-
[show abstract]
[hide abstract]
ABSTRACT: 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<sub>coh</sub>≅(20-40) μm, 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.
Optics Letters 03/2013; 38(6):911-3. · 3.40 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We experimentally demonstrate a nearly wavelength-independent optical reflection from an extremely rough carbon nanotube sample. The sample is made of a vertically aligned nanotube array, is a super dark material, and exhibits a near-perfect blackbody emission at T=450 K-600 K. No other material exhibits such optical properties, i.e., ultralow reflectance accompanied by a lack of wavelength scaling behavior. This observation is a result of the lowest ever measured reflectance (R=0.0003) of the sample over a broad infrared wavelength of 3 μm < λ < 13 μm. This discovery may be attributed to the unique interlocking surface of the nanotube array, consisting of both a global, large scale and a short-range randomness.
Applied Optics 05/2011; 50(13):1850-5. · 1.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A key to the success of solid-state lighting is an ultraefficient light extraction, ∼90%. Recent advances in nanotechnology, particularly in creating nanorods, present an unprecedented opportunity to manipulate optical modes at nanometer scales. Here, we report an optically pumped nanorod light-emitting diode (LED) with an ultrahigh extraction efficiency of 79% at λ = 460 nm without the use of either a back reflector or thin film technology. We demonstrated experimentally three key mechanisms for achieving high efficiency: guided mode-reduction, embedded quantum wells, and ultraefficient light out-coupling by the fundamental HE(11) mode. Furthermore, we show that size reduction at nanoscale represents a new degree-of-freedom for alternating and achieving a more directed LED emission.
Nano Letters 02/2011; 11(2):476-81. · 13.20 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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 times 1 mm<sup>2</sup> in-area LED incorporated with the 2DPC is around 4 V, and the light extraction efficiency is enhanced by a factor of 2.1.
IEEE Photonics Technology Letters 02/2008; · 2.19 Impact Factor
-
Proceedings of the 2006 Joint Conference on Information Sciences, JCIS 2006, Kaohsiung, Taiwan, ROC, October 8-11, 2006; 01/2006
-
[show abstract]
[hide abstract]
ABSTRACT: Bi4Ge3O12 single crystals doped with different concentration of Ru were grown by the Czochralski technique. Optical absorption bands were induced by illumination with ultraviolet light at room temperature. The absorption coefficient values increased with increasing ruthenium concentration. The induced photochromic effect was completely reversible: all samples recovered their transparency after thermal treatment. Preliminary holographic recording experiments showed a fast response time and a relatively slow erase time during the reading process.
Journal of Materials Science Materials in Electronics 09/2003; 14(10):857-858. · 1.08 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present a joint transform correlator for color image recognition by using three liquid-crystal spatial light modulators. A method for simultaneously obtaining the correlation peaks of red, green, and blue is proposed and experimentally demonstrated.
Applied Optics 04/2002; 41(8):1500-4. · 1.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The 3-amino-9-ethyl carbazole (AEC)/Dispersed Orange 3 (DO3)/diglycidyl 1,2 cyclohexanedicarboxylate (DCD) main chain copolymers are synthesized and studied on their photorefractive (PR), photoconductive, and holographic characteristics. They are good hologram recording media because not only the stored hologram exhibits excellent fringe contrast with the resolution at about 20 μm, but also the image can be stored, erased, and overwritten. The UV/Vis spectra shows that AEC segments may form charge transfer complexes with either DO3 segments or TNF sensitizers. By incorporating the sensitizer or increasing the charge transfer component concentration, the grating growth rate can be speeded up. Applying an electric field on the polymer film containing no sensitizer helps to elevate the grating growth speed, but it shows little influence on the grating growth speed of the films with sensitizers. More nonlinear optical (NLO) segments in the copolymer result in higher diffraction efficiency. The dark decay of the film depends on the dark conductivity. Incorporating sensitizers or more charge transport segments leads to more dark decay because of increasing dark conductivity. The dark decay of the PR properties at elevated temperature can also be evaluated by the thermal stimulated discharge current (TSDC) spectroscopy technique. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1057–1068, 1999
Journal of Polymer Science Part B Polymer Physics 04/1999; 37(11):1057 - 1068. · 1.53 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We adapt a model proposed by Yariv to analyze the two recording procedures via the kinetics of the recording, fixing, and developing processes under either short circuit or preexposed open-circuit boundary condition. From the analysis, we deduce the optimal condition (in terms of the fixing temperature and the compensation time) for each procedure. The results provide useful guides to design thermal fixing procedures for reaching the maximum fixing efficiency
Lasers and Electro-Optics, 1999. CLEO/Pacific Rim '99. The Pacific Rim Conference on; 02/1999
-
[show abstract]
[hide abstract]
ABSTRACT: The most impressive abilities of associative memory are its
capability of fault tolerance and associated retrieval. In an ordinary
memory of a conventional computer, every piece of the stored information
has a specific address. One must know the complete address to retrieve
particular information. By contrast, in an associative memory one needs
to know only partial information relative to the contents for
accomplishing a complete recall. In a hetero-associative memory, by
inputing a partial pattern of one category, an associated pattern of
another category can be obtained. It is well known that this can be
achieved by an optical holographical method, in which two associated
patterns are utilized to the record interconnection weights at the
Fourier plane. However, due to the grating degeneracy, the number of the
associated pairs is limited because of the serious cross-talk between
different pairs. In the paper, we present our studies on the properties
of a hetero-associative memory of multiple-pairs. We use a phase
modulated liquid crystal television (LCTV) as the reference pattern to
record holographic memories and we propose a novel technique applied to
generate phase only interconnection weights. The results show that the
cross-talk between different pairs of memories can be significantly
reduced by the phase only filter technique
Lasers and Electro-Optics, 1999. CLEO/Pacific Rim '99. The Pacific Rim Conference on; 02/1999
-
[show abstract]
[hide abstract]
ABSTRACT: We present a hetero-associative memory for multiple-associative pairs by using the phase-multiplexing technique. Two methods for reducing the cross-talk between different association pairs are proposed. An optical experiment for the edge-enhancement associative memory is also demonstrated.
Optics Communications 176:347-353. · 1.49 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The modulation transfer function (MTF) of a pixelated liquid crystal spatial light modulator (LC-SLM) has been derived as a function of the fill factor. Based on the formula, we have investigated the dependence of the MTF on the orientations and spatial frequency of the input patterns. Furthermore, we have proposed and demonstrated a method for improving the MTF of a LC-SLM.
Optics Communications.
-
[show abstract]
[hide abstract]
ABSTRACT: Bi12TiO20 (BTO) single crystals nominally pure and doped with ruthenium are grown by top-seeded solution growth method. The effect of ruthenium concentration on optical and photorefractive properties is studied. Strong influence of doping on these properties is observed. It is shown that optical transmission of crystal samples with higher ruthenium content is shifted to the near IR spectral region, while the absorption coefficient is considerably increased. The optical activity of Ru doped crystals is further reduced in comparison with undoped BTO. Photochromic effect is observed in strongly doped crystal. Photorefractive properties are experimentally investigated using two-beam coupling. Response time and diffraction efficiency are changed with ruthenium content.
Optics Communications.
