Traveling-Wave-Induced Nonreciprocal Absorption and Zero Reflection in Physically Separated Dual Photonic Resonators

Nonreciprocal perfect absorption of electromagnetic waves has enabled many applications, including ultrasensing sensors, one-way cloaking, and detection. This study experimentally investigates strong nonreciprocal reflectivity and absorptivity, achieving nearly zero reflection and near-perfect absorption in a dual photonic resonator system. This system consists of two physically separated inverted split-ring resonators (ISRRs) with adjustable distances between them. We also observed an electromagnetically induced-transparency (EIT)-like peak, attributed to traveling waves along a shared microstrip line that dissipatively couple the dual ISRRs. Finally, the observed unidirectional absorptions with zero reflection are attributed to a non-Hermitian origin. This work advances our understanding of indirect coupling induced by traveling waves in photonic resonators, without magnetic coupling. It sets guidelines for creating novel, multifunctional nonreciprocal devices, and sensors with broad applications in wireless communication, radar cloaking, high-sensitivity sensing, and molecular detection.