Abstract

Different techniques are possible to excite optical waves in waveguides. Distributed couplers are generally used for the excitation in a planar waveguide where prism and grating constitute the two major alternatives. However, but-coupling is widely used for channel waveguides although it requires nice surfaces which can be difficult to realize in some soft materials. In addition the coupling efficiency can be strongly limited by the overlap integral between the incident beam profile and the guided mode. Distributed couplers are an interesting alternative in this case, when associated with an integrated focusing component, for instance a taper or a curved grating. Then, the coupling efficiency in the channel waveguide is essentially limited by input coupler efficiency which can be very high in the case of a grating with a special profile.

© 1994 IEEE