Spice Analysis for the DC Behavior of the Light Amplifying Optical Switch (LAOS)

Abstract

A heterojunction phototransistor (HPT) is integrated in series with a light-emitting diode to form an optoelectronic device called Light Amplifying Optical Switch. This device has been shown to switch from low current region to high current region at a voltage called breakover voltage. This switching has been attributed to the presence of optical and electrical feedback mechanisms as well as to gain nonlinearity. A circuit model for such device that took into account different factors affecting the switching behavior has been proposed previously. In this paper, a modification to the previously published circuit is made and a spice model is presented for the modified circuit and hence for the LAOS. The spice results presented here are compared to published results and showed a good qualitative agreement. In addition, several factors that affect the switching behavior of such device are analyzed and a good agreement with published results is achieved. The spice model presented here can be very helpful to engineering students in studying optoelectronic circuits and systems that use LAOS.