SPR-based fiber optic sensor in NIR region

Abstract

A surface plasmon resonance (SPR) based fiber optic sensor is simulated and analyzed in near infrared (NIR) region for normal (N) and malignant human liver tissue (MET) detection. Proposed five layered sensor consists of samarium-doped chalcogenide core, silver layer (Ag) deposited on the polymer clad, followed by graphene monolayer and analyte layer. Transfer matrix method for N layer model has been used for normalized reflection coefficient (R) calculations for the proposed multilayer structure. Furthermore, sensor structure utilizes the selective ray launching where incident angle (α) is varied at fiber input end (angular interrogation) and power transmitted through sensing region of length ‘L’ is measured in dB. At resonance (i.e., α = αSPR), sharp power loss peak is obtained where, αSPR shifts to other angle (i.e. δαSPR) with a change in analyte refractive index (RI). The prime focus of the present study is to optimize the radiative damping (i.e., optimum radiative damping (ORD)) at Ag-graphene junction to bring significant enhancement in the sensor’s performance. At resonance condition, the interference between incident light and back-scattered light known as radiation damping is responsible for excessively large sensor’s figure of merit (FOM). Hence, the coupled role of metal layer thickness (dm) and wavelength (λ) with 2D material layer plays important role as extent of radiation damping changes significantly, which leads to massive increase in FOM. For the proposed sensor structure value of L/D is taken as 25 (D represents the fiber core diameter) achievable with various L and D combinations (e.g., L = 1 cm and D = 400 μm). The combination of dm = 35 nm and λ = 865 nm leads to a maximum FOM of 4910.32 RIU-1. The coupled effect of dm and λ leads to significantly higher value of FOM, enables the graphene-based fiber-optic sensor for biosensing and other applications.