Precise optical characterization of SNAP structures with a reference fiber

A method of precise characterization of surface nanoscale axial photonics (SNAP) structures with a reference fiber is proposed, analyzed, and demonstrated experimentally. The method is based on simultaneous coupling of a microfiber to a SNAP structure under test and to a reference optical fiber. Significant reduction of measurement errors associated with the environmental temperature variations and technical noise of the spectrum analyzer is demonstrated. The achieved measurement precision of the effective radius variation of the SNAP structure is 0.2 Å.

Effect of laser surface treatment on microstructure and properties of MRI 230D Mg alloy

A creep resistant Mg alloy MRI 230D was subjected to laser surface treatment using Nd:YAG laser equipped with a fiber optics beam delivery system in argon atmosphere. The laser surface treatment produced a fine dendritic microstructure and this treatment was beneficial for the corrosion and wear resistance of the alloy. Long-term linear polarisation resistance and Electrochemical Impedance Spectroscopy measurements confirmed that the polarisation resistance values of laser treated material were twice as high as that for the untreated material. This improved behaviour was due to the finer and more homogenous microstructure of the laser treated surface. The laser treatment also increased surface hardness two times and reduced the wear rate by 25% due to grain refinement and solid solution strengthening.

Editorial optical computing circuits, devices and systems

Information forms the basis of modern technology. To meet the ever-increasing demand for information, means have to be devised for a more efficient and better-equipped technology to intelligibly process data. Advances in photonics have made their impact on each of the four key applications in information processing, i.e., acquisition, transmission, storage and processing of information. The inherent advantages of ultrahigh bandwidth, high speed and low-loss transmission has already established fiber-optics as the backbone of communication technology. However, the optics to electronics inter-conversion at the transmitter and receiver ends severely limits both the speed and bit rate of lightwave communication systems. As the trend towards still faster and higher capacity systems continues, it has become increasingly necessary to perform more and more signal-processing operations in the optical domain itself, i.e., with all-optical components and devices that possess a high bandwidth and can perform parallel processing functions to eliminate the electronic bottleneck.

Effect of Net-Fluence on waveguide formation in ultrafast laser inscribed chalcogenide glass

Waveguides were fabricated on GeGaSEr chalcogenide glass using ultrafast laser inscription method. The thermal diffusion model is discussed for understanding the light matter interaction and shown the effect of net-fluence in waveguide formation on chalcogenide glass. (C) 2012 Optical Society of America

Non-Destructive Evaluation of Defects and Damage in Composite Materials and Structures

The mechanical behaviour of composite materials differs from that of conventional structural materials owing to their heterogeneous and anisotropic nature. Different types of defects and anomalies get induced in these materials during the fabrication process. Further, during their service life, the components made of composite materials develop different types of damage. The performance and life of such components is governed by the combined effect of all these defects and damage. While porosity, voids, inclusions etc., are some defects those can get induced during the fabrication of composites, matrix cracks, interface debonds, delaminations and fiber breakage are major types of service induced damage which are of concern. During the service life of components made of composites, one type of damage can grow and initiate another type of damage. For example, matrix cracks can gradually grow to the interface and initiate debonds. Interface debonds in a particular plane can lead to delaminations. Consequently, the combined effect of different types of distributed damage causes the failure of the component. A set of non-destructive evaluation (NDE) methods is well established for testing conventional metallic materials. Some of them can also be utilized for composite materials as they are, and in some cases with a little different approach or modification. Ultrasonics, Radiography, Thermography, Fiber Optics, Acoustic Emision Techniques etc., to name a few. Detection, evaluation and characterization of different types of defects and damage encountered in composite materials and structures using different NDE tools is discussed briefly in this paper.

一种同时测量温度和应变的光纤光栅传感器

报道了一种新型实用的用单根光纤布拉格光栅(FBG)实现温度和应变分离传感的技术。当光纤光栅一部分包层直径变小时，整个光栅可以看成由两个周期相同但直径不同的子光栅连接而成。理沦分析和实验都证实了这两个子光栅具有相同的温度敏感性和不同的应变敏感性．由此实现光纤光栅传感器中温度和应变两参数的分离测量，而且这两个子光栅的中心波长间距可以直接测量应变大小．温度变化不影响所测量的应变值。实验中光栅的一部分包层直径被HF酸腐蚀到82μm．获得了两子光栅应变响应系数分别为0．00201nm/με．0．000858nm/μ

高分辨率光纤光栅温度传感器的研究

报道了一种具有高分辨率和高效且价廉的解调系统的光纤布拉格光栅(FBG)温度传感器。提出了光纤光栅的金属槽封装技术，以提高传感光栅的温度灵敏性。研究了金属槽封装光栅的温度灵敏性，理论分析和实验结果表明，封装光栅的温度灵敏系数比普通裸光栅提高了3．6倍。系统利用一长周期光栅(LPG)作为线性滤波器，宽带光源经此长周期光栅调制后入射到传感光栅，可解调布拉格传感光栅的波长位移。理论分析与实验结果一致，系统可达到的温度分辨率为0．02℃。

光纤光栅高温传感器的研究

提出了一种能够测量高温的光纤布拉格光栅（FBG）传感器结构。利用线膨胀系数和长度均不同的两种金属细杆和光纤布拉格光栅设计而成的传感头，能够将被测温度转化为光栅的应变，解调由应变引起的光栅波长漂移，即可得知待测的温度。目前在实验室实现了500℃的动态范围和1℃的温度分辨率，实验结果与理论分析一致。

长周期光纤光栅波导色散因子和有效折射率热光系数的测量

对串联的长周期光纤光栅(CLPFG)的透射谱特性进行了理论分析和实验研究。分析表明，长周期光纤光栅中纤芯模和包层模之间的马赫-曾德尔干涉效应导致在长周期光纤光栅谐振峰内的梳状滤波结构特性；其峰值位置和峰间距同串联区光纤的长度以及光纤的波导色散因子有关。测量了长周期光纤光栅的透射谱，并研究了其温度特性。根据测量数据，得到对应于1554nm波长处，所用单模光纤HE14模的波导色散因子γ为0．874；纤芯／包层有效折射率差的热光系数为4．8×10^-5℃^-1。并对这一测试方法和结果，以及长周期光纤光栅的应用进

基于3×3耦合器的马赫-曾德尔干涉仪的光纤光栅波长解调技术

介绍了一种基于3×3和2×2光纤耦合器构成的非平衡马赫-曾德尔干涉仪的波长解调方案。理论分析和数据对比表明，相对于由两个2×2光纤耦合器构成的马赫-曾德尔干涉仪，本干涉仪具有宽谱的灵敏度、能跟踪波长的变化方向和相位展开的优点，实验方案用于测量固定在悬臂梁上的传感光纤布拉格光栅（FBG）的峰值波长变化，获得了±1pm的静态波长解调精度，在10Hz处的动态分辨率为27nε/√Hz。相位展开算法使得应变测量范围达到了2014με，对应的相位变化为3．22π。