Browsing by Author "Shen, Linfang"

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50/50 beam splitter using a one-dimensional metal photonic crystal with parabolalike dispersion
(2007-06-18)
Shen, Linfang
;
Yang, Tzong-Jer
;
Chau, Yuan-Fong
;
電子物理學系
;
Department of Electrophysics
The spatial dispersion properties of a one-dimensional metal photonic crystal have been analyzed and five types of dispersion curves have been shown at a normalized frequency less than 1. It is demonstrated that by exploiting a parabolalike dispersion behavior, a metal photonic crystal slab can be used to realize an exactly 50/50 beam splitter. (c) 2007 American Institute of Physics.
Effect of internal period on the optical dispersion of indefinite-medium materials
(2008-05-01)
Shen, Linfang
;
Yang, Tzong-Jer
;
Chau, Yuan-Fong
;
電子物理學系
;
Department of Electrophysics
The effect of internal period on the optical dispersion of indefinite medium material (IDMM) is analytically studied under the condition of the period much smaller than the operating wavelength, based on a simplified dipole model for the material. Interesting phenomena associated with the internal period, such as upper cutoff for wave vector, additional propagating mode, and parabolic dispersion in a limiting case are demonstrated in detail. However, for the normal wave vector (k) region, where vertical bar k vertical bar similar to k(0) or vertical bar k vertical bar << k(0) (k(0) is the free-space wave number), the hyperbolic dispersion behavior can still be realized by IDMM as long as its internal period is small enough. Our analysis also shows that unlike the homogeneous indefinite medium, there exists no special boundary for IDMM, on which the refraction problem cannot be physically solved. Finally, the dispersion properties obtained from the dipole model are verified by using a real example of layered IDMM.
Interaction Between Negative and Positive Index Medium Waveguides
(2008-11-01)
Yan, Wei
;
Shen, Linfang
;
Yuan, Yu
;
Yang, Tzong Jer
;
電子物理學系
The coupling between negative and positive index medium waveguides is investigated theoretically in this paper. A coupled mode theory is developed for such a waveguide system and its validity is verified. Interesting phenomena in the coupled waveguides are demonstrated, which occur in the case when the negative index medium waveguide in isolation guides its mode backward. A new type of coupled mode solution that varies exponentially with the coupling length is found in the special case when the propagation constants of two individual waveguides are nearly the same. A coupler operating in this case is insensitive to the coupling length, and its coupling efficiency can reach 100% as long as the coupling length is long enough. However, when the propagation constants of the two individual waveguides differ greatly, the coupled mode solution is still a periodic function of the coupling length, but the coupled power is output backward. In addition, the modes in the composite waveguide system are also studied using the coupled mode theory, and their fundamental properties are revealed.
Terahertz surface plasmon polaritons on periodically corrugated metal surfaces
(2008-03-03)
Shen, Linfang
;
Chen, Xudong
;
Yang, Tzong-Jer
;
電子物理學系
;
Department of Electrophysics
Based on a modal expansion of electromagnetic fields, a rigorous method for analyzing surface plasmon polaritons (SPPs) on a periodically corrugated metal surface has been formulated in this paper. This method takes into account the finite conductivity of the metal as well as higher-order modes within the grooves of the surface structure, thus is able to accurately calculate the loss of these spoof SPPs propagating along the structured surface. In the terahertz (THz) frequency range, the properties of the dispersion and loss of spoof SPPs on corrugated Al surfaces are analyzed. For spoof SPPs at THz frequencies, the strong confinement of the fields is often accompanied with considerable absorption loss, but the performance of both low-loss propagation and subwavelength field confinement for spoof SPPs can be achieved by the optimum design of surface structure. (C) 2007 Optical Society of America.