Ablation Of Silica Fiber And Direct Inscription Of Fiber Grating With A Femtosecond Laser

Recently, using a femtosecond laser which is of sub-diffraction limit and cold-machining, the fabrication of micro-optical device in glass and crystal is greatly developed, The method of the direct inscription of fiber grating by a femtosecond laser is demonstrated to be no phase mask, free design, unhydrogenated fiber, structure stable. In this dissertation, we firstly systematically study the ablating threshold and surface morphology on fiber material. Furthermore, we give the elementary results on writing fiber end surface grating in crystal fiber by a femtosecond laser, show the method of directly writing long period fiber grating(LPFG) in single mode fiber and the optical properties of fiber grating are also tested and analyzed. The main contents are classified as follow:(1) The physical mechanism of transparent materials ablated by a femtosecond laser pulse is summarized, which focuses on the fused silica material. The relationship between the resonant wavelength of long period fiber grating (LPFG) and the grating period is analyzed.(2) Damage threshold of fiber materials is experimentally studied, which illustrates that there is a linear relationship between the single pulse ablation area of fiber material and laser pulse energy density. And the incubation and accumulation effect is found in multi-pulse ablation. The ablation morphology of fiber materials is obtained by emission scanning electron microscopy (SEM). The research on ablation threshold of fiber optimize the parameter of direct inscription by a femtosecond laser and provide a experimental basis to write the fiber gratings.(3) The end surface diffraction grating structure whose pitch is d=2μm fabricated with a femtosecond laser pulse on the large mode area of photonic crystal optical fiber. A diffraction beam pattern created by the grating structure is measured using a charge coupled device (CCD) with a white light source. The zeroth-order and the first-order diffraction are observed. The principles and methods of the inscription of LPFG are primarily investigated. The direct writing technology of LPFG in single-mode fiber is experimentally studied. The transmission spectrum of the grating and the effect of band-pass filter at 915nm and 1550nm respectively are also obtained.