A flexible metamaterial with negative refractive index at visible wavelength

In this paper, we demonstrated a realization of a flexible metamaterial with negative refractive index operating at visible wavelength. With the help of Finite-Difference Time-Domain (FDTD) method, we could establish design rules for the metamaterial and analyze the characteristics of it. To this end, the fishnet structure with the unit cell size 185 nm by 240 nm was fabricated. Due to the polymer dielectric spacer between the metal-layers, the metamaterial is freestanding without base substrate and additional backside etching process.     

三维荧光光谱多峰校正测量水中汽油浓度

针对荧光峰值法浓度测量中最佳激发和发射波长的选择问题,提出基于三维荧光光谱的多峰线性回归参数比较法。以市售93号和97号汽油为例,首先利用FS920型稳态荧光光谱仪扫描纯水和纯油品的三维荧光光谱,确定特征荧光峰峰位和强度;其次按不同体积比分别配置7种浓度的油水混合液样品,提取不同样品的荧光峰峰位、强度等特征参量,发现浓度对荧光峰特征参量有较大干扰;然后用排除法确定了93号和97号油水混合液样品分别有23个和22个特征峰;最后采用最小二乘法对每个峰的强度与浓度作线性回归,通过对校正决定系数、F值、灵敏度和截距等参数的比较得出,93号和97号油水混合液的最佳激发/发射波长分别为275/302 nm和285/322 nm。实验结果表明,根据最佳峰校正模型,93号和97号汽油浓度测量的绝对误差分别为0.006‰、0.007‰,比传统的最强峰校正模型精度高1个数量级。     

Strengths and diameter variations of fused silica fibers prepared in oxy-hydrogen flames

Abstract

The efficacy of using oxy-hydrogen torches as heat sources for preparing optical fibers has been investigated. It was found that fibers with uniform diameters and high strengths can be prepared routinely in kilometer-lengths, using torches of the surface mixing type. Feed back control of drawing speed was not used; diameter variations were nevertheless comparable to those obtained in furnace drawing under similar conditions (3～5%). Fibers drawn from Suprasil-2 F rods and coated with a General Electric thermally curable silicone were consistently strong regardless of whether they were prepared with torches made from metal or from quartz tubes. Several kilometer-lengths exhibited strengths ranging from about 3.5 GPa (500 KSI) to 6.9 GPa (1,000 KSI) when tested in 20-m gauge length. However, the strengths of the fibers prepared from TO-8 F rods varied widely and depended strongly on the level of contamination in the as-received glass rods.     

基于激光近红外的稻米油掺伪定性-定量分析

该文主要研究激光近红外光谱分析技术结合化学计量学方法对稻米油掺伪进行定性-定量分析。分别将大豆油、玉米油、菜籽油、餐饮废弃油掺入稻米油中,按照不同质量比配置189个掺伪油样,利用激光近红外光谱仪采集光谱;对采集的稻米油掺伪图谱数据进行多元散射校正(MSC)、正交信号校正 (OSC)、标准正态变量变换和去趋势技术联用算法(SNV_DT)三种不同预处理并与原始数据进行比较。采用连续投影算法(SPA)对经过预处理的光谱数据进行特征波长提取,应用支持向量机分类(SVC)方法建立稻米油掺伪样品的定性分类校正模型,选择网格搜索算法对模型参数组合(C,g)进行寻优,确定最优参数组合。另采用后向间隔偏最小二乘法(BiPLS)和SPA对预处理后的光谱数据进行特征波长提取,分别应用偏最小二乘法(PLS)和支持向量机回归(SVR)建立掺伪油含量的定量校正模型,并选用网格搜索算法对SVR模型参数组合(C,g)进行寻优,建立最优参数模型。研究表明,建立的SVC模型预测集和校正集的准确率分别达到了95%和100%;对比SVR和PLS方法建立的数学模型对稻米油中掺杂油脂的含量的预测,两种方法均能够实现含量预测,SVR模型的预测能力更好,相关系数R高于0.99,均方根误差(MSE)低于5.55×10-4,预测精度高。结果表明,采用激光近红外光谱分析技术可以实现稻米油掺伪的定性-定量分析,同时为其他油脂的掺伪分析提供了方法。     

Fundamental limitations of sensitivity of whispering gallery mode gyroscopes

We analyze theoretically both the fundamental and the technical quantum limitations of the sensitivity of a passive resonant optical gyroscope based on a high finesse monolithic optical microcavity. We show that the quantum back action associated with the resonantly enhanced optical cross- and self-phase modulation results in the standard quantum limit of the angle random walk of the gyroscope, which reaches approximately 0.2 deg/hr^1/2 for a millimeter scale CaF₂ whispering gallery mode resonator based device.     

Role of absorption in grating erasure

In this paper, we have investigated the grating erasure of a reduced LiNbO₃:Fe crystal with different erasing wavelengths. The overall hologram evolution in the process of grating erasure is nonexponential due to strong absorption which is contrary to the mono-exponential law. The hologram in the rear part of the crystal can persist for a long time in the grating erasure due to weak erasing light intensity by strong absorption, which can enlarge the erasure time constant. From the erasure experiments, the global absorption d≈5 can be taken as the optimum absorption to acquire a good trade-off between the sensitivity and hologram strength in the crystal.     

自由空间微闪耀光栅解复用器

波分复用/解复用器件在光纤通信中具有重要的应用。设计了一种自由空间的微闪耀光栅解复用器,通过对其衍射光场的复振幅分布的研究,得到了满足1级闪耀输出的光栅方程,实现了复合波长信号光在空间上的解复用。通过对微闪耀光栅解复用器的衍射效率和串扰进行分析后表明,微闪耀光栅解复用器具有很高的衍射效率,信号间串扰非常小,而且元件尺寸小,结构紧凑,集成度高,在光通信和光信息处理中具有一定的应用价值。     

Simultaneous dual-wavelength lasing of an erbium-doped fibre laser over wide spectrum range by intracavity loss optimisation

This letter reports a new technique to achieve a wide range of simultaneous dual output lasing of an erbium-doped fibre laser. The range covers a wide spectrum of 30 nm. This range is achieved by optimising the intracavity loss of the fibre loop in the laser. The wavelength is tuned via a tuneable bandpass filter. These dual lasing outputs are kept within a 0.5 dB power difference.     

Measurement of the spectral dispersion curves of low birefringence polymer fibres

A method is suggested to overcome the difficulties of measuring the spectral dispersion of low birefringence fibres, that produce small optical path difference, δ<3λ, where δ is the optical path difference and λ is the wavelength of light used. This method depends on variable wavelength interferometry (VAWI). The suggested method is used to measure the spectral dispersion of birefringence of polypropylene fibre with a draw ratio 4 (low birefringence fibre). This method is also used to measure the spectral dispersion of birefringence of a polyester staple from ICI (high birefringence fibre). Also, the conventional VAWI method is used to measure the spectral dispersion of this fibre to confirm the results obtained by the suggested method. Microinterferograms are given for illustration.     

低磁场谐振腔切仑科夫振荡器-锥形放大器的初步实验研究

设计了一种能工作在低磁场高功率的慢波器件,该器件通过谐振腔将切仑科夫振荡器与锥形放大器有机地结合,充分利用电子的能量,实现了高效的微波产生.给出了初步的实验结果,在束流电压450kV,电流2.3 kA,导引峰值磁场0.6T的情况下,得到230 MW,频率为10.33 GHz,模式TM01的微波输出,效率达到23%.实验结果与粒子模拟结果基本吻合.