Research Of Micro-structural Mach-Zehnder (MZ) Interferometer Based On Hollow-core Optical Fiber

Miniature fiber optic interferometer has a more compact structure and high sensitivity, especially in the field of space-constrained sensor which can play its inherent advantages. Hollow-core optical fiber is a special fiber which has a unique structure and transport properties of the medium. These properties make it able to take full advantage in the micro-sensor field.In this paper, hollow-core optical fiber MZ interferometer is studied and the main contents are as follows:1) The relationship between the length of the hollow-core fibers, the diameter of hollow-core fiber and interference spectrum were explored, respectively. Founding that in some range, the longer length of hollow-core optical fiber the better interference and the bigger diameter of hollow-core fiber the worse interference.2) Offset type hollow-core optical fiber MZ interferometer is studied deeply. The research shows that the offset can enhance the interference effect, which provides a strong basis to change the air-core optical fiber length to make the MZ interferometer flexible application under certain conditions.3) Based on the existing concave pyramidal structure MZ interferometer, an innovation concave tapered MZ interferometer based on a multi-mode fiber and hollow-core fiber is proposed. And it could gain considerable output optical power, which provides a reference research direction in pull cone MZ interferometer.4) On the basis of study about the hollow-core optical fiber and a variety of parameters based on hollow-core optical fiber MZ interferometer, this paper presents an air bubble type MZ interferometer. Moreover, it also has verified the feasibility of the interferometer by experiments and simulations.5) In order to improve the interference effect of bubble type MZ interferometer instrument, the bubble type MZ interferometer has been improved to be a composite structure MZ interferometer which constituted by the air bubbles and hollow-core fiber. The improved air bubble type MZ interferometer can obtain a more ideal output power, but also has a very substantial extinction ratio. Its insertion loss is less than 10dB and extinction ratio is able to 24dB.6) Putting the improved hollow-core optical fiber MZ interferometer which air bubble diameter is 50μm and hollow-core optical fiber length is 500μm into refractive index sensing analysis. The sensing effect is so considerable that minimum sensitivity is 140mm/RIU and the maximum can reach 1270nm/RIU.