Multimode Optical Fiber Sensor Modified With Gold Nanorod Arrays

This letter presents the design and fabrication of a multimode fiber sensor, enhanced with a gold nanorod (GNR) array to improve its refractive index sensitivity. The cladding is etched with hydrofluoric acid (HF) to allow light leakage from the core, followed by magnetron sputtering of a 40 nm thick silver film onto the fiber surface. Subsequently, a GNR array, prepared using the anodic aluminum oxide (AAO) template method, is transferred onto the silver film. Compared to sensors with only a silver film on the fiber, the sensor with the GNR array exhibited a 31.85% increase in refractive index sensitivity. Furthermore, the GNR on the sensor was coated with the humidity-sensitive material polyvinyl alcohol (PVA) to measure environmental relative humidity. The results indicate that the surface plasmon resonance (SPR) peak wavelength shift has a strong linear correlation with relative humidity within the range of 30-80% RH, achieving a sensitivity of 0.431 nm/%RH.