Light-extraction enhancement and directional emission control of GaN-based LED with transmission grating

We theoretically analyze the improvement in light extraction efficiency (LEE) of GaN-based LEDs with transmission grating. Light propagation and extraction was simulated using the finite-difference time-domain (FDTD) method for conical, cylindrical, and hemispherical grating. The simulations show that the use of transmission grating leads to increase in the LEE of GaN-based LEDs. The enhancement in LEE is attributed to the decrease in the Fresnel reflection and the effective increase in the photon escape cone. The maximum LEE enhancement of 2.3 times was achieved by employing hemispherical grating. The directional emission pattern converged by employing conical grating.     

Effect of grating on IR LED device performance

The electroluminescence in the range of 3–4.5 μm and 6–10 μm from a Sb-based type II interband quantum cascade structure is reported. We measured the light emission from the top surface of the LED device with different grating structures. We used different etch depths for the grating formation. The light–current–voltage (LIV) characteristics measured at both room and cryogenic temperatures show that the device with 45° angle grating and 1.0 μm deep etch onto the GaSb surface has the highest emission power.     

Low threshold voltage light-emitting diode in silicon-based standard CMOS technology

Low-voltage silicon(Si)-based light-emitting diode(LED) is designed based on the former research of LED in Si-based standard complementary metal oxide semiconductor(CMOS) technology.The low-voltage LED is designed under the research of cross-finger structure LEDs and sophisticated structure enhanced LEDs for high efficiency and stable light source of monolithic chip integration.The device size of low-voltage LED is 45.85×38.4(μm),threshold voltage is 2.2 V in common condition,and temperature is 27 ℃.The external quantum efficiency is about 10-6 at stable operating state of 5 V and 177 mA.     

有源层受主浓度对InGaAsP/InP双异质结发光管特性的影响

本文研究了有源层受主浓度(Pa)对InGaAsP/InP双异质发光管特性的影响。有源层受主浓度Pa≈2×1017～1×1018cm-3的器件,具有较大的光输出功率P≥1mW;截止频率fĉ为30～80MHz,并且有正常的Ⅰ-Ⅴ特性。有源层浓度高于上述浓度的器件,光输出功率降低,并且具有异常的Ⅰ-Ⅴ特性。在器件光谱半宽△λ=(λ2/1.24)nkT关系式中,n值是有源层受主浓度(Pa)的函数。上述结果表明:有源层受主浓度(Pa)是影响器件特性的重要因素之一。     

布儒斯特角附近的透射光栅传输特性

 减小光栅表面的反射率以得到更高的衍射效率是目前光栅设计与制造中需要解决的重要问题之一。提出利用偏振光沿布儒斯特角入射时具有的特性来实现降低光栅表面反射率的方案,介绍了这种方案的物理模型,并利用严格耦合波分析法进行了模拟计算。计算结果显示,对入射光为TM偏振,波长0.35 μm,当光栅周期较长为2.80 μm时,以布儒斯特角入射的光波,它的表面反射被大大抑制;当光栅周期较短为0.21 μm时也有类似的结论,并且透射光的一级衍射效率极大值出现在刻槽深度为3.50 μm处附近,衍射效率大于95%。     

A broadband grating-coupled silicon nitride waveguide for the mid-IR: characterization and sensitive measurements using an external cavity quantum cascade laser

We present the design and fabrication of a single-mode slab waveguide structure for mid-infrared spectroscopy optimized for broadband coupling. The sensor uses grating couplers for robust off-axis coupling and a silicon nitride guiding layer for mechanical robustness. An external cavity quantum cascade laser-based transmission method is introduced for characterizing the structure’s broadband coupling behavior. Light from an external cavity quantum cascade laser with a spectral range of 0.5 μm around 6 μm was coupled into the waveguide without the need for moving parts. First spectra taken with this sensor are presented.     

Improved light extraction efficiency of GaN-based LEDs with patterned sapphire substrate and patterned ITO

To improve the light extraction efficiency of GaN-based light-emitting diodes (LEDs), periodic semisphere patterns with 3.5 μm width, 1.2 μm height, and 0.8 μm spacing were formed on sapphire substrate by dry etching using BCl₃/Cl₂ gas chemistry. The indium tin oxide (ITO) transparent conductive layer was patterned by wet etching to reduce the total internal reflection existing along between p-GaN, ITO, and air. At 350 mA injection current, the high power LED by integrating patterned sapphire substrate with patterned ITO technology exhibited a 36.9% higher light output power than the conventional LEDs.     

(2+1)维光折变波导阵列的制作

对四个点光源进行光学傅里叶变换,在自散焦光折变晶体中成功地制作了6μm×6μm间隔的并行(2+1)维阵列波导300余条,并证明了阵列波导实质上是二维体相位栅.实验研究了点光源间距、点光源尺寸及写入时间对阵列波导制作的影响,并分析了在自散焦光生伏打光折变介质中形成阵列波导的原理.     

电致发光的完全悬空超薄硅衬底氮化镓基蓝光LED器件的制备与表征

为提升硅衬底氮化镓基LED(发光二极管)器件的光电性能和出光效率,本文提出了一种利用背后工艺实现的悬空薄膜蓝光LED器件.结合光刻工艺、深反应离子刻蚀和电感耦合等离子体反应离子刻蚀的背后工艺,制备了发光区域和大部分正负电极区域的硅衬底完全掏空,并减薄大部分氮化镓外延层的悬空薄膜LED器件.对悬空薄膜LED器件进行三维形...     

软X射线位相型金透射光栅的设计与制作

根据衍射光栅的标量理论,计算并讨论了金透射光栅在软X波段衍射效率对光栅厚度和占宽比的依赖关系.结果表明,选择合适的光栅槽深和占宽比,高达 21.9%的衍射效率可能被获得,远高于振幅型光栅的+1级衍射效率10.14%.通过全息光刻与电镀转移技术制作的位相型金透射光栅由300nm的聚酰亚胺薄膜支撑,光栅槽深200nm,占宽比为0.55,周期为1μm,面积为20mm×5mm.在国家同步辐射装置上,测得其+1级透射衍射效率在波长λ=7.425nm时获得最大值,约为16%. 关键词： 透射位相光栅 全息光刻 电镀     

Sm-activated gadolinium molybdate: an intense red-emitting phosphor for solid-state lighting based on InGaN LEDs

Sm³⁺-activated gadolinium molybdate, Gd₂(MoO₄)₃:Sm³⁺ red-emitting phosphor was prepared by conventional solid-state method. The structure, morphology, and luminescent properties of these powder samples have been investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and fluorescent spectrophotometry, respectively. The as-obtained phosphor has a monoclinic structure with single crystalline phase. Its mean particle size is about 6-8 μm with pseudo-pompon shape and large surface area, which is suitable for manufacture of white LEDs. The phosphor can be efficiently excited by incident light of 348-445 nm, well matched with the output wavelength of a near-UV InGaN-based chip, and re-emits an intense red light peaking at 650 nm. By combing this phosphor with a 405 nm-emitting InGaN chip, a red LED was fabricated, so that the applicability of this novel phosphor to white LEDs was confirmed. It is considered to be an efficient red-emitting conversion phosphor for solid-state lighting based on InGaN LEDs.     

Enhanced transmission through nano-aperture on a tapered metallic substrate

The optical transmission and distribution through a subwavelength slit on a tapered metallic substrate was investigated. By using a 45° tapered structure rather than a traditional metallic plate, a 6-fold transmission enhancement could be achieved. This is due to the asymmetrical excitation of surface waves and the matching of propagation constants between the surface waves and slit waveguide. In addition, by patterning surface corrugations in the exit plane, the beam could be focused. By tuning the period of the surface corrugations, we were able to adjust the focal length. For an input wavelength of 0.5 μm, the focal point could be kept within 0.6 μm with a focal length extending from 0.5 μm to 2.5 μm and a grating period ranging from 0.5 μm to 0.6 μm.     

全息技术制作二维光子晶体蓝宝石衬底提高发光二极管外量子效率

为了提高GaN基发光二极管(LED)的外量子效率,在蓝宝石衬底制作了二维光子晶体.衬底上的二维光子晶体结构采用激光全息技术和感应耦合等离子体(ICP)干法刻蚀技术制作,然后采用金属氧化物化学气相沉积(MOCVD)技术在图形蓝宝石衬底(PSS)上生长2μm厚的n型GaN层,4层量子阱和200nm厚的p型GaN层,形成LED结构.衬底上制作的二维光子晶体为六角晶格结构,晶格常数为3.8μm,刻蚀深度为800nm.LED器件光强输出测试结果显示,在PSS上制作的LED(PSS-LED)的发光强度普遍高于蓝宝石平 关键词： 全息 发光二极管 图形蓝宝石衬底 外量子效率     

GaAs/GaAlAs双异质结发光管退化特性的研究

本文研究了GaAs/GaAlAs双异质结发光管的退化特性。有快、慢二种退化类型。器件的慢退化是由于有源区有暗缺陷(DSD)产生和长大,引起光功率下降。文中研究了老化过程中I-V特性和I-P特性与EL图象的变化规律,并与相同结构的InP/InGaAsP双异质结发光管的退化特性进行了比较,结果表明:它们有着不同的退化机理。     

双重复合式液晶/聚合物电调谐光栅的制备

采用一次性全息曝光的方法同时在样品上制备了周期分别为1μm和4μm,衍射效率电场可调的双重复合式液晶/聚合物光栅.使用He-Ne激光器对复合光栅的衍射特性进行了实验研究,发现光栅存在两个1级衍射极强峰.对峰值衍射效率的测定结果表明,周期1μm的光栅衍射效率为90%,周期4μm的光栅,60%.结合耦合波理论计算了周期1μm和4μm光栅的衍射效率理论值,分别为92.57%和63.68%.实验结果与理论值符合得非常好.对电光特性的测试表明该复合光栅内的两套子光栅的驱动电压V₉₀关键词： 光栅 液晶     

High channel-count comb filter based on multi-concatenated sampled chirped fiber Bragg gratings

A high channel-count comb filter based on multi-concatenated sampled chirped fiber Bragg gratings(MC-SCFBGs) is proposed and optimally designed by using several chirped gratings with different fundamental grating periods,instead of non-grating sections of SCFBGs.The numerical simulations of the reflection spectra show that the channel spacing and the channel bandwidth in MC-SCFBGs are smaller than those in multi-concatenated chirped fiber Bragg gratings(MC-CFBGs) and that the spectral bandwidth of MC-SCFBGs can be greatly broadened by increasing the cascade number of the grating sections in each sampling period.     

Efficient excitation and amplification of the surface plasmons

One dimensional (1D) grating has been fabricated (using focused ion beam) on 50 nm gold (Au) film deposited on higher refractive index Gallium phosphate (GaP) substrate. The sub-wavelength periodic metal nano structuring enable to couple photon to couple with the surface plasmons (SPs) excited by them. These grating devices provide the efficient control on the SPs which propagate on the interface of noble metal and dielectric whose frequency is dependent on the bulk electron plasma frequency of the metal. For a fixed periodicity (Λ = 700 nm) and slit width (w = 100 nm) in the grating device, the efficiency of SPP excitation is about 40% compared to the transmission in the near-field. Efficient coupling of SPs with photon in dielectric provide field localisation on sub-wavelength scale which is needed in Heat Assisted Magnetic recording (HAMR) systems. The GaP is also used to emulate Vertical Cavity Surface emitting laser (VCSEL) in order to provide cheaper alternative of light source being used in HAMR technology. In order to understand the underlying physics, far-and near-field results has been compared with the modelling results which are obtained using COMSOL RF module.Apart from this, grating devices of smaller periodicity (Λ = 280 nm) and slit width (w = 22 nm) has been fabricated on GaP substrate which is photoluminescence material to observe amplified spontaneous emission of the SPs at wavelength of 805 nm when the grating device was excited with 532 nm laser light. This observation is unique and can have direct application in light emitting diodes (LEDs).     

Colossal light-induced refractive-index modulation for neutrons in holographic polymer-dispersed liquid crystals

We report strong diffraction of cold neutrons from an only 30 micro m thick holographic polymer-dispersed liquid crystal (H-PDLC) transmission grating. The light-induced refractive-index modulation for neutrons is about 10(-6), i.e., nearly 2 orders of magnitude larger than in the best photo-neutron-refractive materials probed up to now. This makes H-PDLCs a promising candidate for fabricating neutron-optical devices.     

非相干光纤激光组束系统耦合效率的优化分析

单光束耦合效率是决定非相干组束系统输出功率的关键,它受到透镜焦距、光栅周期和光斑半径等参数的影响。为了寻求较为优化的系统参数,通过理论分析和仿真研究,结果表明对于中心波长1060nm的光纤激光,应当选择透镜焦距20cm,光栅周期5μm,并且需要将光斑半径控制在50μm左右。通过反解光栅频率及组束波长带宽的第一个零点来选择组束阵列宽度一定条件下较优的光栅参数。通过理论分析和数值计算,结果表明较小的光栅频率和光栅厚度对提高衍射效率是有利的。     

三角形谱啁啾光纤光栅的制备及其在光纤无线单边带调制系统中的应用

本文涉及一种三角形谱啁啾光纤光栅的制备以及其在光纤无线(radio over fiber,RoF)单边带调制系统中的应用.基于相位掩模法和变速度折射率调制,实验制备了底部变化范围1.9 nm、透射深度0—15 dB的三角形谱啁啾光纤Bragg光栅,利用其透射谱具有较大负向斜边,研究了其在RoF系统中的应用.方案仅使用一个三角形谱光纤光栅,实现了以下两种功能: 1)双边带调制信号到单边带调制信号转换; 2)降低信号的载波边带比(carrier-to-sideband ratio,CSR),提高接收灵敏度.并 关键词： 光纤通信 微波光子 光纤布拉格光栅 单边带调制