锥形光纤模场直径极小值特征研究

模场直径是光纤波导基模的特征参量。单模光纤中的功率密度与模场直径成反比。随着光纤激光器单模输出功率的不断攀升,纤芯中的功率密度不断增加,过高的功率密度会使光纤波导产生光学损伤和热损伤。基于锥形光纤模场分布近似模型,研究发现不同参数的拉锥光纤模场直径最小值位置对应的归一化频点具有规律性。采用有限差分波束传播法（FD-BPM）对不同波长、不同数值孔径下纤芯直径和模场直径的对应关系进行模拟,结果表明:模场直径最小值位置在归一化频率1.8附近,与光纤参数和波长的选取没有直接关系。这个特征参数可为高功率激光在光纤中功率密度最大值位置的快速确定提供依据,也为光纤光学理论增加了新的内涵。     

测量单模光纤模场直径的一种新方法

本文根据单模光纤模场直径的横向位移定义,提出了一种测量模场直径的新方法——远场高斯掩模匹配法.讨论了几种测量及数据处理方法.最后给出了初步的实验结果.     

一种基于模间干涉的亚波长直径光纤气体折射率传感

设计了一种基于模间干涉的亚波长直径光纤气体折射率传感方案,并分析了其测量灵敏度.将标准单模光纤和一段仅传输基模与二阶模的无包层亚波长直径光纤结合形成传感头,通过分析传感头外气体折射率的变化对两个模式干涉谱峰值移动的影响,研究了这种传感器的折射率测量灵敏度.结果表明,这种传感器的灵敏度高于利用折射率引导型光子晶体光纤的基于模间干涉的折射率传感器.因为没有气体向微孔扩散的过程,这种基于模间干涉的亚波长光纤折射率传感器可用于实时探测.     

一种基于模间干涉的亚波长直径光纤气体折射率传感

设计了一种基于模间干涉的亚波长直径光纤气体折射率传感方案,并分析了其测量灵敏度.将标准单模光纤和一段仅传输基模与二阶模的无包层亚波长直径光纤结合形成传感头,通过分析传感头外气体折射率的变化对两个模式干涉谱峰值移动的影响,研究了这种传感器的折射率测量灵敏度.结果表明,这种传感器的灵敏度高于利用折射率引导型光子晶体光纤的基于模间干涉的折射率传感器.因为没有气体向微孔扩散的过程,这种基于模间干涉的亚波长光纤折射率传感器可用于实时探测.     

光纤熔接机加热扩芯制作模场适配器的研究

为了改善不同类型光纤熔接时的模场失配,通过调整普通光纤熔接机的熔接参数,对模场直径较小的光纤进行加热扩芯,实现了10/130μm大模场面积双包层光纤和6/125μm单模光纤的低损耗熔接,光纤耦合效率可达到91%,并成功应用于自主研发的小型1064nm光纤激光器中。对利用光纤熔接机加热扩芯制作模场适配器进行了理论分析,并用1064nm光纤激光器测量其实际传输损耗。实验结果表明:采用普通光纤熔接机,适当的调整熔接参数,可以有效地提高大模场面积光纤到单模光纤的耦合效率,为制作模场适配器提供了一种简单实用的方法。     

光纤截止波长的依赖关系

光纤截止波长是单模光纤的一个重要参数，它与许多因素如模场直径、长度、弯曲、衰减等有关。本文分析研究与截止波长相关的这些因素后，指出在制造光纤光缆时要尽可能减少对光纤截止波长不利的因素，将最小工作波长提高到60－70nm作为设计光纤的截止波长上限，从而有利于降低光纤弯曲损耗。     

W型单模单偏振光纤隧道效应的模场分析

给出了W型单模单偏振光纤基模模场在截止前,截止时和截止后的具体计算方法,利用基模模场分析了W型单模单偏振光纤隧道效应发生的过程,强弱和方向,得出了W型单模单偏振光纤隧道效应随其基模的截止而显著增强,并且主要集中在椭圆内包层短半轴方向的结论。     

一种特殊截止单模光纤的传输性能研究

为了提高特殊截止单模光纤的弯曲可靠性,采用气相沉积工艺制作了包层直径80μm碳涂覆的特殊截止单模光纤,测试了光纤的截止波长、模场、衰减谱、宏弯、色散等传输性能和应力腐蚀敏感性参数。测试结果表明光纤截止波长小于915nm,能够实现915nm以上波长单模工作,在常用的几个波段具有较低的传输损耗,光纤的零色散波长红移到1 670nm。采用碳涂覆工艺提高光纤的应力腐蚀敏感性参数达到35,结合小包层直径预期可以提高光纤的使用寿命。     

基于粉末烧结技术制备镱铝共掺大模场光子晶体光纤

采用粉末烧结技术制备出高浓度镱铝共掺石英棒,Yb3+掺杂浓度为12 000ppm(wt).利用此掺镱石英棒作为纤芯,拉制出镱铝共掺大模场光子晶体光纤,光纤模场面积为550μm2,模场直径26μm.实验结果表明:光纤在近红外波段(850～1 033nm)出现一个宽的吸收带,主吸收峰波长位于976nm,在此波长处吸收损耗高于10dB/m;采用波长为971nm的激光泵浦光纤,在1 050～1 125nm波长范围内产生高斯型的荧光峰,峰值波长位于1 088nm处,荧光半宽高45nm.     

基于粉末烧结技术制备镱铝共掺大模场光子晶体光纤

采用粉末烧结技术制备出高浓度镱铝共掺石英棒,Yb3+掺杂浓度为12 000 ppm(wt).利用此掺镱石英棒作为纤芯,拉制出镱铝共掺大模场光子晶体光纤,光纤模场面积为550μm2,模场直径26 μm.实验结果表明:光纤在近红外波段(850～1 033 nm)出现一个宽的吸收带,主吸收峰波长位于976 nm,在此波长处吸收损耗高于10 dB/m;采用波长为971 nm的激光泵浦光纤,在1 050～1 125 nm波长范围内产生高斯型的荧光峰,峰值波长位于1 088 nm处,荧光半宽高45 am.     

Stimulated four-photon mixing and efficient polychromatic visible light generation in SiO2-based single-mode optical fibers pumped at 1.319 μm

The generation of near-infrared and intense visible light through stimulated multi-wave mixing processes in single-mode silica-based optical fibers pumped by a Q-switched and mode-locked Nd:YAG laser operated at 1.319 μm is described. The experimental results show that intense infrared light around 1.2 μm is produced via selp-hase-matched four-photon mixing at the minimum group velocity dispersion region of pure SiO₂-core and P₂O₅-doped silica fibers. In the visible spectral region, from 580 nm to 600 nm, 20 W peak power 100-ps pulses were generated by pumping single spans of single-mode P₂O₅-doped and undoped SiO₂-core fibers with 1.319-μm laser pulses. The signal light generated in such fibers propagated in the LP₀₂ fiber mode and exhibited a threshold power that depended upon the fiber length and a critical length that was power dependent. Also, it exhibited an asymmetrical spectrum of a few nanometers bandwidth, with a long tail toward high frequencies. For GeO₂-doped silica-based fibers, a multiple-wavelength visible signal propagating in several high-order fiber modes was generated.     

Stimulated four-photon mixing and efficient polychromatic visible light generation in SiO2−based single-mode optical fibers pumped at 1.319 μm

Abstract

The generation of near-infrared and intense visible light through stimulated multi-wave mixing processes in single-mode silica-based optical fibers pumped by a Q-switched and mode-locked Nd:YAG laser operated at 1.319 μm is described. The experimental results show that intense infrared light around 1.2 μm is produced via selp-hase-matched four-photon mixing at the minimum group velocity dispersion region of pure SiO₂?core and P₂O₅?doped silica fibers. In the visible spectral region, from 580 nm to 600 nm, 20 W peak power 100-ps pulses were generated by pumping single spans of single-mode P₂O₅?doped and undoped SiO₂?core fibers with 1.319-μm laser pulses. The signal light generated in such fibers propagated in the LP₀₂ fiber mode and exhibited a threshold power that depended upon the fiber length and a critical length that was power dependent. Also, it exhibited an asymmetrical spectrum of a few nanometers bandwidth, with a long tail toward high frequencies. For GeO₂?doped silica-based fibers, a multiple-wavelength visible signal propagating in several high-order fiber modes was generated.     

Splicing of index-guiding microstructured optical fibers and single-mode fibers by controlled air-hole collapse: an analytical approach

Low-loss splicing of index-guiding microstructured optical fibers (MOFs) and conventional single-mode fibers (SMFs) can be achieved by enlarging the mode field diameter of MOFs, which leads to an optimum mode field match at the joint interface. We study analytically the low-loss fusion splicing between an MOF and an SMF by expanding the modal field of MOF, using the controlled air-hole collapse method. Our method is simple and offers analytical solution for light coupling between MOFs and SMFs. Comparisons with available experimental and simulation results have also been included.     

Guiding Properties of a Tapered Photonic Crystal Fiber Compared with Those of a Tapered Single-Mode Fiber

We have fabricated tapered photonic crystal fibers using a fusion splicer and experimentally observed the near-field mode distribution and the beam divergence of it. We have also compared characteristics of the tapered photonic crystal fiber with those of a tapered standard single-mode fiber. Unlike a tapered standard single-mode fiber, the mode field profile of a tapered photonic crystal fiber shows a good confinement of its field within the core region. The numerical apertures of tapered photonic crystal fibers are increased as the diameter of the fiber is decreased.     

Near-infrared sources in the 1–1.3 μm region by efficient stimulated Raman emission in glass fibers

Low-loss glass fiber waveguides are found to be excellent media for Raman lasers and amplifiers in the near-infrared region of the spectrum. Multiwavelength emission in the 1–1.3 μm range is readily obtained by efficient stimulated Raman scattering in single-mode silica fibers. With a 1.064 μm pulsed pump of 250 W in a 175-m, 6-μm diameter single-mode silica fiber we observed four orders of Stokes radiation at 1.12 μm, 1.18 μm, 1.23 μm and 1.3 μm, respectively. Our results imply that pulsed tunable stimulated Raman emission in this wavelength region is possible using kW tunable infrared dye lasers near 1 μm as pumps. These sources are useful for studying the dispersion of glass fibers as well as for other spectroscopic applications.     

Guiding Properties of a Tapered Photonic Crystal Fiber Compared with Those of a Tapered Single-Mode Fiber

We have fabricated tapered photonic crystal fibers using a fusion splicer and experimentally observed the near-field mode distribution and the beam divergence of it. We have also compared characteristics of the tapered photonic crystal fiber with those of a tapered standard single-mode fiber. Unlike a tapered standard single-mode fiber, the mode field profile of a tapered photonic crystal fiber shows a good confinement of its field within the core region. The numerical apertures of tapered photonic crystal fibers are increased as the diameter of the fiber is decreased.     

Guiding mode in elliptical core microstructured polymer optical fiber

A kind of microstructured polymer optical fiber with elliptical core has been fabricated by adopting insitu chemical polymerization technology and the secondary sleeving draw-stretching technique. Microscope photography demonstrates the clear hole-structure retained in the fiber. Though the holes distortion is visible, initial laser experiment indicates that light can be strongly confined in the elliptical core region,and the mode field is split obviously and presents the multi-mode characteristic. Numerical modeling is carried out for the real fiber with the measured parameters, including the external diameter of 150μm, the average holes diameter of 3.3μm, and the averageole spacing of .3μm by using full-vector plane wave method. The guided mode fields of the numerical simulation are consistent with the experiment result.This fiber shows the strong multi-mode and weak birefringence in the visible and near-infrared band, and has possibility for achieving the fiber mode convertors, mode selective couplers and so on.     

一种基于MEMS光栅光调制器的近红外光谱探测系统

基于微机电系统技术的近红外光谱探测系统已成为了近红外光谱仪研究的一个新方向。文章提出了一种基于光栅光调制器的新型近红外光谱探测系统。该系统采用微加工技术制造的光栅光调制器阵列与单点近红外探测器相结合使用的方法进行光谱探测。设计了该光谱探测系统的光学结构, 论述了系统光谱探测原理, 并使用经表面微加工工艺得到的光栅光调制器器件进行了系统分辨本领、波长准确性、系统稳定性、器件响应频率等特征参数测试实验。结果表明,该探测系统在1 320到1 400 nm波长范围内,分辨本领小于10 nm, 波长准确性小于1 nm, 系统稳定性小于0.5%, 光栅光调制器的响应频率为5kHz。实验结果证明了该近红外光谱探测系统的可行性, 为研制基于微机电系统光栅光调制器的微型化近红外光谱仪提供了理论基础及实验指导。     

Quasi-Rayleigh light scattering by internal elements of a metamaterial in a light-carrying core of a single-mode optical fiber based on the Veselago effect

At present, single-mode optical fibers composed of metamaterials—so-called “left-handed” optical media—for the far- and mid-IR ranges have already been created. In the near future, left-handed singlemode optical fibers for the visible and near-IR ranges will be created, light-carrying cores of which will be composed by an ordered structure of dielectric elements, the dimensions of which will be much smaller than the light wavelength, while the effective refractive index of the structure will be negative; i.e., the structure will possess the so-called “Veselago effect.” We show that, because the dimensions of these dielectric elements many times exceed the dimensions of molecules of optical media, the elements should strongly scatter light, with this scattering considerably exceeding the Rayleigh (molecular) light scattering that occurs in conventional quartz single-mode optical fibers. We propose to term this phenomenon the quasi-Rayleigh light scattering. Numerical estimates of the quasi-Rayleigh light scattering for left-handed single-mode optical fibers at a light wavelength of λ = 1.55 μm have been made.     

Influence of a holey cladding structure on spectral characteristics of side-polished endlessly single-mode photonic crystal fibers

We experimentally investigate the spectral characteristics of side-polished endlessly single-mode photonic crystal fibers of different polishing depths and radii of curvature that are important to mode field diameter, evanescent coupling, waveguide losses, higher-order mode excitation, and dispersion slopes of photonic crystal fiber components. A polished photonic crystal fiber with a greater polishing depth or a larger radius of curvature shows a more dispersive characteristic. In contrast to conventional single-mode fibers, in photonic crystal fibers the evanescent field is more strongly localized, and the propagating light can be more efficiently guided within the deformed core.