K. Tai

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/ (u2009μm)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.

External off and on switching of a bistable optical device

A GaAs etalon has been switched on in a detector‐limited time of 200 ps by a 10‐ps, 600‐nm, 1‐nJ pulse and switched off in ⩽20 ns by a 7‐ns, 600‐nm, 300‐nJ pulse.

Observation of continuous-wave on-resonance "self-focusing".

We report what to our knowledge are the first observations of an increase in the on-axis intensity of an intense cw on-resonance beam resulting from nonlinear absorption and diffraction during its propagation through a highly absorbing medium (sodium vapor). This self-focusing is not a self-lensing; instead it is modeled well by placing an aperture part way through the cell: The stripping by the aperture approximates the effect of the nonlinear absorption, and then Fresnel diffraction results in on-axis minima and maxima.

Optical cross talk between nearby optical bistable devices on the same étalon.

This Letter is concerned with the parallel operation of optical bistable devices. The two-beam side-by-side case has been simulated numerically. Diffraction coupling from one device operating in the upper branch can cause the other one, operating in the lower branch, to switch to the upper branch if the separation of the two beams is too small. The separation required for independent operation is usually a few beamwidths. The results give promise for performing parallel operations with optical bistable devices on the same étalon.

Mirrorless dispersive optical bistability due to cross trapping of counterpropagating beams in sodium vapor.

We report the first observation to our knowledge of mirrorless optical bistability based on a dispersive effect, namely, cross-trapping optical bistability due to the mutual interaction of two counterpropagating beams. The phase conjugation of a probe beam generated by four-wave mixing in such a system is sensitive to the intensities of the counterpropagating beams and has been used to monitor the bistability.

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.

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.

Intracavity phase switching and phase-plane dynamics of a bistable optical device

Abstract Since the field inside an optical cavity is a complex quantity, analysis in the phase plane gives a deeper insight into its time evolution. This was emphasized by the findings of Hopf and Meystre. We have extended their numerical analysis to include the possibility of Ikeda instabilities, showing that parameters can be selected that avoid Ikeda instabilities but permit intracavity phase switching. Switching, both up and down, can always be accomplished by applying an external pulse which changes the cavity detuning for an appropriate number of round trips. Inclusion of diffraction effects in one transverse dimension does not prevent switching. Clear, preset, and flip-flop operations, analogous to electronic operations, can also be achieved by properly choosing the external control pulses.

Cross-Trapping Optical Bistability of Two Counter-Propagating Beams in Sodium Vapor

The interaction of two counterpropagating beams in a nonlinear medium leads to many interesting phenomena. One such phenomenon is the occurrence of optical bistability arising from the mutual interaction of the two beams [1]. This type of cross-trapping optical bistability is similar to one of those proposed by Kaplan [2]. The physics of cross-trapping optical bistability is similar to the self-focusing bistability [3] where self-trapping occurs in a single-beam/singlereflector setup. Cross-trapping bistability differs in that it has no external feedback and therefore is the first mirrorless bistability not based on an increasing absorption effect.

Switching Of A GaAs Bistable Etalon: External Switching On And Off, Regenerative Pulsations, Transverse Effects, And Lasing

Switching between states of an intrinsic bistable device is usually accomplished by changing the input intensity II, increasing it above the switch-up value It or below the switch-down value With a constant input intensity satisfying I↓⪅ II < I↑, switching can be actuated by external pulses. Switch-on by a 10-ps, 600-nm, 1-nJ pulse in less than the 200-ps detector response time is attributed to screening of the GaAs free excitons by hot carriers. Switch-off in ≤20 ns by a 7-ns, 600-nm, 300-nJ pulse is attributed to heating the etalon and increasing I4, until it exceeds the constant II. Under certain con-ditions the competition between excitonic and thermal effects causes the etalon to switch on and off repeatedly in a relaxation oscillation fashion. These regenerative pulsations could be the basis of an all-optical oscillator. The transverse profile has been examined for switching actuated by intensity modulation of the input. Whole-beam switching is observed, i.e., when switch-on occurs, it occurs out to large radii simultaneously. Computer simulations show whole-beam switching for strong diffractive coupling but show radially dependent switching for weak diffraction, neglecting transverse diffusion. The same etalon emits a near-band-gap laser pulse when pumped sufficiently by an above-band-gap pulse, serving as a wavelength converter. All of these modes of operation of the GaAs etalon, i.e., switchable memory, oscillator, and wavelength converter, could be useful in all-optical logic and computing systems.