| Fiber grating is a recently developed optical device. Its advantages over competing technologies include all-fiber geometry, low insertion loss, high return loss or extinction, and potentially low cost. All these characters present a broad application field for fiber grating in the field of optical fiber communications. The optical properties of the optical fiber core would be changed eternally when it is exposed to UV light. Using this photosensitive property, optical fiber grating is made to have a periodical index change along the fiber core. When light is transmitted through such a kind of waveguide, it experiences periodical phase changes. In this thesis, the transmission characteristics of FBG and LPFG. The reflectivity spectrum of common fiber Bragg grating will greatly deteriorate the filtering properties. By inserting one of more phase shifts, narrow transmission peaks could be created in the stop band of the reflectivity spectrum. Using the matrix approach, we analyzed the main characters of the phase-shifted fiber grating like the linewidth, the number, the location and the transmission ratio of the transmission peaks. These theoretical results will guide our application and fabrication of the phase-shifted fiber grating. A novel grating is proposed to produce multi-wavelength output with inscribing phase-shifted fiber Bragg grating (FBG) in polarization-maintaining fiber (PMF). The reflective spectrum of grating is analyzed by a transfer matrix method. In this case, the two sets of polarized reflected waveband could be aligned along the fast-axis and the slow-axis of high-birefringence (Hi-Bi) fiber, respectively. If Δn eff represents the effective refractive index difference between the two orthogonal states of polarization of the fundamental mode, two different resonance wavelengths will result with spacing. As a consequence, the effective refractive index difference will change and the frequencies of the reflection peaks of the two polarizations and the wavelength splitting will change accordingly. These frequency changes with low-birefringence (Low-Bi) fibers can be to a few gigahertz. For gratings in high-birefringence (Hi-Bi) fibers, the frequency spacing could be up to hundred GHz. Thus, phase shifted Bragg gratings in polarization-maintaining fibers prepared in low-or high-birefringence fibers and used as laser mirrors can greatly improve the fiber laser properties. The following are two possible schemes. Scheme A: The Δn eff has important effect on the reflection spectrum of the phase-shifted FBG in PMF and it is in the order of 10 -6-10-3 which results in two wavebands separated from sub-nm to nm. During the change of the Δn eff, there are two most important cases. Firstly, if the Δn effis higher than...
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