Ultra-broadband coherent perfect absorption via elements with linear phase response

Coherent Perfect Absorption of Arbitrary Wavefronts at an Exceptional Point

A coherent perfect absorber exploits the interferometric nature of light to deposit all of a light field's incident energy into an otherwise weakly absorbing sample. The downside of this concept is that the necessary destructive interference in coherent perfect absorbers gets easily destroyed both by spectrally or spatially detuning the incoming light field. Each of these two limitations has recently been overcome by insights from exceptional-point physics and by using a degenerate cavity, respectively. Here, we show how these two concepts can be combined into a new type of cavity design, which allows broadband exceptional-point absorption of arbitrary wavefronts. We present two possible implementations of such a massively degenerate exceptional-point absorber and compare analytical results with numerical simulations.

Coherent perfect absorption from asymmetry transmissive Helmholtz resonator metamaterials

We propose an asymmetry transmissive (AT) Helmholtz resonator metamaterial to interact with dual incidences of different polarizations from opposite directions to achieve coherent perfect absorption at a terahertz regime. More specifically, the proposed design will solely allow the x-polarized incidence tunnel into the Helmholtz resonator cavity array with roughly half the energy reflected. Meanwhile, the transmitted fields will be converted into the y-polarized counterparts so as to go out through the metamaterial and finally coherent canceled with the partially reflected fields of the other incidence. Our design, introducing the Helmholtz resonator array in the electromagnetics with an extension of the principle of polarization conversion under the coherent perfect absorption, should pave the way for the quest of building up more advanced wave trapping meta-devices for various applications in different disciplines.

Coherent perfect loss with single and broadband resonators at photonic crystal nanobeam

Coherent perfect absorption (CPA) has been studied in various fields, such as metasurface, photonics, and acoustics, because of its ability to perfectly absorb light at a specific wavelength. However, the narrow bandwidth of CPA makes its application to on-chip photonics challenging. This limitation can be overcome by using a broadband resonator. Here, we demonstrate the coherent perfect loss (CPL) with respect to a single and broadband resonator at photonic crystal nanobeam. By using the finite element method, both cases of the CPL were simulated and optimized for the single and broadband resonators. In the optimized structure, a CPL occurs for both resonators. These results confirm that the perfect loss region for the broadband resonator is wider than that for the single resonator. These results are experimentally verified by fabricating both cases of CPL cases on a silicon-on-insulator by using electron beam lithography. An almost perfect loss of more than 95 % is observed for both single and broadband CPLs. Furthermore, the almost perfect loss region at the broadband resonator broadens more than that at the single resonator. The optimized structure for CPL has the potential for easy applications to on-chip photonics, such as optical switches, modulators, sensors, and logic gates.