Polarization-independent coupled-waveguide grating filters

Theoretical analysis and design principles for a polarization-independent optical wavelength filter based on phase-shifted gratings are developed and presented. Side-lobe suppression is demonstrated by chirping the ratio of the length of phase-shifted section to that of grating section. A design guideline is explained for the polarization-independent filter with side-lobe suppression. It is shown that identical spectral responses for the two polarizations can be achieved despite the polarization-dependent coupling strengths. Tunability of such devices is studied, and the polarization-dependent modal loss is discussed at last.