Abstract

Optical switching devices are of much interest in optoelectronic computing systems, especially for optoelectronic integrated circuits. Several types of optical switching devices have previously been developed, such as the self electro—optic effect device (SEED), double heterojunction optoelectronic switch (DOES), an integrated combination of a heterojunction phototransistor (HPT) and a light—emitting diode (LED) called a light amplifying optical switch (LAOS), and pnpn switches. With the exception of the SEED, all of these switches have demonstrated a similar switching I—V curve composed of a high—impedance off-state, a low—impedance on—state and a differential negative resistance region connecting the two as shown in Fig. 1. Most of the switches discussed above can be triggered on with an input light pulse, but they cannot be turned off optically. The only way to turn the switch off without using additional components is to reduce the electrical bias to zero. This switching has been utilized in the implementation of an optical memory which is electrically erasable [1], and an optoelectronic flip-flop based on two parallel pnpn switches using the bias pulse as a clock [2]. From the I—V curve of Fig. 1, it can be seen that there are two possible ways to optically turn the switch off: i) Place an optically sensitive element in shunt with the switch which can reduce the bias across the switch to a level lower than the holding voltage (usually about 0.8 ~ 1.2V); or ii) Place an optical element in series with the switch in order to reduce the current passing through the switch below the critical current. The first approach has been applied successful to the fabrication of an all—optical bistable switch with optical set/reset pulses [3]. This device incorporates an additional HPT in parallel with the switch. We have implemented the second technique by placing an HPT in series with the switch to form a gated optical latch.

© 1991 Optical Society of America