, as shown in Fig. multilayer reflective film 12a
, 12b, 14a, and 14b do not need to be the same, and the relationship between recording sensitivity, recording laser power, and relative speed,
The optimum value may be determined based on the relationship between the sharpness of the stripes and the SNR, and may be asymmetrical.

In addition, in the examples, the refractive index nM and wavelength λ were focused on as optical parameters of the etalon, but the change in phase difference ψ is generally expressed by the following equation (12), and is determined by the thickness d. There are also changes.

Tt”... (1
3) In the above embodiment, Δd=o, but according to the present invention, it is also theoretically possible to record the phase difference Δψ through the thickness change Δd and read it out as Δλ. . Also, due to changes in both Δd and Δn, Δ
It is also possible to record ψ. However, the change in thickness △d
In the case of , it is a physical shape change, so it is disadvantageous to arrange each cell densely in order to reduce the crosstalk between each cell while maintaining the multiple interference effect. On the contrary, unnecessary △
If d exists, it can be corrected by providing a reference cell as shown in the embodiment of FIG.

Further, in the above embodiments, the case where the present invention is applied to a reflective recording medium has been described, but the present invention can also be applied to a transmissive recording medium. In this case, the transmittance T of the etalon. is expressed by equation (13).

ψ 1+Fsin''- Since the transmittance T and the reflectance R1 have the relationship shown by equation (14), sharp and bright interference fringes appear in the transmitted light.

R, +T, = 1 - (14) Therefore, by placing the signal detector at a position facing the optical head with respect to the recording medium 1,
A pulse waveform obtained by inverting the pulse waveforms 20, 21, 23, and 25 of b) is obtained.

FIG. 7 shows a transmission type embodiment corresponding to FIG. 6. By using a transmissive type as described above, a certain degree of complexity increases, such as the arrangement of the detector and the movement in synchronization with the optical head. However, many defects, scratches, dust, etc. on the medium absorb and scatter light, and the detector output often has a downward pulse-like waveform. If the signal is an upward pulse like waveform 27, it is basically advantageous against errors caused by medium defects. Note that other characteristics are the same as in the previous embodiment.

In addition, in the above embodiments, the refractive index change of the medium is
Although the explanation has been given as a change in the real part of the complex refractive index, the present invention is also applicable to general cases including the imaginary part of the complex refractive index N. The complex refractive index N is as described above (, (15)
It is expressed by the formula.

N=n+iK −(15) where K is an attenuation coefficient. nK represents the amount related to the absorption of light by the substance, and in the case of a heat mode optical memory, represents the efficiency of converting light into heat.

In a heat mode optical memory medium, nK≠0, that is, ≠0. Furthermore, in many media, laser heating causes not only a change in refractive index (but also a change in attenuation coefficient).

In the present invention, if a material with K≠0 and Δ≠0 is used as a medium, the phase ψ of the etalon in equation (3) will be as follows (16 ) can be expressed by the formula.

Therefore, the above-mentioned equation (7) can be expressed as equation (17).

4π(nv+ΔnM) ψ = ψ+ Δψ= (φ10 Δφ)λ (17) This becomes the phase difference recorded on the etalon medium.

Reproduction is possible by changing the wavelength to cancel this change in phase difference and by detecting the wavelength on the time axis, as in the previous embodiment. In this way, the present invention is applicable even to media in which the complex refractive index changes.

[Effects of the Invention] As explained above, according to the present invention, multilevel information is recorded by changing the phase of the optical multiple interference effect, which not only makes it possible to achieve a high SNR (
This has the effect of achieving a high level of information. Therefore,
Although the SNR is high, the information recording density can be further increased, so that high reliability and high density recording can be achieved at the same time. In addition, since changes in phase are converted into changes in wavelength using the spectral characteristics of the multiple interference effect, and the wavelength changes are detected by detecting time, the reproduction system can be easily configured without the need for any special equipment. It has the advantage of being configurable.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an information reproducing apparatus of the present invention, FIG. 2 is a sectional view showing an embodiment of an optical information recording medium of the present invention, and FIG. 3 is a diagram showing the main parts of the recording medium. FIG. 4 is a characteristic diagram showing the multiple interference effect characteristics of the recording medium, FIG. 5 is a time chart showing the reproduction operation of the above embodiment, and FIGS. 6 and 7 are diagrams showing other embodiments. 3 is a time chart showing an example reproduction operation. Recording medium 2; Semiconductor laser for recording 3.5; Collimator lens 4; Semiconductor laser for refocusing 6.7: Beam splitter 8; Pick-up lens 9; Sensor lens 10. Optical detector 11a, ll
b; Substrates 12a, 12b; First reflective layers 13a, 13b; Medium layers 14a, 14b; Second reflective layer 15, adhesive layer 31, recording laser drive circuit 32; Modulation circuit 33: Clock signal generation circuit 34; Reproduction Laser drive circuit 35; beak detection circuit 36; clock circuit 37; information reproducing circuit

Claims (7)

[Claims] (1) The first and second reflective layers are arranged parallel to each other at a predetermined interval, and are provided between these reflective layers so that the light reflected from each layer causes multiple interference, and the light is irradiated. An optical information recording medium comprising a medium layer whose refractive index changes by changing the refractive index. (2) The medium layer is made of TeOx, InSeTlCo, Ge
TeSbTl, GeTeSe, anthraquinone dielectric,
2. The optical information recording medium according to claim 1, which comprises either a sioquikedine compound or a trifed thiazine compound. (3) The optical system according to claim 1, wherein each of the first and second reflective layers comprises a multilayer reflective film in which a dielectric with a low refractive index and a dielectric with a high refractive index are alternately laminated. information recording medium. (4) From first and second reflective layers arranged parallel to each other at a predetermined interval and a medium layer provided between these reflective layers so that the light reflected from each causes multiple interference. The refractive index of the medium layer is changed according to the intensity of the irradiated light beam by irradiating the medium layer with a light beam whose intensity is modulated according to the information to be recorded using an optical information recording medium consisting of: Information recording method. (5) The first and second reflective layers are arranged parallel to each other at a predetermined interval, and the refractive index of the first and second reflective layers is provided so that the light reflected from each layer causes multiple interference. A process of irradiating a reproducing light beam onto an optical information recording medium consisting of a medium layer on which information is recorded as a change, a process of sweeping the wavelength of the light beam within a predetermined range, and a process of reflecting or transmitting light of the light beam by the medium. An information reproducing method comprising a process of receiving light and detecting a wavelength that causes multiple interference, and a process of determining information recorded on a medium from the detected wavelength. (6) A device for reproducing information recorded on an optical information recording medium by irradiating a light beam onto the medium and detecting reflected light or transmitted light of the light beam by the medium, wherein the medium is reflected by each of the medium. The first and second lights are arranged parallel to each other at a predetermined interval so that multiple interference occurs in the received light.
means for sweeping the wavelength of the light beam within a predetermined range; An information reproducing device comprising means for receiving light and detecting a wavelength that causes multiple interference, and means for determining information recorded on a medium from the detected wavelength. (7) the sweeping means changes the wavelength at a predetermined rate;
The wavelength detecting means detects the wavelength causing multiple interference by measuring the time from the start of the sweep to the time when a peak appears in the amount of reflected light or transmitted light. The information reproducing device according to scope 6.