METHOD FOR ADJUSTING COUPLING LENGTH OF SEMICONDUCTOR DIRECTIONAL OPTICAL COUPLER

摘要

PURPOSE:To adjust the coupling length of the semiconductor directional optical coupler by partially constituting mixed crystals in a part of the superlattice which constitutes a 1st waveguide and changing the refractive index to change the effective length of the coupling part to a 2nd waveguide. CONSTITUTION:The partial mixed crystal constituting part of the optical waveguide 1-2 and a part of the optical waveguide 1-1 adjacent thereto are substantially equiv. to the absence of an optical coupling waveguide as light is not coupled therein by the deviation in phase speed. The length of the coupling part can be controlled by this method. Namely, the refractive index in a part of the superlattice 4 of the 1st waveguide 1-2 is changed by partially constituting the mixed crystals therein, by which the phase speed in the mixed crystal constituting part of the 1st waveguide 1-2 is changed to generate a difference with the part corresponding to the 2nd waveguide 1-1 and to lower the degree of coupling. The mixed crystal constituting part of the 1st waveguide 1-2 is removed from the coupling region of the directional coupler in this way and the coupling length of the directional coupler is eventually adjusted.