Temperature and Humidity Measurement Based on Taper-Assistant Michelson Interferometer and Polymeric Microsphere

Environmental temperature and relative humidity (RH) sensing is always an important research direction because of its extensive application prospects, such as the oil and gas pipelines and agricultural monitoring. In this article, a compact Michelson interferometer (MI) is fabricated via fusing two tapered fibers on the end face of a single-mode fiber (SMF), along with a polystyrene microsphere fixed between the two tapered fibers. Two optical beams in both silica tapered fibers interfere with each other to form the MI. Furthermore, the optical beam emitted into the polystyrene microsphere reflects on its two surfaces to realize the Fabry-Perot interferometer (FPI). MI and FPI superimpose together to form the total reflection spectrum with two different types of lineshapes. The envelope line shape, primarily based on the FPI, shows the high fiber-optic sensitivities because of the polymeric material of microsphere, including the temperature sensitivity of 159.2 pm/°C and the humidity sensitivity of up to 569 pm/%RH. The dense and fine interference fringes, primarily based on the MI, have the relatively small sensitivities of 13.4 pm/°C for the temperature case and 4.1 pm/%RH for the humidity case. This hybrid structure of MI-coupled polystyrene microsphere could be conveniently utilized for the simultaneous sensing of temperature and RH.