Multipoint Hydrogen Sensing of Hetero-Core Fiber SPR Tip Sensors With Pseudorandom Noise Code Correlation Reflectometry

In this paper, we describe multipoint hydrogen sensing in real time using surface plasmon resonance (SPR) fiber optic hydrogen tip sensors with Au/Ta
₂
O
₅
/Pd multilayers film combined with a time-domain interrogating system based on pseudorandom noise code correlation reflectometry. This method uses the correlation between a launched pseudorandom noise code signal and its reflection enabling simultaneous measurement at many points along the optical fiber in real time with a high signal-to-noise ratio. In a light intensity-based experiment with an 850-nm LED, the tested three hetero-core optical fiber hydrogen tip sensors proved to be reproducible responses with and without hydrogen absorption, with showing the similar time response and sensitivity compared with those of our previously reported sensor. Multipoint hydrogen detection was demonstrated using four SPR hydrogen tip sensors. Our experimental results showed that four sensors using the 25 nm Au/60 nm Ta
₂
O
₅
/5 nm Pd multilayer film exhibited a response time of ~25 s for a 4% hydrogen concentration. In addition, it was found that all sensors can detect the hydrogen concentration with sufficient sensitivities in real time.