Tunable terahertz coherent perfect absorption in a monolayer graphene

TL;DR

This paper demonstrates tunable, broadband, and polarization-dependent coherent perfect absorption in monolayer graphene at terahertz frequencies, controllable via phase modulation and Fermi energy tuning, with potential applications in terahertz detection.

Contribution

It introduces a non-resonant, tunable CPA mechanism in monolayer graphene exploiting phase modulation and Fermi energy control, expanding the scope of 2D material-based terahertz devices.

Findings

Existence of quasi-CPA point in terahertz regime for graphene

Broadband angular selectivity with polarization dependence

Tunable absorption via gate-controlled Fermi energy

Abstract

Coherent perfect absorber (CPA) was proposed as the time-reversed counterpart to laser: a resonator containing lossy medium instead of gain medium can absorb the coherent optical fields completely. Here, we exploit a monolayer graphene to realize the CPA in a non-resonant manner. It is found that quasi-CPA point exists in the terahertz regime for suspending monolayer graphene, and the CPA can be implemented with the assistant of proper phase modulation among two incident beams at the quasi-CPA frequencies. The graphene based CPA is found of broadband angular selectivity: CPA point splits into two frequency bands for the orthogonal $s$ and $p$ polarizations at oblique incidence, and the two bands cover a wide frequency range starting from zero frequency. Furthermore, the coherent absorption can be tuned substantially by varying the gate-controlled Fermi energy. The findings of CPA with non-resonant graphene sheet can be generalized for potential applications in terahertz/infrared detections and signal processing with two-dimensional optoelectronic materials.