Browsing by Author "Hsieh, Mei-Li"

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A compact in-situ ellipsometer using the liquid crystal variable retarder
(2014-01-01)
Shih, Wen-Tse
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Hsieh, Mei-Li
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Chao, Yu Faye
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光電工程學系
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Department of Photonics
For monitoring the optical properties of material under a dynamical processing, we design a compact in-situ ellipsometry by using a liquid crystal (LC) phase retarder. Since the key issue of an accurate ellipsometer is the alignment of each optical component in the system, hence we not only proposed the alignment procedure, we also calibrated the phase retardation of LC retarder for this in-situ ellipsometry. The azimuths of polarizers and phase retarders can be aligned by the analytical solutions of the azimuthal deviations. The phase retardation can be directly determined by the intensity ratio technique.
A low cost and large-scale synthesis of 3D photonic crystal with SP2 lattice symmetry
(2019-08-01)
Hsieh, Mei-Li
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Chen, Shu-Yu
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Kaiser, Alex
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Yan, Yang-Jhe
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Frey, B.
In this work, a novel lithographic method is proposed to prepare three-dimensional (3D) photonic crystal (PC) that is different from conventional top-down and bottom-up approaches. The method combines a 2D optical mask and off-the-axis double optical exposures to create a desirable 3D PC structure. Since the method uses only two optical exposures of a photo-resist layer, it is inherently a low-cost, high throughput and wafer-scale lithographic method. The method is implemented to make a slanted post 3D PC having the SP2 lattice symmetry. Three types of SP2 3D PC structures were successfully fabricated with a minimum feature size of d=1.5 mu m over a large scale of 8x10 mm(2), without any observable fabrication defects. The SP2 PCs are: (i) SU8 posts in air background, (ii) air pores in CdS background and (iii) Pt coated on SU8 SP2 templates. A spectroscopic study of the SP2 PCs shows select spectral regions of high reflectance, indicating the existence of a photonic stop band. This low-cost and large-scale method could enable broader technological impacts of 3D PC materials in areas such as thermo-photovoltaics and above room-temperature Bose-Einstein Condensation. Furthermore, this off-axis method could lead to the creation of an entirely new class of slanted-rod based photonic crystals, such as topological photonic crystal in 3D. (C) 2019 Author(s).
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
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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.
An Efficient Solar Concentrator using Volume hologram
(2011)
Hsieh, Mei-Li
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Lin, Shiuan-Huei
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Hsu, Ken Y.
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Burr, Jim A.
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Lin, Shawn-Yu
In this paper, we propose a simple technique to realize a compact and nearly all-angle solar energy concentrator using a volume holographic element (VHE). Our theoretical calculation predicts up to a fivefold concentration of energy per unit area of photovoltaic material. Hence, our holographic approach can offer an exceedingly high solar-concentration, a universal solution that can be easily integrated to any solar cells. Both the analysis and design of the volume holographic element will be described and demonstrated.
An In-situ and Direct Confirmation of Super-Planckian Thermal Radiation Emitted From a Metallic Photonic-Crystal at Optical Wavelengths
(2020-03-23)
Lin, Shawn-Yu
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Hsieh, Mei-Li
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John, Sajeev
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Frey, B.
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Bur, James A.
Planck's law predicts the distribution of radiation energy, color and intensity, emitted from a hot object at thermal equilibrium. The Law also sets the upper limit of radiation intensity, the blackbody limit. Recent experiments reveal that micro-structured tungsten can exhibit significant deviation from the blackbody spectrum. However, whether thermal radiation with weak non-equilibrium pumping can exceed the blackbody limit in the far field remains un-answered experimentally. Here, we compare thermal radiation from a micro-cavity/tungsten photonic crystal (W-PC) and a blackbody, which are both measured from the same sample and also in-situ. We show that thermal radiation can exceed the blackbody limit by >8 times at lambda = 1.7 mu m resonant wavelength in the far-field. Our observation is consistent with a recent calculation by Wang and John performed for a 2D W-PC filament. This finding is attributed to non-equilibrium excitation of localized surface plasmon resonances coupled to nonlinear oscillators and the propagation of the electromagnetic waves through non-linear Bloch waves of the W-PC structure. This discovery could help create super-intense narrow band thermal light sources and even an infrared emitter with a laser-like input-output characteristic.
Controllable fabrication of the micropore shape of two-dimensional photonic crystals using holographic lithography
(2008-05-01)
Hsieh, Mei-Li
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Lan, Yi-Sheng
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光電工程學系
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Department of Photonics
In this study, the micropore shape of two-dimensional (2D) photonic crystal structures can be modified and controlled by the intensity ratio of the incident beams of the holographic lithography. By adjusting the intensity ratio of the incident beams, the micropore shape of 2D hexagonal photonic crystal structure could be adjusted from being circular to being elliptical. Hence, we defined and analyzed the ellipticity of the micropore shape on a 2D photonic crystal structure as a function of the intensity ratio of the incident beams. In addition, we set up an optical holographic system by using three incident beams with different intensities to demonstrate the influence of the intensity ratio of the incident beams on the micropore shape. The optical experimental results show that the ellipticity of the micropore shape decreased with increasing the intensity ratio of the incident beams, which is the same trend as with the theoretical analysis. (C) 2008 American Vacuum Society.
Direct observation of quasi-coherent thermal emission by a three-dimensional metallic photonic crystal
(2013-03-15)
Hsieh, Mei-Li
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Bur, James
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Kim, Yong-Sung
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Lin, Shawn-Yu
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光電工程學系
We report a direct observation of a quasi-coherent thermal emission from a heated three-dimensional photonic-crystal sample. While the sample was under Joule heating, we observed multiple oscillations in its emission interferogram and deduced a coherent length of L-coh congruent to 20-40 mu m, 5-10 times longer than that of a blackbody at comparable wavelengths. The observed, relatively long coherent length is attributed to coupling of thermal emission into lossy Bloch modes that oscillate coherently over a distance determined by decay length and the slow light nature of Bloch modes at the band-edges. (C) 2013 Optical Society of America
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.
Experimental demonstration of broadband solar absorption beyond the lambertian limit in certain thin silicon photonic crystals
(2020-07-16)
Hsieh, Mei-Li
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Kaiser, Alex
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Bhattacharya, Sayak
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John, Sajeev
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Lin, Shawn-Yu
The tantalizing possibility of 31% solar-to-electric power conversion efficiency in thin film crystalline silicon solar cell architectures relies essentially on solar absorption well beyond the Lambertian light trapping limit (Bhattacharya and John in Nat Sci Rep 9:12482, 2019). Up to now, no solar cell architecture has exhibited above-Lambertian solar absorption, integrated over the broad solar spectrum. In this work, we experimentally demonstrate two types of photonic crystal (PhC) solar cells architectures that exceed Lambertian light absorption, integrated over the entire 300-1,200 nm wavelength band. These measurements confirm theoretically predicted wave-interference-based optical resonances associated with long lifetime, slow-light modes and parallel-to-interface refraction. These phenomena are beyond the realm of ray optics. Using two types of 10-mu m thick PhC's, first an Inverted Pyramid PhC with lattice constant a=2,500 nm and second a Teepee PhC with a=1,200 nm, we observe solar absorption well beyond the Lambertian limit over lambda =950-1,200 nm. Our absorption measurements correspond to the maximum-achievable-photocurrent-density (MAPD), under AM1.5G illumination at 4-degree incident angle, 41.29 and 41.52 mA/cm(2) for the Inverted Pyramid and Teepee PhC, respectively, in agreement with wave-optics, numerical simulations. Both of these values exceed the MAPD (=39.63 mA/cm(2)) corresponding to the Lambertian limit for a 10-mu m thick silicon for solar absorption over the 300-1,200 nm band.
Experimental observation of anomalous thermal radiation from a three-dimensional metallic photonic crystal
(2015-06-12)
Hsieh, Mei-Li
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Lin, Shawn-Yu
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Bur, James A.
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Shenoi, Rajeev
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光電工程學系
We report some striking results on thermal radiation properties of a resonantly coupled cavity photonic crystal (PhC) at elevated temperatures (T = 400-900 K). We experimentally found that at resonant wavelengths, lambda = 1.1, 1.64, 2.85 mu m, the PhC emission is spectrally selective, quasi-coherent, directional, and shows significant deviation from Planck\'s blackbody law at equilibrium. The presence of non-equilibrium effects, driven by strong thermal excitation and cavity resonance, may be the major cause for our experimental observation.
Holographic information recording and reproducing apparatus for the same
(2009-05-14)
Hsieh, Mei-Li
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Lin, Shiuan-Huei
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Wang, Jui-Hsin
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Hsu, Ken-Yuh
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Chiang, Don-Yau
In a holographic information recording and reproducing apparatus, an optical fiber guides a reference beam toward a recording medium for holographic recording, and a precision rotator is turned, so that the reference beam is incident on the recording medium at different angles and interferes with a data-carrying signal beam to complete the recording of holographic information on the recording medium. To reproduce the holographic information, the optical fiber guides a reading beam, and the reading beam is incident on the recording medium at an angle the same as the reference beam for the recording to reproduce the holographic information stored on the recording medium. With the optical fiber and the precision rotator, a simplified light path system and a wide range of incident angles for the reference and reading beams may be achieved, and the transmissive, reflective, and 90-degree holographic storage techniques may be integrated in one single apparatus.
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
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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.
Lens-less bending and concentration of light by volume hologram
(2015-12-01)
Hsieh, Mei-Li
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Peng, Cheng-Te
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Chen, Hong-Yu
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Lin, Shawn-Yu
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光電工程學系
In this paper, a new approach is proposed to realize a lens-less and 90 degrees light-bending by a volume-holographic element, consisting of 3D sub-wavelength index-gratings throughout the sample. In this approach, a top incident plane-wave is diffracted by 90 degrees and guided into a planar volume hologram. Conversely, a side-incident light may be guided and diffracted out of the top sample surface. The diffraction-efficiency eta of light was studied in real-time during light-exposure and also in the dark after exposure to observe "dark-enhancement". It is shown that 90 degrees light-bending at normal incidence can be achieved with a high efficiency, eta similar to 70%, and a small angular-tolerance, Delta theta=0.02 degrees. It is further shown, as a proof-of-concept, that a 5 degrees cylindrical-wave top-incident beam may be used to improve angular tolerance to Delta theta=5 degrees, but with a reduced efficiency of eta similar to 0.80%. Crown Copyright (C) 2015 Published by Elsevier B.V. All rights reserved.
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
One-shot exposure for patterning two-dimensional photonic crystals to enhance light extraction of InGaN-based green LEDs
(2008-01-01)
Hsieh, Mei-Li
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Lo, Kuo-Chang
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Lan, Yi-Sheng
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Yang, S. Y.
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Lin, C. H.
To promote the feasibility of using photonic crystals to enhance light extraction of light-emitting diodes (LEDs) for industrial applications, the request for the high-yield and simple exposure process to pattern two-dimensional photonic crystals (2DPCs) becomes rather urgent. In this work, we developed a one-shot three-beam laser interference system-to fabricate a 2DPC on an InGaN-based green LED to address its performance for backlight display applications. Using the current exposure system we develop here, a submicro-patterned area of 6 mm in diameter can be achieved. The experimental results show that the operating voltage of a 1 x 1 mm(2) in-area LED incorporated with the 2DPC is around 4 V, and the light extraction efficiency is enhanced by a factor of 2.1.
Optimization of light diffraction efficiency and its enhancement from a doped-PMMA volume holographic material
(2013-11-01)
Hsieh, Mei-Li
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Chen, Wei-Cheng
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Chen, Hong-Yu
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Lin, Shawn-Yu
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光電工程學系
In this paper, we study the diffraction efficiency from the volume gratings in holographic materials, PQJ PMMA, and their efficiency-enhancement in an optically dark environment (dark enhancement). We show that the diffraction efficiency is increased in real-time by light-exposure and then by a slow diffusion process in the dark after light-exposure. We observe strong correlations between the efficiency, the light-exposure energy and the dark-enhancement. Furthermore, we establish an optimum condition for light-exposure and dark-enhancement. Accordingly, we simultaneously achieve the best diffraction-efficiency of 82% for a 2 mm thick PQ/PMMA and an efficiency-enhancement of 3.1 times after exposure, approaching the theoretical limit of 4 times. Published by Elsevier B.V.
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
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John, Sajeev
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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)
Probing the intrinsic optical Bloch-mode emission from a 3D photonic crystal
(2016-10-14)
Hsieh, Mei-Li
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Bur, James A.
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Du, Qingguo
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John, Sajeev
;
Lin, Shawn-Yu
We report experimental observation of intrinsic Bloch-mode emission from a 3D tungsten photonic crystal at low thermal excitation. After the successful removal of conventional metallic emission (normal emission), it is possible to make an accurate comparison of the Bloch-mode and the normal emission. For all biases, we found that the emission intensity of the Bloch-mode is higher than that of the normal emission. The Bloch-mode emission also exhibits a slower dependence on (h(omega)/k(b)T) than that of the normal emission. The observed higher emission intensity and a different T-dependence is attributed to Bloch-mode assisted emission where emitters have been located into a medium having local density of states different than the isotropic case. Furthermore, our finite-difference time-domain (FDTD) simulation shows the presence of localized spots at metal-air boundaries and corners, having intense electric field. The enhanced plasmonic field and local non-equilibrium could induce a strong thermally stimulated emission and may be the cause of our unusual observation.
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
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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.