Abstract

Nonreciprocal devices, such as optical isolators and circulators are needed to reduce reflections of the lasers own radiation into itself in order to improve the spectral stability of lasers. Most proposals for thin-film optical isolators are based on nonreciprocal TETM mode conversion in magnetooptic waveguide^[1-2]. The crucial problem of this concept is that a precise phase matching between the interacting TE and TM modes is necessary (e.g. by orienting the optical axis of the materials and by controlling the film thickness precisely). These requirements are difficult to achieve in practice. The devices which are easier to realize are the isolators (or phase-shifters) based on the nonreciprocity of TM-modes (i.e. dependence of the propagation constant on the direction of propagation) propagating in opposite directions in an asymmetric magnetooptic waveguide in the presence of a de magnetic field applied transversely to the direction of propagation in the plane of the film (Voigt configuration)^[3-4]. For nonreciprocal devices, the difference Δβ of propagation constants (or difference of the cutoff thicknesses) of two counterpropagating TM modes is an important device parameter. Nonreciprocity in Voigt configuration is attributed to TM modes only and requires an asymmetric waveguiding structure.

© 1992 IQEC