Abstract

Planar waveguide grating couplers are often fabricated by first etching a surface-relief grating into the substrate material and then depositing a thin film waveguide on top. Unless the film thickness is much greater than the corrugation depth of the grating, the top surface of the waveguide will inevitably have ripples following the periodic corrugation of the etched grating. The propagation and radiation characteristics of the grating coupler will be influenced by both surface corrugations by means of optical interference. The consideration of this interference effect is very important in the actual design and analysis of grating couplers. However, this issue has not received any attention in the literature until recently, when Avrutsky et al^1,2 analyzed (using an approximate method) and experimentally demonstrated single-order couplers utilizing phase-shifted double corrugations. In this paper, planar waveguide grating couplers with double surface corrugations are analyzed by using a rigorous vector diffraction grating model. The effects of both the relative corrugation depth and the relative phase shift on the total radiation loss and the radiation branching ratio are investigated.

© 1992 Optical Society of America