Research On Fabrication Of Fiber Bragg Grating By Femtosecond Laser And Its Packaging Technique

Fiber Bragg grating (FBG) have widespread applications in the rapidlygrowing field of optical fiber sensors, especially in harsh environments, due toits advantage of anti-electromagnetic interference, small volume, corrosionresisting and distributed measurable. In the last few years, FBG fabricated byuseing of femtosecond laser pulses(Fs-FBG) have attracted considerableattention in research. Fs-FBG have excellent thermal stability and hightemperature sensing characteristic, as a result of the forever refractive indexmodulation caused by femtosecond laser pulses,which has ultra short pluses,ultra fast velocity and ultra high peak power. The mechanism of that aremultiple photons absorb and ionization, when femtosecond laser was foursedinto the material. However, the mechanical strength of the fiber becomessignificantly weak, which makes it brittle. In addition, the temperaturesensitivity of naked FBG is low,as the same as UV induced FBG. In order toincrease the mechanical strength and temperature sensitivity, manyresearchers are devoting in enhancing the mechanical strength andtemperature sensitivity of FBG. Metal coating is a simple and efficient method,which not only enhances the mechanical strength but also increases thetemperature sensitivity of FBG. In practical application, the UV induced FBGshave weak stability at high temperature, which are unsuited to metal coatedand to text hich temperature. Fs-FBG could be applied as a robust highsensitivity probe that can text hich temperature,.combined with metalpackaging.The thesis carries out the research in the above background. Firstly, thespectrum of the FBG is analysed by perturbation couple mode theory and themechanism of the FBG fabricationg are main multiple photons absorb andmultiple photons ionization. Secondly, Type II-FBGs that can bare hightemperature are fabricated by phase-mask method and point-by-point method, repeatedly, and the naked FBG is tested in high temperature. The temperaturesensitibity is14.8pm/℃. In the end, the naked FBG is metal coated by nickelelectroplating (Ni-coated FBG), and the Ni-coated FBG is meaured in hightemperature. The temperature sensitibity is32.2pm/℃. The theoretical modeof the Ni-coated FBG in the high temperature is also established. Thetemperature sensitibity we simulated is32.3pm/℃the simulation result isaccorded well with the experimental result.