Mode conversion and optical filtering of obliquely incident waves in corrugated waveguide filters

By employing a coupled-mode analysis, we reveal the presence of strong coupling between TE and TM modes in a periodically corrugated optical-waveguide when the wave propagates obliquely with respect to grating vector. The evidence of such mode coupling has been obtained by the polarized transmission and reflection experiment; then the measured strengths of coupling among various modes are successfully compared with calculated values. The effect of such coupling on the performance of a frequency demultiplexer is discussed with some preliminary experiments.