Browsing by Author "Lee, Ray-Kuang"

Now showing 1 - 13 of 13

A simple model for cavity enhanced slow lights in vertical cavity surface emission lasers
(2008-04-01)
Chou, Chia-Sheng
;
Lee, Ray-Kuang
;
Peng, Peng-Chun
;
Kuo, Hao-Chung
;
Lin, Gray
We develop a simple model for the slow lights in vertical cavity surface emission lasers (VCSELs), with the combination of cavity and population pulsation effects. The dependences of probe signal power, injection bias current and wavelength detuning for the group delays are demonstrated numerically and experimentally. Up to 65 ps group delays and up to 10 GHz modulation frequency can be achieved at room temperature at a wavelength of 1.3 mu m. The most significant feature of our VCSEL device is that the thickness of the active region is only several micrometers long. Based on the experimental parameters of quantum dot VCSEL structures, we show that the resonance effect of the laser cavity plays a significant role in enhancing the group delays.
Band structures of a dipolar Bose-Einstein condensate in one-dimensional lattices
(2008-08-01)
Lin, YuanYao
;
Lee, Ray-Kuang
;
Kao, Yee-Mou
;
Jiang, Tsin-Fu
;
物理研究所
We derive the effective Gross-Pitaevskii equation for a cigar-shaped dipolar Bose-Einstein condensate in one-dimensional lattices and investigate the band structures numerically. Due to the anisotropic and the long-ranged dipole-dipole interaction in addition to the known contact interaction, we elucidate the possibility of modifying the band structures by changing the alignment of the dipoles with the axial direction. With the considerations of the transverse parts and the practical physical parameters of a cigar-shaped trap, we show the possibility to stabilize an attractive condensate simply by adjusting the orientation angle of dipoles. Some interesting Bloch waves at several particle current densities are identified for possible experimental observations.
Carrying an arbitrarily large amount of information using a single quantum particle
(2020-08-25)
Hsu, Li-Yi
;
Lai, Ching-Yi
;
Chang, You-Chia
;
Wu, Chien-Ming
;
Lee, Ray-Kuang
Theoretically speaking, a photon can travel arbitrarily long before it enters into a detector, resulting in a click. How much information can a photon carry? We study a bipartite asymmetric "two-way signaling" protocol as an extension of that proposed by Del Santo and Dakic. Suppose that Alice and Bob are distant from each other and each of them has an n-bit string. They are tasked to exchange the information of their local n-bit strings with each other, using only a single photon during the communication. It has been shown that the superposition of different spatial locations in a Mach-Zehnder (MZ) interferometer enables bipartite local encodings. We show that, after the travel of a photon through a cascade of n-level MZ interferometers in our protocol, the one of Alice and Bob whose detector clicks can access the other's full information of the n-bit string, while the other can gain one bit of information. That is, the wave-particle duality makes two-way signaling possible, and a single photon can carry an arbitrarily large (but finite) amount of information.
Curvature-assisted wave localization in Vertical Cavity Surface Emitting Lasers
(2017-01-01)
Hong, Kou-Bin
;
Lin, Chun-Yan
;
Chang, Tsu-Chi
;
Liang, Wei-Hsuan
;
Lai, Ying-Yu
By implementing surface structures in vertical cavity surface emitting lasers as manifolds for curved space, we experimentally study the impacts of geometrical constraints on wave localization. We observe localized waves pinned to the maximal curvature in an ellipticalring, and confirm the reduction in the localization length of waves by measuring near and far field patterns, as well as the corresponding dispersion relation. Theoretically, analyses based on a dissipative model with a parabola curve give good agreement remarkably to experimental measurement on the transition from delocalized to localized waves. The introduction of curved topology allows to control and design lasing modes in the nonlinear regime.
Effects of size and shell thickness of TiO2 hierarchical hollow spheres on photocatalytic behavior: An experimental and theoretical study
(2014-04-05)
Tsai, Min-Chiao
;
Lee, Jeng-Yi
;
Chen, Po-Chin
;
Chang, Yuan-Wei
;
Chang, Ya-Chen
Through a self-sacrificing template method, highly uniform hollow-spheres of TiO2 anatase are synthesized with controllable diameter from 365 nm to 930 nm. Compared to large hollow spheres, a large enhancement in the photocatalytic activity is reported for the small hollow spheres (with a thickness of 50 nm). By extending Mie\'s scattering theory from solid- to hollow-spheres, for a spherical scatter with a diameter of 300-900 nm, theoretical calculation reveal that each singular hollow sphere has absorption power equivalent to a solid sphere as the shell thickness parameter reaches a critical value of 0.3-0.6. This critical thickness parameter is independent to the size of a single hollow sphere, demonstrating that hollow spheres have quantitative advantages over solid spheres of the same weight. Moreover, calculation supported that small hollow spheres have stronger absorption power than large hollow spheres due to higher thickness. This greatly enhance the performance of small hollow spheres under a photocatalytic test. Our theoretical results showed good agreement to the experimental measurements, and provided a framework for the design of hollow-sphere nano-particles for optimized absorption power. (C) 2013 Elsevier B.V. All rights reserved.
Entangled Quantum Nonlinear Schroumldinger Solitons
(2009-07-03)
Lai, Yinchieh
;
Lee, Ray-Kuang
;
光電工程學系
;
Department of Photonics
Considered as a multipartite quantum system, time-multiplexed nonlinear Schroumldinger solitons after collision are rigorously proved to become quantum entangled in the sense that their quadrature components of suitably selected internal modes satisfy the inseparability criterion. Clear physical insights for the origin of entanglement are given, and the required homodyne local oscillator pulse shape for optimum entanglement detection is determined.
Flexible Organometal-Halide Perovskite Lasers for Speckle Reduction in Imaging Projection
(2019-05-01)
Wang, Yu-Chi
;
Li, Heng
;
Hong, Yu-Heng
;
Hong, Kuo-Bin
;
Chen, Fang-Chung
Disorder is emerging as a strategy for fabricating random laser sources with very promising materials, such as perovskites, for which standard laser cavities are not effective or too expensive. We need, however, different fabrication protocols and technologies for reducing the laser threshold and controlling its emission. Here, we demonstrate an effectively solvent-engineered method for high-quality perovskite thin films on a flexible polyimide substrate. The fractal perovskite thin films exhibit excellent optical properties at room temperature and easily achieve lasing action without any laser cavity above room temperature with a low pumping threshold. The lasing action is also observed in curved perovskite thin films on flexible substrates. The lasing threshold can be further reduced by increasing the local curvature, which modifies the scattering strengths of the bent thin film. We also show that the curved perovskite lasers are extremely robust with respect to repeated deformations. Because of the low spatial coherence, these curved random laser devices are efficient and durable speckle-free light sources for applications in spectroscopy, bioimaging, and illumination.
Generation of Crescent Waves in Vertical Cavity Surface Emitting Lasers with an Surface Elliptical Ring
(2014)
Lai, Ying-Yu
;
Chang, Tsu-Chi
;
Li, Ya-Chen
;
Lin, Chun-Yan
;
Lu, Tien-Chang
We tailor the lasing modes in the vertical cavity surface -emitting laser into a crescent wave using a surface elliptical ring. The crescent wave was observed to be localized at the semi-major axis of elliptical ring.
Lasing on nonlinear localized waves in curved geometry
(2017-11-13)
Hong, Kou-Bin
;
Lin, Chun-Yan
;
Chang, Tsu-Chi
;
Liang, Wei-Hsuan
;
Lai, Ying-Yu
The use of geometrical constraints exposes many new perspectives in photonics and in the fundamental studies of nonlinear waves. By implementing surface structures in vertical cavity surface emitting lasers as manifolds for curved space, we experimentally study the impacts of geometrical constraints on nonlinear wave localization. We observe localized waves pinned to the maximal curvature in an elliptical-ring, and confirm the reduction in the localization length of waves by measuring near and far field patterns, as well as the corresponding energy-angle dispersion relation. Theoretically, analyses based on a dissipative model with a parabola curve give good agreement remarkably to experimental measurement on the reduction in the localization length. The introduction of curved geometry allows to control and design lasing modes in the nonlinear regime. (C) 2017 Optical Society of America
Lasing on surface states in vertical-cavity surface-emission lasers
(2014-10-01)
Su, Yonan
;
Lin, Chun-Yan
;
Hong, Ray-Ching
;
Yang, Wen-Xing
;
Jeng, Chien-Chung
We report experimental observation of lasing on surface states, in the form of standing waves at the termination of a defect-free photonic crystal on top of vertical-cavity surface-emission lasers. Direct images of lasing modes at the truncated periodic potential, along one side of a square lattice, are demonstrated by collecting near-field radiation patterns, as well as in numerical simulations. Our results provide a step toward realizing surface and edge states in optical cavities. (C) 2014 Optical Society of America
Optimum detection of quantum entangled fiber solitons
(2008)
Lai, Yinchieh
;
Lee, Ray-Kuang
;
光電工程學系
;
Department of Photonics
Two-partie and multi-partie time-multiplexed fiber solitons after nonlinear interaction are rigorously proved to be quantum entangled in the sense that their quadrature components of internal modes satisfy the EPR non-local criterion. The optimum homedyne local oscillator pulse-shape for entanglement detection is determined. (C) 2007 Optical Society of America
Quantum squeezing and correlation of self-induced transparency solitons
(2009-09-01)
Lee, Ray-Kuang
;
Lai, Yinchieh
;
光電工程學系
;
Department of Photonics
A general quantum theory of self-induced transparency (SIT) solitons is developed with nonlinear quantum effects of atoms taken into account. The quantization starts from the coarse-grain-averaged light-atom interaction Hamiltonian by which the quantum effects of ensemble atoms are modeled. The calculation of quantum properties is performed by the backpropagation method, which takes into account the contribution of the field continuum parts and the atomic fluctuations. The detectable squeezing ratio with a general homodyne local oscillator can be simulated for practical experimental realizations. Schemes for generating quantum correlation through SIT soliton interaction are also proposed and analyzed.
Scattering resonance enhanced dye absorption of dye sensitized solar cells at optimized hollow structure size
(2014-12-05)
Tsai, Min-Chiao
;
Lee, Jeng-Yi
;
Chang, Ya-Chen
;
Yang, Min-Han
;
Chen, Tin-Tin
This study elucidates the size effect on dye-sensitized solar cells (DSSCs) by synthesizing highly uniform hierarchical hollow sphere TiO2 samples, with the diameters from 220 nm to 800 nm. Experimental results indicate that the optimum conversion efficiency using N719 dye can be achieved around 5.5%, as the diameter of hierarchical hollow spheres is 450-550 nm. According to the incident photon-to-current conversion efficiency (IPCE) spectra, large-sized hierarchical hollow spheres significantly enhance the light harvesting by scattering; whereas small-sized hallow spheres (<360 nm) improve negligibly. Additionally, mesoporous and solid spheres with an identical diameter, 440 nm in this study, are also studied as a comparison. Our results demonstrate that hollow spheres perform the same conversion efficiency as that of mesoporous spheres owing to the equivalent adsorption of dye molecules in both hierarchical structures - regardless of the surface area of the interior of mesoporous structure, which shows that hollow spheres have higher conversion efficiency per unit volume than that of mesoporous spheres. (C) 2014 Elsevier B.V. All rights reserved.