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

Suwun Suwunnarat,Yaqian Tang,Ulrich Kuhl,Mattis Reisner,Tsampikos Kottos,Fabrice Mortessagne

doi:10.1038/s42005-021-00782-2

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.

Highlights

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
In the case of perfect coupling of the resonators with the interrogating antennas, the system supports a different type of nonlinear CPA (NLCPA) modes which demonstrate a square-root frequency degeneracy in the neighborhood of a critical magnitude of the incident wave amplitudes– remnant of an exceptional point (EP) degeneracy occurring in linear non-hermitian systems
The incident and reflected waves of the system are separated by circulators connected to the source cable, the antenna, and the measuring port of the vector network analyzer (VNA)

Summary

Introduction

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. At the core of this activity is the promise that perfect absorption can be beneficial to a variety of applications ranging from stealth technologies[3,11,12], energy harvesting and photovoltaics[13], sensing[14,15], and photodetection[16,17] Along these lines, the quest for low-cost/power all-optical switching and modulation schemes that simultaneously utilize coherent interaction of light beams and absorbing matter for extreme absorption is recently gaining a lot of attention[18,19,20]. The scheme has been initially proposed in the framework of classical optics[21,22], as the time-reversed process of a laser, it turns out that its implementation does not require time-reversal symmetry[23,24,25] It rather solely relies on wave interference effects that entrap the incident radiation inside the lossy cavity, leading to its complete absorption. We provide a paradigm of EP degeneracies associated with steady-state non-linear solutions of the wave operator, with incoming boundary conditions, that are responsible for a broad-band (near-) perfect absorption

Methods

Results

Conclusion