Tapered mismatched couplers

The criteria for adiabatic power flow along tapered mismatched directional couplers are discussed. The authors present the coupled local normal mode equations for tapered mismatched directional couplers. From these, the authors derive an optimally short profile for obtaining quasi-adiabatic power propagation. Apart from the trivial case where the mismatch is a constant, this is the only known mismatch profile for which analytical solutions of the coupled local normal mode equations exist. Conditions for which an adiabatic coupler can be used to obtain approximately 100% power transfer from one core to the other are also given