Nonlinear Coherent Perfect Absorbers*

Coherent perfect absorber (CPA) is a resonant mechanism in which a cavity with a minimal amount of losses can completely absorb incident radiation with an appropriately tailored waveform. The cavity acts as an interferometric trap that confines the incident light for long times and thus amplifies the net absorption. Although in current studies, it was assumed that the medium inside the cavity is linear, there are realistic scenarios where nonlinear mechanisms are engaged.

Here we develop the theoretical framework for the design of CPA waveforms under nonlinear conditions. As an example, we use a photonic circuit consisting of an array of coupled resonators with a nonlinear target embedded in the array. A general solution for the design of the incoming waveform is proposed, and a plethora of CPA frequencies that depend on the intensity of the incident radiation is found–a feature that was not present in linear CPAs. Furthermore, we have demonstrated that under appropriate conditions one can realize a CPA degeneracy, which resembles an exceptional point singularity.