Magneto-optical Fiber Bragg Grating Magnetic Field Sensing Property

As a new technology of photon field, the sensing technology based on fiber Bragg grating has been widely concerned. Nowadays,sensor systems built with FBG as sensing apparatus have already become a dominating direction in these fields. In this paper the spectral properties and the sensing applications of magneto-optical fiber Bragg grating (MFBG) was discussed. Some promising applications of magneto-optical Fiber Brag Gratings in optical information processing were also discussed. The work is listed in the following:1. The coupled-mode functions of magneto-optical fiber Bragg grating (MFBG) were deduced based on coupled mode theory and magneto-optics theory, and these obtained functions can be used to analyze the transport characteristics in the magneto-optical fiber Bragg grating (MFBG).The simulation model can be used to study spectral characteristics of the magneto-optical fiber Bragg grating. Due to the Faraday magneto-optical effect, y-polarized light will be produced when x-polarized light input into the magneto-optical fiber Bragg grating (MFBG) that is exposed to external magnetic field. Two SSLs(sharp spectral lines) in the transmission spectrum of y-polarized light are directly proportional to the external magnetic component in the propagating direction. This characteristic is of great use in magneto-optic sensing.2. The influences induced by the physical parameters of the grating, e.g. the Bragg wavelength, the magneto optical coefficient of the material, to the sensor's sensitivity together with the dynamic range are discussed in details. The increase of the Bragg wavelength of the FBG can achieve positive enhancement of both the sensitivity and the dynamic range of a MFBG sensor, higher magneto optical coefficient can make the sensor more sensitive but limit the dynamic range a sensor covering, the environmental temperature fluctuation lead a SSLs (sharp spectral lines) shift alone the wavelength axes while maintaining the interval of the SSLs, which means temperature unconsciousness of the sensor base on it. In order to increase the dynamic range of the sensor, the condition under which the circular polarized light was guided into the MFBG was discussed. The reflect-spectral of the left rotational polarized light and right rotational polarized light of the input circular polarized light shows possibility and merits to sense the magnetic field, with inferior sensitivity but unlimited dynamic range compared to the line polarized light input.3. The sensor signal demodulation methods were studied. Polarization dependent loss (PDL) was used to detect the signal of magneto-optical fiber Bragg Grating (MFBG) sensor. The grating parameters such as grating length, the refractive index modulation depth which have distinct impacts of PDL were researched. The wavelength shift method and the PDL method are discussed comparatively focusing on the sensitivity ,and temperature dependence and complexity for realization.4. The unique property that the light field can be controlled by external magnetic field in MFBG is quite valuable in all optical signal processing. Some applications such as optical switch, optical RAM and comb filter for optical time recovering based on MFGB are discussed briefly to show its great practical potential.