Nonreciprocal coupling induced chiral absorption

In the past decades, metamaterial absorbers that show customizable absorption and reduced thicknesses have witnessed an impressive success in a variety of applications in light manipulation. Here, we study the nonreciprocal coupling effect between the resonant modes in absorbers and discover a chiral absorption behavior under asymmetric phase coupling. A coupled-mode theory is established to quantitatively analyze the inherent nonreciprocal chiro-optical effects and the degeneration mechanism of chiral resonances for time-reversed breaking absorption is disclosed. A prototype nonreciprocal metamaterial absorber is proposed to achieve perfect absorption in the forward channel and total reflection in the time-reversed channel. Our findings provide an alternative avenue toward spin-selective nonreciprocal photonics.