Preparation And Properties Of Fiber Microstructure Based On Femtosecond Laser

The devices based on optical fiber have been widely applied in the optical fiber sensing technology due to their low weight, anti- interference, low loss and corrosion resistance. Nowadays, micromachining and application of optical fiber devices attract more attention. Femtosecond laser has been used gradually in material micromachining process for its high peak power and short pulse.The development and the advantages in micromachining process of femtosecond laser are elaborated in this thesis. Next the development of fabricating microstructures on fiber based on femtosecond laser both home and abroad is presented, and the interaction of femtosecond laser and materials is analyzed. Then, propagation equations of cladding and fiber core are introduced, followed by the mode coupling of long-period fiber grating.The influence of energy density and number of femtosecond laser on diameter of fiber optic ablation hole is studied, and optimum conditions for laser micromachining processing are identified. A single point microstructures with space of 2μm and 5μm are obtained by using femtosecond laser ablation. The microstructure is about 7μm long and 2μm wide. And the spectral changes and temperature properties of two kinds of microstructures above are measured and analysized.Long-period fiber grating in the optic fiber core is obtained by the method of femtosecond laser lateral direct writing. The etching length of the fiber grating is 200μm; the period is 400μm and the total length is 2mm. The etching length is just half of its period. At the same time, its spectral changes and temperature properties are measured and analyzed.A way using Ronchi grating to obtain two interferent femtosecond laser beams for fabricating fiber grating with period of 20μm and 12 um is presented. The spectral changes and temperature property of the fiber is also analyzed.