Abstract

Integrated optical directional couplers with parallel waveguides¹ have large device lengths due to the guide separation regions. Curved/straight waveguide transitions cause excess loss. In this paper we present passive couplers with circular waveguides. We investigate the following structures shown in Fig. 1: an asymmetric coupler consisting of a curved and a straight guide (a); a symmetric coupler with two oppositely curved guides (b) with the coupling distance d₀ (center to center) at z = 0. In contrast to parallel guides the phase fronts of both guides are tilted with respect to each other. Thus mode coupling occurs along curved phase planes with the effective distance d(z).²

© 1986 Optical Society of America