Design of Polarization-Insensitive Demultiplexing Lattice Filters in SOI

In this paper, we propose a novel optimization technique that make use of nonlinear cost functions to design polarization-insensitive wavelength division demultiplexing (DEMUX) lattice filters in silicon-on-insulator (SOI) waveguides. These waveguides are characterized by large effective index and group index birefringences that are fully taken into account in the simulations. The optimization takes advantage of the periodicity of spectral responses of the various elements building a lattice filter. In performing the design, we consider design sensitivity to parameter variations and propose solutions that are compatible with CMOS processes using a waveguide thickness of 220 nm. The design can nonetheless be generalized to other waveguide dimensions and filter topologies for the realization of more complex integrated photonic circuits. Finally, we illustrate the approach by designing and simulating four channel demultiplexers with 200 and 800 GHz channel spacing in both the O- and C-band. Compared to the conventional polarization diversity scheme, this polarization-insensitive design methodology may reduce the total footprint and power consumption by up to 50%, and is therefore of great interest for short reach data communication applications.