Investigation On The Evanescent Wave Characteristics And The Sensing Application Of The Fiber Taper

As the key component of many photonic devices,the fiber taper has special characteristics of evanescent wave transmission and plays a decisive role in the performance of these modern optical devices.In this paper,taking advantage of the strong mode coupling effect and great evanescent wave intensity of the non-adiabatic fiber taper,the fiber taper was used in the micro-displacement sensing based on the analysis of the optical field transmission and distribution characteristics of fiber taper in detail.High sensitivity micro-displacement sensing has been obtained.The related work may be a good topic to research and has high market value.The main achievements and conclusions are as follows.1.Based on the optical fiber mode theory,the transmission characteristics of the adiabatic fiber taper and the non-adiabatic fiber taper are analyzed comparatively.The typical structures and fabrication methods of the non-adiabatic optical fiber taper are also introduced.2.The mode cutoff condition and the single-mode operating wavelength range of the fiber taper are theoretically analyzed.Beam propagation method is used to investigate the working characteristics of the single-mode curved fiber taper and the multimode linear fiber taper respectively focus on two important parameters including waist diameter and taper angle.The change of mode power and the optical field distribution at the end surface of the fiber tapers are analyzed.Conclusion are obtained that the output beam emitted from single-mode fiber taper with a smallest waist diameter has the maximum divergence angle,the highest mode coupling efficiency and the maximum effective mode field area,which lays a foundation for the subsequent design and characteristic analysis of micro-displacement sensing applications based on fiber taper.3.Two novel structures of the lateral micro-displacement sensor based on the non-adiabatic fiber taper are proposed in this paper,including the double fiber tapers structure(composition of two fiber tapers)and the single fiber taper structure(composed of a fiber taper and a single mode fiber).According to the simulation,comparison of the output power,the maximum measurement range and the sensitivity of two structures with different waist diameters were made.It is found that the output optical power of the two structures is approximately linear with the transverse offset of the fiber axis,so they can be used for micro-displacement sensing.And we summarized that the double fiber tapers structure with 40?m waist diameter has the best micro-displacement sensing performance.In the experiment,a maximum measuring range of at least 28?m and a sensitivity of-1dB/?m were obtained by this structure,and the structure was also confirmed with good temperature stability experimentally.