应用于相干成像的一种螺旋多芯光纤设计  

A Helical Multicore Optical Fiber Design for Coherent Imaging

作　　者：郑金虎 徐炳生 沈赫男 于飞 陈建 ZHENG Jinhu;XU Bingshen;SHEN Henan;YU Fei;CHEN Jian(School of Optical-Electrical and Computer Engineering,University of Shanghai for Science and Technology,Shanghai 201800,China;The R&D Center for High Power Laser Components,Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences,Shanghai 201800,China;School of Physics and Optoelectronic Engineering,Hangzhou Institute for Advanced Study,Hangzhou 310024,China)

机构地区：[1]上海理工大学光电信息与计算机工程学院,上海201800 [2]中国科学院上海光学精密机械研究所高功率激光单元技术实验室,上海201800 [3]国科大杭州高等研究院物理与光电工程学院,杭州310024

出　　处：《光子学报》2024年第1期212-221,共10页Acta Photonica Sinica

基　　金：国际科技合作计划(No.2018YFE0115600);国家自然科学基金(Nos.61935002,12274299);国家重点研发计划(No.2020YFB1312802);中国科学院基础前沿科学研究计划从0到1原始创新项目(No.ZDBS‒LYJSC020)。

摘　　要：用于内窥成像的多芯光纤在弯曲条件下传输的光场相位容易出现复杂的随机扰动,为相干成像中的相位恢复带来极大挑战。本文提出了一种可以用于相干成像的螺旋多芯光纤设计,通过调控纤芯尺寸、纤芯间距和螺距来抑制弯曲等外界扰动对纤芯间群时延差和功率串扰的影响。本文建立了弯曲条件下螺旋多芯光纤纤芯光程的数学模型;根据变换光学基本原理,利用有限元仿真软件对螺旋多芯光纤的模式特性进行数值仿真计算。设计的螺旋多芯光纤具有20μm的芯间距和20π/m的扭转率,共有6层91个纤芯,不同层的纤芯尺寸不同。无弯曲时芯间群时延差小于6 fs/m;当弯曲半径大于5 cm时,芯间群时延差的变化小于32 fs/m,100 m长度上纤芯间串扰的仿真计算结果低于−550 dB。螺旋多芯光纤的芯间群时延差对弯曲不敏感,在相干成像中代替普通光纤束传递光场,有助于降低相干图像恢复方法的复杂度,可以广泛应用于光纤显微成像、超快激光成像等领域。Multicore Fiber(MCF)/imaging fiber bundle is a key device of flexible optical endoscope.In imaging applications,MCFs are widely used in the non-coherent imaging which transmits the intensity distribution only.The bending sensitive distortion of phase plane and inter-core crosstalk bring challenges in the coherent imaging application.In this paper,a Helical-Core MCF(HC-MCF)is designed for the application of coherent imaging.Due to the intricate nature of HC-MCF,neither semi-analytical models nor empirical methods can fully resolve the modal properties.Consequently,a full-vector finite-element method is employed for numerical simulation of HC-MCF.By utilizing the optical transformation technique,HC-MCF in the natural space is equivalently represented in the helical coordinate maintaining the translation invariance.The original isotropic permeability and dielectric constant(both scalars)of the optical fiber material are adjusted to equivalent dielectric constant and equivalent permeability values.This simplification can effectively reduce the computational complexity of the field distribution and equivalent effective refractive index of fundamental mode in HC-MCF.By using this method,the inter-core group delay differences of HC-MCF is simulated for optimization of fiber design.Then,an optimized design of HC-MCF is proposed.In order to minimize the distortion of phase front after transmission in HC-MCF,each core of HC-MCF should have a similar optical path.An appropriate core spacing should be selected to balance between the spatial sampling density and crosstalk among fiber cores.The helix period is preferred smaller than the critical bend radius in the application.Our final design of HC-MCF are arranged in a densely stacked hexagonal configuration,comprising 6 layers with a total of 91 cores.The radii of the fiber cores are 4μm,3.3μm,3.1μm,3μm,2.9μm and 2.8μm from the inside to the outside,with a core pitch of 20μm and helical pitch of 10 cm.The inter-core group delay difference per unit length of straight H

关 键 词：多芯光纤 相干成像 串扰 群时延 螺旋线 

分 类 号：TN253[电子电信—物理电子学]