Controlling coherent perfect absorption via long-range connectivity of defects in three-dimensional zero-index media.

Abstract

Coherent perfect absorption (CPA), as time-reversed lasing, arises from appropriate wave interference within absorbers, offering flexible control over wave absorption. Typically, this control involves tuning the phase difference between two counter-propagating incident beams. Here, we elucidate the critical role of defect connectivity within three-dimensional zero-index media for realizing and controlling CPA. Specifically, the realization of CPA critically depends on the establishment of long-range connectivity of defects in a specific direction. Once the long-range connectivity is established, the CPA exhibits remarkable resilience against defects' deformation, changes in size and shape of the zero-index media, as well as variations in number and orientation of incident channels. Notably, a minor disruption to this connectivity will result in a complete reduction of absorption to zero, highlighting an ultra-sensitive absorption property in response to connectivity perturbations. Our findings not only unveil a physical mechanism for realizing CPA but also open up promising avenues for advanced CPA control with versatile functionalities.