Optical bistable behaviour of nematic liquid crystals in Fabry-Perot cavity has been discussed. The normal and abnormal bistable loops were also discussed. Considering thermal conductivity in F-P cavity, a theory to get very low critical switching power optical bistability was developed.
The properties of intrinsic optical bistability in nematic liquid crystals were studied. This kind of optical bistability is without resonant optical cavity and electric feedback. We find that the nematic ROTN-200 film can exhibit bistability when applying a constant ac electric field (≊560 kHz) that is greater than a tricritical voltage VTc=2.614 V. The bistable interval is measured and the hysteresis loop is characterized at each different voltage. The splay and bent elastic constants k11 and k33 are obtained to calculate the numerical result. It is found that the experimental results are in good agreement with theory. The experimental setup with which we can easily observe the bistable phenomena is illustrated. Under the consideration of the finite size of the laser beam, the thermal effect and finite beam size effect are discussed. In addition, some new interesting phenomena about the diffraction ring structure of nematic liquid crystal are reported.
An analysis is made of nonlinear optical phenomena associated with a change in the orientation of the director of a liquid crystal induced by an optical field and resulting in optical bistability. The usual configurations with a nonlinear Fabry-Perot resonator and several other configurations are considered. Bistable cells with cholesterics are proposed: in these cells the nonlinearity is associated with the absorption of the incident and reflected light and is related—via the temperature of the cell—to the cholesteric helix period. Devices are considered in which switching from one state to another takes place as a result of a change in radiation parameters (such as the frequency or polarization) other than the power.
We have studied theoretically and experimentally the nonlinear Fabry-Perot transmission of a cavity with a thin nematic liquid-crystal film. Various modes of operation have been observed, using a moderate-power cw laser. In the limit of small reorientation angles, the optically induced molecular reorientation of the birefringent crystal and the nonlinear phase shift is solved for a homeotropically aligned crystal. Multiple-valued Fabry-Perot transmission is obtained by solving the nonlinear equations that couple the optical phase shift with the cavity transmission. The time-independent nature of the process and the explicit quantitative expressions involving the nematic liquid-crystal parameters allow a direct comparison between the thoery and experimental results. Good quantitative agreement is demonstrated.