A miniature optical humidity sensor

A miniature optical humidity sensor based on a polymer infiltrated photonic crystal fiber interferometer (PCFI) is reported for the first time. Compared to previously reported PCFI based humidity sensors, the sensitivity is improved by infiltrating the microholes of the PCF with a hygroscopic polymer. The sensor shows a high sensitivity to relative humidity (RH) variations with a change in its reflected power of about 12 dB for a humidity change of 84 %RH. The sensor demonstrated has the advantage of a very compact length of 1 mm and along with the end-type probe configuration makes this sensor suitable for monitoring humidity in microenvironments.