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 × 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 µm and 1.55 µm 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.