B. S. Wherrett

Optically bistable interference filters: optimization considerations

Design considerations for optically bistable narrow-bandpass interference filters are surveyed. Optimization for low incident laser irradiance levels is presented in terms of the reflective stacks, the spacer thickness, operational laser frequencies, the semiconductor thin-film materials, and the laser spot size. Conditions under which either thermal or electronic nonlinearities dominate are described.

Thermal dispersive optical bistability and absorptive bistability in bulk ZnSe

We report successive refractive and then absorptive optical bistability in bulk ZnSe at room temperature, at 35- and 300-mW power levels, respectively, for the 476-nm argon-ion laser line. Analysis shows the results to be consistent with the observed thermal shift of the interband absorption. These first observations of dispersive bistability in bulk ZnSe occur in lowest order for temperature changes as low as 2 K; many bistable orders are obtained.

Near-infrared optical nonlinearities in amorphous chalcogenides

Abstract The measurement of the nonresonant third-order nonlinearity of three chalcogenide glasses is reported. Using the Z-scan technique, both the refractive and the absorptive parts of the nonlinearity are resolved, including their sign. It is shown that Ag-doping of As 2 S 3 produces a change of sign and a dramatic enhancement of the nonlinear refractive index.

Nondegenerate two-photon absorption spectra of ZnSe, ZnS and ZnO

Abstract Subpicosecond time-resolved white-light continuum measurements of the nondegenerate two-photon absorption spectra of ZnSe, ZnS and ZnO, with pump photon energy 1.76 eV, are reported. The spectra presented cover a photon energy range of 1 eV. The results are found to agree well both in absolute value and frequency dependence with a model for the two-photon transition probability incorporating the Kane band structure and nonparabolicity.

Theory of optical bistability in metal mirrored fabry-perot cavities containing thermo-optic materials

Abstract We present and analyse a new method for achieving all-optical bistability, in metal mirrored Fabry-Perot cavities containing thermo-optic material. It is shown how “butterfly” bistability is achieved in metal/metal mirrored cavities. Optimisation for low switching powers is considered for a dielectric/metal mirrored cavity. The use of nematic liquid crystals with such a system makes submilliwatt switching powers easily achievable.

Near-resonant third-order optical nonlinearities in p-toluene sulfonate polydiacetylene

We report single-wavelength subpicosecond and nanosecond excite-probe and four-wave mixing experiments near the exciton resonance in p-toluene sulfonate polydiacetylene. Contributions to the third-order susceptibility χ(3) resulting from phase-space filling, photoinduced absorption, and two-photon absorption are identified. A three-level rate-equation model that accounts for the change in sign of the nonlinear absorption observed at near-resonant frequencies is discussed.

Continuous-wave laser-pumped optical bistability in thermally deposited and molecular-beam-grown ZnSe interference filters

We observe and compare conditions for cw optical bistability in both thermal-vacuum-deposited and molecular beam grown ZnSe-based interference filters, at He–Ne-laser (633-nm), Kr (647-nm), and Ar-ion (514-nm) wave-lengths. Bistability is observed at 514 and 647 nm and, by inference, should be observable at a number of intervening wavelengths for a single molecular-beam-grown sample. From our theoretical analysis we also demonstrate that observed drift instabilities in filter nonlinear responses correlate with the highest internal irradiance levels.

Spectrally resolved third-order nonlinearities in polydiacetylene microcrystals: influence of particle size

The on- and near-resonant third-order nonlinear optical response of polydiacetylene microcrystals in suspension was studied by the Z-scan technique with tunable picosecond pulses. The absorptive and refractive contributions to the excitonic-dominated nonlinearity were fully resolved at several wavelengths. Microcrystals of two different average sizes were studied, and a comparison of their nonlinear coefficients was made. A three-level model for the nonlinear response is presented that shows good agreement with the experimental data.

Polarization dependence of ultrafast nonlinear refraction in an AlGaAs waveguide at the half-band gap

We have obtained the polarization dependence of ultrafast nonlinear refraction by measuring the orientational dependence of self-phase modulation and cross-phase modulation in an Al0.18Ga0.82As waveguide at a frequency just beneath the two-photon absorption edge. It was found that nonlinear refraction exhibits a considerable anisotropy in accordance with theoretical calculations for GaAs. It was also found, as predicted, that perpendicular cross-phase modulation behaves differently from the isotropic Kleinmann result appropriate to silica fibers.

Near-resonant refractive nonlinearity in polydiacetylene 9-BCMU thin films

The spectral dependence of the third-order nonlinear susceptibility χ(3) (ω; ω, −ω, ω) of the polydiacetylene 9-BCMU has been measured, and the imaginary component is found to change sign in the exciton absorption tail. In the red-phase material, a significant refractive nonlinearity was observed around the 1.93-eV input energy range, whereas the absorption change was too small to quantify. A magnitude for the nonlinear refractive index coefficient |n2| = 1.9 (±1.0) × 10−10 cm2 W−1 was measured at this Im χ(3) = 0 position, indicating good figures of merit for all-optical switching.