Based On The Chemical Etching Method Of Interferometric Fiber Optic Sensor

With the invention of a low-loss optical fiber and the development of optical fibercommunication, optical fiber sensor technology gradually formed as an emergingtechnology. Its working principle could be summarized as light as a carrier, opticalfiber as a transmission medium, to achieve sensing of the measured parameters.Compared with conventional electrical sensors, the characteristics of optical fibersensors were high sensitivity, strong anti-electromagnetic interference, safe, combinedsensing and transmission together, achieving multiplexing and distributedmeasurement, etc. These unique advantages of fiber optic sensors made up for manylimitations of conventional sensors in applications, and greatly promoted thedevelopment of sensing technology and measuring techniques.It is discussed to fabricate fiber-optic interferometric sensors by chemical etchingmethod and based on multimode interference in this dissertation. The main work isprovided as follows:1. Double-beam interference optical fiber Fabry-Perot sensors fabricated bychemical etching method based on graded-index multimode fiber. The Fabry-Perotcavity length of this sensor is about17.5μm. High fringe contrast of22dB is obtainedin the air. Strain experiments show that the strain sensitivity is determined to be about7.82pm/με with a linearity factor of0.99982in the range of0⁸45με at roomtemperature. The sensor has high mechanical strength and can withstand the strain ofabout3760με. Temperature experiments show that the temperature sensitivity isdetermined to be about5.01pm/°C with a linearity factor of0.99809in the range of10°C⁹0°C.2. Three-beam interference optical fiber Fabry-Perot sensors fabricated bychemical etching method based on graded-index multimode fiber. The graded-indexmultimode fiber length of this sensor is about505μm. High fringe contrast of18.21dB is obtained in deionized water. Refractive index experiments show that the fringecontrast of the reflective spectrum near1564.26nm as a function of the externalrefractive index can be fitted by a quadratic functionV277.46n2899.46n724.48 with the determination coefficient of0.99942in the solution with the refractive indexbetween1.3329and1.4459. The sensitivity can be expressed by the formula554.92n0899.46dB/RIU. The maximum sensitivity of about-159.8dB/RIU isavailable in deionized water. Temperature experiments show that the temperaturesensitivity is determined to be10.4pm/°C. Good linearity of0.99951and0.99936areobtained at resonant peak near1563.5nm and resonant notch near1564.5nm,respectively.3. Multimode interference optical fiber sensors based on step-index multimodefiber. The step-index multimode fiber length of this sensor is about36.5mm. Severalnotches in the transmitted spectrum of the SMS fiber structure are generated due to themultimode interference effect. The dependence of the wavelength shifts and intensitychanges of three transmission notches on the applied curvature are different from eachother. The maximum sensitivities of wavelength-curvature and intensity-curvaturerelationships are^-10.38nm/m-1and-130.37dB/m^-1, respectively. By properlychoosing to measure wavelength shifts or intensity changes, high sensitivitymeasurement of curvature over a large scale can be obtained.