Study On Optical Fiber Magneto-Optical Devices

Optical fiber magneto-optical devices are widely used in many fields and have attracted increasing attention of the experts and scholars due to their advantages, including small size, simple structure and resistance to electromagnetic interference, etc. Optical fiber magnetic field sensors and the tunable optical attenuators controlled by magnetic are the significant objects among them, and play a decisive role in the fields such as military, medical, biological and so on. In order to improve the magnetic field sensitivity and the measurement accuracy, we design and develop two optical fiber magnetic field sensors by merging new nano materials and fiber laser technology, respectively. One of the optical fiber magnetic field sensors is fabricated by combining the magnetic fluid and an asymmetric tapered fiber, and another one is based on demodulation of the polarization mode beat frequency in fiber laser. In addition, we propose an all optical fiber tunable attenuator controlled by magnetic based on magnetic fluid and a microstructure fiber processed by femtosecond laser. The main contents are as followings:(1) We report an in-fiber Mach-Zehnder magnetic field sensor by merging the advantages of magnetic fluid and an asymmetric optical fiber taper which is directly fabricated on a single-mode fiber by using a commercialization arc fusion splicing machine with the best arc parameters. The sensing principle of the sensor has been theoretically studied and the response of the interference spectrum to external magnetic field has been experimentally demonstrated. Experimental results show that the sensing performances of the sensors are controllable by designing the parameters of the asymmetric-tapered structure, the sensor with axial offset of 168?m and taper waist diameter of 45?m not only has good optical properties but also a relatively high magnetic-field sensitivity of ~162.06pm/mT ranging from 0 to 21.4mT. The proposed sensors would find potential applications.(2) A highly sensitive magnetic field sensor based on an optical fiber laser has been proposed and experimentally demonstrated. The magnetic field sensor was fabricated by introducing a rotary apparatus modulated by an external magnetic field into the fiber cavity to twist one section of the fiber. Due to the remarkable birefringence change induced into the laser cavity, the beat frequency generated between two polarizations of the laser is sensitive to the variation of applied magnetic field intensity. Experimental results show that the polarization mode beat frequency linearly shifts with the increment of magnetic field intensity and the sensitivity reaches up to 10.4 KHz/Oe in the range of 0-270 Oe. To enlargement the magnetic measurement range and further improve the measurement accuracy, a fiber ring laser with a shorter cavity length is used to replace the linear laser and a PS-FBG is used to filtering. The magnetic field measurement range of the modified system has been broadened to 437 Oe with the sensitivity of 7.09 KHz/Oe, and the measurement accuracy has been also enhanced as a result of the linewidth compression of beat frequency.(3) We propose a fiber tunable attenuator by combining a microstructure optical fiber fabricated by femtosecond laser machining technology with magnetic fluid to detect the light attenuation under magnetic field with different directions. The responses to parallel and vertical magnetic field have been experimental and theoretical studied. Experimental results show that the output light intensity increases with the increment of parallel magnetic field strength but decreases with the increment of vertical magnetic field strength when the input light intensity is a constant. Thus an all-fiber tunable attenuator controlled by magnetic with the tunable range from-15 dB to 15 dB can be realized by the fiber attenuation system which merging parallel and vertical magnetic field.