The present invention relates to a multi-layer optical planar waveguide
which is vertically coupled using multimode-interference couplers and to
the method of manufacturing the same. The purpose of this invention is to
increase the degree of integration on the multi-layer optical planar
waveguide by applying the concept of via holes of the multi-layer printed
circuit board (MLPCB) used in electronic circuits to the optical waveguide
devices. According to the present invention, particularly, a multimode
interference coupler of a stepped structure has the higher coupling ratio
at relatively short length of interference than the usual multimode
interference coupler. The present invention can implement a multimode
interference coupler at a specialized spot while reducing evanescent field
interference between the upper and lower optical waveguides out of the
spot by separating the layers enough.
