Optical modelling of cone concentrators for positive and negative IR emitters

Abstract

InSb optical cone concentrators are modelled to assess their optical performance in positive and negative emission modes. The output distribution from the active layer is shown to be isotropic for thin active regions, tending towards Lambertian distribution as the layer thickness increases. Refraction from the emitting surface is shown to make the distribution more Lambertian. Optical efficiencies of straight-sided and Winston cone concentrators are modelled using a ray-tracing program, and those of straight-sided cones also determined using an analytical approximation, which allows use of the distribution derived earlier. The effect on the active layer thickness on the positive and negative emission is also determined. Normal light emitting diode structures are found to be poor positive emitters and to draw large currents when used as negative emitters. A Winston cone of area gain equal to n ² is found to be the best option for devices required to work in both positive and negative modes. Intermediate structures are also considered. The optimum active layer thickness is derived for three emitter configurations.     

Direct Laser‐Patterned Micro‐Supercapacitors from Paintable MoS2 Films

Micrometer‐sized electrochemical capacitors have recently attracted attention due to their possible applications in micro‐electronic devices. Here, a new approach to large‐scale fabrication of high‐capacitance, two‐dimensional MoS₂ film‐based micro‐supercapacitors is demonstrated via simple and low‐cost spray painting of MoS₂ nanosheets on Si/SiO₂ chip and subsequent laser patterning. The obtained micro‐supercapacitors are well defined by ten interdigitated electrodes (five electrodes per polarity) with 4.5 mm length, 820 μm wide for each electrode, 200 μm spacing between two electrodes and the thickness of electrode is ～0.45 μm. The optimum MoS₂‐based micro‐supercapacitor exhibits excellent electrochemical performance for energy storage with aqueous electrolytes, with a high area capacitance of 8 mF cm^?2 (volumetric capacitance of 178 F cm^?3) and excellent cyclic performance, superior to reported graphene‐based micro‐supercapacitors. This strategy could provide a good opportunity to develop various micro‐/nanosized energy storage devices to satisfy the requirements of portable, flexible, and transparent micro‐electronic devices.     

High performance horizontal gate-all-around silicon nanowire field-effect transistors

Semiconducting nanowires have been pointed out as one of the most promising building blocks for submicron electrical applications. These nanometer materials open new opportunities in the area of post-planar traditional metal-oxide-semiconductor devices. Herein, we demonstrate a new technique to fabricate horizontally suspended silicon nanowires with gate-all-around field-effect transistors. We present the design, fabrication and electrical measurements of a high performance transistor with high on current density (～150?μA?μm(-1)), high on/off current ratio (10(6)), low threshold voltage (～?-?0.4?V), low subthreshold slope (～100?mV /dec) and high transconductance (g(m)?～?9.5?μS). These high performance characteristics were possible due to the tight electrostatic coupling of the surrounding gate, which significantly reduced the Schottky-barrier effective height, as was confirmed experimentally in this study.     

Infrared glasses

Driven by applications in hot fields such as optical communications, lasers, sensors, etc. infrared glasses have to be considered as key components in the development of devices for telecom signal amplification, fibre-laser emission as well as for passive functions related to IR remote spectroscopy or thermal imaging. Stable vitreous materials with low-phonon energies are found in the family of fluorides and chalcogenides glasses; they offer the advantage of excellent transparency in the mid-IR and weak nonradiative relaxation when doped with rare earth elements. Despite the number of candidates only a very limited number of glass compositions can be shaped into good optical waveguides such as channel or fibre. When possible, this led to remarkable amplification in the 1.3 μm region and lasing emission in the blue or mid-IR. Non-linear optical properties of chalcogen-based glasses are also of special interest for fast all optical switching and photo-induced effects.     

Elliptical concentrators

Nonimaging optics is a field devoted to the design of optical components for applications such as solar concentration or illumination. In this field, many different techniques have been used to produce optical devices, including the use of reflective and refractive components or inverse engineering techniques. However, many of these optical components are based on translational symmetries, rotational symmetries, or free-form surfaces. We study a new family of nonimaging concentrators called elliptical concentrators. This new family of concentrators provides new capabilities and can have different configurations, either homofocal or nonhomofocal. Translational and rotational concentrators can be considered as particular cases of elliptical concentrators.     

Integrated capillary electrophoresis devices with an efficient postcolumn reactor in planar quartz and glass chips

Methods to fabricate planar capillary electrophoresis devices integrated with a postcolumn reactor in fused silica (quartz) and Pyrex glass are presented. Quartz is etched at ～1 μm/min with a 2.1:1 width-to-depth ratio using a Cr/Au/Cr metal mask and concentrated HF/HNO(3). On-chip postcolumn reaction of o-phthaldialdehyde (OPA) and amino acids gave theoretical plate numbers up to 83?000 and ～90 ms peak widths, corresponding to 14 plates/V and a 0.5 μm theoretical plate height. The reactor geometry caused only a 10% degradation in efficiency.     

Efficient Single Photon Detection from 500 nm to 5 μm Wavelength

We report on superconducting nanowire single photon detectors (SNSPDs) based on 30 nm wide nanowires with detection efficiency η ～ 2.6-5.5% in the wavelength range λ = 0.5-5 μm. We compared the sensitivity of 30 nm wide SNSPDs with the sensitivity of SNSPDs based on wider (85 and 50 nm wide) nanowires for λ = 0.5-5 μm. The detection efficiency of the detectors based on the wider nanowires became negligible at shorter wavelengths than the 30 nm wide SNSPDs. Our 30 nm wide SNSPDs showed 2 orders of magnitude higher detection efficiency (η ～ 2%) up to longer wavelength (λ = 5 μm) than previously reported. On the basis of our simulations, we expect that by changing the optical coupling scheme and by integrating the detectors in an optical cavity, the detection efficiency of our detectors could be increased by a factor of ～6.     

Evaluation and optimization of the optical performance of low-concentrating dielectric compound parabolic concentrator using ray-tracing methods

We present a detailed design concept and optical performance evaluation of stationary dielectric asymmetric compound parabolic concentrators (DiACPCs) using ray-tracing methods. Three DiACPC designs, DiACPC-55, DiACPC-66, and DiACPC-77, of acceptance half-angles (0° and 55°), (0° and 66°), and (0° and 77°), respectively, are designed in order to optimize the concentrator for building fa?ade photovoltaic applications in northern latitudes (>55 °N). The dielectric concentrator profiles have been realized via truncation of the complete compound parabolic concentrator profiles to achieve a geometric concentration ratio of 2.82. Ray-tracing simulation results show that all rays entering the designed concentrators within the acceptance half-angle range can be collected without escaping from the parabolic sides and aperture. The maximum optical efficiency of the designed concentrators is found to be 83%, which tends to decrease with the increase in incidence angle. The intensity is found to be distributed at the receiver (solar cell) area in an inhomogeneous pattern for a wide range of incident angles of direct solar irradiance with high-intensity peaks at certain points of the receiver. However, peaks become more intense for the irradiation incident close to the extreme acceptance angles, shifting the peaks to the edge of the receiver. Energy flux distribution at the receiver for diffuse radiation is found to be homogeneous within ±12% with an average intensity of 520 W/m2.     

Shape-engineerable and highly densely packed single-walled carbon nanotubes and their application as super-capacitor electrodes

We present a rational and general method to fabricate a high-densely packed and aligned single-walled carbon-nanotube (SWNT) material by using the zipping effect of liquids to draw tubes together. This bulk carbon-nanotube material retains the intrinsic properties of individual SWNTs, such as high surface area, flexibility and electrical conductivity. By controlling the fabrication process, it is possible to fabricate a wide range of solids in numerous shapes and structures. This dense SWNT material is advantageous for numerous applications, and here we demonstrate its use as flexible heaters as well as supercapacitor electrodes for compact energy-storage devices.     

Electromagnetic shielding effectiveness of amorphous metallic spheroidal-and flake-based magnetodielectric composites

Flexible,lightweight,conductive materials,having both high rf losses and high permeability,are extremely desirable for applications as electromagnetic(EM)shielding.Gas atomized spherical FeSi-based ferromagnetic metallic particles,having a mean diameter of 14.6 μm with a standard deviation of 7.3 μm,were measured to have a room temperature saturation magnetic flux density of 1.49 T with a coercivity of 160 A/m.Ball milling of the amorphous particles led to aspect ratios from 1:1(spherical)to＞100:1(flake-like).Flake-like particles,suspended in paraffin,were found to not only increase the surface area of fillers enhancing the polarization mechanism but also increase the complex permeability and complex permittivity,and thus provide broadband shielding effectiveness.A loading factor of 40 vol.％of the～15 μm diameter powders provided the largest △WRL=-20dB of 9.49 GHz(i.e.,6.55＜f＜16.04 GHz)at a coating thickness of 2 mm.Overall,powder composites show a wide absorption potential above 18 GHz for＜1.5 mm thicknesses.The optimized flake-based composites exhibit strong EM wave absorption with an SE of-40 dB and SE＜-10 dB of 17.57 GHz at 40 vol.％filler at a thickness of 1.6 mm.     

Electrical and photoelectrical transport properties of Langmuir-Blodgett films and a discussion of possible device applications

A rather comprehensive review is given of the electrical and photoelectrical transport properties of Langmuir-Blodgett (LB) built-up monolayers and multilayers. Both conventional (fatty acid) and unconventional materials are included. It is shown that this field has undergone enormous progress in the last few years; many promising scientific areas have opened up and a wide range of device applications can now be considered. The feasibility of several devices using insulating LB films has in fact been demonstrated, and it is now possible to design complex structures and supermolecular “organizates” to fulfil specific “active” electrical functions, and to fabricate them predictably. An extensive review is given of the possible device applications for LB films; these extend from a whole range of electronic devices utilizing the thinness and perfection of insulating LB films, to complex supermolecular structures designed for such purposes as solar energy conversion and high temperature superconductivity. The last possibility is discussed in some detail and is concluded to be a very promising area for future research.     

Fabrication of Cd(3)As(2) nanowires by direct vapor-solid growth, and their infrared absorption properties

In this work the authors introduce and provide details of the synthesis and spectral characterization of single-crystal nanowires in less common, high performance, group II-V semiconductors such as Cd(3)As(2). The growth mechanism critically deviates from a known vapor-liquid-solid one by being completely non-catalytic and involving only two states: vapor and solid. The resultant nanowires range from ～50 to 200?nm in diameter and reach lengths up to tens of micrometers, with their fast growth direction being normal to the (112) crystal planes. According to infrared (IR) optical absorption measurements, the nanowires have several IR active direct type light absorption transitions at 0.11, 0.28 and 0.54 eV, suggestive of their possible utility in low cost optoelectronic devices and photodetectors operating in the long wavelength range of the electromagnetic spectrum.     

Precise slit-width control of niobium apertures for superconducting LEDs

We introduce a novel three-step procedure for precise niobium (Nb)-etching on the nanometer-scale, including the design of high contrast resist patterning and sacrifice layer formation under high radio frequency (RF) power. We present the results of precise slit fabrication using this technique and discuss its application for the production of superconducting devices, such as superconductor-semiconductor-superconductor (S-Sm-S) Josephson junctions. For the reactive ion etching (RIE) of Nb, we selected CF(4) as etchant gas and a positive tone resist to form the etching mask. We found that the combination of resist usage and RIE process allows for etching of thicker Nb layers when utilizing the opposite dependence of the etching rate (ER) on the CF(4) pressure in the case of Nb as compared to the resist. Precise slit-width control of 80 and 200 nm thick Nb apertures was performed with three kinds of ER control, for the resist, the Nb, and the underlying layer. S-Sm-S Josephson junctions were fabricated with lengths as small as 80 nm, which can be considered clean and short and thus exhibit critical currents as high as 50 μA. Moreover, possible further applications, such as for apertures of superconducting light emitting diodes (SC LEDs), are addressed.     

Optical properties of hydrogenated hard carbon thin films

Hydrogenated amorphous carbon (a-C:H) films were deposited onto glass, silicon and germanium substrates. The films are transparent in the IR and are extremely hard (Mohs' hardness of about 8). The a-C:H coatings were prepared in an r.f.-excited discharge sustained by various hydrocarbon gases.The thickness, density, refractive index (at 0.3 μm and 2–10 μm) and relative hydrogen content were determined. Variations in the IR refractive index and the relative hydrogen content could be correlated with the deposition conditions. With a refractive index of approximately 2 a-C:H is an ideal antireflection coating for germanium (n = 4).Laser calorimetric measurements of optical absorption at 10.6 μm give a loss as low as 3% for a coating 1.3 μm thick on germanium (λ/4 for n = 2 at 10.6 μm).     

空间光学薄膜技术

随着空间技术的快速发展,光学薄膜技术在我国空间技术中的应用越来越显著,应用领域也越来越广泛。本文概述了目前光学薄膜技术在我国空间技术领域的应用情况以及未来可能的应用领域。鉴于空间环境的特殊性,光学薄膜技术在空间的应用具有特殊的要求,总结了空间环境对于光学薄膜的特殊要求。最后,介绍了表面工程技术重点实验室近年来研究的各类空间用光学薄膜,包括红外滤光片、闪电探测用超窄带滤光片以及线性渐变滤光片等的研究情况及研究结果。     

Design of an in-line, digital holographic imaging system for airborne measurement of clouds

We discuss the design and performance of an airborne (underwing) in-line digital holographic imaging system developed for characterizing atmospheric cloud water droplets and ice particles in situ. The airborne environment constrained the design space to the simple optical layout that in-line non-beam-splitting holography affords. The desired measurement required the largest possible sample volume in which the smallest desired particle size (～5 μm) could still be resolved, and consequently the magnification requirement was driven by the pixel size of the camera and this particle size. The resulting design was a seven-element, double-telecentric, high-precision optical imaging system used to relay and magnify a hologram onto a CCD surface. The system was designed to preserve performance and high resolution over a wide temperature range. Details of the optical design and construction are given. Experimental results demonstrate that the system is capable of recording holograms that can be reconstructed with resolution of better than 6.5 μm within a 15 cm(3) sample volume.     

Flexible visible-infrared metamaterials and their applications in highly sensitive chemical and biological sensing

Flexible electronic and photonic devices have been demonstrated in the past decade, with significant promise in low-cost, light-weighted, transparent, biocompatible, and portable devices for a wide range of applications. Herein, we demonstrate a flexible metamaterial (Metaflex)-based photonic device operating in the visible-IR regime, which shows potential applications in high sensitivity strain, biological and chemical sensing. The metamaterial structure, consisting of split ring resonators (SRRs) of 30 nm thick Au or Ag, has been fabricated on poly(ethylene naphthalate) substrates with the least line width of ～30 nm by electron beam lithography. The absorption resonances can be tuned from middle IR to visible range. The Ag U-shaped SRRs metamaterials exhibit an electric resonance of ～542 nm and a magnetic resonance of ～756 nm. Both the electric and magnetic resonance modes show highly sensitive responses to out-of-plane bending strain, surrounding dielectric media, and surface chemical environment. Due to the electric and magnetic field coupling, the magnetic response gives a sensitivity as high as 436 nm/RIU. Our Metaflex devices show superior responses with a shift of magnetic resonance of 4.5 nm/nM for nonspecific bovine serum albumin protein binding and 65 nm for a self-assembled monolayer of 2-naphthalenethiol, respectively, suggesting considerable promise in flexible and transparent photonic devices for chemical and biological sensing.     

Linear excitation schemes for IR planar-induced fluorescence imaging of CO and CO2

A detailed discussion of linear excitation schemes for IR planar-induced fluorescence (PLIF) imaging of CO and CO2 is presented. These excitation schemes are designed to avoid laser scattering, absorption interferences, and background luminosity while an easily interpreted PLIF signal is generated. The output of a tunable optical parametric amplifier excites combination or overtone transitions in these species, and InSb IR cameras collect fluorescence from fundamental transitions. An analysis of the dynamics of pulsed laser excitation demonstrates that rotational energy transfer is prominent; hence the excitation remains in the linear regime, and standard PLIF postprocessing techniques may be used to correct for laser sheet inhomogeneities. Analysis of the vibrational energy-transfer processes for CO show that microsecond-scale integration times effectively freeze the vibrational populations, and the fluorescence quantum yield following nanosecond-pulse excitation can be made nearly independent of the collisional environment. Sensitivity calculations show that the single-shot imaging of nascent CO in flames is possible. Signal interpretation for CO2 is more complicated, owing to strongly temperature-dependent absorption cross sections and strongly collider-dependent fluorescence quantum yield. These complications limit linear CO2 IR PLIF imaging schemes to qualitative visualization but indicate that increased signal level and improved quantitative accuracy can be achieved through consideration of laser-saturated excitation schemes.     

Area scalable optically induced photorefractive photonic microstructures

A convenient approach to fabricate area scalable two-dimensional photonic microstructures was experimentally demonstrated by multi-face optical wedges. The approach is quite compact and stable without complex optical alignment equipment. Large-area square lattice microstructures are optically induced inside an iron-doped lithium niobate photorefractive crystal. The induced large-area microstructures are analyzed and verified by plane wave guiding, Brillouin-zone spectroscopy, angle-dependent transmission spectrum, and lateral Bragg reflection patterns. The method can be easily extended to generate other more complex area scalable photonic microstructures, such as quasicrystal lattices, by designing the multi-face optical wedge appropriately. The induced area scalable photonic microstructures can be fixed or erased even re-recorded in the photorefractive crystal, which suggests potential applications in micro-nano photonic devices.     

Monodispersed Colloidal Spheres: Old Materials with New Applications

This article presents an overview of current research activities that center on monodispersed colloidal spheres whose diameter falls anywhere in the range of 10 nm to 1 μm. It is organized into three parts: The first part briefly discusses several useful methods that have been developed for producing monodispersed colloidal spheres with tightly controlled sizes and well‐defined properties (both surface and bulk). The second part surveys some techniques that have been demonstrated for organizing these colloidal spheres into two‐ and three‐dimensionally ordered lattices. The third part highlights a number of unique applications of these crystalline assemblies, such as their uses as photonic bandgap (PBG) crystals; as removable templates to fabricate macroporous materials with highly ordered and three‐dimensionally interconnected porous structures; as physical masks in lithographic patterning; and as diffractive elements to fabricate new types of optical sensors. Finally, we conclude with some personal perspectives on the directions towards which future research in this area might be directed.