Abstract: Logic circuits employ photoresponsive GaAs field effect transistors to directly drive GaAs laser diodes to provide optical output signals in response to optical input signals. Since the only electrical inputs are DC bias voltages, each such circuit can be readily decoupled, such as for use in electrically noisy environments. The optical output represents a predetermined logic condition in response to a predetermined operating current applied to the laser diode as a result of the operation of the photoresponsive device. Two photoresponsive devices may be used to apply two different operating current magnitudes to the laser diode to produce two different optical output signals.