D. A. Weinberger

Room‐temperature excitonic optical bistability in a GaAs‐GaAlAs superlattice étalon

The quantum wells provided by a superlattice increase the binding energy of the free excitons in GaAs, permitting 300 K bistable operation of a superlattice etalon. The superlattice consists of 61 periods of 336 A GaAs and 401 A Ga0.73Al0.27As. The intensities required are about 1 mW/ ( μm)2 and the switching times are 20–40 ns, similar to the low‐temperature pure GaAs values. Room‐temperature operation of semiconductor etalons enhances the likelihood of all‐optical logic and switching.

Semiconductor nonlinear etalons

Previous observations of optical bistability in nonlinear etalons of ZnS, CuCl and GaAs are summarized. Emphasis is placed upon recent results in GaAs: similar room-temperature optical bistability at powers under 10 mW in bulk and multiple quantum-well etalons; room-temperature bistability achieved with a diode laser as a light source; NOR and other logic operations; optical fibre signal regeneration and continuous wave operation.

Optical Nonlinearity and Bistability Due to the Biexciton Two-Photon Resonance in CuCl

We have investigated the nonlinear dielectric function close to the biexciton two-photon resonance in CuCl, taking into account the background absorption due to the exciton tail in the vicinity of the biexciton as well as the broadening of the biexciton resonance with intensity. This analysis predicts biexcitonic optical bistability with ~10 MW/cm2 intensity for a ~10-µm-thick CuCl etalon with 90% reflecting mirrors. Our experimental results, obtained with 8- to 12-µm-thick CuCl films sandwiched between 90% reflecting mirrors, verify these predictions. Optical limiting and bistability were observed with ~15 to 30 MW/cm2 intensity. Subnanosecond switching times are limited by the response time of the detection system.

Observation of Thermal Optical Bistability, Crosstalk, Regenerative Pulsations, and External Switch-Off in a Simple Dye-Filled Etalon

Continuous-wave optical bistability was easily achieved with the single-wavelength outputs from a cw visible Ar laser, rhodamine B or 6G dye lasers, and a He-Ne 632.8-nm laser. Input powers ranged from 5 mW to 2 W. A switch-on time as short as 20 μs was achieved with 100 mW of cw dye laser input. Using two adjacent or overlapping bistable transmission regions on the same etalon, we observed light by light control, with possible applications in optical signal processing. With two dye etalons in series we produced an optical flip-flop, permitting external switch-off as well as switch-on of an intrinsic bistable device. The simple etalon construction and flexibility in choice of lasers should encourage widespread use in testing various bistable operations, as well as in demonstrations and student labs.

Self-Defocusing and Optical Crosstalk in a Bistable Optical Etalon

Two transverse phenomena associated with a bistable optical etalon are discussed. The first is self-defocusing1 of the laser beam due to the nonlinear dispersion of the medium inside the bistable Fabry-Perot etalon. Good agreement is found between GaAs data and one-dimensional numerical simulations. The second is crosstalk2 between nearby bistable regions in the same etalon due to diffraction coupling, which is studied numerically in both one and two transverse dimensions.

Resonant two-photon absorption and emission in single-crystal thin films of CuCl

Abstract A comparative study of the luminescence and absorption spectra of excitonic molecules in thin films of cuprous chloride grown on sodium chloride and fused quartz is reported. Thin films of CuCl on NaCl are in single-crystalline form while CuCl on quartz are polycrystalline as evidenced by X-ray diffraction analysis. Under resonant excitation at 7 K, the two-photon absorption spectra for CuCl grown on NaCl exhibit a reduction in linewidth and an increase in the peak absorption as compared with those for CuCl grown on fused silica quartz. Also, the emission lines arising from the decay of excitonic molecules to exciton states are sharper in the single-crystal thin film. These results suggest that the recently grown CuCl single-crystal thin films are substantially superior to polycrystalline thin films for studies of picosecond biexcitonic optical bistability and Bose-condensation of excitonic molecules.

Advances in GaAs Bistable Optical Devices

The achievements in GaAs bistable optical devices of room-temperature operation, external switch-on and switch-off, and advances in device fabrication are described.