Bistability optical

Singh and Prasad observed optical bistability in a planar quasi-waveguide at 0.653 Mm and O.7 Mm wavelength with upper switching threshold power of 2.55 MW/cm and 3 86 MW/cm corresponding to extremely large values of nonlinear refractive index 5 10 cm /MW suggesting that it is a thermal effect. 

Sasaki et al. (I988) used a hybrid waveguide composed from PDA LB film, glass waveguide and a silica substrate. Two types of optical listability they have observed one originating from coupling between a prism and 

PDA hybrid waveguide. The second one they observed in the hybrid waveguide with a nonlinear distributed Bragg reflector of the PDA top layer. In both cases input-output curves with hysteresis characteristics were obtained. However, as state the authors, they are not sure whether the observed optical bistability is electronic, or thermal in origin. 

Thermal optical bistability with a Fabry-Perot cavity filled with a PDA solution was also observed by Blau (1987) with very low switching power (less than 4 MW). 

Optical bistability studies in conjugated polymers is still at the beginning and it requires a more important effort. New structures, like that proposed recently by Haelterman and Waelbroeck (1990) and new materials have to be examined in an appropriate wavelength range (e.g. around one or two photon resonances). 

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It is the strong interaction between the excited state and the ground state via the conical intersection that hinders the optical bistability of the CP-DHA compound. In contrast CN-DHA shows a much smaller efficiency of the internal conversion which indicates that no conical intersection is involved. We can therefore raise the question whether a photoinduced backreac-tion from the transient CN-VHF-cis ground state is possible. 

B. Fluctuations and Fluctuational Transitions in an OB (Optically Bistable) System... 

However, in many cases the fluctuating systems of interest are far from thermal equilibrium. Examples include optical bistable devices [45], lasers [23,46], pattern forming systems [47], trapped electrons that display bistability and switching in a strong periodic field [48-50], and spatially periodic systems (ratchets) that display a unidirectional current when driven away from thermal equilibrium [51-56]. 

A simple model that makes it possible to describe optical bistability in a variety of systems is a plane nonlinear Fabry-Perot interferometer, filled with a medium whose refractive index is intensity dependent [106]. The slow kinetics of a... 

In the experiments we have used two approaches. First, we have simulated the kinetics of a bistable optical system in the Debye relaxation appoximation for different forms of potential by means of electronic analog simulation. Secondly, we have investigated the kinetics of a double-cavity membrane system (DCMS) driven by two modulated laser beams at different wavelengths. This system is known to display optical bistability [111]. 

H. Gibbs, Optical Bistability Controlling Light with Light, Academic, New York, 1985. 

Fayer. 143) A recently reported example is of rhodamine 6G in boric acid glasses.(144) Concentrated solutions of some dyes, e.g., fluorescein, are also known to be capable of optical bistability.(145,146) Dirk and Kuzyk report... 

All Optical Bistability of Vacuum Evaporated Polydiacetylene (PDA.12-8) Film Waveguide with a Grating Coupler... 

In this report, vacuum evaporated PDA(12-8) film is used as an optically nonlinear layer with a grating coupler for nonlinear coupling for all optical bistability. Grating coupler on a substrate was prepared at the same periodicity and depth as the SHG devices. Vacuum evaporation of PDA on a substrate with previously rf-sputtered Corning 7059 buffer layer film were carried out at 5 x 10 5 torr with tungsten boat heater. Rapid evaporation can avoid thermal polymerization of the undesirable red phase PDA during the process. UV polymerization of the film for the useful blue phase PDA was carried out by Xe lamp 500 w for 20 min. at a... 

Conceptual structure of the four-layered waveguide device is depicted in Fig 7. In figure dashed trapezoidal pattern was surrounded by grating. This is a method to realize appropriate wave-guiding for various vacuum evaporated PDA film. Experimental setup for all optical bistability with a pulsed Nd YAG laser 1064 nm is shown in Fig 8. 

Conceptual structure of four-layered waveguide with grating coupler for all optical bistability. 

Figure 9. The output-input curve with all optical bistability at 200 ns pulse width Nd YAG laser.

Figure 10. All optical bistability at 20 ns pulse width N d Y A G laser.

B) A11 optical bistability device with grating coupler was realized at off-angle coupling for pulsed Nd YAG laser. This bistability was very sensitive for the angle of incoming light beam. 

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