Browsing by Author "Chang, Hung-Chun"

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A Multidomain Pseudospectral Mode Solver for Optical Waveguide Analysis
(2012-07-01)
Chiang, Shun-Fan
;
Lin, Bang-Yan
;
Chang, Hung-Chun
;
Teng, Chun-Hao
;
Wang, Chih-Yu
We propose a pseudospectral mode solver for optical waveguide mode analysis formulated by the frequency-domain Maxwell equations. Special attention is paid upon identifying the required boundary operator for the formulation and the relationships between the derived operator and the physical boundary conditions. These theoretical results are adopted into a Legendre pseudospectral multidomain computational framework to compute the propagation characteristics of optical waveguides. Numerical experiments are conducted, and the expected spectral convergence of the scheme is observed for smooth problems and for problems having field jumps at material interfaces. For dielectric waveguides with sharp corners, the spectral convergence is lost due to the singular nature of fields at the corner. Nevertheless, compared with other methods, the present formulation remains as an efficient approach to obtain waveguide modes.
A network address translation approach to the inbound session problem in private networks
(2007-02-01)
Hsieh, Ming-Deng
;
Chang, Hung-Chun
;
Tseng, Chien-Chao
;
Wang, Tsan-Pin
;
資訊工程學系
This paper proposes a Dynamic-Configurable NAT (DCNAT) approach to the inbound session problem for private networks behind NAT routers. DCNAT is a port-based NAT scheme that adopts a registration procedure for a host to register a session with a DCNAT router before originating a communication session to a host behind the DCNAT router. With the registration procedure, the DCNAT router can create NAT binding entries dynamically for address: port translation before the inbound session starts. Furthermore the dynamic creation of NAT binding entries makes DCNAT very flexible in supporting inbound accesses to a large number of services opened dynamically by the private nodes behind an NAT router. Although DCNAT requires minor modification to the originating host and the NAT router, it is highly suitable for proxy-based applications, such as web browsing, or instant message delivery.
Pseudospectral Modeling of Nano-Optics in Ag Sphere Arrays
(2010-10-01)
Lin, Bang-Yan
;
Teng, Chun-Hao
;
Chang, Hung-Chun
;
Hsiao, Hui-Hsin
;
Wang, Juen-Kai
We report a Legendre pseudospectral modeling of silver sphere arrays illuminated by light waves. A special feature of the present computation is that the dispersive nature of silver is described by a Drude-Lorentz model with model parameters obtained by fitting the frequency-domain complex-valued dielectric constants measured experimentally. Numerical validations are conducted based on solving both the near and far fields of the Mie scattering problem, and we observe good convergence on the numerical fields. The far-field patterns of the Ag sphere arrays are simulated. The results are compared to those obtained by the dipole-coupling-model method, and we observe very good agreement between these results. The near-field patterns are also computed, and localized enhanced electric fields in the inter-particle gap regions due to plasmonic coupling between Ag particles are visualized. As the gap between Ag particles is reduced the strength of the localized enhanced electric field is increased.
Pseudospectral Modeling of Nano-Optics in Ag Sphere Arrays
(2010-10-01)
Lin, Bang-Yan
;
Teng, Chun-Hao
;
Chang, Hung-Chun
;
Hsiao, Hui-Hsin
;
Wang, Juen-Kai
We report a Legendre pseudospectral modeling of silver sphere arrays illuminated by light waves. A special feature of the present computation is that the dispersive nature of silver is described by a Drude-Lorentz model with model parameters obtained by fitting the frequency-domain complex-valued dielectric constants measured experimentally. Numerical validations are conducted based on solving both the near and far fields of the Mie scattering problem, and we observe good convergence on the numerical fields. The far-field patterns of the Ag sphere arrays are simulated. The results are compared to those obtained by the dipole-coupling-model method, and we observe very good agreement between these results. The near-field patterns are also computed, and localized enhanced electric fields in the inter-particle gap regions due to plasmonic coupling between Ag particles are visualized. As the gap between Ag particles is reduced the strength of the localized enhanced electric field is increased.
Simulations of Dielectric and Plasmonic Waveguide-Coupled Ring Resonators Using the Legendre Pseudospectral Time-Domain Method
(2012-06-01)
Chung, Shih-Yung
;
Wang, Chih-Yu
;
Teng, Chun-Hao
;
Chen, Chung-Ping
;
Chang, Hung-Chun
The accurate Legendre pseudospectral time-domain (PSTD) method is applied in this paper to the study of optical behaviors of 2-D dielectric and plasmonic waveguide-coupled ring resonators. Based on its inherent multidomain scheme with curvilinear-quadrilateral subdomain partitioning, the PSTD method possesses superior advantage in fulfilling field continuity conditions across material interfaces, which provides better numerical handling upon circular or even more complicated ring structures. Accordingly, investigations of several plasmonic nanoring resonators of different shapes with surface plasmon polariton (SPP) waves propagating on the metal/dielectric/metal waveguides are made with the aids of a well-fitted Drude-Lorentz material-dispersion model through analyzing their characteristics in the near-infrared and visible parts of the light spectrum. Especially, the racetrack-shaped ring is carefully designed with optimized track length to avoid the over-or under-coupling problem between the ring and input waveguides and, thus, achieve excellent spectral performance.
THz Fiber Directional Coupler
(2007)
Chen, Hung-Wen
;
Lu, Ja-Yu
;
Chen, Li-Jin
;
Chiang, Po-Jui
;
Chang, Hung-Chun
We demonstrated a THz subwavelength fiber coupler for future millimeter wave applications. Unlike traditional optical fiber couplers, its coupling ratio is independent of the length of the coupling region because of the anti-symmetric mode cutoff. (C) 2007 Optical Society of America