Optical instability in optoelectronic bistable circuits

Relaxation oscillation can occur in a bistable system when the nonlinearity has two contributions of opposite sign and different time constants. 1 Optoelectronic bistable laser diode or light emitting diode (BILD or BILED) circuit is a promising optical logic device. 2 Here we present the observation and analysis of optical regenerative pulsation in a system constructed of a liquid crystal switch and BILED circuit. Sine wavelike pulses were obtained in our experiment, and the experimental results show that the oscillation frequencies were stable. The frequency can be adjusted by changing the voltage supply. In our experiment the output from an argon laser is controlled by a LC switch, which is connected to a BILED circuit. The voltage applied across the LC switch is provided by an amplifier, and it is proportional to the output of the BILED circuit. The BILED circuit has two output signals of feedback. One is the light emitted from the LED in the circuit. The other is a part of the laser beam transmitted from the LC switch. As oscillation occurs in the circuit, the laser beam is modulated into a train of pulses by the LC switch.