Investigation of adjoint method inverse design applied to photonic integrated circuit fiber-to-chip edge couplers

Inverse width taper edge couplers are the staple of low-loss photonic fiber-to-chip coupling. However, adiabatic mode conversion consumes large die area, which contradicts efforts towards dense integration. By leveraging the advantages of inverse design, we analyze a lithographically manufacturable method for designing fiber-to-chip edge coupling components. Adjoint method optimization is executed via the open-source Stanford Photonic Inverse design Software (SPINS-b) optimization framework to design a preliminary silicon nitride (SiN) fiber-to-chip coupler. Simulation results are validated with Ansys Lumerical finite-difference time-domain (FDTD) solver. Adjoint method inverse design in-plane coupling is evaluated as a solution for photonic integrated circuits with strict size constraints. The design methodology is material and application agnostic, promoting dense photonic integration.