Highly sensitive humidity sensor based on tapered dual side-hole fiber

We proposed and demonstrated a highly sensitive humidity sensor based on a fiber Mach-Zehnder Interferometer (MZI). This sensor is composed of a short section of tapered dual side-hole fiber (DSHF) sandwiched between two single mode fibers. At the tapered section, both the fundamental and higher order cladding modes are stimulated and interfere with each other, forming an inter-modal MZI. The existence of air holes in the DSHF makes the cladding mode more easily excited and has higher refractive index sensitivity. In addition, by coating graphene oxide (GO) film with large specific surface area on the tapered DSHF, the humidity sensitivity of the sensor has been further improved. Experimental results show that the humidity sensitivity of the sensor can reach -0.142 nm/%RH, which increased 7.9 times than that without GO coating. In addition, the rising and falling time of respiration were 0.23 s and 2.19 s, respectively. The excellent performance demonstrates it is a good candidate for humidity measurement.