Tunable and ultrasensitive sensor covering terahertz to telecommunication range based on a Fabry–Perot interference of graphene plasmonic waves

Abstract

We present an ultrasensitive tunable terahertz (THz) sensor that comprises monolayer graphene-based gratings integrated with a Fabry-Perot (FP) cavity through precisely numerical modeling. Due to the vertical polarization of the incident light on the graphene gratings, they act as an electric dipole, which causes interference in the propagation of plasmonic waves, and provides an excellent foundation for a wide range of ultrasensitive refractive index (RI) sensing with an ultra-high-quality factor (Q). The main advantage of the proposed structure is not only sensing a wide range of refractive indices but due to its unique physical mechanism, it covers electromagnetic waves from a few terahertz to 300 THz, including the telecommunication bands. The primary physical mechanism in the proposed sensor is the FP interference in its active area. Also, due to the extreme sensitivity of FP interference (FPi) to the (RI) of the medium and the active area, the proposed structure owns an ultra-high sensitivity and Q. Our full-wave electromagnetic simulations demonstrate a frequency sensitivity of up to 83 THz per RI unit (RIU) and a high value of Q near 275. In addition, the proposed structure for index sensing has the functionality to be tuned in any desired frequency of interest from THz to the Mid-IR range and telecommunication band, which entirely covers 1–300 THz. The chemical potential of graphene can be electrically controlled to tailor the sensing capability and incident frequency. According to the applied gate voltage, the proposed structure can detect ammonia concentration in water with a high sensitivity of 70–85 THz/RIU and a quality factor of more than 275. The error of the ammonia concentration sensing is smaller than 0.5%. In addition, the proposed structure can detect different types of matter, including various microfluidics, air, gasoline, liquid paraffin, ethanol, glycerin, and glucose. The graphene plasmonic grating method suggested here is a good contender for on-chip integrated THz to mid-IR, including telecommunication bio-sensors.