感光性树脂应用于发光二极管平面自适应封装技术

采用感光性树脂+荧光粉进行了发光二极管平面自适应涂覆技术,实现了白光发光二极管荧光粉涂层的平面化工艺,使器件出光的亮度、空间色度均匀性较之传统封装工艺器件有了明显的改善,光斑及单管间色度、亮度偏差均小于6%.综合聚乙烯醇的感光和硅胶的物化、光学性能,在粉浆法工艺中采用乳化技术,实现了聚乙烯醇+硅树脂的多相结构的荧光粉平面涂层,有助于进一步改善荧光粉层的物化性能,而多相涂层有效折射率的提高更有利于提高器件的整体出光效率.由于感光性树脂其感光波长覆盖范围非常广,另外还可以通过光增感等技术使其感光波长范围变得其与发光二极管的发光波长相匹配,这样,对于各种荧光粉转化的白光发光二极管都可以实现平面涂层技术.由于大部分感光材料对紫外部分的吸收更强烈,所以对于紫外+三基色荧光粉的传统灌封技术将会得到明显的改善.     

感光性树脂应用于发光二极管平面自适应封装技术

采用感光性树脂+荧光粉进行了发光二极管平面自适应涂覆技术,实现了白光发光二极管荧光粉涂层的平面化工艺,使器件出光的亮度、空间色度均匀性较之传统封装工艺器件有了明显的改善,光斑及单管间色度、亮度偏差均小于6%.综合聚乙烯醇的感光和硅胶的物化、光学性能,在粉浆法工艺中采用乳化技术,实现了聚乙烯醇+硅树脂的多相结构的荧光粉平面涂层,有助于进一步改善荧光粉层的物化性能,而多相涂层有效折射率的提高更有利于提高器件的整体出光效率.由于感光性树脂其感光波长覆盖范围非常广,另外还可以通过光增感等技术使其感光波长范围变得其与发光二极管的发光波长相匹配,这样,对于各种荧光粉转化的白光发光二极管都可以实现平面涂层技术.由于大部分感光材料对紫外部分的吸收更强烈,所以对于紫外+三基色荧光粉的传统灌封技术将会得到明显的改善.     

白光数码管色坐标位置对光通量的影响

应用荧光粉转换法制备的白光数码管作为实验对象,利用同一批次蓝光芯片,调整荧光粉和环氧树脂不同混合比例,研究白光数码管色坐标位置和光通量关系.在20mA额定工作电流,环境温度25℃,湿度54％条件下,对被测白光数码管进行光通量和色坐标的测试,实验结果表明荧光粉比例增加致使白光光谱中黄绿光部分的发光能量增强,色坐标由(0.331,0.369)到(0.313,0.345)变化,光通量的值逐渐增加,这一实验结果和理论计算结果的发展趋势基本一致.在测试样品中最大光通量和最小光通量的值相差24.49mlm.研究结果表明利用色度学原理,调整荧光粉和环氧树脂混合比例,可以在一定程度上提高输出光通量.     

大功率LED荧光粉胶涂覆流动铺展的实验研究

为实现蓝光LED(LAght emitting diode)芯片向白光LED照明的转化,大功率LED封装工艺流程中存在一个关键的环节——荧光粉涂覆,即通过点涂方式将荧光粉硅胶涂覆于LED芯片周围.荧光粉硅胶涂覆工艺是一个两相流动过程,它直接决定了荧光粉硅胶层的几何形貌及物理特性,并影响LED最终的光学和热学性能;因此对其中流动过程物理机制的理解有利于提升荧光粉涂覆质量,实现高性能LED产品。基于以高速摄像机为核心的光学实验平台,对荧光粉硅胶在平坦基板表面涂覆流动铺展过程的形貌进行了捕捉,并研究了涂覆高度、荧光粉浓度和基板表面温度对流动过程的影响.实验结果表明,依据相对铺展速度的变化特性可以将荧光粉涂覆流动过程分为撞击阶段、铺展阶段和稳定成形阶段;涂覆高度、荧光粉浓度、基板表面温度的改变会对流动铺展不同阶段的接触线长度和相对铺展速度dL/(D·dt)造成影响,基板温度的改变还会影响到最终接触线长度。     

基于Mie散射理论的白光发光二极管荧光粉散射特性研究

基于Mie散射理论,对大功率发光二极管封装中荧光粉的光激发、吸收、散射等作用进行数值模拟,仿真计算在不同白光色温时前后向散射光的强度比例,研究了荧光粉的颗粒大小对白光发光二极管最大光通量的影响.对保型荧光粉涂覆结构中不同直径荧光粉颗粒和不同色温时的光效进行了分析,还分析了同样色温下不同荧光粉颗粒直径、涂层的厚度对白光发光二极管出光的空间色温分布均匀性的影响.研究中所采用的器件激发光谱和发射光谱都为材料的实测光谱,而并非假设的单一光谱.研究表明:在采用保型荧光粉涂覆结构的前提下,当荧光粉颖粒直径为0.5μm时能使发光二极管光通量达到最大;荧光粉颗粒越小,发光二极管空间色温分布均匀性越好;对给定的封装结构,荧光粉涂层厚度为0.8 mm时空间色温分布均匀性最佳.     

荧光粉封装方式对多芯片阵列LED封装效率的影响

针对荧光粉封装的多芯片LED,用Monte Carlo光线追迹的方法仿真光线在蓝光芯片和荧光粉中的传播,并分析了荧光粉封装方式对多芯片阵列LED封装效率的影响.结果表明:随着荧光粉层和芯片之间的距离增大,保型涂覆的LED封装效率先增加后减小,最大封装效率为59%;平面涂覆的LED在芯片间距为0.2mm、荧光粉层和芯片之间的距离为0.28mm时,封装效率为77.183%;荧光粉层的曲率半径对封装效率的影响较小.     

半导体激光激发荧光粉转换白光照明系统设计

单管蓝光半导体激光器功率相对较低,为了获得高功率激光,利用多单管光纤耦合技术实现10 W蓝光激光输出,输出的激光激发荧光粉片合成的白光光源作为汽车远光灯光源。根据汽车照明法规要求设计了汽车远光灯照明系统并详述了抛物面反光罩、双凹透镜和荧光粉片的光学结构及对反光罩曲线参数、双凹透镜和荧光粉片的放置位置对光源色温均匀性及照度的影响。模拟设计了顶端19 mm×31.6 mm椭圆形开孔、底部直径5 mm圆形开孔、高60 mm的椭圆抛物面反光罩,荧光粉片置于距反光罩底部15 mm处时,在距光源25 m处的接收面上得到了5 m×12 m的椭圆光斑,白光光源的光通量为1 025 lm,中心色温为5 880 K,中心色坐标为(x=0.322 6,y=0.369 2),该汽车远光灯照明系统满足汽车照明法规要求。     

应用点胶压盖技术提高白光数码管发光效率

由于采取蓝光芯片与黄色荧光粉YAG:Ce3+复合产生的空封白光数码管存在光通量低的缺点,提出采用点胶技术,利用环氧树脂折射率高可以增加数码管光子逸出数、光衰效应低等优点,提高数码管的发光强度和发光效率.实验测试了各20个空封贴片白光数码管、不封装蓝光数码管和点胶压盖白光数码管,数码管基板固晶蓝光芯片主波长为460-462.5nm,使用透明环氧树脂胶、YAG:Ce3+黄色荧光粉,在20mA正向电流作用下,测试光通量、发光强度、发光效率3个指标,获得3种数码管的曲线比较图.结果显示,应用点胶压盖技术数码管的发光强度和发光效率比空封数码管分别提高60.94％和46.54％,测试结果较好地显示了应用点胶压盖技术数码管的优点.     

大功率LED荧光粉硅胶点涂工艺的实验及模拟研究

为得到白光LED照明产品,大功率LED封装工艺流程中,荧光粉硅胶混合物需通过点涂等方式涂覆于LED芯片上。荧光粉硅胶涂覆工艺的本质是一个两相流动过程,它直接决定了荧光粉硅胶层的几何形貌及物理特性,并最终影响LED产品的性能,因此准确描述这一成形过程特别重要。基于高速摄像机的实验平台,通过实验捕捉荧光粉硅胶形貌的动态成形过程。应用格子Boltzmann方法,建立荧光粉硅胶流动模型,对荧光粉硅胶点涂工艺进行模拟,得到荧光粉硅胶点涂成形过程及最终形貌。结果表明:荧光粉硅胶点涂工艺中,存在撞击、铺展及稳定成形三个阶段;格子Boltzmann方法能够正确模拟荧光粉硅胶点涂这一流动过程,并能够预测荧光粉硅胶层的最终形貌,为后续研究中对点涂工艺的优化提供了理论基础。     

双层荧光粉涂覆对COB封装LED出光的影响

为了提高LED出光量，基于传统的荧光粉涂覆设计了一种双层荧光粉涂覆结构。通过对上下涂覆层浓度及上层涂覆量的研究，探究双层涂覆结构对COB封装LED出光的影响。结果表明在通电电流为440 mA时，可在实验中实现15 W的COB封装结构的白光LED:涂覆单一黄色荧光粉，上下层胶粉比为14.2～28且上层涂覆体积为下层的0.8倍时，COB封装LED的光通量为2 179 lm，光效可达145.3 lm/W，显指为63，出光量最大提升为7.82%；荧光粉调整为黄绿粉和红粉的配合使用后，最终实现色温、光效及显指分别为4 854 K、129.7 lm/W和81.2。因此，双层荧光粉涂覆结构可以提高COB封装LED的光学性能，对实际生产有一定的应用价值。     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.