Fully Distributed Multi-Channel Fiber-Optic Sensor for Simultaneous Relative Humidity and Temperature Measurement With Finer Gauge Length Based on Spatial-Domain Time-Delayed Multiplexing

In this study, a distributed multi-channel fiber-optic sensor for simultaneous measurement of relative humidity (RH) and temperature with finer gauge length based on spatial-domain time-delayed multiplexing is proposed and experimentally demonstrated. Simultaneous acquisition of multi-channel signals can be realized by reconfiguring the system layout in a spatial-domain time-delayed multiplexing manner by re-routing the Rayleigh backscattered signals for split-channel processing using only extra delay fibers and couplers instead of any optical switches extending the acquisition time or acquisition unit increasing the system cost. Sensing units comprised of copper (Cu)-coated fiber and polyimide (PI)-coated fiber are used to extract the changes of RH and temperature in the environment simultaneously thanks to the distinct sensitivities on RH and temperature of the two fibers. Experimental results show that the sensing system is able to realize multi-channel simultaneous measurement of RH and temperature with gauge length up to 10 mm. Besides, the system is proved to have excellent stability and reliability in high humidity environments. This novel and simple sensing technique for multi-channel dual-parameter simultaneous measurement will provide new ideas for development of economical, reliable, and practical RH and temperature sensing network.