Inverse design of polymer-based polarization-insensitive wavelength demultiplexers

The unpredictable polarization of light in network fibers necessitates polarization-independent wavelength demultiplexing for reliable optical communications. This work combines polymer refractive index tunability with topology optimization-based inverse design to develop high-performance two- and four-channel polarization-insensitive wavelength demultiplexers (PIWDMs) for O-band and C-band operation. Optimization studies reveal that a polymer refractive index of 1.7 enables strong mode confinement and minimizes scattering loss, making it ideal for polymer-based PIWDMs. The best-performing two-channel PIWDM achieves an insertion loss (IL) below 1 dB, crosstalk (CT) under -17<i>d</i><i>B</i>, and polarization-dependent loss (PDL) below 0.32 dB. Fabrication tolerance analysis confirms device robustness within a -10 to +20<i>n</i><i>m</i> error range. Using optimized structures across different footprints, the four-channel PIWDM achieves an IL between 0.87 and 1.48 dB, a CT from -17.28 to -23.66<i>d</i><i>B</i>, and a PDL below 0.61 dB. These PIWDMs offer an efficient, easily manufacturable solution for integrated photonic systems.