Abstract
THz waves have interesting applications in refractive index sensing. A THz gas sensor based on the guided Bloch surface wave resonance (GBSWR) in a one-dimensional photonic crystal (1DPhC), which consists of periodic polycarbonate (PC) layers and polyvinylidene fluoride (PVDF) layers, has been proposed. Numerical results based on finite element method (FEM) show that the photonic band gap that confines Bloch surface waves (BSWs) lies in the regime of 11.54 to 21.43 THz, in which THz wave can transmit in both PC and PVDF with the ignored absorption. The calculated sensitivity of hazardous gas HCN in angle is found to be 118.6°/RIU (and the corresponding figure of merit (FOM) is 227) and the sensitivity in frequency is 4.7 THz/RIU (the corresponding FOM is 301.3). The proposed structure may also be used for monitoring hazardous gases which show absorption to the incident THz wave. Further results show that for N2O gas, the maximum sensitivity goes up to 644 (transmittance unit/ one unit of the imaginary part of the refractive index). The proposed design may find applications in the detection of dangerous gases.
Highlights
Gas sensors have wide applications in toxic monitoring, explosive detection and pollution control.One method for detecting dangerous gas is based on surface plasmon resonance (SPR) [1,2,3]
According to the simulation results based on finite element method (FEM), the proposed gas sensor is sensitive to the change of refractive index real part of HCN, as indicated by the high figure of merit (FOM) measured by frequency ~147.3 /RIU
Where k0 = 2π/ λ and kBSW are the magnitudes of the free space wave vector and grating Bloch surface waves (BSWs) wave vector respectively, n0 is the refractive index of the sensing gas, θ is the incident angle, Λ is the grating period and m is an integer [16,17], the negative sign “−” means the propagation direction of the BSW is opposite that of incident k0 vector that horizontally projected
Summary
Gas sensors have wide applications in toxic monitoring, explosive detection and pollution control. According to the simulation results based on finite element method (FEM), the proposed gas sensor is sensitive to the change of refractive index real part of HCN, as indicated by the high FOM measured by frequency ~147.3 /RIU and FOM measured by the incident angle ~301.3◦ /RIU. The high and low refractive index layers are PC and PVDF materials, respectively and their dielectric constants are 2.56 and 1.9570-0.0004i at 10 THz. where k0 = 2π/ λ and kBSW are the magnitudes of the free space wave vector and grating BSW wave vector respectively, n0 is the refractive index of the sensing gas, θ is the incident angle, Λ is the grating period and m is an integer [16,17], the negative sign “−” means the propagation direction of the BSW is opposite that of incident k0 vector that horizontally projected.
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