Low-temperature optical bistability of photocurrent in gallium arsenide

Dan G. Allen

Seth Ovadia, H. M. Gibbs, Jack L. Jewell +2 more

The minimum power (=5 mW) for room-temperature optical bistability is very similar in bulk and multiple-quantum-well (MQW) etalons. No exciton resonance is obvious in the absorption spectrum of bulk GaAs at 300 K because it blends into the band edge, but it is present, and its area is two-thirds that of the MOW heavy-hole exciton. It is shown that the excitonic nonlinear index change is consistent with the observed bistability.

Stanley Desmond Smith, Brian S. Wherrett

Shlomo Ovadia

The fundamental limitations on the operation of optical bistable devices in a ring cavity and in GaAs etalons are investigated. Experimental results of spontaneous transitions due to shot noise fluctuations are found in good agreement with various "ladder" models, if one allows the counting rates to vary accordingly. Stability analysis for two-photon homogeneously broadened media reveals single-wavelength instabilities for the laser but not for absorptive optical bistability. Appreciable regions of sidemode gain exist for both problems allowing for multiwavelength instabilities to occur. GaAs bistable devices show attractive features such as low power and high speed at room temperature for optical processing. However, experimental evidence in GaAs confirm the computer simulations of bistability that cavity losses, due to unsaturable background absorption, limit the switching power at room temperature. Methods to overcome the different limitations in GaAs devices toward parallel computation are then addressed from a system approach.

В. С. Днепровский

P. R. Tapster, John G. Rarity, J.S. Satchell

We drive a high-efficiency gallium arsenide light emitting diode (LED) with a low-noise current and measure the noise in the detected photocurrent from a high-quantum-efficiency silicon photodiode collecting most of the emitted light. The drive current is obtained from a resistor in series with a low-noise voltage supply. The Johnson noise in the current is much less than shot noise whenever the voltage across the resistor is large compared with 50 mV (2kT/e at room temperature). The LED converts electrons to photons directly with some efficiency η.