Design And Sensing Characteristics Research Of In-Line MZI Based On Thin Fiber

Compared with the traditional fiber optic sensor,in-line fiber Mach-Zehnder interferometer?In-line MZI?has the advantages of high sensitivity,compact structure,and low cost,which has been widely studied at home and abroad in recent years.In-line MZI is generally fabricated by ordinary optical fiber or special optical fiber through micro-nano processing methods such as tapering,ball burning,misalignment splicing,side polishing,etc.,and then uses the fiber inter-mode interference to achieve the measurement of refractive index,temperature,strain and other environmental physical quantities.New in-line MZIs based on thin clad special optical fibers have been designed and proposed in this paper,and the interference principle was analyzed using mode theory.The beam propagation method was used to numerically simulate the influence of various parameters on the sensing performance.The interferometers were fabricated based on the optimized data of simulation and their sensing characteristics were experimentally verified.The main research contents and results are as follows:1.A new in-line MZI based on the cascade structure of thin fiber and fiber ball was proposed for the measurement of liquid-level,refractive index,temperature and axial strain.The spectral characteristics of the interferometer were numerically simulated by the beam propagation method,which provides a theoretical basis for the experiment.The interference spectrum with the extinction ratio of more than 26 dB was obtained by choosing the appropriate thin fiber length and the core offset.The sensing characteristics of the interferometer were studied by measuring the wavelength shift of resonant dips,and the multi-parameter simultaneous measurement was realized by combining the sensitivity coefficient matrix.The experimental results show that the highest refractive index,liquid level,temperature and axial strain sensitivities of the in-line MZI are-131.7092 nm/Refractive Index Unit?RIU?,-120.7pm/mm,0.0390 nm/?and-4.84×10^-4 nm/??,respectively.2.A new in-line MZI based on the cascade structure of ultrathin fiber-thin fiber-ultrathin fiber was proposed for simultaneous measurement of refractive index and temperature.The effects of various parameters on the interferometer's spectral characteristics were numerically simulated and experimentally tested.The ideal interference spectrum was obtained by choosing suitable fiber length according to the optimized results of simulation,and the sensing characteristics of interferometer were studied by measuring the wavelength shift of two resonant dips.Experimental results show that the two resonant dips have different wavelength responses to refractive index and temperature,which indicates that the in-line MZI can realize simultaneous refractive index and temperature measurement.The maximum sensitivities measured in the experiment are-169.0879 nm/RIU and 0.0464 nm/°C,respectively.Based on the above theoretical analysis,numerical simulation and experimental research results,the in-line MZIs proposed in this paper have the advantages of low cost,simple fabrication,compact structure,strong mechanical performance,high refractive index and liquid level sensitivities,etc.,which show good application prospects in food safety,medical diagnostics,environmental quality inspection,petrochemical industry and other fields.