Numerical and experimental demonstration of inverse designed low-index polarization-insensitive wavelength demultiplexer

The computational inverse design has paved the way for the design of highly efficient, compact, and novel nanophotonic structures beyond human intuition and trial-and-error approaches. Apparently, with nanophotonic design power, the exploration and implementation of multi-objective, complex, and functional nanophotonic devices become feasible. Herein, we used a recently emerged inverse design framework to demonstrate the design of a 1 x 2 polarization-insensitive wavelength division multiplexer (PIWDM) made of a low-refractive-index material with an index of 1.55. The inversely designed PIWDM structure successfully steers toward the targeted channels for 1.30 mu m and 1.55 mu m with TE and TM polarizations. Taking advantage of the design with a low refractive index material, we scaled the structural dimensions corresponding to the microwave region, fabricated the compact device using a 3D printer, and conducted an experiment as a proof of concept. The transmission values of the fabricated PIWDM device were -4.87 and -2.18 dB for TE and -2.19 and -2.23 dB for TM polarization at WG-I and WG-II, respectively.