Abstract

Grating anomalies are natural phenomena associated with diffraction gratings. Three categories are defined to distinguish the different types of anomaly: Rayleigh wavelength, resonance, and surface plasmon. In this paper, the guided-mode resonance characteristics of dielectric waveguide diffraction gratings are studied by the rigorous coupled-wave theory. For weakly modulated gratings, it is shown that elementary waveguide theory can be used to locate the resonances and define associated parametric ranges. It is also shown that the transverse field equation describing the field distribution across waveguide structures can be used to express the ratio of the complex amplitudes of the spectral orders on the grating boundaries. It is found that unslanted dielectric diffraction gratings at the first Bragg condition or normal incidence exhibit almost complete energy exchange between the forward and backward propagating zeroth orders. For waveguide gratings with identical parameters, the resonance characteristics are compared for TE and TM polarized input light. The resonances generally occur at different locations and the linewidths of the propagating zeroth orders are also different.

© 1991 Optical Society of America