Demonstration of optical interference filters utilizing tunable refractive index layers

Optical interference filters utilizing tunable refractive index layers are shown to have higher spectral fidelity as compared to conventional filters consisting of non-tunable refractive index layers. To demonstrate this increase in spectral fidelity, we design and compare a variety of optical interference filters employing both tunable and non-tunable refractive index layers. Additionally, a five-layer optical interference filter utilizing tunable refractive index layers is designed and fabricated for use with a Xenon lamp to replicate the Air Mass 0 solar irradiance spectrum and is shown to have excellent spectral fidelity. (C) 2010 Optical Society of AmericaX116sciescopu

Broadband omnidirectional antireflection coatings optimized by genetic algorithm

An optimized graded-refractive-index (GRIN) antireflection. (AR) coating with broadband and omnidirectional characteristics-as desired for solar cell applications-designed by a genetic algorithm is presented. The optimized three-layer GRIN AR coating consists of a dense TiO2 and two nanoporous SiO2 layers fabricated using oblique-angle deposition. The normal incidence reflectance of the three-layer GRIN AR coating averaged between 400 and 700 nm is 3.9%, which is 37% lower than that of a conventional single-layer Si3N4 coating. Furthermore, measured reflection over the 410-740 run range and wide incident angles 40 degrees-80 degrees is reduced by 73% in comparison with the single-layer Si3N4 coating, clearly showing enhanced omnidirectionality and broadband characteristics of the optimized three-layer GRIN AR coating. (C) 2009 Optical Society of AmericaX1149sciescopu

Quantification of porosity and deposition rate of nanoporous films grown by oblique-angle deposition

We propose an analytic model that accurately predicts the porosity and deposition rate of nanoporous films grown by oblique-angle deposition. The model employs a single fitting parameter and takes into account geometrical factors as well as surface diffusion. We have determined the porosity and deposition rate from the measured refractive index and thickness of SiO(2) and indium tin oxide nanoporous films deposited at various incident angles. Comparison of experimental data with the model reveals excellent agreement. The theoretical model allows for the predictive control of refractive index, porosity, and deposition rate for a wide range of deposition angles and materials. (C) 2008 American Institute of Physics.open116165sciescopu

Design of multilayer antireflection coatings made from co-sputtered and low-refractive-index materials by genetic algorithm

Designs of multilayer antireflection coatings made from co-sputtered and low-refractive-index materials are optimized using a genetic algorithm. Co-sputtered and low-refractive-index materials allow the fine-tuning of refractive index, which is required to achieve optimum antireflection characteristics. The algorithm minimizes reflection over a wide range of wavelengths and incident angles, and includes material dispersion. Designs of antireflection coatings for silicon-based image sensors and solar cells, as well as triple-junction GaInP/GaAs/Ge solar cells are presented, and are shown to have significant performance advantages over conventional coatings. Nano-porous low-refractive-index layers are found to comprise generally half of the layers in an optimized antireflection coating, which underscores the importance of nano-porous layers for high-performance broadband and omnidirectional antireflection coatings. (C) 2008 Optical Society of America.X11112sciescopu

Realization of a near-perfect antireflection coating for silicon solar energy utilization

To harness the full spectrum of solar energy, Fresnel reflection at the surface of a solar cell must be eliminated over the entire solar spectrum and at all angles. Here, we show that a multilayer nanostructure having a graded-index profile, as predicted by theory [J. Opt. Soc. Am. 66, 515 (1976); Appl. Opt. 46, 6533 (2007)], can accomplish a near-perfect transmission of all-color of sunlight. An ultralow total reflectance of 1%-6% has been achieved over a broad spectrum, lambda=400 to 1600 run, and a wide range of angles of incidence, theta=0 degrees-60 degrees. The measured angle- and wavelength-averaged total reflectance of 3.79% is the smallest ever reported in the literature, to our knowledge. (C) 2008 Optical Society of AmericaX11165188sciescopu

Refractive-Index-Matched Indium-Tin-Oxide Electrodes for Liquid Crystal Displays

Refractive-index-matched indium-tin-oxide (ITO) electrode for thin-film transistor liquid crystal displays is presented to reduce optical losses caused by Fresnel reflections. Simulations show a 24% improvement in optical transmittance when the conventional dense ITO is replaced with the refractive-index-matched ITO in a stack of glass/ITO/liquid crystal/ITO/glass, The refractive-index-matched ITO, fabricated by oblique-angle deposition technique, shows higher optical transmittance and smaller dependency on film thickness and wavelength than conventional dense ITO. (c) 2009 The Japan Society of Applied PhysicsX114138sciescopu

Nanostructured Multilayer Tailored-Refractive-Index Antireflection Coating for Glass with Broadband and Omnidirectional Characteristics

The design, fabrication, and characterization of a broadband, omnidirectional, graded-index anti-reflection (AR) coating on a glass substrate, fabricated by using nanostructured low-refractive-index (n = 1.05-1.40) silica, is reported. The AR coating is designed by using a genetic algorithm and fabricated by using oblique angle deposition. The AR coating is designed for the wavelength range of 400 to 2500 nm and 0 to 40 degrees angle of incidence. The measured average optical transmittance between 1000 and 2000 nm is improved from 92.6 to 99.3% at normal incidence by using a two-layer AR coating deposited on both surfaces of the glass substrate. (C) 2011 The Japan Society of Applied PhysicsX113023sciescopu

Elimination of total internal reflection in GaInN light-emitting diodes by graded-refractive-index micropillars

A method for enhancing the light-extraction efficiency of GaInN light-emitting diodes (LEDs) by complete elimination of total internal reflection is reported. Analytical calculations show that GaInN LEDs with multilayer graded-refractive-index pillars, in which the thickness and refractive index of each layer are optimized, have no total internal reflection. This results in a remarkable improvement in light-extraction efficiency. GaInN LEDs with five-layer graded-refractive-index pillars, fabricated by cosputtering TiO(2) and SiO(2), show a light-output power enhanced by 73% and a strong side emission, consistent with analytical calculations and ray-tracing simulations.open115059sciescopu