A Remark on the Decay of Correlations for Mixed-Range Spin Vector Models

In this short note we present some explicit conditions under which the Theorem of Braga et al. (J. Stat. Phys. 129:587–591, 2007) can be extended to spin-spin correlation functions of mixed short-range/long-range ferromagnetic vector spin models in the disordered phase.     

Optimization of photonic bandgap fiber long period grating refractive-index sensors

Long period gratings in low-index contrast solid-core photonic bandgap fibers are a promising platform for fiber-based fluid refractive index sensing with very low detection limits. We provide a comprehensive investigation of the possibilities for refractive index sensing using that principle in a commercial photonic crystal fiber filled with a fluid: using an acoustic grating, we map out the cladding bands, and use this data to optimize a long period grating’s sensitivity. We then implement the optimized long period grating, again using an acoustic grating, and directly measure its sensitivity to refractive index. We demonstrate a sensitivity of 17,900 nm/RIU (6.94 nm/°C) which corresponds to a smallest detectable index change of the fluid of 8.4 × 10⁻⁶.     

Comparison study of the luminescent properties of the white-light long afterglow phosphors: CaxMgSi2O5+x:Dy(x=1, 2, 3)

A series of Dy³⁺-doped calcium magnesium silicate phosphors: CaMgSi₂O₆:Dy³⁺, Ca₂MgSi₂O₇:Dy³⁺, and Ca₃MgSi₂O₈:Dy³⁺ with white long-lasting afterglow were prepared and investigated. The characteristic intra-configurational 4f emissions of Dy³⁺ were observed in the emission spectra as well as the afterglow spectra under ultraviolet excitation. The combination of the 480 nm blue emission corresponding to the ⁴F_9/2→⁶H_15/2 transition and the 575 nm yellow emission corresponding to the ⁴F_9/2→⁶H_13/2 transition yielded white-light emission. The white-coloured afterglow emission can last more than 1 h for most of the samples under study. The concentration dependence of the ratio of the yellow emission intensity with blue emission intensity was also examined and found to be varied for the different hosts. The thermoluminescence spectra above room temperature are employed for the discussion of the origin of the traps and the mechanism of the persistent luminescence.     

长周期啁啾光纤光栅级联作为波分复用隔离滤波器的数值研究

用矩阵传输法对长周期啁啾光纤光栅用于波分复用隔离滤波器的特性进行了分析,讨论了设计该类型高性能的波分复用隔离滤波器的关键技术,给出了仿真结果,表明该类型滤波器具有大的可用带宽、频率等间隔、隔离度高和通带内的色散可以忽略等优点,并指出通过调谐级联长周期光纤光栅之间的光纤长度可以实现频率间隔的调谐.     

新型长周期光纤光栅的横向负载特性及其偏振相关性研究

发现高频CO2激光脉冲写入的长周期光纤光栅谐振波长的横向负载特性具有较强的负载方向相关性,而损耗峰幅值的横向负载特性的方向相关性较弱.不同圆周方向的横向负载对谐振波长偏振相关性的影响差异较大,但对损耗峰幅值偏振相关性的影响差异较小.利用横向负载引起双折射进而导致光栅的光学主轴旋转的相关理论,合理解释了该长周期光纤光栅独特的横向负载特性及其偏振相关性.     

铁-邻菲咯啉配合物的循环伏安-光谱电化学研究

以循环伏安及循环伏安-光谱电化学方法研究了铁-邻菲咯啉配合物的电化学行为,Fe2 与邻菲咯啉生成1∶3配合物,给出一对受扩散控制的可逆氧化还原峰。自由Fe2 在-0.24V电位处,给出了一表面控制的不可逆还原峰。由氧化过程中的光谱电化学数据获得式电位为E0=0.875V(vs.Ag/AgCl)和电子转移数为n=1.0。由还原过程的循环伏安-光谱电化学数据发现,[Fe(phen)3]3 的电化学还原过程为产物弱吸附的自加速过程,获得裸电极上的标准速率常数为k0=1.14×10-3cm/s,电子转移系数为α=0.189。Langmuir吸附常数β=0.059(±0.007),吸附表面上的电子转移系数为αa=0.313,反应速率常数为k0a=1.24(±0.17)×10-3(cm/s),式电位为:0.11±0.01V(SD=0.184)。     

High Sensitive Long Period Fiber Grating Sensor for Detection of Nitrite

A high sensitive long period fiber grating(LPFG) sensor for the detection of nitrite is proposed, which is realized by coating multiple poly(sodium 4-styrensulfonate)(PSS) and poly(diallyldimethylammonium) chloride (PDDA) layers on the fiber grating surface. The sensitivity of this LPFG sensor is maximum when the number of assembled layers is 70. Under this condition, a nitrite concentration of 3×10-3 mol/L, which is lower than the National Food Additive Standard, 4.2×10-3 mol/L, can be distinguished. The s...     

基于微机电系统红外光源的长光程气体检测

针对红外气体传感器对光源的要求,选用了一种宽波长、高调制频率、低功耗的小体积微机电系统(micro-electro-mechanic system, MEMS)红外光源作为辐射源,其各项性能均能很好的满足红外传感系统对于光源的要求。由于其面光源的朗伯辐射特性,整形之后的红外光数值孔径仍然很大,采用传统的长光程气室结构很难实现长光程从而提高系统的检测灵敏度。本文结合双波长单光路的差分检测方法,设计了一种基于积分球特性的吸收气室,有效地解决了MEMS红外光源在高灵敏度气体检测应用中难于实现长光程的问题;并运用光在传输过程中光通量守恒的原理,推导了此积分球吸收气室的等效光程,解决了积分球气室等效光程计算的难题;同时采用FPGA主控芯片对MEMS红外光源进行高频调制并处理探测器的输出信号,使得外围电路的设计更加简单、灵活。设计中,使用直径为5 cm的积分球吸收气室便可实现166.7 cm的等效光程,研究结果显示系统可测得的最小甲烷浓度达0.001×10-6,极大地提高了红外检测系统的灵敏度。     

新型波长解调技术在干涉型光纤传感器输出解调中的应用

提出了一种改进型边缘滤波波长解调技术,解决干涉型或谐振型光纤传感器输出的干涉谱波长的快速解调问题。该波长解调技术基于啁啾光栅和长周期光栅的光谱特点,以啁啾光栅作为矩形滤波器,提取传感器输出干涉谱的一个干涉峰;以长周期作为边缘滤波器,将干涉峰的波长信息转化为光强信息进行检测。该波长解调技术波长解调范围为传感器输出干涉谱的一个自由光谱范围(FSR),解调速度快,克服了当前波长解调技术中存在的测量范围与测量速度难以同时提高的问题,同时还具有系统成本低 ,体积小,能够灵活多路扩展的特点。详细介绍了解调系统的工作原理以及系统结构,并将其实际应用于一种干涉型光纤电流传感器输出干涉谱的波长解调中。通过实验证明电流传感器工作在工频及脉冲电流(脉冲宽度25 μs)情况下,该解调系统对传感器输出干涉谱具有准确、快速的解调效果。该研究对推进干涉或谐振型光纤传感器的实际工程化水平的提高具有重要意义。     

Temperature sensitivity of long period fiber grating in SMF-28 fiber

In this paper we have presented long period fiber grating (LPFG) as temperature sensor. Temperature based sensors have found a number of applications in commercial and industrial fields. In LPFG based temperature sensors, they respond to shift in various peak resonant wavelengths corresponding to various attenuation bands of the transmission spectrum. Temperature effect on the various attenuation bands of a LPFG have been investigated to create a highly sensitive measurement device. The temperature sensitivities of various attenuation bands of a LPFG over the wavelength region of 1.1–1.7 μm, for a grating period of 280 μm period, are obtained by monitoring the wavelength shift of each peak resonant wavelength with temperature increment of 20 °C, ranging from 0 °C to 100 °C.