OPTICAL WAVE-GUIDE DIFFRACTION GRATINGS - COUPLING BETWEEN GUIDED MODES

This chapter discusses the interaction between the modes of a planar optical waveguide and a periodic surface corrugation. The specific case of the grating-induced coupling between two guided waves in a planar waveguide structure is emphasized. The physical nature of the interaction is understood as being because of the Bragg scattering. Approximations lead to agreement with each other for transverse electric (TE)-polarized guided waves, and disagree with each other for transverse magnetic (TM)-polarized guided waves. A recent experiment was able to distinguish among classes of theories. The chapter discusses the various techniques used to attack the problem of a guided wave interacting with a waveguide diffraction grating. The various approaches to enable a comparison among the various treatments are formulated. A new formulation of the local normal mode approximation avoided the complexities of earlier versions of the theory and made it easy to identify the principal features of the approximation that made it successful. A theoretical description of the guided-wave Bragg-reflection problem can be relied upon for the shallow surface corrugations. © 1991, Elsevier B.V. All rights reserved.