Tunable multichannel nonreciprocal perfect absorber based on resonant absorption

A tunable multichannel nonreciprocal perfect absorber with the asymmetric metal-photonic crystal hetero-structure is theoretically proposed. By using the transfer matrix method, the linear and nonlinear properties of the absorber are investigated. An ultra-narrow perfect absorption channel is realized in the linear case due to the impedance matching, and the channel number can be adjusted by changing the period of the photonic crystal. Bistable absorption and reflection are achieved in the nonlinear case due to the positive feedback between the metal nonlinear permittivity and the inner electric field, while the bistable thresholds can be altered by varying the incident light wavelength. Moreover, the absorber exhibits the intrinsic nonreciprocity in both absorption and reflection, and shows the polarization-independent directional characteristics when the incident angle is less than 40°.