Optical fiber humidity sensor based on a tapered fiber coated with agarose gel

An optical fiber humidity sensor (OFHS) has been fabricated using a hydrophilic gel (agarose) deposited on the thinner zone of a biconically tapered single-mode optical fiber. A variation of up to 6.5 dB of the transmitted optical power was obtained with relative humidity (RH) changes between 30% and 80%. Furthermore, the sensor shows an invariant behavior with time. This inexpensive material showed a good reproducibility with low hysteresis and its use with tapered optical fiber makes it useful for industrial and environmental applications.