Simulation and properties of Erbium-Doped Distributed Bragg Reflectors (ED-DBRs) and Fiber Bragg Gratings (ED-FBGs)

The structure of an active Erbium-Doped Distributed Bragg Reflector (ED-DBR) and a Fiber Bragg Grating (ED-FBG) is simulated using a rigorous transmission line model and an approximate version of the coupled-mode theory, respectively. The basic calculation steps and assumptions of the proposed simulation models are described and the key parameters that determine the devices’ reflection characteristics are in detail discussed. By applying the proposed transmission line model, numerical results are provided for both spectral reflectivity and transparency response for an active-slab DBR with increased erbium-ion concentration. In addition, using coupled-mode theory for the simulation of the cylindrical geometry of the ED-FBG device, the pump power-dependent reflection and transmission coefficients are obtained and their potential use in active sensor applications are discussed.     

Micropillar Cavity Design for 1.55-μm Quantum-Dot Single-Photon Sources

The 1.55-μm quantum-dot (QD) micropillar cavities are strongly required as single photon sources (SPSs) for silica-fiber-based quantum information processing. Theoretical analysis shows that the adiabatic distributed Bragg reflector (DBR) structure may greatly improve the quality of a micropillar cavity. An InGaAsP/InP micropillar cavity is originally difficult, but it becomes more likely usable with inserted tapered (thickness decreased towards the center) distributed DBRs. Simulation turns out that, incorporating adiabatically tapered DBRs, a Si/SiO₂-InP hybrid micropillar cavity, which enables weakly coupling InAs/InP quantum dots (QDs), can even well satisfy strong coupling at a smaller diameter. Certainly, not only the tapered structure, other adiabatic designs, e.g., both DBR layers getting thicker and one thicker one thinner, also improve the quality, reduce the diameter, and degrade the fabrication difficulty of Si/SiO₂-InP hybrid micropillar cavities. Furthermore, the problem of the thin epitaxial semiconductor layer can also be greatly resolved by inserting adiabatic InGaAsP/InP DBRs. With tapered DBRs, the InGaAsP/InP-air-aperture micro-pillar cavity serves as an efficient, coherent, and monolithically producible 1.55-μm single-photon source (SPS). The adiabatic design is thus an effective way to obtain prospective candidates for 1.55-μm QD SPSs.     

Universal Design Rules for Flory–Huggins Polymer Photonic Vapor Sensors

Multilayered photonic sensors that rely on polymer-solvent Flory–Huggins interactions are drawing increasing interest owing to their broad-band selectivity, even among mixtures, without the need for chemical targeting. Moreover, these sensors provide simple colorimetric responses, and easy, quick fabrication both on laboratory and industrial scales. However, complex optical responses and slow response times are limiting their development. In this work, the behavior of different photonic sensor architectures is analyzed to speed up response time and define a strategy to simplify their spectral behavior. To this end, the effect of interfaces, materials order, and thickness on the diffusion kinetics of a single reference analyte in the multilayered sensors is studied to design the optimal structure.     

High precision (1 part in 10) reflectivity measurement for the study of reflective materials used in solar collectors

A new method of reflectivity measurement for the study of reflective materials in solar energy technology is reported in this paper. The method employs a fast rotating reference mirror and certain geometry configuration to alternatively deliver the light via a sample mirror or by passing it to a photo detector. It has been proved to reach a precision of 10⁻⁴. With a good repeatability of the method, outdoor exposure tests of sample mirrors have been carried out in a relatively short period (1 month) and significant specular reflectance losses due to an aging process have been observed.     

Cubic InGaN/GaN multi-quantum wells and AlGaN/GaN distributed Bragg reflectors for application in resonant cavity LEDs

In this contribution, we present results on the growth and characterization of c-InGaN/GaN MQWs and c-AlGaN/GaN DBRs, which may be used as building blocks of green (510 nm) resonant cavity light emitting diodes, which have a high potential as light sources for local area networks using plastic optical fibers. First, the impact of the indium and gallium flux on the growth of cubic-InGaN by plasma assisted molecular beam epitaxy has been studied. Indium is observed to incorporate into the c-GaInN films only when the gallium flux is reduced significantly below the value needed for stoichiometric c-GaN growth. A decrease of the surface roughness of the InGaN layers and an increase of their photoluminescence intensity per unit thickness at the transition from metal-flux limited to active nitrogen-limited growth is observed. High quality c-InGaN/GaN multi-quantum wells were grown with superlattice peaks clearly resolved in high resolution X-ray diffraction and a strong room temperature photoluminescence with a full width at half maximum of 240 meV. Cubic-AlGaN/GaN distributed Bragg reflectors with a maximum reflectivity of about 50% at 515 nm and a stop bandwidth of 33 nm have been realized. Enhanced 526 nm room temperature photoluminescence has been observed from a combined structure of a c-InGaN/GaN multi-quantum well and a c-AlGaN/GaN distributed Bragg reflector.     

Efficiency (>15%) for thin‐film epitaxial silicon solar cells on 70 cm2 area offspec silicon substrate using porous silicon segmented mirrors

We report on the beneficial use of embedded segmented porous silicon broad‐band optical reflectors for thin‐film epitaxial silicon solar cells. These reflectors are formed by gradual increase of the spatial period between the layer segments, allowing for an enhanced absorption of low energy photons in the epitaxial layer. By combining these reflectors with well‐established solar cell processing by photolithography, a conversion efficiency of 15·2% was reached on 73 cm² area, highly doped offspec multicrystalline silicon substrates. The corresponding photogenerated current densities (J_sc) were well above 31 mA/cm² for an active layer of only 20 µm. Copyright © 2010 John Wiley & Sons, Ltd.     

角反射器在不同条件下光学性能变化实验研究

介绍了卫星激光角反射器在激光测距中须引入直角误差来克服速差效应带来的影响,并对角反射器的远场衍射能量分布进行了实验研究。另外,分析了空气抖动和机械应力等外界因素对远场能量分布的影响。     

High-performance reflective STN-LCD with a blazed reflector

Abstract— A reflective super-twisted-nematic liquid-crystal display (STN-LCD) using a blazed reflector is proposed. Application of the blazed reflector improves luminance and contrast ratio in reflective LCDs by directing the reflected image toward the observer and also by misaligning it from the direction of the surface reflection. The reflector needs proper scattering to eliminate casting a background by a specular image. Therefore, we studied two methods: one which makes the surface of the reflector uneven and the other which applies light-scattering material between the display and the reflector. Key features include almost a doubling in brightness and contrast ratio using the blazed reflector with the light-scattering material. Moreover, good white representation is obtained to optimize the refractive index in the normal direction of the retardation film.     

Micro-structured reflector surfaces for a stationary asymmetric parabolic solar concentrator

One of the main problems in using parabolic concentrators with standard photovoltaics (PV) cells is the highly non-uniform illumination of the cells. The non-uniform irradiation causes high resistive losses in the standard cells due to their relatively high series resistance. This results in a considerably lowered efficiency. To solve the problem, we introduce three different structured reflectors that will create a more uniform illumination, and also increase the concentration ratio in certain cases. The structures were evaluated in an existing trough system by Monte Carlo ray tracing, and it was found that structures improve the system performance mainly by homogenizing the light on the cells. The yearly irradiation collected in the evaluation system is slightly lower than for a reference with smooth reflectors, but the more uniform illumination of the cells will generate a net increase of the total system performance compared to a system that was optimized with smooth reflectors. The benefit of the increased concentration ratio is increased flexibility in designing new systems with concentration ratios surpassing the limit of existing trough concentrators.