Abstract

A variety of analytical formalisms and numerical techniques have been used to describe guided-radiation mode coupling by waveguide diffraction gratings. Motivated by the development of integrated optic devices such as grating couplers and DFB lasers, the focus of this work has been on the case of normal incidence, where the projections of the mode propagation vectors in the plane of the waveguide are parallel to the grating vector. Recent interest in the use of grating couplers at non­normal incidence, as in the case of focusing grating couplers, has led to the extension of previous analyses to the more general case of oblique incidence.¹² We present the results of a local normal mode analysis of shallow periodic surface corrugation grating couplers for the case of non-normal incidence.² Our results are compared with those obtained using an ideal mode expansion as well as to the results of the quasioptical technique employed by Wlodarczyk and Seshadri.¹ It is shown that all the formalisms predict TE-TM and TM-TE mode coupling for the case of oblique incidence. We consider the effects of such coupling on the operation of straight-line and focusing grating couplers.

© 1988 Optical Society of America