Study On Fabrication Of Optical Fiber Microlens And Its Optical Properties

Many kinds of optical devices based on optical fiber have been widely used in fiber-optic communication,biomedicine,and fiber-optic sensors.Due to optical fiber devices not only have the advantages of small size,low cost and anti-electromagnetic interference,but also can be used as light guiding medium and high sensitive sensing element,which makes it easier for fiber-based sensing systems to achieve multi-function and compact structures than other systems.In optical fiber devices,the large divergence angle of the beam directly output from the fiber,the coupling efficiency between the optical fiber devices will be reduced,and the quality of the outgoing beam will sometimes limit the performance of the optical fiber sensor,such as the measurement of the deep hole,etc.In order to improve the coupling efficiency between fibers and other optical devices,and improve the performance of fiber-based sensing devices,microlenses are often used to adjust the size and shape of the output beam of the fiber.Most of the discrete aspherical and gradient refractive index lenses used for collimating the optical fiber are large in size,and the typical diameter is the order of millimeter.The fabrication process of this kind of optical fiber combined with lens requires high alignment stability and large insertion loss.Recently,in order to solve these problems,we prefer to use fiber microlenses fabricated directly on the fiber endface to produce a fiber-optic device,since it can decreases difficulty of assembling between the lesns and the fiber,as well as reduces the insertion loss.This kind of fiber microlens sensing devices have important application prospects in the fields of optical fiber sensing such as micro-optical fiber medical imaging,pipeline micro-leakage detection and so on,which have attracted extensive attentions.In this paper,aiming at the defects of the existing optical fiber micro-lens manufacturing method,we proposed and experimentally proved a liquid drop curing method to make a fiber micro-lens by using the spherical forming mechanism of the surface tension of the liquid.The manufacturing process of the optical fiber micro-lens takes only two steps:dripping and curing.The diameter of the optical fiber micro-lens is matched with the size of the optical fiber,the surface is smooth,and the minimum diameter of fiber lens is only 10 ?m.the micro-lens topography can be adjusted through a plurality of dripping-curing steps.The beam transmission characteristics of the fiber microlens were numerically simulated and analyzed by using Beam Propagation Mehthod(BPM)to optimize the lens parameters.We realized the convergence of the emergent beam of the optical fiber microlens.The shortest focal length was 20 um,and the minimum spot diameter was 10.89 ?m.In addition,we also studied the influence of the fiber surface properties on the formation of the microlens,the loss factor of the fiber microlens,and the shape change of fiber micro-lens by using the multiple-dripping-curing method.In chapter 1,the development of micro-optics are introduced and the applications of different types of fiber-optic microlenses are emphasized.Then,various methods of fabricating microlenses were introduced,which elaborate their advantages and disadvantages by comparing these methods,and we choose a simpler and low-cost droplet solidification method to produce the fiber micro-lens.In chapter 2,the classification of optical fiber and the principle of light transmission are introduced,as well as the calculation method of divergence angle of single-mode optical fiber.The distribution of Gaussian beam passing through thin lens was analyzed theoretically.We also presents the relationship between the wettability of fiber end surface and the formation of microlens,which revealed the importance of the hydrophobic treatment.In chapter 3,we introduced the steps of fabrication of optical fiber microlens that the handle of the optical fiber face before fabrication,the fabrication process of the fiber cone,and the influence of each step on the light intensity.Finally,a smooth and regular hemispherical lens is fabricated on the end face of single mode fiber and multimode fiber.In chapter 4,beam propagation method was introduced to investigate the output field of microlens with different sizes on single-mode fiber and multi-mode fiber,and the experimental study is carried out.The light intensity of these microlenses at different positions was measured by the "transverse migration method",and the light intensity distribution map was obtained.Compared with the simulation results,the light intensity of the microlenses was in good agreement with simulation results.In chapter 5,we summarized the results of the experiment,propounds some proposals for improvement,and points out the direction of future work.