GB2220519A - Information storage and reproduction - Google Patents

Description

1 - Information storaae and reDroduction 2220 5 1; 9 0.Z. 0050139933 The

present invention relates to a novel process for storing and reproducing information on and from an optical storage medium c ontaining a dye as the radiationsensitive substance by means of a read and a write laser, each based on a semiconductor laser, the wavelength of the write laser being less than that of the read laser.

Optical storage media are known. The recording materials they contain are substances which on irradiation with high energy density, for example with focused laser light, undergo a locally confined change of state. This thermally initiated change of state, for example vaporization, change of flow characteristics or fading. is accompanied by a change in the optical properties. for example the reflectivity or absorption, which can be utilized for information or data recording.

The recording materials for this type of information storage are for example thin layers of metals (including alloys), for example tellurium or bismuth, or organic compounds, ' for example dyes, such as phthalocyanine compounds, methine dyes or squaric acid derivatives.

Such optical storage media which contain a base and a radiationsensitive,, dye-containing layer, are described for example in EP-A-241, 696 and in earlier German Patent Applications DE-A-3,703,985j, DE-A-3,711f7621 DE-A-3,716,734r DE-A-3,733,173, DE-A-3,810,642 and DE-A-3, 810,956.

Apparatuses which make possible the writing of the layers of optical recording media and the reading back of the written information are based in some instances on the DRAW (direct read after write) system using two lasers.

Semiconductor lasers, being very small, have advantages over gas lapers (for example HeNe lasers) for the construction of drives. Of particular suitability here are A1GaAs lasers. which operate within the 1 1 _k O.Z. 0050/39933 wavelength range from about 750 to 950 nm. Owing to the small size of the component, its high optical efficiency and the possi bility of direct modulation of the optical output through modulation of the electric drive current, such laser types are particularly highly suitable. It should be added that to optimize beam guidance performance in the writing and reading back of information, write lasers and read lasers are operated at different wavelengths.

In the art it is customary to write with a semiconductor laser of a longer wavelength and generally higher energy (for example an AlGaAs laser at a wavelength of 830 nm) and read with a semiconductor laser of a shorter wavelength and generally lower energy (for example an AlGaAs laser at a wavelength of 780 nm).

on application to optical storage media where the radiation-sensitive substance is a dye, there is a problem in that the energy of the read laser can alter the storage layer in written or even in unwritten areas.

It is true that these changes can be suppressed by reducing the power of the read laser to a critical threshold value, but then in many cases the reflected read laser beam is no longer sufficiently powerful for satisfactory functioning of the tracking and focus servo means. In addition, the signals are only readable with a low signal-to-noise-ratio.

It is an object of the present invention to provide for dye-containing optical recording media a process for storing and reading back information where the abovementioned disadvantages are no longer present.

We have found that this object is advantageously achieved by storing information in an optical recording medium containing a base and a radiation-sensitive, dyecontaining layer by means of a semiconductor write laser and by reading the information thus stored by means of a semiconductor read laser when the wavelength of the write laser is less than that of the read laser.

0, A- !t - 3 - 0.Z. 0050139933 As already mentioned, the dye-containing optical recording media for the process according to the invention and their manufacture are known and described for example in the patent applications cited at the beginning.

In the course of manufacture, the layer containing one or more dyes with or without a binder is applied to a transparent base, for example a polycarbonate or polymethacrylate base, in a conventional manner, such as vapor deposition under reduced pressure or spincoating from a solution.

This layer can be written and read not only from the open side but also from the back through the transparent base plate. The write and read lasers used are commercial lasers of the type described at the beginning.

It has proved to be particularly advantageous for the difference in the wavelengths between the read laser and the write laser to be from 20 to 90 nm, preferably about 5 0 ran.

The process according to the invention makes it possible to obtain higher contrast during reading and higher sensitivity during writing. Moreover, the power output of the read laser can be distinctly increased without noticeable alteration to the unwritten layer or even the written pits.

This effect can be augmented by selecting those types of radiationsensitive dyes which absorb little, if at all, in the region of the wavelength of the read laser.

The Examples will further illustrate the inven- tion.

EXAMPLE 1

A Plexiglas disk was vacuum vapor deposited with zincnaphthalocyanine from a tantalum boat by means of resistance heating.

The reflection at 786 nm was 19.4% and at 836 nm I 1 j is 0.Z. 0050/39933 26.6%.

To perform the write and read experiments, a test drive was used having the following characteristic data: ist laser: A1GaAs semiconductor laser, wavelength x = 786 m 2nd laser: A1GaAs semiconductor laser, wavelength x 836 nm The pits were written by means of rectangular light pulses. The power outputs from the write laser peak to 3.6 mW at the recording layer in each case. The duration of the light pulses was varied via the varying width of the current pulse between from 0.1 psec to psec.

The lasers were focused using a commercial actuator with a focusing lens (numerical aperture: 0.44).

The pits were read with a CW power at the recording layer of 0.14 mW in each case.

A writing energy of 2.2 nJ/pulse (1st laser. 786 nm) gave a read signal level (2nd laser, 836 nm) of 1. 05 V.

EXAMPLE 2 (COMPARISON) Example 1 was repeated,, except that the wavelength of the lst laser was 836 nm and that of the 2nd laser 786 nm. This time a writing energy of 2. 2 nJ/pulse (836 nm) gave a read signal level (786 nm) of only 0.53 V.

EXAMPLE 3 (COMPARISON) Example 1 was repeated. except that a wavelength of 786 nm was used for both writing (2.2 nJ/pulse) and reading. The signal level was only 0.82 V.

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Claims (9)

1. A process for storing information in an optical recording medium containing a base and a radiation-sensitive, dye-containing layer by means of a semiconductor write laser and for reading the information thus stored by means of a semiconductor read laser, wherein the wavelength of the write laser is less than that of the read laser.

2. A process as claimed in claim 1, in which the base is transparent whereby information can be written or read from either side of the recording medium.

3. A process as claimed in claim 2, in which the base is a polycarbonate or polymethacrylate.

4. A process as claimed in claim 2 or claim 3, in which the layer containing one or more dyes with o:r7 without a binder is applied to the transparent base by vapor deposition under reduced pressure.

5. A process as claimed in claim 2 or claim 3, in which the layer containing one or more dyes with or without a binder is applied to the transparent base by spincoating from a,solution.

6. A process as claimed in any preceding claim, in which the waVelengths between the read laser and the write laser is from 20 to 90 nm.

7. A process as claimed in any preceding claim, in which the wavelengths between the read laser and the write laser is substantially 50 nm.

8. A process as claimed in any preceding claim, in which a radiationsensitive dye is used which absorbs little, if at all, in the region of the wavelength of 6 - the read laser.

9. A process for storing information in an optical recording medium substantially as hereinbefore described in the foregoing Example 1.

1 Published 1989 atThePatent Offte, State House, 66f7l High Holborn. London WC1R 4TP. Further copiesmaybe obtamedfrom The PatentOfnce. Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques lid, St Mary Cray, Kent. Con. 1/87