Optimization of adiabaticity in coupled-waveguide devices using shortcuts to adiabaticity.

Conventional strategies to design adiabatic coupled-waveguide devices focus on optimizing the system adiabaticity but can only guarantee 100% efficiency at specific lengths. We establish a simple technique allowing the optimization of device adiabaticity and ensuring 100% coupling/conversion efficiency at any physically realizable length. Specifically, we use the shortcuts-to-adiabaticity technique to represent the system state precisely and engineer the system evolution to be as close to the adiabatic state as possible. Smooth parameters are derived for coupled-waveguide devices, which feature good robustness against wavelength and fabrication variations at the same time. The proposed device is verified with beam propagation simulations.