ANALYSIS AND OBSERVATION OF FINITE BEAM BRAGG-DIFFRACTION BY A THICK PLANAR PHASE GRATING

A numerical-impulse-response technique for studying the propagation an d diffraction of finite-width beams in planar phase gratings is descri bed. It can account for both symmetric and asymmetric diffractions. Th e grating-length-to-beam-width ratio is shown to govern the extent of beam-profile distortion and selectivity sidelobe suppression. Trade-of fs between diffraction efficiency and beam profile have also been demo nstrated. Theoretical results have been verified by experimental obser vations in a planar waveguide geometry of diffracted beams that change from a single diffraction peak to multiple peaks as the grating-lengt h-to-beam-width ratio increases. (C) 1996 Optical Society of America