Electrodynamics analysis on coherent perfect absorber and phase-controlled optical switch

A coherent perfect absorber is essentially a specially designed Fabry-Perot interferometer, which completely extinguishes the incident coherent light. The one- and two-beam coherent perfect absorbers have been analyzed using classical electrodynamics by considering index matching in layered structures to totally suppress reflections. This approach presents a clear and physically intuitive picture for the principle of operation of a perfect absorber. The results show that the incident beam(s) must have correct phases and amplitudes, and the real and imaginary parts of the refractive indices of the media in the interferometer must satisfy a well-defined relation. Our results are in agreement with those obtained using the S-matrix analysis. However, the results were obtained solely based on the superposition of waves from multiple reflections without invoking the concept of time reversal as does the S-matrix approach. Further analysis shows that the two-beam device can be configured to function as a phase-controlled three-state switch.