JPH0229931A - Method of storing and reproducing information - Google Patents

Abstract

PURPOSE: To enable writing with high sensitivity and reading out with a high contrast by executing storage of information in an optical recording medium contg. dyes as a photosensitive material by using laser for writing of the wavelength shorter than the wavelength of a laser for reading out. CONSTITUTION: The information is stored by using a semiconductor laser as the laser for writing in the optical recording medium consisting of a base and the photosensitive layer contg. the dyes and the stored information is read out by using the semiconductor laser as the laser for reading out when the wavelength of the laser for writing is shorter than the wavelength of the laser for reading out. The high contrast in the reading out process and the high sensitivity in the writing process are attained in such a manner.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses an optical recording medium containing a dye as a photosensitive material as a storage medium, and the writing method is based on semiconductor lasers, in which the wavelength of the writing laser is shorter than the wavelength of the reading laser. A novel method for storing and reproducing information using lasers and reading lasers.

Optical recording media are known. This includes, as a recording material, a material whose state can be changed locally by a focused laser beam of high power density, such as a focused laser beam. Changes in state caused by this heat, such as evaporation,
Changes in flow behavior or discoloration result in changes in optical properties, such as reflectance or absorption, which can be used to record information or data.

Recording materials for information storage of this kind are, for example, thin layers of metals (also alloys), such as tellurium or bismuth, or of dyes, such as phthalocyanine compounds, methine dyes or tetranic acid derivatives.

Such optical storage media consisting of a support and a layer containing a photosensitive dye are described in 1, for example in EP-A 241 696 or D
H-A37Qi5985, DE-A5711762, D
E-A5716734, DE-A3733173, Dg
-A3810642 or DE-A3810956.

Devices that make it possible to write to the layers of an optical recording medium as well as to read written information are partially based on the D RAW method (
'direct read after write'
) is operated using two types of lasers.

Semiconductor lasers include gas lasers (e.g. He Ne-
Its small size compared to a laser (laser) is advantageous for the construction of its output device.

In particular, AlGa operating at wavelengths of approximately 750-950 nm
As-laser may be mentioned. The small size of the components and the high optical efficiency (the optical output can be modulated directly by modulation of the operating current make this type of laser particularly suitable. Optimal writing of information Depending on the method of introducing the light beam for reading and writing, the writing and reading lasers operate at different wavelengths.

In practice, writing requires longer wavelength, typically higher energy semiconductor lasers (e.g. Al with a wavelength of 830 nm).
It is common to use a semiconductor laser with a shorter wavelength and generally low energy (for example, an AlGaAs laser with a wavelength of 780 nm) for readout.

When using an optical storage medium containing a dye as a photosensitive substance, there is a problem in that the energy of the readout laser may also cause changes in the storage layer at written or unwritten positions. It is.

This change can actually be lowered to a critical threshold by reducing the output of the readout laser, but of course in this case, the reflected laser light is often used because the servo devices (tracking servo and focus servo) function without problems. It no longer has sufficient strength necessary for Furthermore, the signal can only be read out with a low S/N ratio.

The object of the invention was therefore to provide a method for storing and reading information in optical recording media containing dyes, which no longer has the above-mentioned disadvantages.

The present inventors used a semiconductor laser as a writing laser in an optical recording medium consisting of a support and a photosensitive layer containing a dye, when the wavelength of the writing laser is shorter than the wavelength of the reading laser. It has been found that it is possible to advantageously carry out storing information using a semiconductor laser and reading out the information thus stored using a semiconductor laser as a reading laser.

As mentioned above, the dye-containing optical recording media used in the method of the invention and their manufacture are known and are described, for example, in the patent applications cited above.

In the production, the layer containing one or more dyes and optionally a binder is applied onto a transparent support, for example a support made of polycarbonate or polymethacrylate, by methods known per se, for example by vapor deposition under reduced pressure or from a solution. Applied by centrifugal application.

Writing and reading of this layer can take place both from the air side (dye layer side) and through the transparent support plate. As writing and reading lasers, commercially available lasers are used, such as those mentioned at the beginning.

The difference in wavelength between the reading laser and the writing laser is 2.
A range of 0 to 90 nm, preferably about 50 nm, has been found to be particularly advantageous.

With the method of the invention, high contrast during the reading process and high sensitivity during the writing process are achieved. Furthermore, the power of the readout laser can be significantly increased without any discernible changes in the unwritten layer or in the written pores.

Furthermore, this effect can be enhanced by choosing the photosensitive dye so that it exhibits no (or very little) absorption within the wavelength range of the readout laser.

The invention will be explained in more detail by the following examples.

Example 1 Tin-naphthalocyanine was deposited by resistance heating from a tantalum bath in high vacuum onto a Plexiglas disk.

Reflectance is 194% at 786 nm and 2 at 836 nm.
It was 6.6%.

To perform write and read experiments, a test drive device having the following characteristic values was used.

1. Laser: AlGaAs-semiconductor laser wavelength λ
= 786 nm 2, laser: AlGaAs-semiconductor laser wavelength λ
A square light pulse was used for writing the -836 nm pores. The maximum power of the writing laser pulse is 3.6 on the recording layer, respectively.
It was mW. The pulse duration of the light pulses was varied within various current pulse ranges from 0.1 μsec to 5 μsec.

A commercially available actuator having a focusing objective lens (numerical aperture: 0.44) was used for focusing the light.

The CW value during readout of the pores is 0°14 on the recording layer, respectively.
It was mW.

2.2 nJ/pulse writing energy (first rule)
The signal height of the readout signal (second laser 836 nm) was 1.05 V.

Example 2 (comparison) The procedure was as in Example 1, except that the wavelength of the first loser was 836 nm.
m, the wavelength of the second laser was 786 nm. 2.2
Writing energy in nJ/pulse (836nm)
The signal height of the read signal (786 nm) is 0.53.
It was just V.

Example 3 (comparison) Operate as in Example 1, but write at a wavelength of 786 nm (
2.2 nJ/pulse) and readout were also performed.

The signal height was only 0.82V.

Claims (1)

[Claims] A semiconductor laser as a writing laser is used to record information in an optical recording medium consisting of a support and a photosensitive layer containing a dye, characterized in that the wavelength of the writing laser is shorter than the wavelength of the reading laser. A method of storing information and reading out the information thus stored using a semiconductor laser as a reading laser.