Abstract: An elementary optical Givens rotation device is disclosed comprising a monolithic integrated optical circuit including crossed waveguides, interdigitated electrode means associated with the crossed waveguides at their crossing point, and electro-optic phase shifter means lying upstream and downstream of the interdigitated electrode means with respect to one of the waveguides. Two mutually coherent, transverse magnetic input light signals are guided simultaneously into each waveguide. A voltage applied to the interdigitated electrode means induces a diffraction grating thereby forming transmitted and diffracted light waves in output sections of the respective waveguides. Phase shifter means include means for applying voltages to each phase shifter which are equal in magnitude but opposite in sign so that the transmitted and diffracted waves combine in phase in one waveguide and combine 180.degree. out of phase in the other waveguide.