Optical modulators and bistable devices using molecular gases

H. M. Gibbs, S. L. McCall, A. Passner +3 more

Robert G. Harrison, W. J. Firth, I. A. Al-Saidi +1 more

There has been considerable interest over the last few years in transitions to chaos in passive optically bistable systems. Ikeda1 showed in 1979 that an optically bistable ring resonator containing the simplest of nonlinear systems, a two-level media, can show a period doubling route to chaos. This was demonstrated by us2 using NH3 gas near resonantly pumped by pulsed CO2 laser radiation. More generally we identified and demonstrated the unique advantages of molecular gases in this field, providing in particular a vast range of laser-molecular coincidences together with control of response time, and therefore switching time and modulation frequency, by varying gas pressure. Subsequent extension of this work to all optical Fabry-Perot resonators revealed huge oscillatory effects3 leading to chaos in the transmitted laser signal. Under other parameter conditions for both NH3 and SF6 a rich variety of optically bistable effects were observed obtained in systems as small as 1 mm for SF64,5.

Shenping Li, Zhonghong Yan, Yizhou Zhang

Shammai Speiser, David Groswasser, Meir Orenstein

We already discussed the bistable behavior of a Fabry Perot resonator filled with molecular media as well as the characteristics of a spatial light modulator (SLM) based on the nonlinearity induced by excited state absorption. In the present paper we present two practical configurations. First we analyze a cavity-less bistable element which removes some of the realization problems related to high finess cavity. In this configuration the nonlinear medium is located in one arm of an optical interferometer. The scheme provides the required amount of positive feedback by the bistable mechanism -- but without a cavity. We applied the nonlinear eikonal approximation, a method which takes care of the detailed propagation effects, and obtained conditions for bistability, as well as optimizing the design parameters such as the output mirror reflectivity, etc.

P. W. E. Smith

Shammai Speiser

A novel spatial light modulator (SLM) based on nonlinear absorption of light by excited molecules is suggested. A kinetic analysis is applied to calculate the relative populations of molecular levels in singlet and triplet manifolds. It is shown that for many actual cases a probe light can be modulated by propagating through a medium excited by another light source. The dependence of the molecular SLM on the photophysical parameters of the SLM medium is discussed. The same type of molecular nonlinearities can be utilized for optical bistability, as is demonstrated for some dyes.