Humidity Sensor Based On Micro-nano Optical Fiber Ring Resonator Is Studied

Humidity is one of the most important Environment Parameters which is hard tomonitoring and huge in affects, according to this, sensors which to monitoring it has therequirements in response time, monitoring range, manufacturing process and service life,however, it is difficult to fully meet the above requirements.In order to manufacture one kind of humidity sensor to meet the aboverequirements, the traditional humidity sensors was studied in this paper first, and theirgeneral principles, advantages and disadvantages were summarized. Then, combinedwith the unique advantages of optical fiber sensors, the idea of using the MicrofiberKnot Resonators (MKR) as the humidity sensor was put forward, and the researchsituations of microfiber and MKR were summarized.Then, the light field transmission characteristics of a single microfiber wasanalyzed by using the coupled-mode theory, based on this, the transmission equation ofthe MKR was inferred. Then the sensing characteristics and effect factors werediscussed in the paper. Based on the above research, the theoretical basis of MKR usedas the humidity sensors was deduced. Combined with the knowledge of the materialscience, the conclusion of medium density change will lead to its refractive indexchange which affect the resonance wavelength of MKR was analyzed. Based on theexisted two kind of hydrophilic materials: polymethyl methacrylate (PMMA) andpolyimide (PAM), we proved our conclusion using the MATLAB.Later, the present commonly used methods of manufacturing microfiber weresummarized, and our manufacturing methods and steps used in the experiments basedon single-mode optical fiber (SM), PMMA and PAM were introduced in details. Basedon this, the methods of manufacturing MKR were introduced, and the output spectrumsof this three kind of MKR we manufactured were researched in our experiments.In the end of this paper, the humidity response characteristics of this threefiber-optic interferometric humidity sensors based on silica/polymer microfiber knotresonator are researched. The silica MKR (S-MKR) has a humidity sensitivity of~12pm/10%RH within a range from14%RH to60%RH, while the PMMA MKR (PM-MKR) has a humidity sensitivity of~88pm/10%RH, with a range from17%RHto95%RH, and the PAM MKR (PA-MKR) has a humidity sensitivity of~270pm/%RH in the range of10%RH to62%RH. The temporal response of the PM-MKR sensorwas less than0.5s and showed excellent reversibility of this kind of humidity sensor.Through these research, we find these tiny humidity sensors are fabricated bysilica and polymer fiber directly，and no need to process with sensitive coating. Theyalso have advantages of compact size, good stability, large dynamic range，highsensitivity and low cost. Could find important applications where micro space,high-resolution and large range is essential.