Fiber Laser Magnetic Field Sensor Based On Ampere Force And Au Sputter Coating

Optical fiber sensor is a new kind of sensor being quickly developing in recent years.Using specially processed optical fiber as sensitive element,together with unique physical properties such as light weight and compact structure,optical fiber sensor can detect many surrounding measurands.Some popular measurands include environment temperature,mechanical strain and stress of structures,surrounding magnetic field,electric current,etc.With rapid development of science and technology in recent years,fiber optic sensors also advance quickly based on new achievements and applications in the area of optical fiber.Fiber optic sensors become more and more diversified in its structure and their performance have also been promoted very much,making them widely used in industrial testing,structural monitoring,military applications.Among of them,optical fiber magnetic field sensor to measure surrounding magnetic field appears to be increasingly important.Currently,Faraday effect,lorentz force and magnetostrictive effect are widely employed principles for fiber-optic magnetic field measurement.This thesis gives a brief introduction to those principles.Moreover,the thesis also introduces a method based on ampere force.Because ampere force is proportional to the strength of magnetic field,magnetic field sensors based on ampere force have good linearity.In this thesis,based on ampere force and orthogonal double-frequency fiber laser coated by a gold layer at the surface to conduct electrical current,a compact optical fiber laser magnetic field sensor is implemented.It shows that,in a magnetic field perpendicular to the fiber laser,through injection of an alternating current into the gold layer of the fiber laser,the ampere force produced by electric current under the effect of magnetic field will be imposed on the laser cavity,and introduce birefringence in the laser cavity and observed laser frequency changes,which realizes measurement of the magnetic field.Experimental results show that the proposed fiber laser magnetic field sensor has good linearity and anti-interference ability.The main contents of this thesis are as follows:(1)With excimer laser and phase mask template,DBR fiber Bragg grating laser was fabricated to meet actual needs.The excimer is a 193-nm excimer laser.Erbium/ytterbium co-doped fiber is used for fiber grating laser inscription.By controlling the excimer laser exposure and the displacement of the platform for inscription,single longitudinal mode laser output is obtained to meet the needs of the subsequent detection in radio frequency domain.The inscribed fiber laser has a high reflection grating of 3 mm,and a lower reflection grating length of 2.5 mm,with a spacing of 3 mm.The overall length is 8.5 mm.(2)A magnetic field sensor is proposed based on ampere force and sputter coated fiber laser.A brief introduction of the principle of the sensor is given at first.Then the preparation of the fiber Bragg grating magnetic field sensor is elaborated.Theoretical analysis is verified by experiment results,which demonstrates effective detection of surrounding magnetic field with quite good linearity.(3)Based on experiment results,through theoretical analysis,the sensitivity of optical fiber grating sensor to magnetic field is discussed,and sensitivity enhancement scheme is proposed to place the foundation for further study on ampere force based fiber-optic magnetic field sensors.(4)The main content of the thesis is summarized with the overall research outcomes discussed.