The Fiber Gratings For Dispersion Compensation And Fiber Lasers

Under the requirements for the systematical and profound research of fiber gratings in completing the subjects of National 863 Programs and National Nature Science Foundations, the theories, the technologies of fabrication and the applications for fiber gratings are deeply investigated. A series of research on fiber gratings are included in this thesis, such as the practical technics of fiber gratings, the realization and adjustment of chirped fiber gratings as dispersion compensators, the application of fiber gratings in rear earth doped fiber lasers, and the theory and fabrication of long period fiber gratings. The main achievements (the main innovation) are as follows:A feasible installation for coating the fiber gratings was designed. This installation is compact, flexible and low-cost, especially fit for coating fiber gratings of long length by one step. The maximal length of the coating can achieve the 200mm. The coat can little deteriorate the characteristics of gratings.A method of packaging fiber gratings using the material of negative temperature coefficient under the high temperature environment was introduced. This packaging keeps the structure compact and doesn't influence the intrinsic characteristic of fiber gratings. The temperature coefficient of the packaged fiber gratings can be reduced to 0.5pm/℃, which is satisfied with the practical requirement and achieves the world's advanced level. The more important is this packaging can keep good stability in a long term. After a year, there is no change in the characteristic of the packaged fiber gratings.An exposure intensity apodization mask is designed according to the relation between the exposure intensity and the variation of refractive index. We presented a method of fabricating the chirped fiber gratings, which is pre-exposing the fiber at the low velocity for more times using the exposure intensity apodization mask. And a method to revise the uniform fiber grating to obtain a chirped fiber grating through post exposure by several times using such mask is also presented.The tapered fiber has been made by controlling the fiber's drawing process. The core and cladding of the tapered fiber have similar shape. Using this fiber, we realized the fabrication of chirped fiber gratings by uniform phase mask. The fiber gratings with different dispersion can be realized by choosing the stress loaded on the tapered fiber during the grating writing process. Also the dispersion can be adjusted by changing the stress.The fiber Bragg gratings of tunable dispersion which can be used as dynamic dispersion compensators was achieved by plating the non-uniform copper film on the outer cladding of fiber gratings. Adjustable dispersion of the fiber grating can be realized by changing the temperatures of the grating or loading the axial stress on the grating. For the first time, a numerical model based on thermal balance equations has been used to analyze the dynamic characteristics of the non-uniform copper coated gratings under the temperature variations. We also established the integrated space balance equations to analyze the characteristics of this type of grating on which the axial stress was loaded. At last, the plating technology is profound studied and the experiment results are consistent with the theory analyses.A novel tunable gain flatness filter has been made using a chirped LPG coated with non-uniform metal cladding. The tuning of the filter is realized by controlling the temperature to change the chirp of the LPG An Erbium doped fiber amplifier with gain variation small than 1.2dB in 35nm bandwidth has been realized using this kind of filter.