JP2703913B2 - Recording / reproducing apparatus and recording / reproducing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]   The present invention has a glass transition point and anisotropic refractive index.
Change the direction of the anisotropy of the refractive index by the electric field
An optical modulation layer made of a compound capable of
Having an optical modulation element having a write state
Writing and writing information on the optical modulation layer with improved properties.
Recording / reproducing method having recording / identification (reproduction) step and method thereof
The present invention relates to a recording / reproducing apparatus used for the method. In particular, the identification step
The optical thickness of the optical modulation layer (n₁d and / or n
_Twod) to control the amount of light reflected from the deflection plate
Recording / reproducing method and recording / reproducing apparatus as identification steps
About.   Where n₁And n_TwoRecords on the optical modulation layer.
Incident light in the multiple reflection state at the
It shows the average refractive index of the layer that is repeatedly reflected. Optics
If a liquid crystal compound is used in the modulation layer,
n₁Or n_TwoTo n_⊥Or n So that
Controlling the optical modulation layer is the amount of change in optical thickness
Will be the largest.   In general, when using a compound having anisotropy in refractive index
Changes in refractive index anisotropy before and after
Select the plane of polarization of linearly polarized light so that the difference in the refractive index is maximized.
Just do it. [Conventional technology and problems]   Conventionally, phase transitions have been used as rewritable high-density recording media.
Using elephants, using magneto-optical phenomena, or
Utilizes electric field alignment of polymer liquid crystal or smectic liquid crystal
Things to do were known. However, the phase transition phenomenon
Recording methods that use
Those that use magnetic phenomena detect minute rotation of the plane of polarization
Therefore, the recording apparatus becomes complicated and expensive. one
Utilizing polymer liquid crystal or smectic liquid crystal electric field alignment
The object is scattered and birefringent by using two polarizing plates for reading
The amount of transmitted light is reduced or not sufficient to take advantage of the effect
Optical thickness must be sufficient to obtain birefringence effect
Satisfactory in terms of sensitivity and density
Was not. [Object of the invention]   Therefore, the present invention provides a simple
Equipment, high density, high density and excellent storage stability
Recording / reproducing apparatus having rewritable optical modulation element and
An object is to provide a recording / reproducing method suitable for the device.
You. [Means and actions for solving the problems]   The present invention has a glass transition point and anisotropic refractive index.
It is possible to change the direction of the anisotropy of the refractive index.
That the optical modulation layer having a functional compound shows a multiple reflection state
Optical modulation element that can be
By applying an electric field above the transition point, the light of the optical modulation layer
Multiple reflection of the optical thickness of the optical modulation layer by changing the optical thickness
Write by making either state or transparent state
The writing state by lowering the glass transition point.
Recording means for storing the reflected light amount of incident light
And a means for reproducing the recording.   Further, the present invention has a glass transition point, and the refractive index
It has anisotropy and can change the direction of the anisotropy of the refractive index.
The optical modulation layer having a compound capable of
Either optical thickness indicating the transmission state or optical thickness indicating the transmission state
Glass transition of the compound relative to the optical modulator controlled to
By applying an electric field above the point, the optical modulation layer
Write by changing the thickness, glass
A recording process that maintains the written state below the transition point,
A reproducing process by identifying the amount of reflected light.
A recording / reproducing method characterized by the following.   In the present invention, the optical modulation layer has a glass transition point (Tg).
And the recording state is reduced below the glass transition point.
This greatly improves record stability.
You. The optical modulation layer stabilized in this way has a spontaneous polarization.
Orientation and size are affected by temperature changes and air charge
Since it does not exist, it can be stored for a long time and the error rate decreases.   Also, if it is fixed below Tg, it will respond to the direction of spontaneous polarization.
Stable reading when utilizing the change in birefringence
Can run out.   Further, the optical modulation layer having the glass transition point is formed by a pair of parallel
The glass modulation for each scanning line is applied to the optical modulator placed between the electrodes.
Means for heating above the transition point and / or writing to apply an electric field
And the written information should be below the glass transition point.
Recording means for fixing (memory) the display state with
Reading is performed using the change in birefringence of the written part
If each optical modulating means has a contra
More effective without lowering strikes or crosstalk
A recording / reproducing device having an optical modulation element is obtained.   Further, the recording / reproducing device includes an optical modulation layer and the optical modulation layer.
Reflection on both sides of the layer directly or through insulating orientation control layer
An optical modulation element having a layer disposed thereon, and the optical modulator
By controlling the optical thickness of the optical modulation layer of the modulation element,
Identify differences in the reflectance of reading light incident on a layer
If you have a means to read by
A recording / reproducing device having a high-density optical modulation element is obtained.   In Fig. 2, the recording medium is irradiated with a laser to perform writing.
A schematic diagram of the device is shown.   In FIG. 2, reference numeral 1 denotes an optical modulation layer, and 10 denotes a laser.
Light, 20 is a voltage application device, 19 is an optical modulation layer driving device
, 18 is the optical system drive, 17 is the optical system, 16 is the reflecting mirror
, 13 is an optical modulator, 14 is a modulation signal generator, and 15 is
Represents a laser oscillator.   Laser emitted from laser oscillator (15) as shown
-Light is focused by the optical system (17) through the light modulator (13).
The points are adjusted and incident on the optical modulation layer (1). At this time,
The writing unit that irradiates the laser light has an optical drive unit (18).
Adjustment is possible with the optical modulation layer drive (19).   This writing method uses a laser beam when an electric field is applied.
By heating the writing part of the mechanical modulation layer above Tg
Do not only irradiate laser light, but also optical modulation layer
If it is possible to change the heating element to a heated state,
Alternatively, writing may be performed.   The writing state will be described in more detail.   The optical modulation layer used in the present invention is heated once and then gradually cooled.
Then, an optical modulation layer that is horizontally oriented with respect to the electrode is formed.
be able to.   Therefore, writing is performed on the optical modulation layer in the horizontally oriented state.
However, if an electric field is applied during slow cooling,
The optical modulation layer becomes an optical modulation layer oriented in a uniform direction.
Then, after orienting in a uniform direction, only the writing part is heated,
Writing by changing the orientation direction by applying a reverse electric field
Can also.   However, after heating the optical modulation layer used in the present invention,
Just cool and orient in the same direction without applying an electric field
The domain of the liquid crystal layer that forms the optical modulation layer
To distinguish it from the recorded state obtained by writing
be able to. Therefore, the writing of the present invention once exceeds Tg.
It can be applied to the optical modulation layer obtained by heating and then gradually cooling.
Wear.   Next, the optical modulation means for reading will be described.   4 (a) and 4 (b) are optical modulation layers used in the present invention.
Are schematically drawn for the explanation of the reading.   That is, FIG. 4 (a) shows the optical structure before the writing means is provided.
3 shows a state of molecules of a modulation layer. In this way, the electrode
The optical modulation layer that has been horizontally aligned by heating
And then fixed below Tg, the optical modulation layer
Is fixed, that is, recorded in the state shown in FIG.
-) Utilizing the difference between the states of the two optical modulation layers
And the amount of change in the optical thickness of the optical modulation layer is arbitrary.
Set to a value and scan.   Therefore, the optical modulation element of the present invention is arranged as shown in FIG.
Formed.   In FIG. 3, reference numeral 1 denotes an optical modulation layer, and 2 denotes an insulating orientation control.
Layer, 3 is a semi-transparent reflective layer, 4 is an electrode, 5 is a transparent substrate, 6
Is a polarizing plate, 7 is a spacer, 8 is a reflective layer, and 10 is writing
Alternatively, it is a reading laser beam.   The anisotropy of the refractive index used in the present invention is controlled by an electric field.
It has a glass transition point and is specifically shown below.
Polymer liquid crystal or ferroelectric polymer liquid crystal.
You.   Optical modulation element comprising an optical modulation layer having the compound
To apply the above reading means to
(See FIG. 5).   First, light is incident from the polarizing plate 6 side. Then
The light passes through the semi-transmissive reflective layer 3 and reaches the electrode / reflective layer 9
I do. The reflection layer 9 reflects light, and
As a result, the reflected light returns to the semi-transmissive reflective layer 3 again.
In this case, incident light is reflected by the electrode / reflection layer 9.
Optics of the optical modulation layer between 3 and 9 so that the light
When the thickness is controlled, light does not pass through the semi-transmissive reflective layer 3
The layer 3 also reflects light, and the semi-transmissive reflection layer 3 and the electrode and the anti-reflection layer 3
Reciprocating between the emissive layers 9 and 3
And is detected as reflected light. In the present invention
Such a state is called a multiple reflection state. The multiple reflection state
Is possible even without the semi-transmissive reflective layer 3
However, it is necessary to obtain the multiple reflection state efficiently.
Preferably. Refractive index of 4 if 3 is not present
Set to satisfy the anti-reflection condition with the refractive index of 2, 1
(Refractive index of 4 × refractive index of 9) = (average refractive index of 2,1,2)
²), A multiple reflection state occurs between 4 and 9.   The multiple reflection state is incident light arbitrarily determined from the value of the optical thickness
And the optical path length increases significantly.
Of light that is slightly incident on the layer that performs multiple reflection
If there is something that absorbs light, it reflects on the incident light
The amount of light that can be detected as light can be minimized
(That is, the reflectance can be minimized.)   And second, optically by an electric field based on the first state.
Changes the molecular state of the modulation layer, and the reflected light is translucent.
3. Make a passable state. Then, the amount of light at that time is
It is identified as the emissivity, and this is the contrast with the time of the first state.
When expressed as a difference between the two, reading can be performed.
As described above, the contrast between the first state and the second state
Compared to the above, it is possible to obtain an unprecedented high sensitivity identification state
Can be.   In the present invention, the reading (reproduction) described above is performed.
Optical modulation means with optical modulation layer below glass transition temperature
The recording layer is slightly affected by the reading light.
Even if heated, the recorded contents may be disturbed by the internal electric field.
Can provide an optical modulator with excellent storage stability
You.   The reading (reproducing) means described above is used when the reflectance is minimal.
And the control when increasing the reflectivity
In the above example, reading was performed after the last time.
Then, on the contrary, first select the state with high reflectance, and gradually
Difference in contrast when the reflectance is lowered
A trimming (reproduction) may be performed.   Δε (dielectric constant) of the compound in the optical modulation layer of the present invention
For negative ones, it is better to align them vertically to the electrode.
No.   The value of the variation Δnd of the optical thickness in the present invention
As a result, preferably 0.2 μm or less, more preferably 0.001 μm
0.20.2 μm. That is, the ordinary refractive index anisotropy
Physical properties of the compound having the property (Δn = 0.001-0.5)
High sensitivity and high cost even when using a very small thickness d
Contrast is obtained. The larger the Δn, the greater the physical thickness
d can be reduced, preferably d = 1 μ
m or less, more preferably 100 to 8000 °.   Also, in order to make the contrast clearer,
May be added with a dye, for example, as an additive
The following can be given:   However, it is not limited to the exemplified dye.   The translucent reflective layer 32 in the present invention has a transmittance of 5 to 95%.
Had a film thickness of 10 to 2000 mm, more preferably a film thickness of 50 to 800
層 Layer or film of metal thin film of aluminum, gold, silver, copper, etc.
10-5000mm thick inorganic oxide film, high refractive index compound such as ZnS
Can be used.   In FIG. 3, the transparent substrate 5 has In_TwoO_Three, SnO_Twois there
Or a transparent electrode composed of a thin film such as ITO (Indium-Tin Oxide).
The poles or electrodes 4 are covered. On top of that polyimide
A thin film of similar polymer with gauze or an acetate flocking cloth
Alignment control to align liquid crystals in the rubbing direction
Layer 2 is formed. Also, as the insulating layer, for example, silicon
Nitride, hydrogen-containing silicon carbide, silicon acid
, Boron nitride, boron nitride containing hydrogen, cerium
Oxide, aluminum oxide, zirconium oxide,
Insulation of inorganic substances such as titanium oxide and magnesium fluoride
A layer is formed, and polyvinyl alcohol and polyimid
, Polyamide imide, polyester imide, polypara
Xylene, polyester, polycarbonate, polyvinyl
Ruacetal, polyvinyl chloride, polyvinyl acetate, poly
Amide, polystyrene, cellulose resin, melamine tree
Resin, urea resin, acrylic resin and photoresist resin
Which organic insulating material is used as the orientation control layer
Orientation control layer may be formed, and inorganic material insulation
Insulating alignment control layer or organic substance
There may be. In addition, the orientation control layer disposed on the substrate is
It may be provided only on the plate. This insulating orientation control layer
If it is inorganic, it can be formed by vapor deposition, etc.
Solution or its precursor solution (solution
0.1-20% by weight, preferably 0.2-10% by weight)
And spinner coating, dip coating, screen printing
Method, spray coating method, roll coating method, etc.
Can be formed by curing under curing conditions (for example, heating)
it can. The thickness of the insulating orientation control layer is usually 20 to 1
μ, preferably 30Å to 5000Å, more preferably 50Å to
3000Å is suitable.   In FIG. 3, the transparent substrate 5 and the reflective layer 8 are
Are kept at arbitrary intervals. For example, given diameter
Using silica beads and alumina beads as spacers
A transparent material is sandwiched between the transparent substrate 5 and the reflective layer 8, and the surrounding area is a sealing material, for example,
There is a method of sealing using an epoxy adhesive. That
In addition, polymer film or glass fiber as a spacer
May be used.   The electrode 4 is connected to an external power supply by a lead wire.
Have been. A polarizing plate 6 is bonded to the outside of the transparent substrate 5.
It is.   The reflection layer 8 is, for example, a metal substrate,
Formed to have both function and function as original reflection layer
(Fig. 5).   Similarly, the surface of the electrode 4 provided on the reflection layer 8 side is referred to as a reflection layer.
If the reflective layer 8 is provided, the reflective layer 8 should not be provided.
You may not.   On the other hand, at least the side of the electrode 4 on which light is incident
Need to be transparent electrodes.   The electrodes 4 are arranged in a matrix as shown in FIG.
May be configured. At that time, the display change part on the display layer
Is the S portion (selected pixel) in FIG. 6 (b),
Comparing the molecular state of N with the N part (unselected pixel),
6 As shown in FIG.   The optical modulator of the present invention shown in FIG.
The writing, recording and reading (reproducing) optics described
When the modulation method is applied, each scan line has a glass transition point or lower.
Write on by applying an electric field after heating on
State by selecting the state
The recording medium under the fixed state.
Implement a method of reading using changes in properties
And And the optics that performed such optical modulation means
Modulation element is essentially unaffected by additional scan lines
It can be a device that has never existed before.   Fig. 1 shows the optical modulation layer read by irradiating it with reading light.
FIG. 1 shows a schematic diagram of a recording / reproducing apparatus of the present invention for performing (reproducing).
Was.   In FIG. 1, reference numeral 1 denotes an optical modulation layer, and reference numeral 20 denotes a voltage application device.
, 19 is an optical modulation layer driving device, 18 is an optical system driving device, 17
Is an optical system, 16 is a reflector, 15 is a laser oscillator, and 23 is polarized light
A plate, 21 is a beam splitter, and 22 is a photodetector.   As shown in the figure, the laser emitted from the laser oscillator (15)
-Adjust the direction of the light with a mirror, and
Irradiate the optical modulation layer through the cutter and reflect the reflected light again
Read through a beam splitter with a photodetector
U. The laser light is applied to the optical modulation means for reading.
The reading unit that irradiates the optical drive (18) and the recording layer drive
Adjustment is possible by the drive (20).   Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
You. [Example 1]   A transparent electrode 4 made of ITO is formed on a glass substrate 5,
Further, a translucent Au3 of 500 mm or less is formed by evaporation.
Polyamic acid solution (PI manufactured by Hitachi Chemical Co., Ltd.)
Q: Non-volatile content 3wt%) spinner coating rotating at 3000rpm
Spread over a cloth machine for 30 seconds, 120 ° C for 30 minutes, 200 ° C for 60 minutes
Heated at 350 ° C. for 30 minutes. The port obtained in this way
The imide film 2 is given a uniaxial orientation by a rubbing method.
Was. On top of this, the dichloroethylene of the polymer liquid crystal of the following formula (A)
Liquid polymer (non-volatile concentration 10wt%) and polymer liquid crystal
To which 0.1% wt of a dye of the following formula (B) is added
With a spinner coater rotating at 3000 rpm and drying at 100 ° C.
Dried. The thickness was about 2000 mm.   The same orientation control as above is applied to the substrate thus formed.
Obtained by sealing the periphery by closely contacting the Al substrate 9 having the layer 2
The temperature of the device is raised to 150 ° C and then gradually cooled.
It was axially oriented (FIG. 5).   While irradiating this element with a 5 mW semiconductor laser 10, ITO
A voltage of 20 V was applied between the electrode and the Al substrate. Laser light 10
After heating to make the glass transition temperature or higher, cool
To align the spontaneous polarization, and then write the written part to the glass transition point.
The write part and the non-write part were as follows.
Polymer of non-writing part by polarization method using conductor laser
The reflectance was measured to match the optical axis of the liquid crystal.
5% in the writing part and 15% in the non-writing part
The display state was obtained. The device was left at room temperature for 20 days
However, the reflectance did not change. [Example 2]   A transparent electrode 4 made of ITO is formed on a glass substrate 6,
In addition, a semi-transparent 150 mm thick Al with a thickness of 500 mm or less is deposited.
Polyamic acid solution (Hitachi Chemical Co., Ltd.)
Industry Co., Ltd. PIQ: Non-volatile content concentration 5wt%) rotated at 3000rpm
Spinner coating machine for 30 seconds, 120 ° C for 30 minutes
During the heating, heating was performed at 200 ° C. for 60 minutes and at 350 ° C. for 30 minutes. like this
The polyimide alignment film 2 obtained as described above is uniaxially rubbed by a rubbing method.
Orientation was given. On top of this, the ferroelectric high
Chloroethane solution of molecular liquid crystal (non-volatile content 5wt%)
And 0.1% wt of the above formula with respect to the polymer liquid crystal.
Spinner with the dye of (B) added at 3000rpm
-Coated with a coating machine and dried at 100 ° C. Al substrate on this substrate
To polyimide alignment film 2 formed in the same manner as above
And the direction of the uniaxial alignment process is the same.
The periphery was sealed.   The substrate obtained in this way is coated with a ferroelectric
Cool slowly from a temperature sufficiently higher than the clearing point of the
After directing, apply 30 V directly to the ITO electrode and Al substrate above Tg.
A flowing voltage was applied.   Next, after cooling to room temperature, a 5 mW semiconductor laser was illuminated.
While applying a voltage opposite to the aforementioned DC voltage,
The conductor laser was stopped, and the application of voltage was stopped. This
After writing, a 0.2mW semiconductor laser
-10, the optical axis of the ferroelectric polymer liquid crystal and the polarization direction match.
And measured the reflectivity.
The emissivity was 10%, and the reflectance was 25% in the non-writing area. Reading
The reflection was repeated over 100 times, but the reflectance did not change. [Example 3]   Translucent Al of less than 500mm on glass substrate by evaporation
Vinylidene fluoride-trifluoroethyl
MEK solution of ren copolymer (75:25) (solids concentration 5% wt)
Is applied over 30 seconds with a spinner coating machine rotating at 3000 rpm
Then, it was dried at 150 ° C. for 1 hour to obtain an alignment film. On top of this
Polymer liquid crystal dichloroethane solution of the formula (D) (nonvolatile content)
10wt%) and 0.1wt% before polymer liquid crystal
Apply the dye of formula (B) above with a spinner coater.
Cloth and dried at 100 ° C. For this substrate,
And the vinylidene fluoride
Alignment film made of fluoroethylene copolymer (75:25)
The surroundings were sealed by tightly attaching the provisions (Fig. 7
(A)).   This element is heated above the clear point of the liquid crystal polymer and slowly cooled.
By doing so, a vertically oriented product was obtained. Corona discharge to this element
Place the corona jar on electrical glass and ground the Al side 9
Heat it with a 5mW semiconductor laser
FIG. 7 (b). Next, stop the semiconductor laser and remove the charge
Write by removing corona chirji by
(FIG. 7 (c)). The recording part of this element
The recording part is a linearly polarized 0.2mW semiconductor laser.
10% reflectance at recorded part, non-recorded part
With this, a reflectance of 3% was obtained. Next, do n’t add the corona jar
After irradiating the recording part with a 5 mW semiconductor laser, cooling
As a result, the reflectance of the re-recorded portion returned to 10%. 〔The invention's effect〕   As described above, according to the present invention, only one polarizing plate is required.
Less loss of light and contrast
Obtaining a recording / reproducing device having an excellent optical modulation element
And high sensitivity and high resolution reading according to the present invention.
Data, and also improved reading durability and storage stability.
New means without degradation due to overwriting can be applied
It has become possible to provide a recording / reproducing device.   Also, the writing, recording, and reading means of the present invention is assembled.
By combining them, a computer with high definition and large screen
Optics with essentially reduced trust and improved crosstalk
A recording / reproducing device having a modulation element was obtained.   Further, a recording / reproducing method suitable for the recording / reproducing apparatus of the present invention is provided.
Could be offered.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a recording / reproducing apparatus which reads (reproduces) an optical modulation layer with a laser beam according to the present invention, and FIG. FIG. 3 is a schematic view of a reproducing apparatus, FIG. 3 is a cross-sectional view showing one example of the optical modulation element of the present invention, FIGS. 4 (a) and (b) are diagrams showing the molecular state of the optical modulation layer in the present invention FIGS. 5 and 6 (a) are diagrams showing another embodiment of the optical modulation element of the present invention, FIG. 6 (b) is a configuration diagram of scanning electrodes and signal electrodes arranged in a matrix, and FIG. 6 (c). 7A is a diagram showing a molecular state of an optical modulation layer in the device of FIG. 6A, and FIGS. 7A, 7B and 7C are diagrams for explaining Example 3. FIG. DESCRIPTION OF SYMBOLS 1 ... Optical modulation layer, 2 ... Insulating orientation control layer 3 ... Semi-transmissive reflective layer, 4 ... Electrode 5 ... Transparent substrate, 6 ... Polarizing plate 7 ... Spacer, 8 ... Substrate 9 ... … Metal substrate 10… writing or reading light 11… scanning electrode 12… signal electrode 13… optical modulator 14… modulation signal generator 15… laser oscillator 16… reflecting mirror 17… optical system , 18 Optical system driving device 19 Optical modulation layer driving device 20 Voltage applying device 21 Beam splitter 22 Photodetector device 23 Polarizing plate

Continuation of front page    (72) Inventor Yutaka Kurabayashi               3-30-2 Shimomaruko, Ota-ku, Tokyo               Inside Canon Inc.                (56) References JP-A-61-64493 (JP, A)                 JP-A-50-87295 (JP, A)                 JP-A-61-90349 (JP, A)                 JP-A-61-26954 (JP, A)                 JP-A-60-107032 (JP, A)                 V. P. Shibaev, M .; V. K               ozlovsky, L .; A. Beres               nev, L .; M. Blinov, N.               A. Plate "Thermotrop               ic Liquid Crystal               ine Polymers, "Ligu               id Crystal Polymer               s Polymer Bulletin                 12, pp. 299-301 (1984)

Claims (1)

(57) [Claims] It has a glass transition point and has anisotropy of refractive index,
An optical modulation element in which an optical modulation layer having a compound capable of changing the direction of the anisotropy of the refractive index can have an optical thickness showing a multiple reflection state, and applying an electric field at a temperature equal to or higher than the glass transition point of the compound Recording means for performing writing by changing the optical thickness of the optical modulation layer by changing the optical thickness of the optical modulation layer to one of a multiple reflection state and a transmission state, and maintaining the written state by lowering the glass transition point or lower. A recording / reproducing apparatus comprising: a recording / reproducing device that identifies the amount of reflected incident light and reproduces the recording. 2. 2. The recording / reproducing apparatus according to claim 1, wherein the compound having a glass transition point is a polymer liquid crystal. 3. 2. The recording / reproducing apparatus according to claim 1, wherein the compound having a glass transition point is a ferroelectric polymer liquid crystal. 4. 2. The recording / reproducing apparatus according to claim 1, wherein the optical thickness of the optical modulation layer changes by changing the direction of the anisotropy of the refractive index. 5. 2. The recording / reproducing apparatus according to claim 1, wherein the amount of change in the optical thickness of the optical modulation layer is 0.2 μm or less. 6. 2. The recording / reproducing apparatus according to claim 1, wherein said optical modulation element has a reflection layer for reflecting incident light. 7. It has a glass transition point and has anisotropy of refractive index,
The optical modulation layer having a compound capable of changing the direction of the anisotropy of the refractive index, the optical thickness showing the multiple reflection state, the optical thickness showing the transmission state, the optical modulation element controlled to any one of A recording step of performing writing by changing the optical thickness of the optical modulation layer by applying an electric field above the glass transition point of the compound, and maintaining a written state below the glass transition point, and the amount of reflected incident light And a reproducing step by identifying the recording and reproducing method. 8. 8. The recording / reproducing method according to claim 7, wherein the optical thickness of the optical modulation layer is changed by changing a direction of the anisotropy of the refractive index.