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Engineering the transport of radiation and its interaction with matter using non-Hermiticity, particularly through spectral degeneracies known as exceptional points(EPs), is an emerging field that has both fundamental and practical implications. Chiral behavior in the vicinity of EPs opens new opportunities in radiation control, such as unidirectional reflection or lasing with potential applications in areas ranging from cavity quantum electrodynamics and spectral filtering to sensing and thermal imaging. However, tuning and stabilizing a system to a discrete EP in parameter space is a challenging task: either the system is operated close to an EP rather than directly at the EP or the true power of EP is obscured by stability issues. Here, we circumvent this challenge by designing a photonic system that operates on a surface of exceptional points, known as an exceptional surface (ES). We achieve this by using a waveguide-coupled optical resonator with an external feedback loop that induces a nonreciprocal coupling between its frequency degenerate clockwise (CW) and counterclockwise (CCW) traveling modes. By operating the system at critical coupling on the ES, we demonstrate, for the first time, the effect of chiral and degenerate coherent perfect absorption (CPA) where input waves in only one direction are perfectly absorbed. This novel type of CPA-EP is revealed through the observation of the predicted and long-sought squared Lorentzian absorption lineshapes. We expect our results and approach to serve as a bridge between non-Hermitian physics and other fields that rely on radiation engineering.
We propose a tunable coherent perfect absorber based on ultrathin nonlinear metasurfaces. The nonlinear metasurface is made of plasmonic nanoantennas coupled to an epsilon-near-zero material with a large optical nonlinearity. The coherent perfect abs
Coherent perfect absorption (CPA) refers to interferometrically induced complete absorption of incident light by a partial absorber independently of its intrinsic absorption (which may be vanishingly small) or its thickness. CPA is typically realized
Coherent perfect absorber (CPA) was proposed as the time-reversed counterpart to laser: a resonator containing lossy medium instead of gain medium can absorb the coherent optical fields completely. Here, we exploit a monolayer graphene to realize the
Here we make use of vanadium dioxide (VO2) to design a bifunctional metasurface working at the same targeted frequency. With the increase of temperature, the functionality of the designed metasurface can switch from a multi-channel retroreflector to
We investigate spontaneous emission from a quantum emitter located within the mode volume of a microring resonator that features chiral exceptional points. We show that this configuration offers enough degrees of freedom to exhibit a full control to