Optical bistability is realized in the active optical device which consists of an avalanche photodiode, a laser diode and transistors. To improve the switching time, it utilizes transistor as a switching device, instead of the switching of laser diode, and laser diode is biased above the threshold current. Switching time is limited from the load impedance of photodiode and about 5 nanosecond is obtained. The logic elements of "AND" and "OR" are realized in the device which consists of a photodiode, a light emitting diode and transistors. The avalanche photodiode is analized and delay time of laser diode biased below a threshold current is also counted.
