Dynamic tunable narrow-band perfect absorber for fiber -optic communication band based on liquid crystal

Abstract

At present, most of the reported metasurface structure absorbers show that its working band cannot be regulated actively. In this study, a dynamic tunable narrow-band perfect absorption structure for fiber-optic communication band based on liquid crystal is proposed and studied. The structure is mainly composed of two effective tiers. The top tier gold array and the bottom tier reflective gold film, which are separated by a SiO2-liquid crystal dielectric medium interlayer to form a metal-dielectric-metal (MDM) structure. Due to the unique optical properties of liquid crystals, its index of refraction can be changed by adjusting the bias voltage and temperature, so as to adjust the resonance wavelength actively. The designed structure is analyzed by finite element method (FEM) and the coupled mode theory (CMT) is used to verify the analysis results. The designed structure has a 99.92% absorption effect in the most commonly used band of fiber-optic communication. Due to the symmetry of the absorber structure, the device is not sensitive to the polarisation state of the excitation source. Moreover, the absorber exhibits an unusual dependence on the incident angle, which can be attributed to the anisotropy of the liquid crystal. Based on the dependence of incident angle, a plasma optical switch with large ON/OFF ratio (η) of 27.395dB and nearly flawless modulation depth (MD) of 99.818% can be realized. It is believed that this structure can provide a method for the dynamic control of near infrared electromagnetic waves, and to be applied in electromagnetic energy absorption, filtering and plasma optical switch system.