JPS5994734A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain an optical recording medium enabling recording and erasing with laser beams and having superior rewriting characteristics by using a liq. crystal causing reversible phase transition from a smectic phase to a nematic phase. CONSTITUTION:A liq. crystal causing reversible phase transition from a smectic phase at room temp. to a nematic phase at high temp. is injected into the space between transparent substrates 5, 6 having transparent electrodes 3, 4. The liq. crystal is represented by formula I or II. The molecules of the liq. crystal are oriented parallel to the surfaces of the substrates in one direction. By applying voltage 8 between the electrodes 3, 4 while irradiating laser light 7 on the record writing section of the resulting recording medium, phase transition from the smectic phase to the nematic phase is caused in the section by heating, and the molecules of the liq. crystal in the section are oriented perpendicularly to the substrates 5, 6. After cooling in the state, the medium is exposed to light 9 through polarizing plates 11, 12. The transmitted light can be utilized to read out the record. The record can be erased by heating the whole medium without applying voltage 8.

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to an optical recording medium, and more specifically, it relates to an optical recording medium, and more particularly, it relates to a medium for optical recording, and more specifically, it relates to a medium for optical recording. This invention relates to an excellent optical recording medium.

(Prior Art) In recent years, in the field of information processing, as the amount and diversity of information has rapidly increased, conventional magnetic memory, which is known as the most common recording method, has become insufficient.
In particular, it tends to be difficult to adapt to the above diversity.

Therefore, as an alternative to such a recording method, an optical recording method using an optical recording medium has been considered, and various studies are being carried out.

Examples of media used in optical recording systems include metal thin films and metal-containing polymer materials, but these write by using a laser beam to melt and evaporate the recording area of the medium to make holes. Erasing and rewriting are impossible.

On the other hand, one example of this rewritable optical recording medium is a medium that combines a thermoglass nub and a photoconductor, but this optical recording medium can only be rewritten about 100 times or so. Anything less than that is not something that can be completely satisfied even now. Another well-known example of optical recording media is magneto-optical materials, which perform reading using the magnetic Kerr effect, but have the disadvantage that the reading S/N is very poor due to the small effect of the magnetic Kerr effect. cannot be avoided. Still another example is one that utilizes photodarkening of amorphous chalcodanide, but this photodarkening photosensitive wavelength is short and there are significant limitations on the wavelengths that can be used.

In this way, many of the conventional optical recording media are
．． The reality is that there are many problems and shortcomings, such as non-replaceability, and rewritable products do not necessarily have sufficient characteristics.

(Purpose of the Invention) As a result of conducting numerous experiments and researches in order to solve these drawbacks, the present inventors have decided to utilize the optical recording function of a liquid crystal that has a reversible phase transition between a smectic phase and a nematic phase. The present invention was achieved by discovering a medium that can be repeatedly erased and rewritable and has significantly improved optical recording properties.

(Structure of the Invention) That is, in this invention, a liquid crystal having a phase transition between a smectic phase and a nematic phase is interposed and held between substrates having electrodes, the liquid crystal molecules are oriented in one direction parallel to the substrate surface, and a laser beam is applied to the liquid crystal. This is an optical recording medium characterized in that recording and erasing are performed using the optical recording medium.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the optical recording medium of the present invention, in which 1 is a liquid crystal material layer, 2 is a spacer, 3.4 is a transparent electrode, and 5 and 6 are transparent substrates, respectively.

As the transparent electrodes 3, 4 and the transparent substrates 5, 6, for example, Nesa glass is used. Apply rubbing treatment. Next, as the spacer 2, a mylar film having a thickness of 8 μm to 16 μm is used.

As the liquid crystal material layer 1, a smectic-nematic liquid crystal (smectic range: 21.1 to 33.5°C, nematic range: 33.5 to 41.5°C) is used. Next, to the optical recording medium configured in this way, a DC voltage of 5 V or more is applied between the electrodes and an argon laser beam (λ=-514, 5
nm, irradiation/'P power 1 mW or less side irradiation time 5)
It was possible to write tiny bits by irradiation. The recorded bits and the unrecorded portion had different optical rotation characteristics, and it was possible to read out the recorded bits by using a polarizing plate. These recorded bits are stable at 25 to 30°C regardless of whether or not a voltage is applied to the transparent electrode, and can be individually erased by irradiating the recorded bits with laser light for the purpose of erasing without applying a voltage. It was possible to erase the recorded bits. Furthermore, by heating the entire medium, all recorded bits are erased, and the recording medium in the above example is
It was confirmed that it had sufficient performance to withstand approximately 500 erasing and rewriting operations.

The function of the liquid crystal side layer of the recording medium of the present invention can be explained as follows.

That is, the liquid crystal used is a liquid crystal having a reversible phase transition, which is a smectic phase at room temperature and a nematic phase at higher temperatures. In this nematic phase, the liquid crystal molecules are easily aligned in the direction of the dipole moment by an external electric field, but in the smectic phase, the orientation is not easily changed by an external electric field. In addition, the nematic phase is pretreated so that the limited beam moment without an external electric field is oriented parallel to the substrate.

FIGS. 2(a) to 2(d) respectively show 1. This figure shows the status before recording (a), recording writing (b), recording holding and reading C), and recording erasing (d).

First, FIG. 2(a) shows a smectic phase, and the die ball moment is oriented parallel to the substrate. Then, the recording/writing section is fully irradiated with laser light 7, and a voltage of 8 is applied between the transparent electrodes 3 and 4.
When a voltage of 8 is applied, the recording/writing section undergoes a phase transition from a smectic phase to a nematic phase due to heating by laser beam irradiation, and a p dipole moment is oriented perpendicular to the substrate (Mb) by a voltage of 8.

In this way, by cooling with voltage 8 applied to form a smectic phase, the orientation of the recording/writing portion is maintained even without voltage application. As mentioned above, the optical rotation characteristics of this recording/writing area are different from those of the unwritten area.As shown in (e), using polarizing plates 11 and 12, the transmitted light 10 is illuminated with light 9 and used for recording. It can be used for reading. Furthermore, as shown in (d) above, in order to erase the recording, the entire medium may be heated without applying a voltage, or the first part may be heated by irradiation with a laser beam without applying a voltage.

The liquid crystal used in this invention preferably has a sufficiently stable smectic phase near room temperature, exhibits a nematic phase in a sufficiently wide temperature range above that level, and has a large dipole moment. In addition to those used in the above embodiments, a mixture of the following may be used, and a mixed liquid crystal containing these as main components may also be used.

(Effects of the Invention) As is clear from the above description, according to the optical recording medium of the present invention, the above-mentioned phase transition between the smectic phase and the nematic phase is utilized as a recording method, and this is achieved by heating by laser beam irradiation. This enables extremely minute recording.

Furthermore, voltage application during this recording is necessary only during writing, and is unnecessary for any of the recording holding, reading, and erasing in the smectic phase. As mentioned above, since writing and erasing use phase transition, the repeatability of erasing and rewriting is significantly improved, and furthermore, it does not use hysteresis and does not require temperature bias. It has extremely advantageous features such as very easy operation control.

Therefore, as mentioned above, it is possible to perform writing and erasing using a large laser beam with high repeatability, which is required for this type of recording system, and its industrial use as a high-density optical recording medium that can replace the above-mentioned magnetic recording. The value is huge.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the medium of the present invention, and FIG. 2 (
a) to (d) are explanatory diagrams of the operating principle of the same medium. DESCRIPTION OF SYMBOLS 1...Liquid crystal, 2...Spacer, 3, 4...Transparent electrode, 5.6...Transparent substrate, 11.12...Polarizing plate. Patent applicant Oki Electric Industry Co., Ltd. Procedural amendment (voluntary) Commissioner of the Patent Office Kazuo Wakasugi 1 Indication of the case Patent application No. 1983-203712 2 Name of the invention Optical recording medium 3 Person making the amendment Relationship with the case Patent application Person (029) Oki Electric Industry Co., Ltd. 4 Agent 5 Detailed explanation of the invention subject to amendment 6 Contents of amendment

Claims (1)

[Claims] A liquid crystal having a phase transition between a +11 smectic phase and a nematic phase is held between substrates having electrodes, the liquid crystal molecules are oriented in one direction parallel to the substrate surface, and a laser beam is used to align the liquid crystal molecules in one direction parallel to the substrate surface. An optical recording medium characterized by being capable of recording and erasing. (2) As a liquid crystal with a phase transition in the above (section 11),
The optical recording medium according to item (1) above, using one or both of the following.