The Propagation Properties Of Optical Fiber Tapers And Relative Characteristics

Light can be limited in subwavelength domain to achieve long-distance and low loss of transmission in microfiber, and this makes it possible to fulfill the miniaturization of optical devices and micro-optical interconnection between the chip via microfiber. Micro-fiber is satisfied with the strong evanescent field and high-power density characteristics, to achieve high sensitivity optical sensing and nonlinear optical devices. These micro-nano fiber made in recent years become a micro-nano photonic study of a new hot spot.Micro-devices and ordinary optical fiber need a transition to make them connected with each other, We call this this transition part micro-fiber taper. Micro-fiber tapers can be obtained when a standard silica optical fiber was drawn to a micron size using a flame. As the lowest order fiber mode propagates through the taper its spot size increases, until, at the taper waist, the modal field is guided by the fiber cladding and external medium surrounding the taper. After passing through the taper waist the cladding mode evolves once more into a core-guided mode. At the taper waist, the evanescent field of the cladding mode can interact with the medium surrounding the taper. In that way, this special structure can have an extensive application including optical communications, sensing, lasers, biology and chemistry. In this paper, the author mainly researches the micro-fiber taper transmission characteristics and do some theoretical and computer simulation study on the impact factors which are important to the micro-fiber taper transition properties.In this thesis, we first introduce the propagation properties of the the three part of micro-fiber taper, include the standard single-mode fiber part (untapered part), the micro-fiber part (the waist of the micro-fiber taper), and the taper transition part. Then we give a simple model of the shape of the fiber taper, in the model we have a clear understanding about the impact factors which can influence the properties of the micro-taper transition properties. Meanwhile, we introduce the arithmetic of the software we used to make in aqueous solution. In the last part, which also is the most important part, the author simulate the transition in the whole fiber taper, we find that when the diameter of the taper waist is 1um, the shortest length of the taper transition is 4500um when the taper reach the adiabatic criteria, at this time, the loss of the taper is less than 0.03dB/mm. This result is very important in the research of the all fiber devices. Besides this, we also simulate the output with the wavelength or environment index change in this thesis. We gain some interesting results. The shape of the fiber taper we use in the simulation is exponential shape, which is the most common shape in all kinds of taper fabrication. It is found that when the diameter is lum, the output will oscillate with the change of the wavelength, but the oscillation was vanished when the input wavelength is 0.93um. This phenomenon can be explained by the single-mode condition in the fiber taper. And the oscillation in the simulation is mainly because of the multi-mode interference in the taper transition part when the taper didn't reach the adiabatic criteria. All this results support our previous study of the theory, the micro-fiber taper have a clearer understanding of direct, it is satisfied that the micro-optical device development and application of very important significance.