Nonlinear Graphene-Transition Metal Dichalcogenides Heterostructure Refractive Index Sensor

Abstract

In this paper, a refractive index sensor based on nonlinear graphene-transition metal dichalcogenides (TMDs) Bragg reflector (BR) is proposed and analyzed. The Bragg wavelength and the reflection width can be engineered by the number of TMD layers and the intensity of the input, and this case is dissimilar to the specified resonance wavelength of the surface plasmon resonances with constant resonance wavelength. The low loss nature and high nonlinearity of TMDs accompanying the graphene brilliant properties let the design of more flexible, narrower resonance, and lower loss sensors. We theoretically compute the dielectric function of the structure utilizing the quantum electrostatic heterostructure method and numerically simulate our proposed sensor by the three-dimensional finite difference time domain. The simulation results reveal that the effective refractive index of the sensor directly controls the Bragg wavelength of the proposed sensor. We tune the Bragg wavelength and the bandwidth of the reflection of the BR sensor by input intensity. In our proposed sensor, the full width at half maximum (FWHM) of the BR reflection spectra decreases from 12 nm in the linear regime to 1.5 nm in the nonlinear regime, which let have 1099 (nm/RIU) sensitivity with an input intensity of 6.18 (MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). In the nonlinear regime, a variation of 0.01 in the refractive index causes 20-nm redshift in the BR wavelength, and with respect to the 1.5-nm FWHM, the reflection spectra are completely recognizable. Due to its sensitivity, this kind of heterostructure sensor can be utilized in the design of sensitive optical biosensors.