The Theoretical Study Of Tapered Optical Fiber

Optical fiber, as one of key elements in optical devices, has been widely used in the fields of fiber sensor technology, laser technology, and high speed optical communication. Meanwhile, the improving of new optical technologies develop the technology of optical fiber. Tapered optical fiber, one kind of special optical fibers, has been studied recently. Variations of radius along tapered fibers result different transmission characteristics along tapered fiber. Today, tapered optical fiber has been widely used in optical couplers, radiation imaging, video imaging, micro-cavity lasers, super-continuum light source and so on. Comparing with comb dispersion decreasing fiber, tapered fiber has advantage of continuous dispersion variations along fiber, which can decrease "walk-off" effect and improve efficiency of nonlinear pulse compression.Based on study of the research in tapered optical fiber and National 863 project named "160Gbit/s one pump and more than fiber optical transmission technology research", we simulation and experimental research on the transmission characteristics of linear slowly varying tapered optical fiber. This thesis includes contents as follows:1. Based on the comprehensive analysis of tapered optical fiber by ray, Monte Carlo theoretical methods and local mode model, the local mode had been built by cutting up the tapered optical fiber to many small slices. With wave theory, the scalar wave equation and mathematical models had been built in the local area of tapered optical fiber.2. By theory and simulation, the propagation constant, mode field diameter and power distribution of tapered single-mode optical fiber had been analyzed. Comparing to the ordinary fiber of G.652, it had been analyzed that the impact of the change of tapered single-mode fiber's radius to the parameters and characteristics.3. Based on the local mode theory, the "local" concept had been used. By simulation, the effective refractive index, the local group delay relationship with the fiber radius in tapered single-mode optical fiber had been analyzed. Meanwhile, it also had been analyzed that the impact of fiber radius and the wavelength to the local dispersion in tapered single-mode optical fiber which include local material dispersion and waveguide dispersion. Meanwhile, the average dispersion of tapered single-mode optical fiber and the dispersion of ordinary single-mode fiber had been experimentally measured and studied.4. The pulse compression experiment using the tapered optical fiber have been presented. The compression efficient of tapered optical fiber have been studied and compared with comb dispersion decreasing optical fibers. In the experiment, we found that it was difficult that compressing pulse to a very short width due to the inhibiting stimulated Brillouin scattering by phase modulator.