Patent US 4,887,877

An optical device and an optical integrated circuit which incorporate an optical switch and have a novel function. Light sources are respectively coupled to two input ends of an X-type 2.times.2 optical switch, and light receivers are respectively coupled to two output ends of the optical switch, thereby obtaining an optical device which is capable of performing both AND and OR logics. A light source is coupled to one input end of an optical switch, and a light receiver is provided at one output end from which the light emitted from the light source emerges when no electric power is supplied to the optical switch, whereby it is possible to construct a system in which, even when one terminal has a power failure, there is no hindrance to other terminals. If an optical switch is arranged such as to use driving electric power as a modulating signal, the optical switch can serve as a modulator in which the output from one output end can be employed to monitor a modulated optical signal. In addition, if the optical switch is formed into, e.g., a carrier injection type optical switch using a semiconductor, the above-described devices can be fabricated as integrated circuit.