JPH0210520A - Recording and reproducing method - Google Patents

Abstract

PURPOSE:To improve the reproducing contrast by performing the reproducing of information with high-order harmonics of recording light on an optical recording medium having a recording layer containing a material capable of varying the scattering strength of light and a light absorption pigment. CONSTITUTION:The reproducing is performed by using the reproducing light consisting of the high-order harmonics of the recording light. The high-order harmonics of the recording light used as the reproducing light of information is shorter in wavelength than the recording light, so that the light scattering strength is larger. Then, in addition to the material for making the light scattering strength variable, the light absorption pigment is comprised in the recording layer of the optical recording medium to heat up the recording layer by absorbing the recording light. That is, the recording light wavelength is absorbed due to the light absorption pigment in the recording layer, and moreover the absorption intensity of the light absorption pigment in the recording light wavelength is larger than the absorption intensity of the light absorption pigment in the reproducing light wavelength, while the reproducing light wavelength is hardly absorbed by the light absorption pigment. By this method, the contrast can be improved.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a recording and reproducing method for an optical recording medium.

[Prior Art] Conventionally, in an optical recording medium, when a large number of minute regions (domains) are formed in the medium, such as in a liquid crystal polydomain state or a phase-separated state of a phase-separated polymer, light is emitted by the domain interfaces. Since it is scattered, it is in a light scattering state.

These materials, such as liquid crystals or phase-separated polymers, can change their light scattering intensity by applying heat or an electric field, so their application as optical recording media has been considered.

For example, in an optical recording medium whose recording layer is a mixture of such materials and a light-absorbing dye, recording can be performed by converting the recording light into heat by the light-absorbing dye and heating the optical recording layer. .

On the other hand, reproduction can be performed by irradiating the recording layer with reproduction light and detecting the difference in light scattering intensity from the recording layer as the difference in the amount of reflected light or the amount of transmitted light.

In recording and reproducing such optical recording media, a laser light source with excellent monochromaticity, coherent property, and light focusing ability is often used, and by changing the output of the same laser beam, recording light and reproducing light can be It was commonly used as a light source.

[Problem 8 to be solved by the invention] However, the recording and reproducing method in which a material whose light scattering intensity changes is used as an optical recording medium and only the difference in laser beam output is changed has the following drawbacks. .

(2) Considering the compactness of the recording/reproducing device, a semiconductor laser is preferable as a light source, but long wavelength light such as a semiconductor laser does not provide sufficient light scattering intensity.

■In order to eliminate the above drawback (■), it is possible to increase the thickness of the recording layer, but if the recording light and reproduction light have the same wavelength, the absorption intensity of the light-absorbing dye will also increase, so the light transmission will be reduced. Even in this state, the amount of reproduced light detected decreases.

Due to these drawbacks, the conventional recording and reproducing method for optical recording media in which only the output difference of laser beams is changed has a problem in that a reproduction contrast ratio of 1-minute cannot be obtained.

The present invention has been made to improve the problems of the prior art, and provides an optical recording medium having a recording layer containing a material capable of changing the scattering intensity of light and a light-absorbing dye. By reproducing information using high-order harmonics of recording light.

It is an object of the present invention to provide a recording and reproducing method that can improve reproduction contrast.

[Means for Solving the Problem] and [Operation] That is, the present invention provides a method for recording and reproducing an optical recording medium having a recording layer containing a material whose scattering intensity of light changes and a light-absorbing dye. This is a recording and reproducing method characterized by performing reproduction using reproducing light consisting of high-order harmonics.

The present invention will be explained in detail below.

In the present invention, light scattering refers to scattering caused by optical non-uniformity of an optical recording medium, such as a liquid crystal polymethine state or a phase separated state of a phase-separated polymer, and the intensity of this scattering increases as the wavelength of the incident light becomes shorter. . Therefore, in the present invention, the higher harmonics of the recording light used as the information reproducing light are
Since the wavelength is shorter than that of the recording light, the light scattering intensity is also greater.

Furthermore, the recording layer of the optical recording medium used in the present invention contains, in addition to the material that changes the scattering intensity of light, a light-absorbing dye for absorbing recording light and heating the recording layer. In order to increase the light scattering intensity, it is necessary to increase the thickness of the recording layer, but as the thickness of the recording layer increases, the intensity of light absorption of the recording layer by the light-absorbing dye also increases.

Therefore, in the conventional recording and reproducing method in which the wavelength of the recording light and the reproducing light are the same, even when the light scattering state is reduced, most of the incident reproducing light is absorbed by the light-absorbing dye, so that the recording is detected. This results in the inability to increase the light reflectance and light transmittance of the layer, resulting in an inability to obtain a high reproduction contrast ratio. Additionally, providing a new short-wavelength laser light source for reproduction has many disadvantages in terms of equipment and optics.

Therefore, in the second invention, by using high-order harmonics of the recording light as the reproducing light, it was possible to easily obtain a short wavelength reproducing laser beam and to improve the reproducing contrast. In particular, it is preferable that there is absorption by the light-absorbing dye in the recording layer at the recording light wavelength, and that the absorption intensity of the light-absorbing dye at the recording light wavelength is greater than the absorption intensity of the light-absorbing dye at the reproduction light wavelength; teeth,
In order to improve contrast, it is preferable that there is almost no absorption by the light-absorbing dye at the reproduction light wavelength.

In the present invention, a polymer material is used as the material whose light scattering intensity changes. In particular, polymer materials allow for easy production of recording layer films and are highly stable against oxidation, photodegradation, etc., making optical recording media excellent in environmental stability and durability for recording and reproduction. can be made cheaply. Furthermore, polymeric materials have good compatibility with additives such as light-absorbing dyes, and blending of polymeric materials with one another is possible, allowing the creation of a wide variety of optical recording media.

Such polymeric materials include, for example, phase-separated polymers or polymeric liquid crystals. These materials can reversibly change the light scattering intensity by changing the rapid cooling or slow cooling after heating, or by applying or not applying an electric field or magnetic field after heating. Since it has the property of being able to be maintained at high temperatures, it can be used as a recording layer of a rewritable optical recording medium.

Examples of phase-separated polymers include systems in which two or more types of amorphous polymers are mixed, and these change into a compatible state and a phase-separated state depending on the temperature. In the phase separated state,
If the system is separated into micro regions having a certain specific polymer composition, and the Ah refraction index of light of each composition is different, light will be strongly scattered at the interface of the micro regions. Therefore, the phase separation state is a light scattering state. On the other hand, in a compatible state, no such interface exists, so light is not scattered. The phase-separated state and the compatible state can be distinguished, for example, by detecting light reflectance or light transmittance, depending on their respective light scattering characteristics.

Due to the change pattern of compatibility-phase separation with temperature, these phase-separated polymers have LC3T (Lo-erCrit).
ical 5solution Temperature
) type and U(:5T(Upper Cr1tical 5
The former exhibits a phase-separated state on the high-temperature side and the compatibility state on the low-temperature side, and the latter is the opposite.

Examples of UC3T type include polystyrene-polyisobutyne system, polystyrene-polybutadiene system, polypropylene oxide-polybutadiene system, etc., and LC3T type includes polyvinyl chloride-polymethacrylic acid-rhohexyl system, styrene acrylonitrile copolymer-polymethacrylate system, etc. Examples include, but are not limited to, acid methyl type, polyvinylidene fluoride-polymethyl acrylate type, and the like.

In addition, by slowly cooling these phase-separated polymers after heating, it is possible to change the state of compatibility or phase separation on the high temperature side to the state on the low temperature side. Because it has the characteristic of being able to retain data even after cooling, it can be applied to optical recording media, including rewritable media.

On the other hand, polymer liquid crystals are thermotropic liquid crystals, and nematic, smectic, or cholesteric types can be used as the intermediate phase. Polymer thermotropic liquid crystals have the advantage of not only being able to form a thin film but also being easier to maintain a recording state than low molecular weight liquid crystals.

For example, polymer thermotropic liquid crystals (hereinafter simply referred to as polymer liquid crystals) that can be used in the present invention are classified into the following two types.

■Mesogen groups, or relatively rigid and long atomic groups connected by flexible groups.

■ Those with a mesogen group or a relatively rigid and long atomic group in the side chain.

These polymer liquid crystals can be used in combination with several different types of polymer liquid crystals. It is also possible to use a mixture of a polymer liquid crystal and a low molecular liquid crystal, or a mixture of a polymer liquid crystal and a polymer.

Specific examples of polymer liquid crystals are shown below, but the invention is not limited to these.

R:　OCH,.

R: 0CxHt R:　CN CH.

e Since these polymer liquid crystals have the characteristic of being able to maintain their structural state at temperatures below the glass transition point, a recording mode such as, for example, a first-order recording mode is possible.

In the recording mode (1), first, the polymer liquid crystal is held in a polydomain state where the liquid crystal phase is composed of many domains (domains). Next, the polymer liquid crystal is heated to a temperature higher than the temperature at which the liquid crystal phase exhibits an isobic phase. Recording is performed by rapidly cooling the polymer liquid crystal to below the glass transition point and maintaining the polymer liquid crystal in an isotonic phase state.

In the recording mode (2), the polymer liquid crystal is first held in a monodomain state in which the liquid crystal phase consists of a single domain using an electric field, etc. Second, the polymer liquid crystal is heated above the glass transition point and then cooled. By doing so, recording is performed by maintaining the liquid crystal phase in a polydomain state.

In both of these recording modes (1) and (2), the recording state can be returned to the initial state by slow cooling after heating or by a combination of heating and application of an electric field, so it is possible to return the recording state to the initial state, making it a rewritable optical recording medium. It can be used as Therefore, it is also possible to reverse each state of first non-scattering and light scattering to set the recording mode.

As the L method for heating the polymeric material in the two layers of the optical recording medium, a common method is to add a light-absorbing dye to the recording layer and convert the irradiated light into heat.

In the present invention, the wavelength range of the reproduction light, which is a higher harmonic of the recording light, is a region where the absorption of the light-absorbing dye is low, and when considering the absorption characteristics of the optical element, the wavelength range is from the near ultraviolet to visible range. Therefore, as the recording light,
It is necessary that the light has a wavelength in the visible to near-infrared range.

From these points, it is preferable that the recording light be a laser beam having excellent monochromaticity and linear propagation, and a semiconductor laser is particularly preferable from the point of view of compactness and low power consumption.

Next, examples of light-absorbing dyes that absorb light in the near-infrared wavelength region include the following.

Car (Note) However, n is a positive integer, R is an aromatic diamine residue, A is an aromatic tetracarboxylic acid residue, a and b are each independently O or an integer from 1 to 50, and a+b is an integer of 1 to 10.

Note that if He--Ne laser light, Ar ion laser light, etc. are used, light-absorbing dyes having absorption at the respective wavelengths can be used. In particular, when adding it to a polymeric liquid crystal, it is preferable to use a dichroic dye from the viewpoint of compatibility.

Furthermore, additives such as ultraviolet absorbers, antioxidants, and nucleating agents may be added to the recording layer.

In the present invention, a generally known nonlinear optical element can be used as a means for obtaining high-order harmonics. In particular, in consideration of converting semiconductor laser light into near-ultraviolet-visible light and its conversion efficiency, a nonlinear optical element that converts semiconductor laser light into second harmonics is effective.

Nonlinear optical materials that can be used to generate higher harmonics include, for example, KDP, LiNb0. Elements using inorganic crystals such as urea, organic crystals such as 2-methyl-4-nitroaniline, and the like can be mentioned.

In the case of inorganic crystals, it is easy to obtain large single crystals, and by cutting out the obtained single crystal on a specific crystal plane and performing phase matching, higher harmonics such as the second or third harmonic can be generated. It is possible to obtain a wave conversion element. However, the problem with these inorganic nonlinear optical materials is that their nonlinear optical effects are generally small.

On the other hand, organic crystals have larger nonlinear optical effects than inorganic crystals, or because large single crystals cannot be obtained, phase matching can be achieved by encapsulating them in thin film waveguides or capillaries. .

Furthermore, in addition to the above-mentioned organic crystals, crystalline polymers such as polyvinylidene fluoride, liquid crystals (ferroelectric crystals), and polymer liquid crystals can also be used as organic nonlinear optical materials. Also,
Composite systems such as p-nitroaniline and polyethylene oxide may also be used, and these can be easily fabricated into devices, and phase matching can also be easily achieved using techniques such as orientation.

Next, an example of the recording/reproducing method of the present invention will be described.

The element configuration of the optical recording medium is shown in FIG. 1. In FIG. 1, 1 is a substrate, and 2 is a recording layer containing a polymeric material and a light-absorbing dye.

A polymer composition containing a polymer material whose light scattering state can be reversibly changed and the state can be maintained, and a light color absorbing dye is coated on the substrate.Next, the entire surface of the recording layer is heated and then gradually heated. Cool and fix in light scattering state.

Recording, reproduction, and erasing are performed on the optical recording medium thus obtained using an apparatus having the configuration shown in FIG.

In FIG. 2, 3 is an optical recording medium, 4 is a laser light source,
5.5a is a lens, 6 is a reproduction light detection device, 17 is a nonlinear optical element, and 18 is a filter for cutting laser light (fundamental wave).

The laser pulse light from the laser light source 4 is transferred to the optical recording medium 3.
The light scattering intensity is reduced by heating the recording layer and then rapidly cooling it.

Next, the nonlinear optical element 17 is connected to the laser light source 4 and the lens 5.
The recording is reproduced by irradiating the optical recording medium 3 with the second harmonic of the light from the laser light source 4 and detecting the difference in the light scattering intensity of the recording layer by the amount of transmitted light. The output of the laser light from the laser light source 4 is adjusted so that there is no change in the light scattering intensity of the recording layer due to the irradiation of the second harmonic used as reproduction light.

In addition, the nonlinear optical element 17 is moved from the light irradiation optical axis again, the spot diameter of the laser light is increased, and the optical recording medium is irradiated with the laser light to heat and slowly cool the recording layer, thereby increasing the light scattering intensity again. The record will be deleted by pressing the button.

[Examples] Example 1 An optical recording medium (hereinafter referred to as an optical card) having the configuration shown in FIG. 3 was produced.

First of all, it is 1m in size and has a pre-groove.
AI on a thick glass substrate 9! A reflective film 8 is provided, on which 100 parts by weight of a polymeric liquid crystal represented by the following structural formula (1), and (I) 1 part by weight of a light-absorbing dye represented by the following structural formula (II) cpo, e. A solution prepared by dissolving (■) and 500 parts by weight of dichloroethane was coated by a spin cord method. By heating and drying at 110° C. and then slowly cooling to room temperature, the polymer liquid crystal in the recording layer 2 was maintained in a nematic phase polydomain state (light scattering state).

FIG. 3 shows a configuration diagram of the optical card obtained as described above.

Next, recording, reproduction, and erasing of this optical card were carried out using the apparatus shown in FIG. Wax 830 nm included in the laser light source
A semiconductor laser 10 is used.

The laser beam passes through the quarter-wave plate 13, is focused by the lens 5, and is irradiated onto the recording layer of the optical card with an appropriate spot diameter.

1) The reflected light from the reflective film passes through the lens 5 and the quarter-wave plate 13 again, is separated from the incident light by the polarizing beam splitter 11, is further separated by the half mirror 14, and is sent to the photodiode 15 and the photocell. 16.

In addition, a polarizing beam splitter 11 and a semiconductor laser 1
An optical element 20 that generates a second harmonic is installed between the two. The optical element 20 is composed of a nonlinear optical element I7 made of LiNbO3 and a filter 18 that passes the generated second harmonic and cuts off the laser light from the semiconductor laser IO.

To record on the optical card, the optical element 2D is moved so that the laser beam from the semiconductor laser 10 passes through the hole 19 provided in the optical element 20, and a fundamental wave of λwax 830 nm and an output of 8 mW is applied to the recording layer. This was done by irradiating with a spot diameter of 1 pm. At this time, the polymeric liquid crystal in the recording layer is heated to a temperature range in which it exhibits an iso-kissed phase and then rapidly cooled, so that it is maintained in an iso-kissed phase state and the scattering intensity of light is reduced, allowing recording to occur.

To reproduce the recording on the optical cart, the optical element 20 is moved so that the laser beam from the semiconductor laser IO passes through the LiNb0:+ nonlinear optical element 17, and the semiconductor laser IO
Adjust the output of the generated second harmonic (λwax 4
15 nm, power 0.2 mW) onto the recording layer. Then, the intensity of reflected light from the reflective film (Ai) corresponding to the light scattering intensity of the recording layer was detected using a photocell, and the reproduction contrast ratio was 1.5.

(2)o: Reflected light intensity I of the non-recorded area (high light scattering intensity) 2 Reflected light intensity of the recorded area (low light scattering intensity).

The records on the optical card thus obtained can be erased by the following method.

Using the same optical system used during recording, the output of semiconductor laser light was set to 15 W, and the recording layer was irradiated with a spot diameter of about 1.3 g. At this time, the polymeric liquid crystal in the recording area is heated to a temperature range that exhibits an isotonic phase and then slowly cooled, so that it is maintained in a polydomain state of a nematic phase, and the light scattering intensity increases, making it possible to perform erasing. Ta.

Example 2 An optical card having the same configuration as in Example 1 was prepared, and the recording layer of this optical card was heated to 120°C and then rapidly cooled.
The polymer liquid crystal in the recording layer was maintained in a tokiyoshi phase state (first non-scattering state).

For recording on this optical card (light scattering state S of the polymer liquid crystal) and erasing it (first non-scattering state of the polymer liquid crystal), the same erasing and recording methods as in Example 1 were used. Also,
The recording was reproduced in the same manner as in Example 1. The reproduction contrast ratio was -0.60.

Example 3 An optical cart having the same configuration as in Example 1 was prepared, and similarly to Example 1, the polymer liquid crystal in the recording layer was maintained in a nematic phase polydomain state (light scattering state).

Recording, reproduction and erasing on this optical card were carried out using an apparatus having the configuration shown in FIG.

Light from a semiconductor laser IO with an input wax of 830 nm and an output of 20 mW is divided into two by a half mirror 14a.

The intensity of one of the laser beams was modulated by the optical modulator 22 according to the recorded information, and this was used as recording light. The other part of the laser beam is guided to the LiNb0i nonlinear optical element 17, and a second harmonic is generated. Then, only the second harmonic was extracted by the bandpass filter 18, its intensity was adjusted by the ND filter 23, and this was used as reproduced light.

The recording light and playback light obtained in this way are transferred to a half mirror.
14 and irradiated onto the optical card with a spot diameter of about 11 zm. At this time, the outputs of the recording light and reproduction light on the optical cart were 8 mW and 0.2 mW, respectively. As in Example 1, recording could be performed using recording light. Record playback is done by AI! The reflected light from the reflective film is separated by the polarizing beam splitter 11 in the same way as in Example 1, and the second harmonic is detected by the photocell I6 using the band pass filter 18a. , 1.5.

In addition, to erase the record, the output of the semiconductor laser IO was set to 25 mW as in Example 1, and a fundamental wave of λwax 830 nm was applied to the recording layer of the optical cart with a spot diameter of about 1.3 pm.
This could be done by irradiating with an output of 15g+11.

[Effects of the Invention] As explained above, the present invention provides a method for recording and reproducing an optical recording medium having a recording layer containing a material whose light scattering intensity changes and a light-absorbing dye. By performing reproduction using harmonics, the reproduction contrast ratio can be improved.

Moreover, the effect that the recording/reproducing device and the optical system can be made more compact can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an optical recording medium used in the recording/reproducing method of the present invention, FIG. 2 is a block diagram showing an example of an apparatus used in the recording, playback, and erasing method of the present invention, and FIG.
The figure is a block diagram of the optical recording medium of Example 1.2, FIG. 4 is a block diagram showing a device used for recording, reproducing, and erasing of Example 1.2, and FIG. 5 is a block diagram of the recording, reproducing apparatus of Example 3. , is a configuration diagram showing a device used for erasing. 1-...Substrate 2...Recording layer 3...Optical recording medium 4...Laser light source 5.5a...Lens 6...Photodetection device 7---XY X Tailor 8-Aj) Reflection Film 9...Glass substrate 10.
...Semiconductor laser 11...Polarizing beam splitter 12...Moving direction of optical element 13-1/4 wavelength plate 14, 14a...Half mirror 15...Photodiode 16...Photocell 17... - Nonlinear optical element 18 - Filter 18a... Band pass filter 19... Hole 20... Optical element 21.
21a... Prism 22... Light modulation element 23.
・ND filter diagram 1

Claims (6)

[Claims] (1) In a recording and reproducing method for an optical recording medium having a recording layer containing a material whose light scattering intensity changes and a light-absorbing dye, reproduction is performed using reproducing light consisting of higher-order harmonics of the recording light. Characteristic recording and playback method. (2) The recording and reproducing method according to claim 1, wherein the absorption intensity of the light-absorbing dye at the wavelength of the recording light is greater than the absorption intensity of the light-absorbing dye at the wavelength of the reproducing light. (3) The recording and reproducing method according to claim 1 or 2, wherein the reproducing light is a second harmonic of the recording light. (4) The recording and reproducing method according to claim 1, wherein the change in light scattering intensity is a reversible change. (5) The recording and reproducing method according to claim 1, wherein the material whose light scattering intensity changes contains a polymer material. (6) The recording and reproducing method according to claim 5, wherein the polymeric material is a polymeric liquid crystal or a phase-separated polymer.