JPH0364045B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to an optical memory readout method using laser oscillation for a rewritable medium such as an optical disk using a guest-host type liquid crystal.

<Prior art> Optical disk systems have great advantages in terms of recording density, but in particular, there is a need for a system that allows writing, reading, and erasing to be performed easily and repeatedly over and over again. ing. As one such method, conventionally, Fig. 3a,
As shown in b, c, and d, some use a rewritable medium (optical disk) using liquid crystal.

This method will be explained below. First, as shown in FIG. 3a, a dichroic dye 2 is mixed into a host liquid crystal 1 having a smectic-nematic phase transition.
This is placed between a substrate 4 with a transparent electrode 3 and a substrate 6 with a transparent electrode 5. This liquid crystal 1 is in a smectic state (horizontal alignment) at room temperature, but as shown in FIG.
When irradiated with laser light 8 due to its thermal effect,
The irradiated part becomes nematic (vertically oriented) and oriented in the direction of the electric field. That is, the part irradiated with the writing laser beam 8 (vertical state) and the part not irradiated (horizontal state)
The laser light absorption coefficient of dye 2 differs between
This allows information to be written. Next, in order to read out this information, as shown in FIG. The light intensity of the transmitted light 12, 12, 14 depending on the orientation is detected by the photodetector 15, and information is read out. Next, as shown in FIG. 3d, the liquid crystal 1 is heated to erase the stored information.

The optical memory system that utilizes such phase transition of liquid crystal is an advantageous system in terms of reliability of writing and reading. However, when reading out information in this optical memory method, since the liquid crystal, dye, etc. are thin, the absorbance of dye 2 is also small, and therefore reading out information by reading the difference in the absorption coefficient of dye 2 is difficult. It has the principle disadvantage of poor performance, and has the disadvantage of being difficult to put into practical use.

<Object of the Invention> Therefore, an object of the present invention is to dramatically improve the sensitivity when reading information in a rewritable medium using a guest-host type liquid crystal.

<Structure of the Invention> In order to achieve the above object, the present invention provides a rewritable medium using a guest-host type liquid crystal having a smectic-nematic phase transition.
A dye that emits laser light is used as a guest, and when reading information, external laser light is irradiated to cause the dye to emit laser light, which has a different oscillation threshold due to a change in absorption coefficient due to changes in the alignment direction of the liquid crystal. The present invention is characterized in that the presence or absence or light intensity of laser oscillation light from the dye is detected by a photodetector to read out information.

<Examples> The present invention will be described in detail below with reference to illustrated examples.

In FIG. 1a, 21 is a host liquid crystal having a smectic-nematic phase transition, such as octyl cyanobiphenyl, and 22 is a highly luminescent dye, such as a cyanine-based organic dye, which is mixed into the host liquid crystal 21 and easily causes laser oscillation. be.
This cyanine-based organic dye is used, for example, in a GaAlAs-based semiconductor laser (wavelength 780), which is widely used as a light source for writing and reading optical disks.
~830nm) as an excitation light source, it is optimal because the absorption spectrum has a peak at that oscillation wavelength.

Further, 23 and 25 are electrodes made of a metal dielectric material (for example, aluminum) deposited on the substrates 24 and 26, respectively, and have a reflectance so that the dye 22 sealed between the substrates 24 and 26 can easily oscillate as a laser. It's getting bigger.

Although not shown, similar to the conventional example shown in FIG. 3b, writing laser light is irradiated from the outside while an electric field is applied to the electrodes 23 and 25, and the liquid crystal 21 is nematically irradiated as shown in FIG. 1a. state (vertical orientation), orient it in the direction of the electric field, and write information. As shown in Figure 1b, the absorption coefficient α of the laser beam of the dye 22 changes depending on whether the liquid crystal is aligned horizontally or vertically, and the absorption coefficient α changes depending on whether the liquid crystal is aligned horizontally or vertically. It becomes smaller in the horizontally oriented part and becomes larger in the horizontally oriented part.
Even when the reading laser beam 11 is irradiated as shown in FIG. 1a, the alignment state of the liquid crystal 21 does not change, and the difference in absorption coefficient of the dye 22 shown in FIG. 1b is maintained. Therefore, due to this difference in absorption coefficient α, even if the dye 22 is the same, the dye 22 in the vertically aligned portion is less likely to be photoexcited by the readout laser beam 11 than the dye 22 in the horizontally aligned portion, and the first As shown in figure c, dye 2 in the vertical alignment part
The threshold value P ⊥ for laser oscillation of dye 22 in the horizontally aligned portion becomes higher than the threshold value P 2 for laser oscillation of dye 22 in the horizontally aligned portion. Therefore, if the light intensity P ₀ of the readout laser beam 11 is selected so that P < P ₀ < P ⊥, the dye 22 oscillates as a laser in the horizontally aligned portion, as shown in FIG. 1d. Although it emits light,
In the vertically aligned portion, the dye 22 does not oscillate as a laser and does not emit light. As shown in FIG.
The two states can be distinguished by detecting the second laser oscillation light 28 with a photodetector 15 such as a photodiode. In this way, by detecting the presence or absence of the laser oscillation light 28 with the photodetector 15, it is possible to distinguish between recorded areas and non-recorded areas, and to read information.

Such a method based on the presence or absence of laser oscillation light dramatically improves sensitivity compared to the conventional method of detecting the transmitted light of the readout light and reading the difference in absorption coefficient. This is because in the method of the present invention, what is detected is the emission intensity of the laser oscillation light 28, so the rise of the signal from zero is detected.If the sensitivity of the photodetector 15 is increased, the detection signal This is because the S/N level of the signal increases.

Furthermore, since the oscillation wavelength changes depending on the state of the liquid crystal, a dichroic filter 29 is installed in front of the photodetector 15, as shown in FIG. 1a, to pass only light of a specific wavelength. It can also be used for reading. In this case, the output P ₀ of the excitation reading laser beam 11 has no relation to the threshold values P 1 and P ⊥, and the S/N ratio increases as P ₀ becomes larger. In addition,
Figure 2 shows the output of the readout laser beam and the dye 22.
3 is a graph showing the relationship between the output power and the laser light output.

The method of the present invention can be applied not only to optical disk memories but also to display devices and optical computers that perform parallel processing.

<Effects of the Invention> As is clear from the above, the optical memory readout method of the present invention uses a dye that oscillates as a guest in a rewritable medium using a guest-host liquid crystal, and uses a dye that oscillates as a guest to emit laser oscillation light from the dye. Because information is read out based on the presence or absence of light or the intensity of light, the sensitivity is dramatically higher than the conventional method of detecting the transmitted light of the readout light and reading the difference in the absorption coefficient of the dye. This has the advantage that the S/N level of the detection signal increases.

[Brief explanation of drawings]

Figure 1a is an explanatory diagram of one embodiment of the present invention;
Figure b is a graph showing changes in the absorption coefficient, Figure 1 c is a graph showing changes in the laser oscillation threshold of the dye, Figure 1 d is a graph showing the laser output of the dye, and Figure 2 is a graph showing the readout laser beam. Graphs showing the relationship between the output of the dye and the output of the dye laser beam, FIGS. 3a, b, c, and d are explanatory diagrams of the conventional system. 1,21...liquid crystal, 2,22...pigment, 15...
...Photodetector, 3,5,23,25...Electrode, 4,
6, 24, 26... board.

Claims (1)

[Claims] 1. In a rewritable medium using a guest-host type liquid crystal with a smectic-nematic phase transition, a dye that emits laser light is used as a guest, and when reading information, external laser light is irradiated to align the liquid crystal. A dye whose absorption coefficient changes due to a change in direction and has a different oscillation threshold is oscillated as a laser, and a photodetector detects the presence or absence of laser oscillation light from the dye or the light intensity.
An optical memory reading method using laser oscillation of a rewritable medium using a smectic type guest-host liquid crystal for reading information.