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Annual Meeting Optical Society of America

Saturation and nonlocal effect in transverse self-phase modulation bistability

I. C. Khoo, T. H. Liu, J. Y. Hou

Published Jan 1, 1985• 0 citations
Publisher

Abstract

Recently, a new class of optical bistability, involving transverse self-phase modulation effect with a single reflection feedback, has been demonstrated. We present here a detailed theoretical calculation of the effect of saturation and nonlocality on the switching behavior and power. The technique employed is similar to that given in a recent paper but generalized to the case where the nonlinear refractive-index change contains a saturation parameter. It is found that both the switching powers and the hysteresis loops are considerably changed. Multiple close-by switching loops occur. Because of the extreme sensitivity of the transverse bistability switching on the width of the transverse nonlinear phase shift, we have also investigated the effect due to nonlocal response of the thin film subjected to a Gaussian laser beam. Specific detailed calculations were performed for nonlinear thin film where such nonlocal behaviors are expected (e.g., liquid crystal reorientation and diffusive processes in semiconductors). The most prominent result is that a more accurate prediction of the switching intensity is obtained if the nonlocal effects are included.

DOI
10.1364/oam.1985.fu2

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We present a theoretical study, with reference to experimental results, of transverse self-phase modulation effects in the transmission of a laser beam through a nonlinear thin film. The occurrence of interference rings, intensification or dimming of the on-axis beam intensity, and transverse optical bistability in the presence of a feedback can all be systematically documented in terms of geometrical/optical parameter classifications. These studies provide further insights and useful guides for experimental studies.
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A nonlinear thin film bounded by two dielectric media could act as an optical switching and bistability device, owing to two physical mechanisms at work near the total internal reflection state. One is the simple intensity-dependent index change induced by the finite optical field in the film before transmission occurs, and the other is the nonlinear Fabry-Perot interference associated with the high reflectivities at the two interfaces when transmission takes place. We present a detailed theory for these two mechanisms and for the case in which the nonlinearity is also nonlocal (e.g., in a liquid-crystal film). The results for multiple switchings and hysteresis hold in general for any nonlinear thin film.
Nonlinear optical transverse effects, which arise from the interaction of a Gaussian beam with a nonlinear medium, are discussed. They are cw on-resonance enhancement (CORE), cw off-resonance rings, crosstalk, intracavity phase switching, self-defocusing of a bistable etalon, and thin-sample-encoding (TSE) self-lensing (i.e., self-focusing or self-defocusing) bistability and instabilities. CORE is the enhancement of the on-axis intensity of an on-resonance laser beam in a two-level medium. We report the first observation of CORE using sodium vapor. Cw off-resonance rings, resulting from a pure phase encoding or from simultaneous phase and amplitude encodings, are observed using sodium vapor. These rings have been observed many time before, but we have made the first careful comparison with numerical calculations. Parallel operation and external switching are two crucial themes for the application of bistable optical devices (BODs). For parallel operation, crosstalk between nearby BODs on the same etalon due to diffraction coupling may need to be avoided. Minimum separations needed to ensure independent operation are computed. For external switching, intracavity phase switching using a plane-wave input can switch on (or off) a BOD using an external pulse. The validity of this concept for a Gaussian input is numerically simulated. Self-defocusing effects, resulting in some interesting effects in the transverse bistable loops, are observed using a GaAs-GaAlAs bistable etalon. The results are confirmed by numerical simulations. TSE self-lensing bistability is observed using a short sodium cell and a single mirror. TSE self-lensing bistability results from an enhancement in the feedback via self-lensing of the beam. The lack of an optical resonator and the use of a thin medium make TSE setup a good candidate to study the Ikeda instability. We report the first observation of the Ikeda instability in this all-optical passive system using a cw input. Numerical simulations show a rich bifurcation sequence not yet fully studied experimentally.