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

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.

Coherent perfect absorption in the one-dimensional non-magnetized plasma photonic crystals

Electromagnetic (EM) absorption is the basic characteristic of materials that plays an important role in many applications such as solar cells, EM radiation protection, and stealth technology. However, under normal circumstances, the traditional medium's absorption efficiency of EM waves is limited, but the designer can operate by adjusting the structure of the medium. In this paper, the coherent perfect absorption (CPA) is introduced in the one-dimensional (1-D) non-magnetized plasma photonic crystals. Under the premise that the selected material meets the conditions (appropriate thickness and dielectric constant), the absorption amplitude at the frequency point that meets the coherent absorption conditions is greatly improved. The results show that the forward and backward EM waves that meet the CPA conditions and propagate in PPCs can increase the absorption to 99.94% and change the phase difference of the two coherent beams to control the adjustment range of the absorption efficiency to 12.60%-99.94%. In addition, the effects of plasma and collision frequency on the absorption property, and the effects of the periodic constant of dielectric layers and plasma thickness on the frequency and amplitude of coherent absorption are also presented. It is foreseeable that the idea of tunability of light absorption in photovoltaic cells is proposed in this paper, and the application of absorbers in the field of optical switching and light modulation has been further expanded.

Broadband coherent perfect absorption by cavity coupled to three-level atoms in linear and nonlinear regimes

A broadband coherent perfect absorption (CPA) scheme consisting of an optical resonator coupled with three-level atoms excited by single cavity mode is proposed and analyzed. We show the output light field from the system is completely suppressed under specific conditions when the system is excited in linear and nonlinear regimes by two identical light fields from two ends of optical cavity. An analytical broadband CPA criterion for central and sideband excitations of cavity quantum electrodynamics (CQED) system is derived in linear regime. Moreover, we show the resonant excitation criterion for CPA is greatly extended in nonlinear regime. A new type of bistability behavior is found. The output field intensity and the bistability curve can be well tuned by dynamically adjusting system parameters. Our results demonstrate that the CPA is quite universal, and it should be useful in a variety of applications in optical logic and optical communication devices.

Driving plasmonic nanoantennas at perfect impedance matching using generalized coherent perfect absorption

Coherent perfect absorption (CPA) describes the absence of all outgoing modes from a lossy resonator, driven by lossless incoming modes. Here, we show that for nanoresonators that also exhibit radiative losses, e.g., plasmonic nanoantennas, a generalized version of CPA (gCPA) can be applied. In gCPA outgoing modes are suppressed only for a subset of (guided plasmonic) modes while other (radiative) modes are treated as additional loss channels - a situation typically referred to as perfect impedance matching. Here we make use of gCPA to show how to achieve perfect impedance matching between a single nanowire plasmonic waveguide and a plasmonic nanoantenna. Antennas with both radiant and subradiant characteristics are considered. We further demonstrate potential applications in background-free sensing.