Non-linear coherent perfect absorption in the proximity of exceptional points

Abstract

Coherent perfect absorption is one of the possibilities to get high absorption but typically suffers from being a resonant phenomena, i.e., efficient absorption only in a local frequency range. Additionally, if applied in high power applications, the understanding of the interplay of non-linearities and coherent perfect absorption is crucial. Here we show experimentally and theoretically the formation of non-linear coherent perfect absorption in the proximity of exceptional point degeneracies of the zeros of the scattering function. Using a microwave platform, consisting of a lossy nonlinear resonator coupled to two interrogating antennas, we show that a coherent incident excitation can trigger a self-induced perfect absorption once its intensity exceeds a critical value. Note, that a (near) perfect absorption persists for a broad-band frequency range around the nonlinear coherent perfect absorption condition. Its origin is traced to a quartic behavior that the absorbance spectrum acquires in the proximity of the exceptional points of the nonlinear scattering operator.

Meta-programmable analog differentiator

“…In contrast to the intensity-dependent nonlinear CPA-EP in Ref. 99 , our experiment offers this transfer function irrespective of the incident power signal. Moreover, the homogeneous absorption in our system due to Ohmic losses on the walls, as opposed to localized absorption mechanisms, enables the absorption of high-power incident signals without significant localized heating.…”

“…Second, we generalize this concept to toggling between multiple simultaneous zeros of the scattering matrix—that lie on the real frequency axis—of various spectral separations in order to demonstrate parallel wave processing on the same device. Finally, we cascade two tunable chaotic cavities to compute second-order derivatives, thereby engineering a transfer function usually associated with CPA exceptional points 96 – 99 that may also be enticing for applications in broadband near-perfect absorption.…”

Massively degenerate coherent perfect absorber for arbitrary wavefronts

“…Last, but not least, we emphasize that our work has focused on the spatial degrees of freedom of the incoming waves. It would be fascinating to study the potential of cavity designs to achieve comparable advances in the spectral domain [24][25][26], leading potentially to broadband absorption characteristics-a direction in which advances have recently been made using exceptional points and non-linear media [10][11][12]27].…”

Massively degenerate coherent perfect absorber for arbitrary wavefronts

“…Although our work has focused on the spatial degrees of freedom of the incoming waves, it would be fascinating to achieve broadband absorption also in the spectral domain (25)(26)(27), a direction in which advances have recently been made using exceptional points and nonlinear media (11)(12)(13)28).…”