Fiber Interferometer Based On In-line Air-cavity With Micro-channel And Its Sensing Applications

A kind of fiber interferometer based on in-line air-cavity with micro-channel is proposed and manufactured.The sensing principle and response of the fiber interferometer with gas pressure and liquid refractive index are studied and experimentally measured.In addition,the biological sensing of the interferometer is simply researched.The main work includes:1.The fiber interferometer based on in-line air-cavity with micro-channel and its sensing application is proposed and manufactured.The manufacturing process of interferometer includes several steps,etching a section of cleaned single-mode optical fiber by femtosecond laser micro-machining system,splicing by fiber fusion splicer,slightly tapering under heating and punching by femtosecond laser micro-machining system again.Two king of slightly tapered fiber interferometer with in-line air-cavity,with one micro-channel,or with two micro-channels are successfully manufactured.2.The stress,temperature,and gas pressure experiments of an gas pressure sensor based on the interferometer are demonstrated,respectively.Through the stress test,the advantages of stable and firm structure of the sensor has been verified,and a temperature sensitivity of 33.06 pm/°C,a pressure sensitivity of-12.97 nm/MPa are obtained.However,it can be known from the experimental results that the sensor is also affected by the temperature,so that it is difficult to distinguish whether the wavelength drift is caused by the change of the gas pressure or the change of the temperature,that is,there is temperature cross-sensitivity in the gas pressure sensing experiment.An accurate gas pressure sensor should consider temperature compensation in practical application,so in this paper,in order to measure the air pressure accurately,the method of temperature compensation has been used to measure the simultaneous acquisition of air pressure and temperature.The sensor has the advantages of rapid sensing of gas pressure,compact size,and high gas pressure sensitivity.3.The bovine serum albumin(BSA)is selected as the experimental object and the biological sensing of the sensor based on the interferometer was preliminary investigated.Before the biological sensing experiment,since the interferometer was increased from one micro-channel to two micro-channels,stress experiments were performed to detect the structural robustness of the sensor.Considering that light may have great loss in liquid transport,in order to better perform biological sensing experiments,a liquid refractive index experiment of a NaCl solution with a refractive index range close to that of bovine serum albumin solution was performed,and experimental results show a good refractive index sensitivity of-13378.00nm/RIU.It was further applied to biosensing to realize the sensor's measurement of the concentration of bovine serum albumin solution,and its concentration sensitivity was-58.5 nm/(mg/ml),and it was verified that it had good stability.In summary,the slightly tapered fiber interferometer with in-line air-cavity has the advantages of solid structure and compactness.Based on its good pressure sensitivity and liquid refractive index sensitivity,it has a great application prospect in the field of optical fiber applications.