PURPOSE: To make an optical signal whose wavelength has been divided and multiplexed, branched, and also to execute a logical operation in a state of the optical signal by converting photoelectrically one branch light of an output light of an optical waveguide, feeding it back to an optical reverse directional coupler, and inducing a phase mismatching quantity between the optical waveguides.

CONSTITUTION: A periodical uneven part 2 having a refractive index for realizing phase matching is provided between two optical waveguides 1-1, 1-2 distributed and coupled to a crystal substrate having electrooptic characteristics, and electrodes 3-1, 3-2 are provided through a buffer layer on the upper layer of the two optical waveguides 1-1, 1-2. Input light 7-1 applied to the optical waveguide 1-1 by a beam splitter 4 is branched to two, and a part 7-3 of transmitted light is converted photoelectrically by a photodetector 5, and amplified by an amplifier 6. This output voltage is applied to a control electrode 3-1 of an optical reverse directional coupler 8. By a distribution feedback action of the optical reverse directional coupler 8, an output 7-4 is sent out of the optical waveguide 1-2.