Experimental characterization and analysis of an adjoint method inverse design compact edge coupler solution

We present an in-depth analysis from design to test of an inverse design silicon nitride edge coupler for 1550 nm wavelength with a compact footprint of 12 x 4 µm. Component design was performed using an open-source inverse design framework and fabricated in a foundry 300 mm lithography process. Experimental fiber-to-chip coupling loss shows 5.5 dB coupling to the fundamental quasi-TE mode and 2.4 dB coupling in the quasi-TM mode at the design wavelength. In addition to coupling loss analysis of the component design, loss with respect to fiber alignment, and effects of fabrication variations are discussed. The results show that by using this method, it is possible to considerably shorten edge coupler length compared to adiabatic tapers, which can increase integration density in photonic integrated circuits.