Polarisation-insensitive Si wire waveguide add/drop wavelength filter using reflective mode conversion grating and mode split coupler

Reported is an add/drop wavelength filter which operates independently of light polarisation based on silicon wire waveguide technology. The filter is composed of a reflective mode conversion grating and a mode split coupler. Polarisation independence is archioved by waveguide and grating design, and is verified by experiments. Optical crosstalk at the designed add/drop wavelength for transverse-electric (TE) and transverse-magnetic (TM) polarisations are 13 and 18 dB, respectively. The total length of the filter is greatly reduced compared with the previously reported one by more than 50% with the newly proposed design.