Adiabatic tapers based on photonic inverse design

Adiabatic mode evolution is an important concept in photonic devices and is utilized in several applications including spot size conversion, mode coupling between the two waveguides, and broadband power splitters/couplers. In such devices, the linear adiabatic tapers are not always the best choice in terms of the device footprint and hence the taper profile needs to be optimized to provide small footprint while ensuring adiabatic mode evolution. In many instances, the best taper profile can be quite complex, and a parametric design might require a lot of parameters to accurately define the taper profile. In such cases, the traditional optimization using parameter sweep can be challenging. Several techniques such as Fast Quasi Adiabatic (FAQUAD) dynamics and constant loss approach have been proposed in the literature for such optimization. We implement these techniques and conduct a brief comparison using two different integrated photonic components. We also briefly discuss the challenges associated with relying solely on the optimization algorithms (inverse design) without utilizing constraints associated with these techniques.