Perfect absorption in complex scattering systems with or without hidden symmetries

Abstract

Wavefront shaping (WFS) schemes for efficient energy deposition in weakly lossy targets is an ongoing challenge for many classical wave technologies relevant to next-generation telecommunications, long-range wireless power transfer, and electromagnetic warfare. In many circumstances these targets are embedded inside complicated enclosures which lack any type of (geometric or hidden) symmetry, such as complex networks, buildings, or vessels, where the hypersensitive nature of multiple interference paths challenges the viability of WFS protocols. We demonstrate the success of a general WFS scheme, based on coherent perfect absorption (CPA) electromagnetic protocols, by utilizing a network of coupled transmission lines with complex connectivity that enforces the absence of geometric symmetries. Our platform allows for control of the local losses inside the network and of the violation of time-reversal symmetry via a magnetic field; thus establishing CPA beyond its initial concept as the time-reversal of a laser cavity, while offering an opportunity for better insight into CPA formation via the implementation of semiclassical tools.

Experimental Realization of Optimal Energy Storage in Resonators Embedded in Scattering Media

“…We expect these results to trigger new schemes to enhance energy harvesting and non‐linear effects in photonic and phononic materials. [ 58 ] Our framework may also open new perspectives for coherent perfect absorption in random media, [ 52,53,59–61 ] to control random lasing [ 62 ] and for deep imaging through highly scattering samples. [ 63 ]…”

Perfect Absorption in a Disordered Medium with Programmable Meta‐Atom Inclusions

“…Moreover, many realistic scattering systems like our 3D enclosure present significant homogeneous attenuation which prevents full in situ control of attenuation with a single loss center as in refs. [22,23]. Our proposal's ease of implementation (low hardware complexity and cost, no need to tune attenuation) will be a key enabler for the proliferation of PA-based applications in real life.…”

“…refs. [22,23] which rely on the operation frequency being a free parameter, the availability of coherent control of the impinging wave-front and the freedom to tune the random medium's level of attenuation. Naturally, since we consider single-channel excitation as justified above, the simplicity of our setup (Arduino microcontroller and printed-circuit-board metasurface) is in sharp contrast to the immense hardware cost entailed by the need for precise amplitude and phase tuning of the incident wave-front, for example, with 16 IQ-modulators in ref.…”

“…Moreover, it is worthwhile acknowledging that wave-front-shaping-based coherent PA schemes as proposed in refs. [22,23] rely on the frequency as free parameter to find a coherent PA condition, that is, by construction these methods are unable to achieve PA at any desired target frequency.…”

“…In Figure 4a, we show a selection of eight PA and eight nonPA configurations for our modified experimental setup including a second eavesdropper port as depicted in Figure 4b. Note that the ability to achieve eight PA configurations within a 0.04 GHz bandwidth, as well as the ability to dynamically switch between PA and nonPA at each of these nearby frequencies, is a unique feature of our PA technique based on tuned randomness, setting it clearly apart from previous reports on PA in random media [22,23] (see also Section 5). As illustrated in Figure 4c, for each bit, Alice randomly picks one of the eight configurations that yield PA (resp.…”