热拉伸和化学腐蚀相结合制备弯曲光纤探针

提出了原子力/光子扫描隧道显微镜(AF/PSTM)系统的关键部分——双功能弯曲光纤探针的制作方法.采用热拉伸与动态、静态两步化学腐蚀相结合的方法制作出AF/PSTM弯曲光纤探针,弯曲角度约为150°,尖端曲率半径优于100nm,锥角范围为60°—90°.将这种双功能弯曲光纤探针应用在新研制的AF/PSTM系统上,同时获得了样品的光学与形貌图像,实现了图像分解.关键词：原子力/光子扫描隧道显微镜光纤探针热拉伸化学腐蚀     

Characterization of optical waveguides in β-BaB2O4 crystals formed by 3.0 MeV Ni ions implantation

We report on the optical planar waveguides formation and modal characterization in β-BaB₂O₄ crystals by Ni²⁺ ion implantation at energy of 3.0 MeV and doses of 10¹⁴ ions/cm². The prism coupling method was used to investigate the dark-mode property at wavelengths of 633 nm and 1539 nm, respectively. The refractive index profiles of the waveguides with different doses were reconstructed by an effective refractive index method based on the reflectivity calculation method (RCM). The modal analysis indicates that the fields of TM modes can be well restricted in the guiding region, which means the formation of non-leaky waveguide in the crystal.     

暗怪波的相互作用

以耦合非线性薛定谔方程为理论模型,数值研究了两个一阶暗怪波在正常色散单模光纤中的相互作用.基于一阶暗怪波精确解,采用分步傅里叶数值模拟法,从间距、相位差和振幅系数比方面讨论相邻两个一阶暗怪波之间的相互作用.基于二阶暗怪波精确解,讨论了两个一阶暗怪波的非线性相互作用.研究结果表明:同相位情况下,间距参数T1为0、5、20时,相邻两个一阶暗怪波相互作用激发产生“扭结型”暗怪波.相比较于单个暗怪波发生能量的弥散,“扭结型”暗怪波分裂形成多个次暗怪波.反相位情况下,间距参数T1为2、7、12时,相邻两个一阶暗怪波相互作用也可以激发产生“扭结型”暗怪波.并且“扭结型”暗怪波初始激发的空间位置偏离原始单个暗怪波的位置5.振幅系数比越大,该空间位置越接近5.二阶暗怪波可以看作是两个一阶暗怪波的非线性叠加,复合型和三组分型二阶暗怪波与相邻两个一阶暗怪波的相互作用略有相似.     

Mesoscopic effect of spectral modulation for the light transmitted by a SNOM tip

The effect of a tapered metal-coated optical fiber terminated by a sub-wavelength aperture (SWA) on the spectrum of the transmitted light is investigated experimentally. Under certain conditions a remarkable spectral modulation of the transmitted light can be observed. This effect is of a mesoscopic origin, occurring only for a certain interval of SWA diameters. One can conclude that a noticeable modulation appears when the number of the transmitted fiber modes is small but exceeds unity, thus indicating the presence of a phase shift between different modes. To discern between two possible sources of such phase shift, the fiber length dependence of the output spectrum has been studied. According to the results obtained for the used sample of 200 nm SNOM tip, the observed phase shift is mostly caused rather by the inherent modal dispersion of the multimode fiber than by the mode-dependent light slowdown in the tapered region close to SWA due to the coupling to surface plasmons of the metal coating. The SWA acts here mainly as an effective mode filter.     

微纳尺度光纤布拉格光栅折射率传感的理论研究

亚波长直径微纳光纤强倏逝场传输的光学特性,使其对周围介质折射率的变化具有极高的灵敏度.本文提出一种基于微纳尺度光纤布拉格光栅(MNFBG)的折射率传感器,结合微纳光纤倏逝场传输和光纤布拉格光栅(FBG)强波长选择的特性来实现高精度折射率传感,对其制备可行性进行了讨论.论文中对MNFBG折射率传感机理进行了深入的理论分析,并使用OptiGrating软件进行了数值模拟,模拟数据显示MNFBG折射率测量的灵敏度随着光纤半径的减小而增加,其中光纤半径为400 nm的MNFBG灵敏度可达到993 nm/RIU,相比于包层蚀刻的FBG灵敏度增加了170倍,说明MNFBG对发展微型化、高灵敏度折射率传感器具有良好的应用前景.关键词：微纳光纤光纤布拉格光栅折射率传感     

Characteristics of radio transmission over polymer optical fiber for indoor wireless coverage

The characteristics of radio over polymer optical fiber (RoPOF) are evaluated for indoor or in-building wireless coverage. The frequency responses and the third order intermodulation distortion products of the RoPOF link are investigated. The eye diagrams and EVM values of signals carrying quadrature-phase-shift-keyed (QPSK) data and global system for mobile (GSM) signals are measured to evaluate the transmission performance. The interference measurements with FDM are also carried out. The results show that although the nonlinear distortion and power loss deteriorate the system to some extent, making use of passband transmission, RoPOF can provide fairly good transmission performance for wireless applications.     

Higher-order space-charge field effects on the self-deflection of photovoltaic dark spatial solitons

We investigate theoretically the effects of higher-order space-charge field on the self-deflection of photovoltaic dark spatial solitons by numerical method under steady-state conditions. The expression for an induced space-charge electric field, including higher-order space-charge field terms is obtained. Numerical results indicate that photovoltaic dark solitons possess self-deflection process during propagation, and the solitons always bend in the direction of the c-axis of the crystal. The self-deflection of dark solitons can experience considerable increase especially in the regime of high photovoltaic field strengths. Relevant examples are provided.     

Fundamentals of nonlinear optical materials

In this article, we briefly review the fundamental aspects of nonlinear optical materials and their role in modern communication.     

基于软玻璃光纤产生中红外超连续谱研究进展

随着软玻璃光纤的发展和光纤激光器的进步,越来越多的研究人员采用以软玻璃光纤代替石英光纤的方式,得到高功率中红外超连续谱光源.通过广泛阅读国内外关于氟化物玻璃光纤、硫系玻璃光纤和碲酸盐玻璃光纤等软玻璃光纤产生超连续谱的相关文献,本文综述了近年来利用这三类光纤产生中红外超连续谱光源的研究进展.目前氟化物玻璃光纤在实验中的应用最为广泛,且研发进度较快,获得的中红外超连续谱覆盖范围在2～5μm,最大输出功率可达30 W;硫系玻璃光纤产生的中红外超连续谱光源带宽可达10μm以上,但输出功率较低;碲酸盐玻璃光纤由于材料中羟基难以去除,在中红外超连续谱的实验中进展较为缓慢;而氟碲酸盐光纤在近几年发展迅速,可能成为未来中红外超连续谱研究的理想介质.     

亚微米直径光纤的非线性特性研究

用电磁场的严格解分析了亚微米直径光纤的非线性系数,发现光纤直径在700nm左右（亚微米量级）非线性系数较大,喇曼阈值较小,喇曼增益谱线较多;受激喇曼散射特性的分析表明,由于直径小,光纤在较小的泵浦光功率作用下能量密度就很大,因此很容易观察到受激喇曼散射.实验结果表明,理论分析与实验结果吻合得很好.     

非线性光纤信道容量预测

为了计算非线性光纤传输对其信道容量的作用，从信号功率传输特性出发，提出了一种计算非线性光纤信道容量的数值解法，分别得到了非线性信道容量与输入脉冲峰值功率、自发辐射噪音系数、光纤非线性参量及群速色散之间的关系曲线并得出结论：单纯的提高脉冲输入功率并不能提高非线性信道容量，尤其对大功率系统．     

锥形光纤间耦合特性的分析与检测

将通信光纤的末端拉制成锥形,利用光信号在光纤锥形区特有的传输和耦合特性,实现了光纤的耦合、连接和分束。用耦合模理论分析了锥形光纤间的传输和耦合性质,给出了光信号两锥形光纤间的耦合与两锥形光纤的距离和锥形区重叠长度等实验结果。     

Applications of Nonlinear Effects in Highly Nonlinear Photonic Crystal Fiber to Optical Communications

Unique dispersion characteristics and enhanced nonlinearity make the small-core photonic crystal fiber (PCF) an ideal candidate for nonlinear optical devices to telecommunication applications. Some technical reasons behind great research interest of highly nonlinear PCFs in optical communication components are reviewed. Nonlinear effects in highly nonlinear PCFs and their research progress are presented. Several typical applications including WDM sources, optical amplification, optical switching, wavelength conversion, optical regeneration and all-optical demultiplexing etc are introduced, together with state-of-the art performances. Some new possible applications and future prospects are discussed.     

A rigorous analysis of the distribution of power in plastic clad linear tapered fibers

An analytical investigation is presented of the propagation of power in a step-index plastic clad tapered optical fiber operating in the infrared region of the electromagnetic (EM) spectrum. The chosen materials are widely used in low cost optical links. It is assumed that the taper section has a linear profile. Following rigorous analytical approach, the general expressions for power in the core and the cladding sections are derived, and a study is presented of the variation of the relative power along the propagation direction in respect of different (meriodinal and skew) lower order modes. It is observed that, in general, the confinement of power is fairly high in the core section, and the confinement increases with the increase in the taper length and/or mode index. In the cladding region, the confinement decreases for higher taper lengths.     

基于高非线性微结构光纤环镜的脉冲压缩与基座抑制

提出了利用一种高非线性微结构光纤构成非线性光纤环镜（NOLM）进行脉冲压缩和基座抑制的方案.所提出的微结构光纤具有高非线性系数和大反常色散.理论研究了基于这种微结构光纤的NOLM对脉冲的压缩效应,并分析了压缩的机制.数值结果表明,这种NOLM采用较短的光纤长度就能有效地压缩脉冲并明显抑制了基座.对于给定的输入脉冲,存在一个最优的环路长度,可以获得高质量的压缩脉冲.通过适当选择耦合比和环路长度,则可以完全消除脉冲的基座.     

Multiwavelength erbium-doped fiber laser employing a nonlinear optical loop mirror

A stable and broad bandwidth multiwavelength erbium-doped fiber laser is proposed and demonstrated successfully. A nonlinear optical loop mirror which induces wavelength-dependent cavity loss and behaves as an amplitude equalizer is employed to ensure stable room-temperature multiwavelength operation. Up to 50 wavelengths lasing oscillations with wavelength spacing of 0.8 nm within a 3-dB spectral range of 1562-1605 nm has been achieved. The measured power fluctuation of each wavelength is about 0.1 dB within a 2-h period.     

Stability of chirped bright and dark soliton-like solutions of the cubic complex Ginzburg-Landau equation with variable coefficients

We consider an inhomogeneous optical fiber system described by the generalized cubic complex Ginzburg-Landau (CGL) equation with varying dispersion, nonlinearity, gain (loss), nonlinear gain (absorption) and the effect of spectral limitation. Exact chirped bright and dark soliton-like solutions of the CGL equation were found by using a suitable ansatz. Furthermore, we analyze the features of the solitons and consider the problem of stability of these soliton-like solutions under finite initial perturbations. It is shown by extensive numerical simulations that both bright and dark soliton-like solutions are stable in an inhomogeneous fiber system. Finally, the interaction between two chirped bright and dark soliton-like pulses is investigated numerically.     

Photonic Engineering Group of the University of Cantabria: Recent R&D Contributions in Photonic Sensing Technology

The recent research and development results of the Photonic Engineering Group in the photonic sensing field are reported. This article includes a sample of contributions in several of the ongoing R&D lines: fiber sensing using Bragg grating technology; gas sensing, high temperature monitoring; optoelectronic instrumentation for laser welding monitoring; fiber active devices; and, finally, on sensing technology using plastic optical fiber.