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

Abstract

Achieving the very special condition of perfect absorption (PA) in a complex scattering enclosure promises to enable a wealth of applications in secure communication, precision sensing, wireless power transfer, analog signal processing, and random lasing. Consequently, a lot of recent research effort is dedicated to proposing wave-front shaping protocols to implement coherent PA in complex scattering environments with tunable localized absorption as well as a tunable excitation frequency. Here, the conceptually different route of solely tweaking the randomness of the complex scattering environment in order to achieve PA is proposed. An experimental proof-of-concept in the microwave domain is provided where the randomness of a 3D chaotic cavity is tuned with programmable meta-atom inclusions. The achievability and extreme sensitivity of the PA condition are systematically investigated. The presented technique can impose a PA condition at over hundred distinct frequencies within a small frequency band, enabling the proposal and experimental demonstration of a concrete practical application: receiver-powered secure wireless communication in a complex scattering enclosure. The presented fundamentally new perspective on PA applies to all types of wave phenomena; the experimental results foreshadow the large potential of this novel tool for minute wave control in sensing, communication, and energy transfer.

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 ]…”

Angular‐Multiplexing Metasurface: Building Up Independent‐Encoded Amplitude/Phase Dictionary for Angular Illumination

“…[ 1,2 ] During the last decade, many previous endeavors on metasurfaces could exhibit great promise for achieving various practical applications including beam shaping, [ 3–6 ] achromatic lens, [ 7–10 ] hologram, [ 11–17 ] nanoprinting, [ 18–22 ] invisibility cloaking, [ 23,24 ] optical information multiplexing/encryption, [ 25–27 ] and programmable metasurfaces. [ 28–32 ] So far, the majority of controllable optical parameters have been extensively explored and created for new completely independent freedom in light manipulation and optics multiplexing, such as wavelength, [ 33–36 ] polarization, [ 37–30 ] orbital angular momentum (OAM), [ 14–16 ] forward/backward illumination direction (+/‐) [ 39–41 ] as well as the initial phase of the light field. [ 25 ] For instance, by spatially multiplexing elements with different geometric sizes (corresponding to different resonance wavelengths), the metasurface could exhibit different images under different incident wavelengths.…”

Critically coupled Fabry–Perot cavity with high signal contrast for refractive index sensing

“…On the contrary, in the case of a distributed Bragg reflector (DBR), the reflectance can be coarsely tuned by changing the number of multiple DBR pairs, with more possibly only by changing the thickness of the uppermost DBR layer 31 . It is worthy to mention that diverse metamaterial absorbers including actively tunable meta-structure have been reported to achieve perfect absorption in the microwave and terahertz region 32 – 36 .…”