Bragg resonance in a system of AsSb plasmonic nanoinclusions in AlGaAs

The optical reflection from periodic structures based on a semiconductor AlGaAs matrix containing 2D arrays of plasmonic AsSb nanoinclusions is studied. The number of nanoinclusion layers is 12 or 24, and the nominal spatial periods are 100 or 110 nm, respectively. In the experimental spectra of the optical reflection coefficient at normal incidence, we observe resonant Bragg diffraction with the main peaks at wavelengths of 757 or 775 nm (1.64 or 1.60 eV), depending on the spatial period of the nanostructure. The magnitudes of the resonance peaks reach 22 and 31% for the systems of 12 and 24 AsSb–AlGaAs layers, while the volume fraction of the nanoinclusions is much less than 1%. In the case of light incident at inclined angles, the Bragg-diffraction pattern shifts according to Wulff–Bragg’s law. Numerical simulation of the optical reflection spectra is performed using the transfer-matrix method by taking into account the spatial geometry of the structures and the resonance characteristics of the plasmonic AsSb layers.     

Optical properties of GaAs structures containing a periodic system of layers of AsSb metal nanoinclusions

The optical reflectance and transmittance of GaAs structures grown by molecular-beam epitaxy at a low temperature and periodically ??-doped with antimony or phosphorus are studied. The periodicity of the doping corresponded to the Bragg condition for light with a free-space wavelength of ??1.4 ??m. The structures were subjected to annealing at different temperatures in the range from 400 to 760°C. Annealing brings about the formation of a three-dimensional chaotic system of As metal nanoinclusions (quantum dots) inside the GaAs epitaxial layer as well as the formation of two-dimensional layers of AsSb metal nanoinclusions (quantum dots) on the Sb ?? layers. The P ?? layers have no significant effect on the formation of the system of As nanoinclusions. No features that might be attributed to a disordered three-dimensional system of As nanoinclusions are detected in the optical transmittance and reflectance spectra. The periodic system of two-dimensional layers of AsSb metal nanoinclusions manifests itself as a resonance peak in the optical reflectance and absorption spectra. The resonance reflectance and absorption coefficient increase, as the dimensions of the AsSb nanoinclusions increase. The resonance wavelength depends on the angle of light incidence in accordance with Bragg??s law.     

Resonant Optical Reflection from AsSb–AlGaAs Metamaterials and Structures

The optical reflection in periodic structures based on a semiconductor AlGaAs matrix containing two-dimensional arrays of plasmonic AsSb nanoinclusions was studied. The number of periods was 12 or 24. The spatial period was near 110 nm in both cases. In the experimental optical reflection spectra at normal incidence we observed resonant Bragg diffraction with the main peaks at wavelengths of 757 or 775 nm, depending on the spatial period of the nanostructure. The magnitudes of the resonance peaks reached 19 and 31% for the systems of 12 and 24 AsSb–AlGaAs layers, while the volume fraction of the nanoinclusions was much less than 1%. In the case of light incident at inclined angles, the Bragg-diffraction pattern shifted according to Wulff-Bragg’s law. Numerical calculations of the optical reflection spectra were performed using the transfer-matrix method by taking into account the spatial geometry of the structures and the resonance characteristics of the plasmonic AsSb layers.     

Structural and optical properties of InAlN/GaN distributed Bragg reflectors

Structural and optical properties of InAlN/GaN distributed Bragg reflectors grown by MOCVD on sapphire substrates are studied. The influence of growth conditions and thicknesses of the InAlN layers on structural properties of distributed Bragg reflectors is studied. It is shown that optimization of the conditions of epitaxial growth makes it possible to design InAlN/GaN distributed Bragg reflectors with a reflectance of more than 99% and a reflection maximum in the wavelength range of 460–610 nm.     

Wide Dynamic Range in Tunable Electrochromic Bragg Stacks from Doped Semiconductor Nanocrystals

Electrochromic properties can be enhanced by constructing photonic architectures, in which the reflectance contributes to optical modulation along with the intrinsic dynamic absorptivity of the material. However, optimization of reflectance is challenging without a rational design approach. Here, electrochemically tunable Bragg reflectors are demonstrated that are tuned to be highly transparent in the “off” state, achieving synergistic dynamic optical modulation of absorption and reflection in the visible and near‐infrared range. These Bragg stacks are composed of alternating doped semiconductor nanocrystal (NC) layers of 5 nm sized oxygen vacancy‐doped WO_3?x and 15 nm sized 0.4 at% Sn:In₂O₃ NCs. Combining judicious NC selection and processing optimization with guidance from optical simulations, optimized Bragg stacks are implemented for electrochromic window applications. NCs with high absorption coefficients are essential for strong transmission modulation, though this characteristic limits the dynamic range of the Bragg reflectance. Optimal reflectance modulation including a highly transparent “off” state is confirmed with in situ reflectance and transmittance measurement. More broadly, ligand‐stripped NCs can enable fabrication of complex device architectures on low‐cost flexible substrates. These results guide the design rules for accessing different types of doped semiconductor NC‐based tunable Bragg stacks, an exemplary photonic structure, over a broad wavelength range.     

Control of Bragg grating resonant wavelength through its dependenceon the effective index of a waveguide

Fabrication tolerances for control of the Bragg wavelength of gratings in waveguides are studied. Techniques are demonstrated to hold the period of the grating constant to ±0.04 nm over the majority of the exposed wafer area, and ridge waveguides fabricated with standard thin film process equipment are found to have Bragg wavelengths constant to within ±0.2 nm. Additionally, adjacent ridges with differing widths are written in a single photomask/etch process step and found to controllably shift the Bragg wavelength over a 10-20-nm band suitable for a distributed Bragg reflector (DBR) laser array or a monolithic comb filter for wavelength division multiplexing (WDM) filtering/routing arrays     

复合布拉格反射镜高亮度AlGaInP发光二极管

采用光学薄膜理论中干涉矩阵模型计算了峰值波长为630nm的AlGaInP红光LED的Al0.6Ga0.4As/AlAs材料的常规DBR和复合DBR的反射谱特性,用LP-MOCVD方法生长了模拟设计的DBR结构,测量了其白光反射谱,实验与模拟结果基本符合.制备了采用Al0.6Ga0.4As/AlAs复合DBR的LED器件,未封装输出光功率为2.3mW,外量子效率为5.6%,发光效率可达12 lm/W,比常规DBR器件提高了35%.验证了复合DBR与常规DBR相比,可以大幅度提高AlGaInP红光LED的出光效率.     

InAlGaAs bulk micromachined tunable Fabry–Pérot filter for dense WDM systems

In this work we report on micromechanically tunable Fabry–Pérot filter concepts for wavelength division multiplexing (WDM) systems. The optical resonator is designed for a cavity length around 30 μm in order to increase the filter selectivity while relaxing the demands on the required mirror reflectance. The introduction of micromechanical actuators, utilizing electrothermal and electrostatic principles, allows wavelength tuning of the filter over a range of more than 40 nm in the 1.55 μm wavelength regime. The movable Bragg mirror, designed as suspended membrane and fabricated with an InP bulk-micromachining technology, consists of a molecular beam epitaxy-grown InAlGaAs quarter-wavelength multilayer stack. The influence of micromechanical actuation and the effect of intrinsic mechanical stress on the mirror deformation has been investigated systematically to optimize the optical filter performance. Filter losses induced by the light absorption within the epitaxial Bragg mirror have been minimized using a highly doped InGaAs/InAlAs composition. Furthermore, low-loss Fabry–Pérot filters have been fabricated using InAlGaAs/InAlAs Bragg mirrors. The measured full-width at half-maximum (FWHM) is 0.24 nm and a filter insertion loss of 2.8 dB has been observed. The FWHM is kept below 0.35 nm over an entire tuning range of 40 nm for an actuation power of 1.3 mW. The bulk-micromachining technology presented here is open for the future development of WDM components, e.g. tunable receivers or laser diodes.     

808nm InGaAlAs垂直腔面发射激光器的结构设计

为实现垂直腔面发射半导体激光器(VCSEL)在808 nm波长的激射,对VCSEL芯片的整体结构进行了设计。基于应变量子阱的能带理论、固体模型理论、克龙尼克-潘纳模型和光学传输矩阵方法,计算了压应变InGaAlAs量子阱的带隙、带阶、量子化子能级以及分布布拉格反射镜(DBR)的反射谱,从而确定了量子阱的组分、厚度以及反射镜的对数。数值模拟的结果表明,阱宽为6 nm的In0.14Ga0.74Al0.12As/Al0.3Ga0.7As量子阱,在室温下激射波长在800 nm左右,其峰值材料增益在工作温度下达到4000 cm-1;渐变层为20 nm的Al0.9Ga0.1As/Al0.2Ga0.8As DBR,出光p面为23对时反射率为99.57%,全反射n面为39.5对时反射率为99.94%。设计的顶发射VCSEL结构通过光电集成专业软件(PICS3D)验证,得到室温下的光谱中心波长在800 nm处,证实了结构设计的正确性。     

Thermal evolution of the morphology, structure, and optical properties of multilayer nanoperiodic systems produced by the vacuum evaporation of SiO and SiO2

The alternate vacuum evaporation of SiO and SiO₂ from separate sources is used to produce amorphous a-SiO _x /SiO₂ multilayer nanoperiodic structures with periods of 5–10 nm and a number of layers of up to 64. The effect of annealing at temperatures T _a = 500–1100°C on the structural and optical properties of the nanostructures is studied. The results of transmission electron microscopy of the samples annealed at 1100°C indicate the annealing-induced formation of vertically ordered quasiperiodic arrays of Si nanocrystals, whose dimensions are comparable to the a-SiO _x -layer thickness in the initial nanostructures. The nanostructures annealed at 1100°C exhibit size-dependent photoluminescence in the wavelength range 750–830 nm corresponding to Si nanocrystals. The data on infrared absorption and Raman scattering show that the thermal evolution of structural and phase state of the SiO _x layers with increasing annealing temperature proceeds through the formation of amorphous Si nanoinclusions with the subsequent formation and growth of Si nanocrystals.     

Spectral characterization of fiber Bragg grating with etched fiber cladding

A new method is presented to tune Bragg wavelength slightly by using hydrofluoric acid to etch fiber cladding.The spectral characteristics before and after etching and the change properties of Bragg wavelength are studied.Cladding modes are reduced during the etching process.High-order cladding modes are converted into radiation modes,and energy of cladding modes is coupled to the outside.As the cladding radius decreases,the Bragg wavelength shifts to longer direction.Experimental results show that this method can tune Bragg wavelength slightly,and the tunable range is 0.002-0.120 nm.     

Design and Fabrication of AlGaN-Based Resonant-Cavity-Enhanced p-i-n UV PDs

AlGaN-based resonant-cavity-enhanced (RCE) p-i-n photodetectors (PDs) for operating at the wavelength of 330 nm were designed and fabricated. A 20.5-pair AlN/Al_0.3Ga_0.7N distributed Bragg reflector (DBR) was used as the back mirror and a 3-pair AlN/Al_0.3Ga_0.7N DBR as the front one. In the cavity is a p-GaN/i-GaN/n-Al_0.3Ga_0.7N structure. The optical absorption of the RCE PD structure is at most 59.8% deduced from reflectance measurement. Selectively enhanced by the cavity effect, a response peak of 0.128 A/W at 330 nm with a half-peak breadth of 5.5 nm was obtained under zero bias. The peak wavelength shifted 15 nm with the incident angle of light increasing from 0deg to 60deg.     

Monolithic oxide-confined multiple-wavelength vertical-cavitysurface-emitting laser arrays with a 57-nm wavelength grading rangeusing an oxidized upper Bragg mirror

Monolithic, oxide-confined, multiple-wavelength vertical-cavity surface-emitting laser arrays with a very large periodic, wavelength grading span of 57 nm (from 968 to 1025 nm) have been achieved under room temperature, continuous-wave operation, with threshold currents of 4.5 mA±1.5 mA. Almost linear wavelength grading is achieved by organometallic vapor phase epitaxial growth on a patterned substrate. An extended wavelength range is achieved by minimizing the optical loss dispersion by scaling the growth rate of all the epilayers and using a selectively-oxidized upper DBR mirror with a flattened optical reflectance spectrum, plus the higher differential optical gain provided by compressively-strained In_0.2Ga_0.8As-GaAs quantum wells     

光纤光栅滤波器在水下光通信系统中的应用

文章提出了一种基于光纤Bragg光栅(FBG)的用于水下光通信系统接收机前站的滤光方案，并采用耦合模理论分析了FBG的传输特性，数值模拟了Bragg波长为532nm、窄带、高反射率的均匀周期高斯切趾FBG。     

Highly efficient and high transmittance semitransparent polymer solar cells with one-dimensional photonic crystals as distributed Bragg reflectors

We demonstrate that one-dimensional photonic crystals as distributed Bragg reflectors can effectively improve the performance of semitransparent polymer solar cells (PSCs) based on the blend of P3HT:ICBA. The one dimensional distributed Bragg reflectors (1D DBRs) are composed of N pairs of WO₃/LiF which are thermally evaporated on Ag anode. Due to its photonic bandgap, 1D DBRs can reflect the light totally back into the PSCs when the high reflectance range of 1D DBRs is well matched with absorption spectrum of the active layer. A maximum power conversion efficiency (PCE) of 4.12%, a highest transmittance of 80.4% at 660 nm and an average transmittance of 55.6% in the wavelength range of 600–800 nm are obtained in the case of N = 8, corresponding enhancement of 24.1% in PCE when compared with the device without the 1D DBRs.     

Superconducting states of lead nanoinclusions in the stoichiometric PbTe matrix

Phase states of lead nanoinclusions in stoichiometric lead telluride in magnetic fields from 0 to 1 kOe are studied in the region of temperatures below the temperature of transition of lead to superconducting state (T = 1.7?6.5 K). It is shown that the lead nanoinclusions behave like type-I superconductors. The sizes of lead nanoinclusions that are in the superconducting state at 1.7 K are no smaller than 200 nm. The experimental temperature dependence of the diamagnetic additional component can be interpreted in the context of a model that takes into account the existence of an “intermediate” superconducting state caused by the geometric parameters of lead nanoinclusions.     

A unidirectional output optical frequency conversion device with anasymmetric-κ DBR structure

A novel optical frequency conversion device that successfully demonstrates optical frequency conversion and unidirectional transmission of optical signals has been designed and fabricated. The device is composed of a gain region and saturable absorber region with monolithically integrated distributed Bragg reflector (DBR) mirrors with different coupling coefficients. The device structure is optimized to achieve three functions: 1) unidirectional light output, 2) converted-light wavelength tuning, and 3) optically triggered optical frequency conversion. The output power of converted light from the light input-end facet of the device is 30 dB smaller than that from the output-end facet, and the converted light wavelength can be scanned over 4 nm without a bias current to the input-end DBR region, and it is widened to 7.8 nm by injecting current to that region. The device emits converted light only when light input is injected and optical signals are unidirectionally transmitted, and its response frequency is estimated to be 0.8 GHz     

非均匀混浊介质多光谱反射成像的仿真与实验研究

提出了一种采集高动态范围多光谱反射率的实验方 法,并通过测量5个非均匀混浊介 质样品在全视场照射条件下和500~940nm波长范围内的反射图像数据 证明了本方法的可行性。同时 采用在辐射传输理论框架下建立的并行iMC蒙特卡罗仿真模型,通过使用漫反射标准板准确 记录入射光 束能量分布,输入至iMC仿真程序,获得可与反射率测量数据相比较的反射率仿真图像数据 。本文工 作为求解根据反射率确定非均匀混浊介质样品的光学特征与几何参数的逆问题提供了实验与 理论工具。     

Properties of Bragg reflectors composed of isotropic dielectriclayers cladded with birefringent media

The reflectance of an asymmetric periodic dielectric stack comprising a periodic stratified dielectric film bounded by a positive birefringent uniaxial medium on one side and by an isotropic dielectric material on the other side are calculated by using the 4×4 transfer matrix formalism. The results show that the values of the reflectance have a strong dependence on the structure parameters, the incident polarization, and the optical axis orientation. The dependence of the reflectance on the optical axis orientation suggests that this effect could be used for the fabrication of a new kind of Bragg reflector     

The wide-angle perfect absorption based on the optical Tamm states

Based on the optical Talnm states （OTSs）, a metal-distributed Bragg reflector （DBR） structure is presented. The existence of optical Tamm states is demonstrated by the dip of reflectivity spectrum in photonic band gap. The properties of the optical Tainm states are investigated by applying the transfer matrix method. The effects of different metal thicknesses and angles on the absorption are studied by numerical simulation. The wide-angle perfect absorption appears when the metal thickness is 39 nm.