Reversal of amplification and absorption through coupled bound-resonance dual states in non-Hermitian waveguide-coupled double-layer gratings

Integrating an amplifier, absorber and modulator into one device is undoubtedly appealing but difficult. In order to realize this, we design a special non-Hermitian waveguide-coupled double-layer gratings. Through the calculation of eigen-frequencies, we found unique bound-resonance dual states thathave combined the respective features of BIC and Fanoresonance: The infinite Q-value from BIC and energy coupling channel from the Fano resonance. Based on the dual states, thetransport modulation including the reversal between the amplification and absorption isachieved through multiple degrees of freedom: filling fraction, frequency, translational misalignment (TM) and incident directions. The TM can make the reversal between the amplification and absorption continuous and easy to implement. Such a structure functions as an integrated device for simultaneous amplifier, absorber and modulator.