Experimental demonstration of a high-sensitivity humidity sensor based on an Agarose-coated transmission-type photonic crystal fiber interferometer

We present a detailed study of a high-sensitivity relative humidity (RH) sensor based on Agarose-coated transmission type photonic crystal fiber interferometer for what is the first time to our knowledge. The sensor shows a wavelength shift of approximately 56 nm for a humidity change of 58% RH. The repeatability of the coating layer formation and the evolution of the coating layers on passing the device though Agarose solution multiple times are studied in detail by observing the spectral shift resulting from the effect on the effective index of the cladding mode. Also, a detailed study is reported of the sensor performance in terms of its sensitivity, repeatability, and long-term stability. The sensor shows a linear response for an RH change in the range of 40%-80% RH with a humidity resolution of 0.017% RH and a higher humidity resolution of 0.007% RH in the range 80%-95% RH. The measurement accuracy of the sensor in the RH range 40%-80% is ±2% RH, and in the range 80%-95%, the accuracy is about ±1% RH. The response time of the sensor is 86 ms, when RH jumps from 50% to 90%. The temperature dependence of the sensor is found to be ~0.27 nm/°C, which is quite small compared to the RH sensitivity of the sensor.