Study On Novel Special Optical Fibers And Related Devices

Special optical fibers and related devices have great applications in the optical communications, sensing, material process and military fields. In this dissertation, we concentrate on the study of the erbium-doped polarization-maintaining fibers (EDPMF), erbium-doped microstructured fibers and long-period fiber gratings. And the work is supported by the National High Technology Research and Development Programs of China, "Rare-earth doped fibers" and "Novel special optical fibers". The main achievements of this dissertation are listed as follows:1. A novel method called the U-shaped groove method is proposed for fabricating the Panda-type erbium-doped polarization-maintaining fiber preforms. This method is easy to operate and can increase the yield. And the erbium-doped optical fiber preforms are fabricated by the combination of the Furnace-MCVD process and the solution doping technique.2. The structural parameters of the Panda-type EDPMFs are optimized in terms of the design criteria, which take into account the EDPMFs' cutoff wavelengths, mode field diameters, background loss and birefringence. High absorption and high birefringence Panda-type EDPMFs are successfully fabricated by the U-shaped groove method. The absorption coefficient of the EDPMF, whose core is co-doped with Bi, Ga A1 and Er, is about 58dB/m at the wavelength of 1530nm. The birefringence of the EDPMF, whose outer cladding diameter is 125μm, is about 4.8x10^-4. And the background loss is less than 15dB/km at the wavelength of 1200 nm.3. The modified average population inversion iteration method is proposed for calculating the gain and noise figures of erbium-doped fiber amplifiers. The characteristics of erbium-doped microstructured fiber amplifiers are investigated by the combination of the finite element method and the modified average population inversion iteration method. The effects of air holes on the cutoff wavelengths, overlap factors and mode field diameters of the erbium-doped microstructured fibers are analyzed by using the finite element method. The structural parameters of erbium-doped microstructured fibers are optimized in terms of the design criteria, which take into account the cutoff wavelengths, the gain and noise figure of fiber amplifiers and the splice loss between the erbium-doped microstructured fiber and the conventional single-mode fiber. The comparison between the erbium-doped microstructured fiber and the conventional erbium-doped fiber is made.4. The characteristics of the long period fiber gratings, which are ultraviolet-written by the amplitude mask, are studied in detail by using the scalar approximate and coupled-mode theory. The normalization of the individual radiation mode is discussed and the coupled equations between the core mode and radiation modes are deduced. The properties of the coupling constants between the core mode and radiation modes are investigated. The numerical calculation of the resonance wavelengths of the long period fiber gratings is given, when the refractive index of ambient environment is higher than that of silica cladding. The effects of the structural parameters on the resonance wavelengths and the coupling constants of the long period fiber gratings based on the hole-assisted lightguide fibers, are studied by the combination of the finite element method and coupled-mode theory.