Abstract

Grating assisted codirectional couplers are very useful for widely tunable lasers and filters. They consist of a directional coupler with periodic discontinuities. These have to be strong to obtain coupling in relatively short devices. Therefore these devices may show substantial radiation losses. Generally, there are two methods to analyse codirectional couplers, one based on a coupled mode formalism [1] and another using mode matching theory at discontinuities and mode propagation in the straight waveguide sections [2]. Both methods can calculate the wavelength of maximum coupling and the coupling length as a function of the structure parameters. BPM calculations may have difficulties with the large refractive index steps. In this paper we present a method to calculate accurately the radiation losses. An optimised design with respect to losses is now possible for this kind of couplers.

© 1993 Optical Society of America