Research Of Magnetic Field Measurement Based On Polarization Effect

Electro-magnetic environment testing has being one of the most important fields in the Environment Science, which has a great meaning in science researching, industrial producting, residents’life and national defence security. Modern electro-magnetic environment is a environment that a variety of electtomagnetic energy coexists and interacts, which can be simply divided into natrural and man-made energies. The traditional method using in electromagnetic field testing relies on electrical way, using electric dipole and magnetic dipole antenna as the measurement sensing element. The method is stable, reliable and mature, but because of the strong surge current produced by its feeder, it is very possible that leading the damage of minitoring terminal equipment.Optical fiber grating sensor is a new sensing technology developed in the1980’s, because of its advantages as other optical measurements, which is high sensitivity, high accuracy, anti-interfence, corrosion resistance and soon, for temperatue, pressure, stress and other parameters, it has very good measuring performance, so having been widely used in aerospace, health monitoring, resource exploraton, medicine and health care, etc. In view of the optical fiber grating sensing good characteristic, many scholars have tried to its application in the field of measurement field, the use of electromagnetic field in the relationship of electric and magnetic fields, to achieve the purpose of measuring electromagnetic field. For example, coating the magnetostrictive material in fiber Bragg grating measuring surface, or embed it in the fiber grating fiber core, using the mechanical effect measuring magnetic field.The use of magnetosttictive materials can make the optical fiber grating measure magnetic field, but after all, with the passage of time the measuring accuracy of mechanical measurement method will decrease, and the sensing head’s service life will be affected. Therefore, a new optical fiber grating magnetic field measurement method becomes even more important.Magnetic field measurement method based on the polarization effect, using the Fresnel effect of fiber materials and the magnetic light efficiency represented by Faraday effect as theoretical basis, because in the magnetic field in circular birefringence fiber Bragg grating, polarization dependent loss, polarization differential group delay and polarization mode dispersion and other polarization parameter of left-handed and right-handed circularly polarized light will be the relationship between magnetic field, so magnetic field can be measured by measuring the polarization parameters method. From the basic theory and the traditional method of fiber Bragg grating sensor, introducing the sensing principle of temperature, stress, pressure optical fiber grating and the structure of the various sensors; Extracting the essence of the fiber Bragg grating Faraday effect-circular birefringence; Respectively from the measuring principle, measuring performance and cross sensitive research to solve, etc., introducing and researching the magnetic field measurement methods of polarization dependent loss and differential group delay in detail; Put forward a new method of magnetic field measurement based on polarization mode dispersion, and the measurement performance are studied and compared. The conclusion is:under the condition of smaller magnetic field, three kinds of measurement parameters can keep good linear relationship with the size of the magnetic field, but the sensitivity of the measurement and linear range must compromise to consider; Light refractive index of fiber core, grating period and the refractive index modulation depth can affect the performance of the measurement of fiber grating; Temperature and stress does not affect the measurement accuracy but will increase the difficulty of measuring; Changing pressure can seriously affect the measurement of the performance; The inner stress of fiber Bragg grating must be considered when high precision measurement; Compared with the measurement of polarization dependent loss and differential group delay, the mode dispersion measurement method has a wider linear range and smoother measurement curve.