All-optical bistability

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.

All-optical bistability angular dependence, 324 experimental setup, 321,323/ output-input curves, 321,324,325/ thermal effect, 324 All-optical guided wave devices examples, 124,125/126... 

A. D. Lloyd and B. S. Wherrett, All-Optical Bistability in Nenuttic Liquid Crystal at 20 pW Power Levels, Appl. Pliys. Lett. (198.S)... 

All-optical bistability in nematic liquid crystals at 20 pW power levels... 

That the critical switch power is inversely proportional to the magnitude of thermo-optic coefficient dn/dT) was confirmed by experiment, and led to the choice of nematic phase liquid crystals as suitable, low absorption, spacer materials. Their high thermo-optic coefficient dn /dT — —2xl0 K at room temperature) produced all optical bistability at critical power levels of 140//W, allowing the demonstration of submilliwatt laser diode operation of these devices. 

Optical bistability is a third-order effect that occurs when a material with an intensity-dependent refractive index can yield two possible states for a single input intensity. This corresponds to the optical equivalent of the transistor. Although much attention has been given to all-optical computing, it is questionable whether such a devise can economically compete with ever cost-decreasing, performance-increasing modern electronic computers, at least in the... 

For all of the samples studied and for particle sizes down to the lowest studied, 150 nm, very similarly shaped SCO transition curves were observed and taken to imply that no significant size effect influenced the SCO process, at least in these particular nano-objects. Nanocrystals of the 3D coordination polymer [Fe(prazine)Pt(CN)4], which displays SCO properties in the bulk, also preserve the same magnetic, structural and optical bistability for particle sizes on the order of 50 nm. Recent evidence suggests however that this may not always be the case, as in the example of the 2D coordination polymer [Fe(3-fluoropyridine)2M(CN)4] where the bulk SCO properties were shown to be very markedly influenced by the nanoparticle dimen-sions. Detailed discussion of this topic falls outside the scope of this review but we refer to it here because it is an aspect of spin crossover studies that bears fundamentally" " on the practical application in device teehnology of nano-dimensioned SCO materials, which continue to display hysteretie behaviour at such dimensions. 

The exact solution is obtained for describing the external field effects in the optically induced molecular reorientation and bistability in a homeotropic nematic liquid crystal. With a low external field applied transverse or parallel to the laser propagation direction, optical bistability can always be suppressed or enhanced and hence can be seen in all existing nematics at a low laser power (typically < 1 kW/cm ). The fields corresponding to the tricritical point are obtained. 

Polymeric materials are playing an increasingly important role in electronic and photonic applications ". This includes application in active devices utilizing optical effects attributable to the nonlinear polarization of the medium, A number of applications such as frequency mixing, second harmonic generation, optical bistability, optical parametric amplification and oscillation, electrooptic and all optical switching and modulation etc. have been proposed. 

Miroshnichenko AE, Pinkevych I, Kivshar YS (2006) Tunable all-optical switching in periodic structures with liquid-crystal defects. Opt Express 14(7) 2839-2844 Ong HL (1983) Optically induced Freedericksz transition and bistability in a nematic liquid crystal. Phys Rev A 28(4) 2393-2407... 

Recently, particular attention has been devoted to the first-order Freedericksz transition (FT), molecular reorientation, and bistability in nematic liquid crystals (NLC s). In the last few years, Ong has shown that all of the electric and magnetic FT s and most of the optical FT s in a nonconducting homogeneous or homeotropic NLC are second-order transitions. However, applying a suitable static field, the second-order optical FT can be converted to first order in all existing NLC s. Similarly, applying a suitable optical field, the second-order electric or magnetic FT can also be converted to first order ... 

Fig. 1 Steady state bistability in the optical dens1ty at 525 nm as a function of flow rate, all other constraints kept constant ... 

Fig. 6 Steady state bistability in the optical density (- - ) and the Pt-potential —x—) versus mercurous sulfate reference electrode as a function of flow rate. All other constraints kept cons-tant [MnO ] = IxIO M, [H,0Jq = 2x10- M, rS,0Mo = 0-075 M,...

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