Optical fiber humidity sensor based on cascaded peanut-shape structure

We developed a new technique for constructing humidity sensor comprised of two cascaded peanut-shape structure which were coated with polyvinyl alcohol (PVA) and in between was also coated with PVA. The coating changes with the humidity which resulting in the change of the effective refractive index, and lead to the change of the interference wavelength. Experiments show that, with the humidity changes between 27%–72%RH, the sensitivity is −0.55336nm/%RH. We also tested its temperature tolerance, and a sensitivity of 0.06135nm/ °C within the area of 30–90 °C was collected, which shows little influence on humidity sensing when in a relatively stable temperature. Compared with other sensors, our sensor is inexpensive and has a high sensitivity.