Abstract
A novel fiber-optic Mach–Zehnder interferometer based on ${{\rm SnO}_2}$, ${{\rm MoS}_2}$, ${{\rm SnO}_2}/{{\rm MoS}_2}$, and ${{\rm SnO}_2} {-} {{\rm MoS}_2}$ sensing film for cadmium-ion (${{\rm Cd}^{2 +}}$) detection is proposed and fabricated. The photonic-crystal fiber (PCF) is sandwiched between the no-core-fiber-1 (NCF1) and no-core-fiber-2 (NCF2), forming the Mach–Zehnder interferometer with the NCF1-PCF-NCF2 structure, which is regarded as the sensing unit. The ${{\rm SnO}_2}$, ${{\rm MoS}_2}$, ${{\rm SnO}_2}/{{\rm MoS}_2}$, and ${{\rm SnO}_2} {-} {{\rm MoS}_2}$ sensing films are, respectively, coated on the surface of two NCFs’ claddings. The comparative experiment results of the sensors with four membranes (${{\rm SnO}_2}$, ${{\rm MoS}_2}$, ${{\rm SnO}_2}/{{\rm MoS}_2}$, ${{\rm SnO}_2} {-} {{\rm MoS}_2}$) show that the sensors have good sensing performance for ${{\rm Cd}^{2 +}}$ in the concentration range of 0–100 µM. When these sensing films adsorbed ${{\rm Cd}^{2 +}}$, the monitoring wavelength shows blueshift of 0.6931 nm, 1.0252 nm, 1.9505 nm, respectively, and redshift of 3.0258 nm, and the sensitivities are 6.931 pm/µM, 10.252 pm/µM, 19.505 pm/µM, and 30.258 pm/µM, respectively. The sensor with ${{\rm SnO}_2} {-} {{\rm MoS}_2}$ bilayer film exhibits the optimal response to ${{\rm Cd}^{2 +}}$ with excellent selectivity and stability. The proposed sensor has the advantages of simple structure, easy fabrication, small size, etc., having potential application in the monitoring of ${{\rm Cd}^{2 +}}$ in aqueous solution.
© 2021 Optical Society of America
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