Electromagnetic Field Sensors Based On All Fiber Interferometric Technology

All-fiber Mach-Zehnder and Michelson interferometric sensors have theadvantages of high sensitivity, high resolution, all fiber and low cost compaired with thecommon Mach-Zehnder and Michelson interferometric sensors, which attracted moreattentions in recent years. Compared with the traditional electrical electromagneticsensors, fiber optical electromagnetic sensors have much more advantages in solvingnew problems and situations for electromagnetic sensing, such as electromagneticimmunity and other harsh enviroments. The emergency of the new materials and theadvanced research on the fiber optics bring more spaces for fiber electromagneticsensors. In the thesis, we propsed to use the designed all-fiber interferometric sensors tomeasure electromagnetic field. An electromagnetic sensor based on the magnetic fluidwhose refractive index changes with the electromagnetic and the refractive indexcharacteristics of a fiber single side geometry deformation formed Michelsoninterferometric sensor is firstly to measure the external magnetic field. A open cavityMach-Zehnder interferometric sensor based on large lateral offset is then used tomeasure the electric field distributed in the liquid medium amid two parallel plateelectrodes under impulse voltage. The content of this thesis and experimental results areas followings:1. The history and categories of optical electromagnetic sensors are firstlyintroduced in this thesis, and these sensors are compared with each other. In order tomake up for the deficiency of these researches, the in-line fiber Mach-Zehnderinterferometric electromagnetic sensors is proposed. Then the Michelson sensor withsingle-side geometry deformation and Mach-Zehnder sensor with lateral offset structureare simulated by the beam propagation method, verifying that both of these twostructures have the functions of splitting and combining light. It is known from thesimulation results that the fundamental core mode is coupled to the excited LP1,mmodeby the single-side geometry deformation while to the LP2,mmode, which provide thebasis for fabricating the sensors and experiments.2. Based on the simulation results in section one, a geometric deformation isformed by melting the single mode fiber by61.3μm with high-energy laser. Then therefractive index characteristic of the Michelson interferometric sensor formed by thesingle-side geometry deformation is studied. The experimental results show that the fiber Michelson sensor has good linear refractive index response within1.33-1.373, andthe sensitivity is~21.8nm/0.001RI. According to the refractive index response, it isderived that the fundamental core mode is coupled to the excited LP1,4mode.Following that, the refractive index of the new nanometer material magnetic fluid ismeasure to be1.3571and it decreases with the increment of the magnetic field. Thethermo-optic coefficient of the magnetic fluid is6×10(-4)℃(-1). The electromagnetic isthen measure by the Michelson based on the fact that the refractive index of themagnetic fluid changes with magnetic field. The sensitivity of the magnetic sensor is~2.7pm/mT and the minimum detectable magnetic field is3.7mT when the length of thesensing beam is3cm.3. Based on the simulation results in section1, an open cavity in-line fiberMach-Zehner interferometric sensor with large lateral offset up to~62μm is fabricatedmanually. The unperturbed field distributed in the parallel plates under impulse voltageis measured based on the Kerr effect. Experimental results show that the sensitivity ofsuch a sensor is~0.1w/(v/m). The electric field is uniform in the time tf of the impulsevoltage wave, but it becomes unperturbed field due to space charge in the late period ofthe impulse voltage wave, which is analyzed simply in this thesis. And such a sensorcan be used for electric resistance of the high voltage insulating oil.In conclusion, the all-fiber interferometric sensing technique in this project is usedfor electromagnetic field measurement, widening the applications of the interferometricsensors and providing a novel technical mean for measuring the electromagnetic field.Therefore the sensors are of great important academic significance and social value.