nonlinear optical phenomenon u03c7 3 process such as phenomenon caused by the four wave mixing in the 1 55 micrometer wavelength band the output light beam and the optical clock signal are nearly line symmetry with respect to the optical modulation signal in their wavelengths the linbo 3 optical waveguide with the quasi phase matching structure using the cascaded u03c7 2 processes has a larger nonlinear optical constant than that using the u03c7 3 process in the foregoing reference a four centimeter long device generates the output nearly equal to the output of the four wave mixing of an optical fiber of about one kilometer in the conventional configuration the wavelength of the optical modulation signal is set at 1550 nm when a light beam with a different wavelength propagates through the linbo 3 optical waveguide a phase mismatch occurs the phase mismatch u03b4 u03b2 is given by the following equation u03b4 ue89e ue89e u03b2 ue89e u03b2 shg u00b7 u03b2 sig u03b2 out ue89e n shg u03bb shg u00b7 n sig u03bb sig u00b7 n out u03bb out 4 the phase mismatch periodically makes the shg conversion efficiency and dfg conversion efficiency in the linbo 3 optical waveguide zero at the phase 2 u03c0 accordingly extending the waveguide cannot increase the conversion efficiency the domain inversion polarization grating structure compensates for the phase mismatch by inverting the polarization of the crystal in the regions at which the phase mismatch shifts from u03c0 to 2 u03c0 thereby.