Detection of Brillouin scattering temperature signal in Brillouin optical time-domain reflectometer sensing system based on instantaneous frequency measurement technology

We present a simple and practical method for the single-ended distributed fiber temperature measurements using microwave (11-GHz) coherent detection and the instantaneous frequency measurement (IFM) technique to detect spontaneous Brillouin backscattered signal in which a specially designed rf bandpass filter at 11 GHz is used as a frequency discriminator to transform frequency shift to intensity fluctuation. A Brillouin temperature signal can be obtained at 11 GHz over a sensing length of 10 km. The power sensitivity dependence on temperature induced by frequency shift is measured as 2.66%/K. (c) 2007 Society of Photo-Optical Instrumentation Engineers.

Scattering by two degenerate anisotropic modes in square-lattice dielectric photonic crystals

We systematically investigate the square-lattice dielectric photonic crystals that have been used to demonstrate flat slab imaging experimentally. A right-handed Bloch mode is found in the left-handed frequency region by using the plane wave expansion method to analyze the photonic band structure and equifrequency contours. Using the multiple scattering theory, numerical simulations demonstrate that the left-handed mode and the right-handed mode are excited simultaneously by a point source and result in two kinds of transmitted waves. Impacted by the evanescent waves, superposition of these transmitted waves brings on complicated near field distributions such as the so-called imaging and its disappearance.

Detection of Brillouin scattering temperature signal in Brillouin optical time-domain reflectometer sensing system based on instantaneous frequency measurement technology

abstract {We present a simple and practical method for the single-ended distributed fiber temperature measurements using microwave (11-GHz) coherent detection and the instantaneous frequency measurement (IFM) technique to detect spontaneous Brillouin backscattered signal in which a specially designed rf bandpass filter at 11 GHz is used as a frequency discriminator to transform frequency shift to intensity fluctuation. A Brillouin temperature signal can be obtained at 11 GHz over a sensing length of 10 km. The power sensitivity dependence on temperature induced by frequency shift is measured as 2.66%/K. © 2007 Society of Photo-Optical Instrumentation Engineers.}

Effect of water content in sol on optical properties of hybrid sol-gel derived TiO2/SiO2/ormosil film

Sol-gel derived TiO2/SiO2/ormosil hybrid planar waveguides have been deposited on soda-lime glass slides and silicon substrates, films were heat treated at 150 degreesC for 2 h or dried at room temperature. Different amounts of water were added to sols to study their impacts on microstructures and optical properties of films. The samples were characterized by m-line spectroscopy, Fourier transform infrared spectroscopy (FT-IR), UV/VIS/NIR spectrophotometer (UV-vis), atomic force microscopy (AFM), thermal analysis instrument and scattering-detection method. The refractive index was found to have the largest value at the molar ratio H2O/OR = 1 in sol (OR means -OCH3, -OC2H5 and -OC4H9 in the sol), whereas the thickest film appears at H2O/OR = 1/2. The rms surface roughness of all the films is lower than 1.1 nm, and increases with the increase of water content in sol. Higher water content leads to higher attenuation of film. (C) 2004 Elsevier B.V. All rights reserved.

Anomalous scattering factor determined by semicircle fitting near the K-absorption edge of Ge

It is shown that the locus of the f' + if '' plot in the complex plane, f' being determined from measured f '' by using the dispersion relation, looks like a semicircle very near the absorption edge of Ge. The semicircular locus is derived from a quantum theory of X-ray resonant scattering when there is a sharp isolated peak in f '' just above the K-absorption edge. Using the semicircular behavior, an approach is proposed to determine the anomalous scattering factors in a crystal by fitting known calculated values based on an isolated-atom model to a semicircular focus. The determined anomalous scattering factors f' show excellent agreement with the measured values just below the absorption edge. In addition, the phase determination of a crystal structure factor has been considered by using the semicircular behavior.

Precise determination of anomalous scattering factors of Ge by using X-ray resonant scattering

Variations of peak position of the rocking curve in the Bragg case are measured from a Ge thin crystal near the K-absorption edge. The variations are caused by a phase change of the real part of the atomic scattering factor. Based on the measurement, the values of the real part are determined with an accuracy of better than 1%. The values are the most reliable ones among those reported values so far as they are directly determined from the normal atomic scattering factors.

Structural and optical properties of nonpolar m-plane GaN and GaN-based LEDs on gamma-LiAlO2

We report the structural and optical properties of nonpolar m-plane GaN and GaN-based LEDs grown by MOCVD on a gamma-LiAlO2 (100) substrate. The TMGa, TMIn and NH3 are used as sources of Ga, In and N, respectively. The structural and surface properties of the epilayers are characterized by x-ray diffraction, polarized Raman scattering and atomic force microscopy (AFM). The films have a very smooth surface with rms roughness as low as 2nm for an area of 10 x 10 mu m(2) by AFM scan area. The XRD spectra show that the materials grown on gamma-LiAlO2 (100) have < 1 - 100 > m-plane orientation. The EL spectra of the m-plane InGaN/GaN multiple quantum wells LEDs are shown. This demonstrates that our nonpolar LED structure grown on the gamma-LiAlO2 substrate is indeed free of internal electric field. The current voltage characteristics of these LEDs show the rectifying behaviour with a turn on voltage of 1-3 V.

测量薄膜微粗糙度的总积分散射仪

介绍了一种检测光学薄膜表面总积分散射（TIS）分布的总积分散射仪。对仪器的基本结构、理论基础、测量原理以及系统性能等进行了阐述，提出了抑制系统噪音和提高测量精度的有效措施。利用该仪器对K9基底上的银（Ag）膜和氧化锆（ZrO2）薄膜进行了测量，并根据标量散射理论得到了表面均方根（RMS）粗糙度。利用光学轮廓仪和原子力显微镜（AFM）分别测量了上述Ag膜和ZrO2薄膜的表面均方根粗糙度，并与总积分散射仪所得的粗糙度进行了比较。结果表明，根据测量的薄膜表面总积分散射计算得到的表面均方根粗糙度与光学轮廓仪及原子

光学表面的标量散射理论

简要论述了标量散射理论的研究进展做,着重介绍了Beckman的一维标量散射理论和几种典型的多层膜散射模型-非相关表面粗糙度模型、附加表面粗糙度模型和非相关体内不均匀模型,比较了这些模型在中心波长为632.8nm的11层高反膜的散射特性.结果表明,非相关体内的不均匀性引起反射能带边缘散射,反射能带内的散射主要由附加表面粗糙度引起.理想粗糙度对膜系反射带内的散射影响很小,对反射带边缘几乎无影响.预测了标量散射理论的应用领域及前景.

沉积温度对热舟蒸发MgF2薄膜性能的影响

采用热舟蒸发方法沉积了氟化镁（MgF2）材料的单层膜，沉积温度从200℃上升到350℃，间隔为50℃。测量了样品的透射率和反射率光谱曲线，进行了表面粗糙度的标定，并在此基础上进行了光学损耗及散射损耗的计算。同时对355nm波长处的激光诱导损伤阈值进行了测量。结果表明：随着沉积温度的升高，光学损耗增加;在短波长范围散射损耗在光学损耗中所占比例很小，光学损耗的增加主要由吸收损耗引起；在355nm波长处的损伤阈值变化与吸收损耗的变化趋势相关，损伤机制主要是吸收起主导作用。样品的微缺陷密度也是影响损伤阈值的一个重要因素，损伤阈值随缺陷密度的增加而降低。

热舟蒸发LaF_3薄膜的紫外性能研究

研究了沉积温度对热舟蒸发氟化镧薄膜结构和光学性能的影响,沉积温度从200℃上升到350℃,间隔为50℃.采用分光光度计测量了样品的透射率和反射率光谱曲线,并在此基础上进行了光学损耗、光学常数以及带隙和截止波长的计算.采用表面轮廓仪进行了表面形貌和表面粗糙度的标定,采用X射线衍射(XRD)方法测量了不同沉积温度下样品的微结构.发现在短波长波段,随着沉积温度的升高,光学损耗增加,晶粒尺寸增大,表面粗糙度略有增加.不过散射损耗在光学损耗中所占比例均很小,光学损耗的增加主要由吸收损耗引起.随着沉积温度的升高,折射率与消光系数增大,带隙变小,相对应的截止波长向长波方向移动.