JP2619627B2 - Optical memory recording and playback device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical memory recording / reproducing apparatus.

[Conventional technology]

Optical disc memories that can be repeatedly erased and rewritten are about to be put into practical use soon by a magneto-optical recording method and a phase change recording method.

FIG. 2 shows a configuration example of a recording / reproducing apparatus in the case of the phase change recording method. Reference numeral 1 denotes a semiconductor laser, which is controlled by a laser control circuit 2. After modulating a recording signal 3 by a modulation circuit 4, the signal is converted into laser light by the semiconductor laser 1. The laser light is converted into parallel light by the lens 5, passes through the prism 6, and is focused and recorded on the optical disk 8 by the lens 7. The optical disk 8 is rotated at a constant speed by a motor 9 and a servo circuit 10 of the motor. At the time of reproduction, the laser light reflected from the optical disk surface passes through the prism 6 and reaches the photodetector 11. The optical signal received by the photodetector 11 is demodulated by the demodulation circuit 12 and the reproduced signal 13
Becomes

In both the case of the phase change recording method and the case of the magneto-optical recording method shown in FIG.
Using a semiconductor laser of about nanometers, information is recorded by converting the energy of the laser into heat. For this reason, recording information requires a considerable amount of energy, and requires a high-output semiconductor laser, which is expensive.

The same semiconductor laser is used for reading information, and the recording density of information is limited by this wavelength. Of course, the density is overwhelmingly higher than that of a conventional magnetic memory, but in order to achieve higher density recording, it is required to shorten the wavelength of laser light during recording and reproduction.

[Problems to be solved by the invention]

The present invention solves the problems of the above-mentioned conventional rewritable optical disk memory, that is, the need for a high-output and expensive semiconductor laser and the difficulty of further improving the recording density. It is intended to realize a recording / reproducing apparatus for an optical memory having a high density.

[Means for solving the problem]

As means for solving the above problems, an optical memory recording / reproducing apparatus according to the present invention comprises an optical memory comprising a laser light source and a wavelength conversion element having a nonlinear optical effect for converting the wavelength of laser light from the laser light source. The recording / reproducing apparatus is characterized in that the wavelength conversion element is formed of a secondary or higher order organic molecule accumulation film or a liquid crystal layer, and has a control mechanism for converting a wavelength by applying an electric field to the wavelength conversion element.

〔Example〕

FIG. 1 shows a conceptual diagram of an embodiment of an optical memory recording / reproducing apparatus according to the present invention. FIG. 1 has almost the same configuration as FIG. The difference is that a wavelength conversion element 21 exists between the semiconductor laser 1 and the lens 5. Also 22
Is a control mechanism of the wavelength conversion function of the wavelength conversion element 21. By the wavelength conversion element 21 and its control mechanism 22, the oscillation wavelength of the laser 1 and a harmonic such as a half wavelength or a one-third wavelength thereof are selectively irradiated onto the optical disk 8 freely.

At this time, if a photochromic material is used as the recording medium of the optical disc, the recording medium changes state according to the wavelength of the irradiation light. That is, information can be recorded.
Photochromic phenomenon is generally This is a phenomenon represented by the reaction formula: That is, the state of chemical bonding is reversibly changed by irradiation with light of different wavelengths. As a result, the absorption spectrum and reflectivity generally change, so that the optical memory medium can be repeatedly erased and rewritten. Certain organic compounds exhibit such a photochromic phenomenon. In particular, spiropyran, fulgide and the like are excellent in the magnitude and stability of the change of the spectrum, and are preferable as the optical memory medium for the optical memory recording / reproducing apparatus according to the present invention.

A substance having a nonlinear optical effect is used as the wavelength conversion element. For example, due to the second-order nonlinear optical effect, the laser light incident on the wavelength conversion element is converted into a second harmonic whose wavelength is half of the laser light. Therefore, the wavelength conversion element
When the function 21 functions, the optical disk is irradiated with short-wavelength light, and when the wavelength conversion element 21 does not function, the original long-wavelength laser light is irradiated. By such a method, for example, writing with short wavelength light and erasing with long wavelength light become possible. If a semiconductor laser with an oscillation wavelength of 800 nm is used as the laser light source, the wavelength of the writing light will be 400 nm, and the recording density will be theoretically four times higher than the conventional method.

It is desirable that the material used for the wavelength conversion element has a large nonlinear optical effect. As such materials, for example, 2-methylnitroaniline (MNA) and polydiacetylene are known. A single crystal or a cumulative film of these materials can be used as the wavelength conversion element.

A specific control method of the control mechanism 22 of the wavelength conversion element 21 may be various methods. Among them, the simplest method in principle is a method of moving the position of the wavelength conversion element 21. If the wavelength conversion element 21 is present in the optical path of the laser light as shown in FIG. 1, the wavelength conversion is naturally performed. But wavelength conversion element
If 21 is removed from the optical path of the laser light, the wavelength of the laser light is not converted. Therefore, for example, the function of wavelength conversion can be controlled by moving the wavelength conversion element 21 by electromagnetic means.

As another example of the control mechanism 22, there is a method of controlling the wavelength conversion function by applying an electric field to the wavelength conversion element 21. In this case, an element whose wavelength conversion function changes when an electric field is applied must be used as the wavelength conversion element. Examples of the wavelength conversion element having such a function include a cumulative film of organic molecules having a nonlinear optical effect and a liquid crystal layer also having a nonlinear optical effect. FIG. 3 shows the mechanism of the control mechanism for the liquid crystal layer. In FIG. 3, 31 is a glass substrate, 32 is an electrode, 33 is a power supply, 34 is a power switch, and 35 is a liquid crystal layer. FIG. 3A shows a state in which no electric field is applied. At this time, the liquid crystal molecules are aligned parallel to the substrate 31. Even if laser light having a wavelength λ is incident on the liquid crystal layer in such a state from the major axis direction of the liquid crystal molecules, wavelength conversion does not occur. On the other hand, FIG. 3B shows a state where an electric field is applied, and at this time, the liquid crystal molecules are vertically aligned with respect to the substrate 31. At this time, the wavelength of the laser light incident on the liquid crystal layer is converted by the nonlinear optical effect of the liquid crystal layer, and a second harmonic having a wavelength of λ / 2 is emitted.

Thus, the wavelength conversion function can be controlled by applying an electric field to the liquid crystal layer. As a liquid crystal material having a nonlinear optical effect, several materials including MBBA are known.
A significant number of liquid crystal materials are expected to have nonlinear optical effects.

FIG. 4 shows the mechanism of the control mechanism for the cumulative film of organic molecules. In FIG. 4, 41 is a substrate, 42 is an electrode, 43 is a power supply, 44 is a power switch, and 45 is a cumulative film. The cumulative film shown in FIG. 4 is modeled as four layers, but in practice, the number of layers is usually larger. The accumulation film can be formed by several methods such as a so-called Langmuir-Prodget method and a vapor deposition method. The organic molecules used in any of the methods preferably have amphiphilicity.

FIG. 4 (a) shows a state in which no electric field is applied. At this time, the molecules in the accumulated film are arranged in anti-parallel layer by layer, so that even if each molecule has a second-order nonlinear optical effect, the accumulated film as a whole. Is 2
It does not have the following nonlinear optical effects. Wavelength λ
The laser light goes out without change.

On the other hand, FIG. 4 (b) shows an electric field applied state.
At this time, since the molecules direct their permanent dipoles in the direction of the electric field, the directions of all the molecules in the accumulated film are aligned. At this time, since the accumulated film has a second-order nonlinear optical effect, the wavelength of the incident laser light is converted, and a second harmonic having a wavelength of λ / 2 is emitted. Polydiacetylene is known as an example of a cumulative film material capable of controlling the second-order nonlinear optical characteristics by changing the orientation by applying an electric field, but many organic materials seem to have such an effect.

〔The invention's effect〕

According to the present invention, writing can be performed with short-wavelength laser light, so that the recording density can be improved. In addition, a single semiconductor laser can generate laser beams of a plurality of wavelengths, so that an optical memory recording / reproducing apparatus which is inexpensive can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical memory recording / reproducing apparatus according to the present invention. FIG. 2 is a diagram showing a configuration of a conventional optical memory recording / reproducing apparatus. FIGS. 3A and 3B are diagrams showing a method of controlling a wavelength conversion function by an electric field when a liquid crystal layer is used as a wavelength conversion element. FIGS. 4 (a) and 4 (b) are diagrams showing a method of controlling a wavelength conversion function using an electric field when a cumulative film is used as a wavelength conversion element. DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser 2 ... Semiconductor laser control circuit 3 ... Recording signal 4 ... Modulation circuit 5 ... Lens 6 ... Prism 7 ... Lens 8 ... Optical disk 9 ... Motor 10 ... Motor servo circuit 11 ... ... Photodetector 12 ... Demodulation circuit 13 ... Reproduction signal 21 ... Wavelength conversion element 22 ... Wavelength conversion control mechanism 31 ... Glass substrate 32 ... Electrode 33 ... Power supply 34 ... Power switch 35 ... Liquid crystal layer 41 …… Substrate 42 …… Electrode 43 …… Power supply 44 …… Power switch 45 …… Cumulative film

Claims (2)

(57) [Claims] 1. An optical memory recording / reproducing apparatus comprising a laser light source and a wavelength conversion element having a nonlinear optical effect for converting the wavelength of laser light from the laser light source, wherein the wavelength conversion element is a secondary or higher order organic molecule. An optical memory recording / reproducing apparatus, comprising a control mechanism for converting a wavelength by applying an electric field to the wavelength conversion element. 2. An optical memory recording / reproducing apparatus comprising a laser light source and a wavelength conversion element having a non-linear optical effect for converting the wavelength of laser light from the laser light source, wherein the wavelength conversion element is a secondary or higher liquid crystal layer. An optical memory recording / reproducing apparatus, comprising: a control mechanism for converting a wavelength by applying an electric field to the wavelength conversion element.