Novel Long-period Fiber Grating And Its Application In EDFA

In this thesis, the fabrication, characteristics and applications of the novel long-period fiber gratings (LPFGs) induced by focused high-frequency CO2 laser pulses are studied. The main work is summerized as follows: 1. The formation mechanism for LPFGs written by CO2 laser is analyzed and summarized as three factors, including residual stress relaxation, density change, thermo-diffusion of dopants, for the first time, to our knowledge. The residual stress relaxation is considered as the major factor in the formation mechanism of the LPFGs written by high-frequency CO2 laser pulses, and there is no any softening deformation. The CO2 laser incident on the fiber result in an asymmetric refractive-index distribution within the cross-section of the LPFG.2. The mode coupling for the LPFGs is analyzed though both the mode coupling theory and transmission matrix theory . The transmission spectrum of the LPFGs is simulated by means of these theories.3. The growth of the LPFGs written by high-frequency CO2 laser pulses is studied. A number of LPFGs are made by using different optical fibers, for the first time, to our knowledge. The characteristics of these LPFGs are also studied, including temperature, axial stress, refractive index , etching, et al..4. The LPFGs are used in single wavelength Er-doped fiber amplifiers (EDFAs) as a spontaneous emission noise(ASE) filter, and the gain of the EDFA is increased by 7dB and the noise figure(NF) is decreased by 0.5dB, for the first time. The optimization of the position and amplitude of the LPFG in the EDF is also investigated .On the other hand, the EDFA with 1dB gain flatness is demonstrated by using the LPFG as a gain equalizer, and this novel gain equalizer inserted in the Er-doped fiber(EDF) increases the gain by 1.5dB. 5. An optical switch and an optical modulator are proposed based on by the refractive index characteristics of the LPFG. A polarization insensitive LPFG operating at a specific wavelength is achieved by writing the LPFG in a birefringence fiber, for the first time.