基于薄芯光纤模态干涉技术的折射率传感特性实验研究

报道了一种具有微结构缺陷的折射率传感器,并对其折射率特性进行了实验研究.将一部分薄芯光纤熔接于标准单模光纤中,由于插入的薄芯光纤和单模光纤纤芯失配,导致包层的高次模被激发并与纤芯模在单模光纤内形成干涉仪.通过减小薄芯光纤的包层直径,以增强包层中的传输模在环境中的倏逝场,从而提高对环境折射率测量的灵敏度.实验表明,该折射...     

光纤折射率剖面的折射近场法测量的研究

本文叙述了折射近场法(简称RNF)测量光纤折射率剖面的基本原理及实验方法.提供了对单模光纤和多模光纤的测量结果,并与反射法、近场法进行了比较.实验中获得空间分辨率优于0.8μm,折射率灵敏度优于2×10~(-4).     

基于等效折射率方法的微结构光纤单模特性分析

等效折射率方法是在传统光纤理论的基础上发展而来的。阐述了等效折射率方法，利用矢量波动方程分析了微结构光纤包层空间填充基模的传播常数，以及有效折射率与波长的关系，并计算了纤芯缺陷分别为1孔、3孔、7孔时光纤的归一化频率。在传统光纤理论的基础上，通过对归一化频率的分析，讨论得出不同占空比时光纤的无尽单模区，以及单模区与多模区的特性变化，这为设计单模大模场微结构光纤提供了参考。对等效折射率方法做了进一步总结，分析了其应用优点和局限。     

石英系单模保偏光纤的受激拉曼散射传输模式的实验分析

对石英系单模保偏光纤中的受激拉曼散射传输模式进行了实验研究，测得三种不同截止频率的单模保偏光纤中受激布曼散射光谱及其模式的分布，其结果与圆芯多模渐折射率光纤中的受激拉曼散射模式分布完全不同，斯托克斯光谱的光斑尺寸基本不变，而且具以有高阶模传输的特点。这些结果在国内外尚未见报道。     

基于薄芯光纤模态干涉技术的折射率 传感特性实验研究

报道了一种具有微结构缺陷的折射率传感器,并对其折射率特性进行了实验研究.将一部分薄芯光纤熔接于标准单模光纤中,由于插入的薄芯光纤和单模光纤纤芯失配,导致包层的高次模被激发并与纤芯模在单模光纤内形成干涉仪.通过减小薄芯光纤的包层直径,以增强包层中的传输模在环境中的倏逝场,从而提高对环境折射率测量的灵敏度.实验表明,该折射率传感器具有损耗低、成本低、灵敏度高和线性度好等特点.     

基于纤芯失配型马赫曾德尔光纤折射率和温度同时测量传感器的研究

设计和制作了一种基于单模多模细芯单模光纤马赫曾德尔(Mach-Zehnder)干涉仪结构,可同时测量折射率和温度的传感器。该传感器中,多模光纤和细芯单模熔接点充当光耦合器。导入光纤中传输的光经多模光纤后在细芯光纤的纤芯和包层中激发出纤芯模和包层模,不同模式光在细芯光纤中传输时将产生光程差,再经细芯单模熔接点耦合成为导出光纤的纤芯模而干涉。传感器透射光谱随着环境折射率和温度的变化发生漂移,通过监测不同级次的干涉谷可实现折射率和温度的同时测量。通过对传感器的透射光谱进行傅里叶变换分析可知该透射光谱主要由LP01模和LP16模干涉形成。该传感器透射光谱中1535nm附近干涉谷的折射率和温度响应灵敏度的理论值分别为-55.90nm/RIU和0.0501nm/℃(其中RIU为折射率单位);1545nm附近干涉谷的折射率和温度响应灵敏度的理论值分别为-56.26nm/RIU和0.0505nm/℃。在折射率和温度的变化范围分别为1.3449~1.3972和20℃~90℃的环境中对传感器的响应特性进行实验研究,结果表明:透射光谱中1535nm附近干涉谷的折射率和温度响应灵敏度分别为-53.03nm/RIU和0.0465nm/℃;1545nm附近干涉谷的折射率和温度响应灵敏度分别为-54.24nm/RIU和0.0542nm/℃。理论分析与实验结果相一致。该传感器在生物医学领域有较好的应用前景。     

双包层光纤折射率研究及纤芯结构优化设计

采用Matlab和Comsol建立单模光纤内激光传输模型,对双包层内光纤折射率和纤芯结构对光能量分布的影响进行了理论研究。系统分析了光纤芯径与数值孔径、归一化频率和功率填充因子的关系,依据得到的结果进一步采用多模物理耦合仿真方法对不同类型的单模双包层光纤纤芯的能量分布进行仿真,探索了不同折射率分布情况对纤芯能量分布的影响。计算和仿真结果表明:凹面折射率分布光纤的光斑模场面积最大,单位面积的功率分布最低。针对大功率光纤激光器的应用需求设计了工作波长为1.064 m、纤芯直径为10 m、凹面直径为8 m、数值孔径为0.12的单模凹面折射率双包层光纤,为提高光纤泵浦效率、降低纤芯的能量密度提供了思路。     

光纤布拉格光栅嵌入SMS光纤结构的湿度传感器

提出了一种基于光纤布拉格光栅嵌入单模-多模纤芯-单模(single-mode-multimode fiber core-single mode, SMS)光纤结构的湿度传感器。当环境湿度变化时,SMS光纤结构的干涉光谱会发生漂移,而光纤布拉格光栅对湿度不敏感,其纤芯基模保持不变。因此利用SMS光纤结构对环境湿度的敏感性去调制光纤布拉格光栅纤芯基模,通过检测光纤布拉格光栅纤芯基模的反射能量变化就可以实现湿度测量。数值模拟了SMS光纤结构的内部光场分布规律,理论计算了不同环境折射率时,多模纤芯的长度、直径对SMS光纤结构输出能量耦合系数的影响。理论模拟表明,随着环境折射率变化,SMS光纤结构中传输的纤芯基模的输出能量耦合系数会发生变化。同时制作了传感器样品并对其进行了传感实验研究,实验结果表明多模纤芯长35 mm、纤芯直径为85 μm的传感器在45%～95%RH湿度变化范围内,湿度灵敏度为0.06 dBm·(%RH)-1。在20～80 ℃温度范围内,传感器的温度灵敏度为0.008 nm·℃-1,温度所带来的湿度测量误差为0.047%RH·℃-1。传感器具有制作简单、灵敏度高、反射式能量检测等优点,在湿度测量领域有一定的应用价值。     

基于多模光纤的高斯光束平顶化整形技术

高功率平顶光束在激光加工领域具有广泛的应用。针对光束平顶化的问题,提出利用大芯径多模光纤对高斯光束整形的方法。采用RP Fiber Power建立高斯光束传输模型,仿真分析光纤内光束的传输及强度分布特性。研究结果表明,多模光纤对高斯光束具有整形作用。高斯光束经多模光纤传输后,传导模数量增加,能量由中心向径向移动,光束质量下降,能量分布趋于均匀化。光纤的芯径越大,传输长度越长,匀化效果越明显。采用D型纤芯结构,或凹面折射率分布光纤,均可快速匀化光束。     

扩芯光纤原理及其在光器件耦合中的应用

介绍了两种可以增大单模光纤模场直径并出射准直平行光束的扩芯光纤(ECF)的原理和制作方法。分析了单模光纤熔接渐变折射率多模光纤法通过改变渐变折射率多模光纤的长度和自聚焦参量实现模场扩大缩小的原理,制作的扩芯光纤模场直径扩大到16．6μm,出射光束平行效果较好,轴向耦合容限比单模光纤扩大了近6倍。加热扩芯光纤则是通过控制加热温度和加热时间直接使单模光纤掺杂物质发生扩散,从而实现扩束和光束准直,模场直径达到15．4μm,横向、轴向耦合容限都比单模光纤有很大提高。因此扩芯光纤可以简化单模光纤的耦合对准过程,用来制作新型的单模光纤或掺铒光纤连接器,也可以用于其它光器件中与单模光纤的准直。     

Low-Loss Many-to-One Fiber Couplers with Few or Single-Moded Inputs and a Multi-Mode Output

The coupling of light from a number of few or single-moded fibers into a single multi-mode fiber is analyzed using geometric optics, and simple results demonstrating mode conservation are derived. Coupling from multiple single-mode fibers into a multi-mode fiber is investigated in detail using the overlap integral to determine coupling into each mode of the output fiber as a function of the light phase in the inputs. As well as results with practical relevance to fiber tapped delay-line filters and optical CDMA, the analysis provides pedagogic insight into light propagation and the light-gathering properties of fiber.     

Low-Loss Many-to-One Fiber Couplers with Few or Single-Moded Inputs and a Multi-Mode Output

The coupling of light from a number of few or single-moded fibers into a single multi-mode fiber is analyzed using geometric optics, and simple results demonstrating mode conservation are derived. Coupling from multiple single-mode fibers into a multi-mode fiber is investigated in detail using the overlap integral to determine coupling into each mode of the output fiber as a function of the light phase in the inputs. As well as results with practical relevance to fiber tapped delay-line filters and optical CDMA, the analysis provides pedagogic insight into light propagation and the light-gathering properties of fiber.     

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 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.     

Fiber-optic refractive-index sensors based on transmissive and reflective thin-core fiber modal interferometers

We present a new fiber-optic refractive-index sensor based on a fiber modal interferometer constituted by a thin-core optical fiber, whose cut-off wavelength is around three times shorter than normal single-mode fiber. In such a core diameter mismatching structure, the high-order cladding modes are efficiently excited and interfere with the core mode to form a high extinction-ratio filter (>30 dB). Both transmissive and reflective thin-core fiber modal interferometers are experimentally demonstrated, and show a high sensitivity to a small change of external refractive-index (>100 nm/R.I.U.), but a low sensitivity to the change of temperature (<0.015 nm/°C). Such a fiber device possesses an extremely simple structure, but excellent refractive-index sensing properties, and thus is an ideal candidate for fiber-optic biochemical sensing applications.     

单模锥体光纤传输特性的数值分析

本文采用含有轴向坐标参变量的标量波动方程来描写锥体光纤,通过一种简单的变换,将标量波动方程化为一阶微分方程组。用四阶龙格——库塔法的基尔改进式,计算了单模锥体光纤的传输特性。     

Ultrafast pulse sources based on multi-mode optical fibers

Ultrafast pulse sources based on multi-mode optical fibers are discussed. High-power passively mode-locked fiber lasers based on multi-mode rare-earth-doped optical fibers greatly exceed the power limitations of single-mode oscillators. Ultrafast multi-mode fiber amplifiers operating in conjunction with multi-mode oscillators provide even higher power levels, where nonlinear propagation effects enable pulse compression to below 100 fs. Multi-mode fiber oscillators can be combined with single-mode Raman-shifting fibers to produce widely wavelength-tunable sources of femtosecond pulses. Further amplification in Yb fibers allows for the generation of sub-100-fs pulses with W-level average powers.     

Modeling and interference-microscopy characterization of graded index transitions in ion-exchange waveguide integrated elements: transitions between annealed surfaces

We employ interference microscopy to characterize in a direct and local way the graded index transitions at the boundaries of integrated optical elements fabricated by multistep ion-exchange processes, a task not yet possible by other technologies. A particular fabrication method based on purely thermal ion-exchange, which allows local single-mode propagation, is investigated. The refractive-index distribution is modeled on the basis of the linear theory of diffusion and adiabatic transitions of the refractive-index profile. Finally, its validity is analyzed by microinterferometry.     

Refractive-index profiling of azimuthally asymmetric optical fibers by microinterferometric optical phase tomography

Accurate nondestructive refractive-index profiling is needed in the modeling, design, and manufacturing of optical fibers and fiber devices. Most profile measurement techniques cannot correctly characterize fibers with small or irregular refractive-index variations over their cross sections. Microinterferometric optical phase tomography (MIOPT) is a technique that allows measurement of fiber refractive-index profiles exhibiting such variations. We present the first demonstration, to our knowledge, of MIOPT. The profile of a polarization-maintaining fiber is measured by MIOPT and shown to be in agreement with (destructive) fiber end-face measurements. MIOPT is also applied to the limiting case of a symmetric single-mode fiber.