Guiding And Far-field Radiation Properties Of Micro/Nano Optical Fiber

With the development of the design theory and preparation techniques, electronic and photonic devices show the important trends for miniaturization. The devices of microelectronics and optoelectronics with widths or diameters have been decreased to sub-micrometer or nanometer. In recent years, micro/nano optical fibers with the low loss waveguide have been prepared successfully. It is possible to lay a foundation for the future sub-micrometer or nanometer optical devices. Micro/nano optical fibers exhibit a series of interesting properties, such as low loss, large mode area evanescent wave, low dimension and so on, which provide promising building blocks for photonic applications in optical communication, optical sensing and some related areas.The thesis briefly introduces the fabrication and research of micro/nano optical fiber. The history of micro/nano optical fiber devices is summarized. Next the basic theories and design methods of micro/nano optical fiber are discussed and investigated. Finally, guiding and far-field radiation characteristics of micro/nano optical fiber are presented. The main achievements of this work consist of following aspects:(1)In order to study the waveguide characteristics of micro/nano optical fiber, numerical simulation based on waveguide theory were used in this thesis. We investigate the mode fields and energy distribution, both inside and outside the micro/nano optical fiber by solving Maxwell's equation. When the diameter reduces to a certain degree (e.g.,800 nm), the field begins to extend to a far distance with considerable amplitude, indicating that the majority of the field is no longer tightly confined inside or around the fiber. It is found that the micro/nano fibers can have a large mode area evanescent field. The effective mode area can exceed 1000μm2 by appropriate design. The large mode area of the micro/nano optical fiber may have many applications in optical fiber sensing.(2)Based on diffraction theory, the far-field radiation properties of fibers are investigated. compared with experimental results of tapered fibers, it shows that the micro/nano optical fiber can effectively guide the field and radiate it out. These results may offer valuable to the realization of Micro/nano optical fiber.(3)An accurate perturbation method for amplification characteristics of optical fibers with complex refractive-index profile is presented. By solving complex refractive-index profile, we obtain complex refractive-index. Analytic formulas are derived for the fundamental to calculate gain of the step-index Micro/nano optical fiber.