用归一化光谱分布差异表征AlGaInP基LED阵列的平均结温

提出了一种采用归一化光谱分布的总体差异表征AlGaInP基发光二极管(LED)阵列平均结温的新方法。采用光谱仪测量了不同衬底温度、不同注入功率时,3种LED阵列的归一化光谱分布,研究了归一化光谱分布差异与LED阵列平均结温的关系,并将归一化光谱分布差异表征平均结温的准确度与文献报道的中心波长法相比较。研究结果表明:无论是改变衬底温度还是注入功率,采用常用的1nm采样间隔的光谱仪,归一化光谱分布差异与LED阵列平均结温的变化成良好的线性关系,线性度优于中心波长法,因此归一化光谱分布差异可以用于平均结温的测算,且准确度高于中心波长法。     

AlGaInP基LED阵列平均结温的质心波长表征

在驱动电流为350 mA时,测量了LED阵列在不同衬底温度下的归一化光谱功率分布,然后计算质心波长,并分析其与LED阵列平均结温变化量的关系,最后研究了质心波长表征结温的准确度。研究结果表明:采用1 nm采样间隔的光谱仪,质心波长与平均结温的变化成良好的线性关系,其线性度明显优于中心波长法。同时,质心波长的测量精度更高。因此,质心波长测试是一种可以精确表征AlGaInP基LED阵列平均结温的有效方法。     

LED结温与光谱特性关系的测量

采用恒定驱动电流改变环境温度和恒定环境温度改变驱动电流两种方法分别对直径5 mm封装的AlGaInP型红光和黄光LED,InGaN型绿光和蓝光LED,以及InGaN蓝光+荧光粉的白光LED的结温与其光谱特性进行了测量,得到了不同条件下LED结温与光谱特性的关系.结果表明;AlGaInP LED的峰值波长与结温有良好线性关系,InGaN LED的峰值波长则与结温没有明显对应关系;但白光LED发射光谱的白、蓝功率比与结温有良好线性关系;对AlGaInP LED及蓝光激发的白光LED,通过光谱特性测量可快速、准确地确定光源系统中各LED的结温继而预测光源系统的有效寿命.     

LED结温与光谱特性关系的测量

采用恒定驱动电流改变环境温度和恒定环境温度改变驱动电流两种方法分别对直径5 mm封装的AlGaInP型红光和黄光LED,InGaN型绿光和蓝光LED,以及InGaN蓝光+荧光粉的白光LED的结温与其光谱特性进行了测量,得到了不同条件下LED结温与光谱特性的关系.结果表明;AlGaInP LED的峰值波长与结温有良好线性关系,InGaN LED的峰值波长则与结温没有明显对应关系;但白光LED发射光谱的白、蓝功率比与结温有良好线性关系;对AlGaInP LED及蓝光激发的白光LED,通过光谱特性测量可快速、准确地确定光源系统中各LED的结温继而预测光源系统的有效寿命.     

GaN蓝色LED结温的最佳光谱带宽表征

研究了光谱带宽表征Ga N蓝色发光二极管(LED)结温的最优方式。测量了10只Ga N蓝色LED在不同驱动电流和不同热沉温度下的归一化光谱功率分布和结温,采用最小二乘法分析得到不同n值的光谱带宽Δλn表征结温的公式,比较了该公式和电压法得到的结温之间的差别以及差别最小时的最优n值。研究表明采用不同n值的Δλn均能够表征结温。随着n值减小,Δλn表征结温的误差先减小后增大。最优n值与光谱仪的测量误差有关。采用Hass2000型光谱仪时最优n值为0.2或0.3。该研究对提高Ga N基LED结温的测量准确度具有重要意义。     

InGaN基白光LED光谱特征和结温相关性研究

 以InGaN蓝光+荧光粉的白光LED为研究对象,在恒定环境温度下改变驱动电流,利用光谱仪测得不同LED结温下的光谱曲线。通过分析实验数据,得出光谱特征与该型LED结温的关系。结果表明：InGaN基白光LED蓝光和荧光的峰值波长与结温没有明显的线性关系;蓝光的光谱线宽以及荧光和蓝光峰值强度的比值与结温具有良好的线性关系。     

用芯片光谱特征参数表征双荧光粉转换型白色LED结温

采用正向电压法测量不同衬底温度、不同电流驱动时,双荧光粉转换型白色LED的结温,同时采用光谱仪测量归一化光谱分布.选择芯片的蓝色光谱,计算其质心波长和半高全宽,得到质心波长、半高全宽、驱动电流和结温四者之间的变化规律图.然后根据实际点灯状态下芯片的光谱特征参数,结合规律图计算得到实际结温.研究表明:对于环境温度变化引起的结温变化,(B+Y+R)/B法与本文方法准确度相当,测量误差均为2℃左右,无统计性差异.对于电流变化引起的结温变化,本文方法误差仍然约为2℃,而(B+Y+R)/B法误差与电流正相关,变化率为0.048℃/mA.同时在点灯6周内,本文方法误差仅4℃.因此,本文方法不仅适合因环境温度和驱动电流变化引起的结温变化,且无需重新校准,能准确测量长时间点灯LED结温,具有明显的技术优势.     

基于棱镜扫描法的太阳光谱仪光谱定标

为了标定扫描式棱镜太阳光谱仪的棱镜不同转动角度对应的中心波长和光谱带宽,利用了一种棱镜扫描方法对太阳光谱仪的光谱响应函数进行测量。该方法使用固定的单色光波长,控制棱镜转动实现单色光的像在探测器位置扫描,并通过坐标映射得到响应位置的光谱响应函数。文中根据光谱响应函数的定义,推导出棱镜扫描法与单色仪波长扫描方法波长定标原理上的等效性。之后分别以532 nm固体激光器和632.8 nm氦氖激光器为光源,使用棱镜扫描法测量太阳光谱仪对应波长位置的光谱响应函数,并以单色仪波长扫描法实验作为对比。实验结果表明,对于扫描式棱镜太阳光谱仪,棱镜扫描法测量的中心波长分别为531.86和632.67 nm,其准确度优于单色仪波长扫描法测得的531.39和631.97 nm。由于不受单色仪性能的限制,前者测量的光谱带宽值也优于后者。最后以汞灯为光源使用棱镜扫描法对太阳光谱仪进行了光谱定标实验,实现了特征光谱定标法结合棱镜扫描法对中心波长及光谱带宽的标定。该方法同样可以应用于扫描式光栅光谱仪以及单色仪的光谱定标。     

基于相对光谱强度的非接触式LED结温测量法

基于一体化封装高导热铝板,利用蓝光芯片及常用YAG荧光粉,制备了大功率白光LED,并研究了其在不同结温下的光谱变化规律。发现白光LED辐射光谱在波长485 nm处辐射强度具有极小值,并且此波长的辐射强度与LED结温存在良好的线性关系,以此为依据给出了该波长辐射强度与结温的关系公式,测量了LED结温,并与正向压降法及光谱法的测量结果进行对比。实验结果显示：所提出的结温测量方法与正向压降法测量结果差距不超过2 ℃,该方法保持了正向压降法的结温测量较为准确的优点,克服了光谱法的光谱漂移过小,对测试结果带来较大误差的缺点,同样也具有光谱法的实用性强、高效直观、非接触测量、不破坏灯具结构的优点。     

光谱仪测量窄带宽光源光谱分布的七点修正法

针对光谱仪在测量窄带宽光源的光谱分布时出现的光谱变形现象,提出了一种带宽修正方法—七点修正方法。首先,利用泰勒级数和相关的导数公式,得到了七点修正公式的数学解析式;其次,用光谱线型为正弦函数的模拟光谱对七点修正法进行验证,采用正弦函数来模拟真实光谱,通过光谱仪的带宽函数计算出测量值,然后应用七点修正公式,对测量值进行修正;最后利用中心波长为365 nm的LED光源对七点修正法进行了实验验证,用双光栅单色仪来测量LED光源的光谱辐射照度,光谱仪带宽分别选为5与0.5 nm,将七点修正公式应用于测量值,得到修正值。模拟结果表明： 在选定的模拟条件下,修正后得到的中心波长处的峰值可以达到真实值的99%以上;实验结果表明： 修正后中心波长处的峰值可以达到真实值的95%以上。由模拟结果和实验结果可知,七点修正法与三点修正法和五点修正法相比,修正效果有明显提升,这种带宽修正方法可以广泛应用在光谱测量领域。     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet （UV） spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands （320 - 335 nm） using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model （Tracy）. The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.     

Design optimization of highly sensitive LSPR enhanced surface plasmon resonance biosensors with nanoholes

For breaking through the sensitivity limitation of conventional surface plasmon resonance (SPR) biosensors, novel highly sensitive SPR biosensors with Au nanoparticles and nanogratings enhancement have been proposed recently.But in practice, these structures have obvious disadvantages.In this study, a nanohole based sensitivity enhancement SPR biosensor is proposed and the influence of different structural parameters on the performance is investigated by using rigorous coupled wave analysis (RCWA).Electromagnetic field distributions around the nanohole are also given out to directly explain the performance difference for various structural parameters.The results indicate that significant sensitivity increase is associated with localized surface plasmons (LSPs) excitation mediated by nanoholes.Except to outcome the weakness of other LSP based biosensors, larger resonance angle shift, reflectance amplitude, and sharper SPR curves' width are obtained simultaneously under optimized structural parameters.     

Polymer gratings based on photopolymerization for low-order distributed feedback polymer lasers

Novel polymer distributed feedback(DFB)gratings are fabricated based on photopolymerization to reduce lasing threshold of polymer lasers.A photopolymer formulation sensitive to 355-nm ultraviolet(UV)light is proposed for the fabrication of polymer gratings and it can be used to form polymer films by spin-coating process.A very low surface-relief depth ranging from 12.5 to about 1.0 nm has been demonstrated with a refractive-index modulation of about 0.012.The experimental results indicate that such polymer gratings have promising potentials for the fabrication of low-order DFB organic semiconductor lasers.     

A novel methodology for photometric compensation of projection display on patterned screen

We propose a novel methodology based on the projector-camera (ProCam) system to address the photometric compensation issue for the projection display on the patterned screen.The patterned screen is treated as the combination of a perfect white screen and a color modulator.The perfect white screen is used to automatically and accurately characterize the ProCam system offline using the polynomial model,and the parameters of the color modulator can be efficiently recovered by employing only two gray images based on the linear reflectance model.The experimental results show that the color artifacts of the display image can be greatly improved with this methodology,which demonstrates its feasibility and validity in the photometric compensation.