Browsing by Author "Kuang, Ping"

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Achieving an Accurate Surface Profile of a Photonic Crystal for Near-Unity Solar Absorption in a Super Thin-Film Architecture
(2016-06)
Kuang, Ping
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Eyderman, Sergey
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Hsieh, Mei-Li
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Post, Anthony
;
John, Sajeev
In this work, a teepee-like photonic crystal (PC) structure on crystalline silicon (c-Si) is experimentally demonstrated, which fulfills two critical criteria in solar energy harvesting by (i) its Gaussian-type gradient-index profile for excellent antireflection and (ii) near-orthogonal energy flow and vortex-like field concentration via the parallel-to-interface refraction effect inside the structure for enhanced light trapping. For the PC structure on 500-mu m-thick c-Si, the average reflection is only similar to 0.7% for lambda = 400-1000 nm. For the same structure on a much thinner c-Si ( t = 10 mu m), the absorption is near unity (A similar to 99%) for visible wavelengths, while the absorption in the weakly absorbing range (lambda similar to 1000 nm) is significantly increased to 79%, comparing to only 6% absorption for a 10-mu m-thick planar c-Si. In addition, the average absorption (similar to 94.7%) of the PC structure on 10 mu m c-Si for lambda = 400-1000 nm is only similar to 3.8% less than the average absorption (similar to 98.5%) of the PC structure on 500 mu m c-Si, while the equivalent silicon solid content is reduced by 50 times. Furthermore, the angular dependence measurements show that the high absorption is sustained over a wide angle range (theta(inc) = 0-60 degrees) for teepee-like PC structure on both 500 and 10-mu m-thick c-Si.
Effectively infinite optical path-length created using a simple cubic photonic crystal for extreme light trapping
(2017-06-23)
Frey, Brian J.
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Kuang, Ping
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Hsieh, Mei-Li
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Jiang, Jian-Hua
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John, Sajeev
A 900 nm thick TiO2 simple cubic photonic crystal with lattice constant 450 nm was fabricated and used to experimentally validate a newly-discovered mechanism for extreme light-bending. Absorption enhancement was observed extending 1-2 orders of magnitude over that of a reference TiO2 film. Several enhancement peaks in the region from 600-950 nm were identified, which far exceed both the ergodic fundamental limit and the limit based on surface-gratings, with some peaks exceeding 100 times enhancement. These results are attributed to radically sharp refraction where the optical path length approaches infinity due to the Poynting vector lying nearly parallel to the photonic crystal interface. The observed phenomena follow directly from the simple cubic symmetry of the photonic crystal, and can be achieved by integrating the light-trapping architecture into the absorbing volume. These results are not dependent on the material used, and can be applied to any future light trapping applications such as phosphor-converted white light generation, water-splitting, or thin-film solar cells, where increased response in areas of weak absorption is desired.
Integrated three-dimensional photonic nanostructures for achieving near-unity solar absorption and superhydrophobicity
(2015-06-07)
Kuang, Ping
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Hsieh, Mei-Li
;
Lin, Shawn-Yu
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光電工程學系
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Department of Photonics
In this paper, we proposed and realized 3D photonic nanostructures consisting of ultra- thin graded index antireflective coatings (ARCs) and woodpile photonic crystals. The use of the integrated ARC and photonic crystal structure can achieve broadband, broad- angle near unity solar absorption. The amorphous silicon based photonic nanostructure experimentally shows an average absorption of similar to 95% for 400-620 nm over a wide angular acceptance of theta = 0 degrees - 60 degrees. Theoretical studies show that a Gallium Arsenide (GaAs) based structure can achieve an average absorption of > 95% for lambda = 400-870 nm. Furthermore, the use of the slanted SiO2 nanorod ARC surface layer by glancing angle deposition exhibits Cassie- Baxter state wetting, and superhydrophobic surface is obtained with highest water contact angle theta(CB) similar to 153 degrees. These properties are fundamentally important for achieving maximum solar absorption and surface self-cleaning in thin film solar cell applications. (C) 2015 AIP Publishing LLC.
Light trapping and near-unity solar absorption in a three-dimensional photonic-crystal
(2013-10-15)
Kuang, Ping
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Deinega, Alexei
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Hsieh, Mei-Li
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John, Sajeev
;
Lin, Shawn-Yu
We report what is to our knowledge the first observation of the effect of parallel-to-interface-refraction (PIR) in a three-dimensional, simple-cubic photonic-crystal. PIR is an acutely negative refraction of light inside a photonic-crystal, leading to light-bending by nearly 90 deg over broad wavelengths (.). The consequence is a longer path length of light in the medium and an improved light absorption beyond the Lambertian limit. As an illustration of the effect, we show near-unity total absorption (>= 98%) in lambda 520-620 nm and an average absorption of similar to 94% over lambda = 400-700 nm for our alpha-Si: H photonic-crystal sample of an equivalent bulk thickness of (t) over tilde = 450 nm. Furthermore, we have achieved an ultra-wide angular acceptance of light over theta = 0 degrees-80 degrees. This demonstration opens up a new door for light trapping and near-unity solar absorption over broad.s and wide angles. (C) 2013 Optical Society of America
Photonic crystals with a continuous, Gaussian-type surface profile for near-perfect light trapping
(2018-04-01)
Kuang, Ping
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Bhattacharya, Sayak
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Hsieh, Mei-Li
;
John, Sajeev
;
Lin, Shawn-Yu
We show a unique design of teepee-like photonic crystal (TP-PC) structure that possesses a true gradient, Gaussian-type surface profile for smooth and accurate index matching between air and silicon for near-perfect light trapping. Such funnel-like, inverse-conical topography is capable of achieving near-zero optical reflection and near-unity solar absorption with excellent angular response over the entire visible light wavelength range. The fabrication only requires standard microelectronics reactive-ion etching (RIE) process. We demonstrate how various process parameters, such as RIE gas mixture ratio, RIE power, thickness of silicon dioxide (SiO2) coatings, and lattice constant of the photonic crystal, can impact the details of the "Gaussian" profile and further improve the optical performance of the TP-PC structure at broad-lambda, broad-theta, especially in the ultraviolet (UV) wavelength range. Our finite-difference time-domain (FDTD) simulation of the TP-PC structure reveals existence of multiple absorption resonances in the 800- to1100-nm wavelength range. Poynting vector plots show that such strong absorption enhancements at the resonant frequencies are due to long-lifetime photonic modes arising from parallel-to-interface refraction of the incoming sunlight and formation of vortex-like energy flow pattern inside the TP-PC structure. Our design will lead the way for future development of ultrathin, high-efficiency c-Si solar photovoltaics. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)
Review on Recent Progress of Three-dimensional Optical Photonic Crystal
(2014)
Hsieh, Mei-Li
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Kuang, Ping
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Bur, James A.
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John, Sajeev
;
Lin, Shawn-Yu
Over the past two decades, the field of photonic-crystals has become one of the most influential realms of contemporary optics. In this paper; we will review two recent experimental progresses in three-dimensional photonic-crystal operating in optical wavelengths. The first is the observation of anomalous light-refraction, an acutely negative refraction, in a 3D photonic-crystal for light trapping, guiding and near-unity absorption. The second is the observation of quasi-coherent thermal emission from an all-metallic 3D photonic-crystal at elevated temperatures.