Shortcuts to adiabaticity in waveguide couplers-theory and implementation

Adiabatic processes are ubiquitous in physics and engineering. A drawback of such processes is that they tend to be slow, either in time-for atomic systems, for example-or in space-for photonic systems. A number of techniques have been developed over the years, generically referred to as Shortcuts to Adiabaticity, that promise to speed up the evolution of the process without compromising performance. Here we review and compare these techniques, and evaluate their performance using full numerical simulations of realistic two-waveguide couplers, which perform a key function in photonic circuits.