4-WAVE COUPLED-MODE THEORY OF OBLIQUELY INCIDENT PLANE-WAVES ON WAVE-GUIDE DIFFRACTION GRATINGS

Diffraction of plane waves, obliquely incident on a (waveguide) gratin g with infinitely long grooves, is analyzed with the four-wave coupled -mode theory (CMT). Unlike the ordinary analysis that considers only c oupling between pairs (i.e., TE+ <-> TE-, TE+ <-> TM-, TM+ <-> TE-, or TM+ <-> TM-), the simultaneous interaction among these waves is prope rly accounted for. The field variation along the grating and the impul se response representation of the grating (reflectivity and transmissi on as functions of the plane-wave incidence angle) are calculated. Sig nificant differences between the ordinary (two-wave) CMT and the four- wave CMT are observed over a wide range of incident angles. (C) 1998 O ptical Society of America.