Bending dependence of optical delay difference between multicore fiber cores

The group delay difference between modes of multicore optical fiber cores is studied by the interference method using a Mach–Zehnder interferometer and a low-coherence radiation source. The data obtained show that the group delay difference between multicore optical fiber cores is caused by optical fiber bending and increases with decreasing winding radius.     

Suspended twin-core f iber for optical switching

A kind of novel fiber, comprising two fiber cores which are suspended in air inside the outer cladding via a central thin membrane ,is proposed for optical switching application. When a hydrostatic pressure applied on the optical fiber, the pressure-induced refractive index change of the two fiber cores will contribute to the periodical change of the intensity of guided light in the fiber core. The mode coupling of two cores under different hydrostatic pressure and influences of each structure parameter of the proposed fiber on the switching nressure have been numerically invo.stigated.     

The Coupled-mode Theory of Grating-assisted Parallel Optical Fiber Cores

A new coupled-mode formulation is developed for grating-assisted parallel optical fiber cores. The theory is derived from the scalar wave equation by perturbation method. The diffraction caused by grating and coupler in the grating region are both considered. Based on the theory, various experimental phenomena in grating-assisted parallel optical fiber cores can be simulated accurately.     

The Coupled-mode Theory of Grating-assisted Parallel Optical Fiber Cores

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ｇｒａｔｉｎｇ ａｓｓｉｓｔｅｄｄｉｒｅｃｔｉｏｎａｌｃｏｕｐｌｅｒｉｓａｎａｔｔｒａｃｔｉｖｅａｄｄ ｄｒｏｐｆｉｌｔｅｒｆｏｒｄｅｎｓｅｗａｖｅｌｅｎｇｔｈ ｄｉｖｉｓｉｏｎｍｕｌｔｉｐｌｅｘｉｎｇ (ＤＷＤＭ ) .Ａｎｕｍｂｅｒｏｆｓｕｃｈａｄｄ ｄｒｏｐｆｉｌｔｅｒｓｈａｖｅｂｅｅｎｐｒｏｐｏｓｅｄａｎｄｄｅｍｏｎｓｔｒａｔｅｄ[1～ 5] .Ｔｗｏｍａｉｎａｐｐｒｏａｃｈｅｓｈａｖｅｂｅｅｎ ｐｒｏｐｏｓｅｄｔｏｓｉｍｕｌａｔｅ ｇｒａｔｉｎｇｅｆｆｅｃｔｉｎｄｉｒｅｃｔ…     

Wavelength-selective coupling of dual-core photonic crystal fiber and its application

We investigate the coupling characteristics of photonic crystal fiber composed of two cores with different index profiles. The index curves of the fundamental modes of the two cores can cross at a desired wavelength by choosing appropriate index profiles of the cores. As a result, wavelength-selective coupling is achieved. The designed coupler can be applied as an oDtical fiber bandstop filter with 26-nm bandwidth.     

Microwave signal delay line based on multicore optical fiber

A fiber-optic delay line based on the successive transmission of a modulated optical signal through all seven cores of an optical fiber has been fabricated. The total loss of the signal after the transmission through all cores is less than 12 dB. The group delay in the range of modulation frequencies of 6 to 12GHz is found to be 5.62 μs for a fiber as short as 160 m.     

Transverse light guides in microstructured optical fibers

A novel class of microstructured optical fiber coupler is introduced that operates by resonant, rather than proximity, energy transfer by means of transverse light guides built into a fiber cross section. Such a design permits significant spatial separation between interacting fibers, which, in turn, eliminates intercore cross talk owing to proximity coupling. A controllable energy transfer between the cores is then achieved by localized and highly directional transmission through a transverse light guide. The main advantage of this coupling scheme is its inherent scalability, as one can integrate additional fiber cores into the existing fiber cross section simply by placing the cores far enough from the existing optical circuitry to prevent proximity cross talk and then making the necessary intercore connections with transverse light wires, in direct analogy with on-chip electronics integration.     

Fiber-optic delay line using multicore fiber

A fiber-optic delay line based on a multicore optical fiber is fabricated for the first time. Due to the optical pulse sequential passage over all cores, the time delay of the optical signal of 45.0 μs is obtained at the optical fiber length of only 1300 m. The use of the seven-core optical fiber allows a sevenfold reduction in the used fiber length in comparison with single-core fibers, which is promising for developing lines with long signal delays.     

Intensity curvature sensor based on photonic crystal fiber with three coupled cores

An intensity curvature sensor using a Photonic Crystal Fiber (PCF) with three coupled cores is proposed. The three cores were aligned and there was an air hole between each two consecutive cores. The fiber had a low air filling fraction, which means that the cores remain coupled in the wavelength region studied. Due to this coupling, interference is obtained in the fiber output even if just a single core is illuminated. A configuration using reflection interrogation, which used a section fiber with 0.13 m as the sensing head, was characterized for curvature sensing. When the fiber is bended along the plane of the cores, one of the lateral cores will be stretched and the other compressed. This changes the coupling coefficient between the three cores, changing the output optical power intensity. The sensitivity of the sensing head was strongly dependent on the direction of bending, having its maximum when the bending direction was along the plane of the cores. A maximum curvature sensitivity of 2.0 dB/m⁻¹ was demonstrated between 0 m and 2.8 m.     

Miniaturized two-photon microscope based on a flexible coherent fiber bundle and a gradient-index lens objective

We present a miniature, flexible two-photon microscope consisting of a fused coherent optical fiber bundle with 30,000 cores and a gradient-index lens objective. The laser focus of a standard two-photon laser-scanning microscope was scanned over the entrance surface of the fiber bundle, resulting in sequential coupling into individual cores. Fluorescent light was detected through the fiber bundle. Micrometer-sized fluorescent beads and pollen grains were readily resolved. In addition, fluorescently labeled blood vessels were imaged through the fiber bundle in rat brain in vivo.     

Long-period-grating-assisted optical add-drop filter based on mismatched twin-core photosensitive-cladding fiber

A noninterferometric optical fiber add-drop channel filter based on a mismatched twin-core photosensitive-cladding fiber and long-period fiber grating is demonstrated. With assistance from the fiber grating, co-directional spectrally selective cross coupling between the two cores can be realized with an efficiency of 90%.     

长周期多芯手征光纤轨道角动量的调制

基于矢量模式耦合理论,在多模光纤中引入手性耦合纤芯结构,设计了一种光纤型光轨道角动量调制器.使用单根光纤,无需施加扭转或应力,可以实现任意光轨道角动量的调制.通过理论分析与数值仿真,研究了不同结构参数对轨道角动量模式纯度、传输损耗和有效折射率的影响.在中心纤芯和旁纤芯传播常数不变的前提下,旁纤芯数量对损耗影响较大,通过相位匹配条件计算得到的螺距可以在一定数值范围内浮动变化,两种纤芯的间距受限于模式损耗和光纤集成度.     

四芯光纤的远场干涉特性研究

设计了芯间距较小的特殊结构四芯光纤,可用于生成格子光场或用于制作光纤传感器.研究了在采用相干长度较短的LD光源的情况下,经过一段既弯曲又扭转的四芯光纤远程传输后的纤端光场干涉特性.基于叠加原理,出射光场可视为每个独立纤芯的多光源相干叠加和圆孔衍射调制共同作用的结果,推导了相应的理论公式,给出了四芯光纤远场干涉的理论与实验相一致的结果.对光纤弯曲所导致的光程差累积和偏振态衰变效应进行了分析和讨论,并给出了相应的实验结果.     

Optical pulse compression of ultrashort laser pulses in a multi-hollow-core fiber

By numerical simulations and analysis, we proposed a fiber with multi-hollow-core structure for optical pulse compression of high energy ultrashort laser pulses. In this scheme, different parts of a high-energy flat-top pulse are coupled into different hollow cores of such fiber and each of the cores functions as an independent traditional hollow-core fiber compressor. After the multi-hollow-core fiber, the output beams are collimated and compressed to few-cycle level. Then they can be focused to ultra-high intensity. This method can easily be scaled to compressing pulses of large beam size with high energy without limit in principle.     

Dynamic behaviors of optical vortices in dual-core photonic crystal fibers

Novel evolution dynamics of optical vortices propagating in a dual-core photonic crystal fiber (PCF) is investigated, which can be explained well by using the equivalent dipole mode superposition principle. Thanks to the coupling between the two cores of PCF, exciting vorticity splitting and topological charge-flipping are achieved by inducing a vortex beam into one of the two cores of the PCF. What is more, the evolutions of two vortices located in each core separately can be controlled by means of modulating the initial phase difference of them. Our results may offer possibilities for applications of optical vortices, orbital angular momentum modulations, as well as optical communications.     

具有高阶耦合色散系数三芯光纤耦合器非线性光开关特性的研究

利用两种方法研究了高速光脉冲在具有交叉相位调制的等边三角形排列结构的非线性三芯光纤耦合器中传输和开关特性.首先利用变分原理得到三纤芯中传输转移系数随距离变化的方程,然后利用分裂步长傅里叶方法求得了光脉冲的数值解.变分法和数值模拟的结果表明：当一阶模间色散系数较小时,光脉冲仍能在三芯之间周期性耦合传输,并且表现出良好的开关特性,但是随着一阶模间色散系数的增大,脉冲耦合传输的周期性和陡峭的开关特性都遭到破坏,光脉冲在传输中发生分裂;二阶耦合色散系数和初始啁啾都能使光脉冲传输时的耦合长度变短、光脉冲在三纤芯之间 关键词： 三芯光纤耦合器 模间色散系数 耦合长度 开关阈值功率     

Dispersion-Managed Solitons in Multiple-Core Nonlinear Fiber Arrays

The variational principle is employed to obtain the evolution of the parameters of Gaussian and super-Gaussian chirped solitons that propagates through multiple-core nonlinear optical fiber arrays. This is governed by the dispersion-managed nonlinear Schrodinger's equation with strong dispersion management in the presence of linear coupling between the adjacent cores. The results are valid for any configuration of the cores.     

非线性光纤耦合器孤子传输的相敏能量交换特性

从动力学的角度出发,分析了非线性双芯光纤耦器中不同芯层内孤子脉冲的相位对能量交换特性的影响,只要初始注入孤子信号的相位差选择恰当。     

Design of wavelength tunable long-period grating couplers based on asymmetric nonlinear dual-core fibers

We demonstrate a grating coupler using an asymmetric nonlinear dual-core fiber with a pair of long-period gratings (LPGs). Simple formulas for the achievement of 100% coupling efficiency and small sidelobes are derived. The passband exhibits steep band transitions. By launching high-intensity optical pumps to alter the refractive indices of the fiber cores through cross-phase modulation, a wavelength tunable LPG dual-core coupler can be realized.     

高灵敏度光纤温度传感器

针对深井温度变化小,提出了一种可用于深井温度测量的高灵敏度光纤温度传感器。两根陶瓷插芯从铝管的两端插入构成外腔式光纤法珀干涉仪(EFPI)结构,用螺钉固定插芯,再用高强度的环氧树脂密封该结构,达到防水防尘效果。金属铝和陶瓷插芯具有不同的热膨胀系数,温度的变化将引起EFPI腔长变化,采用高灵敏度光纤白光干涉测量技术,就可以通过测量EFPI腔长获得被测温度。分别在固定温度和不同温度下,对腔长为146.5μm的EFPI光纤温度传感器进行了连续测量。测量结果表明,高灵敏度EFPI光纤温度传感器的腔长-温度灵敏度为260nm/℃,温度测量分辨率为0.002℃。