Modal Field And Dispersion Characteristics Of Flattened Mode Micronano Fibers

As the development of preparation technology and devices design theory, the size of optoelectronic devices has reached sub-wavelength magnitude. In the field of micro/nano photonics, micro/nano optical fiber (hereinafter referred to as micro/nano optical fiber) technology is very attractive. Micro/nano optical fibers exhibit a series of interesting properties, such as small size, low loss, tight light constraint, evanescent wave, large waveguide dispersion and so on, which provide promising building blocks for photonic applications in optical communication, optical sensing and some related areas.Micro/nano optical fiber has a strong evanescent field. That is one of its most prominent characteristics. Based on this characteristic, we proposed a large-mode area optical fiber scheme by multifiber combination. To realize the scheme, the flattened mode optical fiber is an ideal choice. In addition, its configuration is special and its waveguide characteristics are worth studying.The thesis firstly briefly introduces research of micro/nano optical fiber, flattened mode fiber and large mode area fiber. Next the basic theories and design methods of micro/nano optical fiber are discussed and investigated. The basic modal field properties of micro/nano optical fiber are also discussed. Finally, the thesis emphatically analyzes the modal field and dispersion characteristics of flattened mode micro/nano fibers. The main achievements of this work consist of following aspects:(1)Based on the fiber modal field theory, using numerical simulation, the modal field characteristics of flattened mode micro/nano fibers are investigated. The results show that through the refractive index distribution rationally design, we can get flattened mode distribution center. The range of flattened mode is directly related to the depression radius, and the flattened modal field distributes approximately from-d-d. The relationship between mode characteristics and depression radius is almost identical. When the distance of index of core and clad is small enough, the fiber effective area increases sharply. And single mode fiber can achieve a large mode area. While the core diameter of general micro/nano optical fiber is 800 nm, its effective mode area can exceed 1000μm2; multiple flattened mode fiber combing can achieve a better coupling efficiency.(2)Using dichotomy to solve the transcendental equation, the dispersions of flattened mode micro/nano fiber and conventional micro/nano fiber are calculated and discussed. Numerical simulations show that the dispersion of the flattened mode micro/nano fiber has different properties from conventional micro/nano fiber and flattened mode fiber. In the wavelength range from 0.3μm to 1.6μm, with the variation of the index, the waveguide dispersion curve's only minimum point increases or decreases regularly, and appears redshift or blueshift; while with the variation of the core size, the waveguide dispersion's minimum point reduces obviously, but the minimum point locates at the same position 0.6μm. However, whether the index or core size changes, in 1.3μm-1.6μm band, the waveguide dispersion increases easing up and value tends to zero gradually, especially when the core size changes, the trend gets more significantly. All the results may be useful in future preparation and application of the micro/nano fibers.