Browsing by Author "Chau, YF"

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Coupling technique for efficient interfacing between silica waveguides and planar photonic crystal circuits
(2004-12-20)
Chau, YF
;
Yang, TJ
;
Lee, WD
;
電子物理學系
;
Department of Electrophysics
We describe a two-step-size tapered structure with one defect pair that can markedly enhance the coupling efficiency at the entrance and exit terminals of a planar photonic crystal (PPC) waveguide. PPC waveguides are composed of circular dielectric rods set in two-dimensional square lattices. On the basis of our simulations, we found that the optimized scheme maximizes the power transmission above 90% at a wavelength of 1.55 mum. Besides, one can control the central frequency for optical communications by determining this defect configuration in an optimization procedure. Moreover, by properly adjusting the defect radii in PPC tapers, one can use the PPC circuit as a good reflector. (C) 2004 Optical Society of America.
Efficient mode coupling technique between photonic crystal heterostructure waveguide and silica waveguides
(2005-09-15)
Chau, YF
;
Yang, TJ
;
Gu, BY
;
Lee, WD
;
電子物理學系
We report an efficient mode coupling technique between silica waveguides (SWGs) and a planar photonic crystal heterostructure waveguide (PPCHWG) composed of two semi-infinite two-dimensional photonic crystals (PCs) with different filling fractions. By calculating the transmittance at output end of SWG, we find that the designed structures possess the merits of high coupling efficiency and relaxing fabricating tolerance. The maximal transmittance exceeds 90% at a wavelength near 1.65 mu m. The high transmission efficiency of PPCHWGs can be achieved without introducing any defect structures for optimal mode matching. Besides, the width of PPCHWGs can be flexibly adjusted via changing the separation of two component PCs in PC heterostructures. (c) 2005 Elsevier B.V. All rights reserved.
Imaging properties of three dimensional aperture near-field scanning optical microscopy and optimized near-field fiber probe designs
(2004-12-01)
Chau, YF
;
Yang, TJ
;
Tsai, DP
;
電子物理學系
;
Department of Electrophysics
A series of finite difference time domain (FDTD) methods for obtaining more insight on the near-field distribution of subwavelength aperture and fiber probes are numerically investigated. The treatment of dispersive materials in a time-domain-dependent fashion is considered. Several significant factors are also considered successively, e.g., the near-field distribution of subwavelength aperture in an infinite aluminum plane with sample interactions, the characteristics between the near-field distribution and the depolarization phenomenon, different types of three-dimensional tip (noncoated and metal-coated) used to illuminate a photosensitive sample and the polarization of an incident electromagnetic field. Moreover, the FDTD designs of two types of improved probe are illustrated and a suggestion for fabricating an optimal probe is given. Our proposed structures will yield useful information and guidelines for designing high-performance near-field probes.
Near-field optics simulation of a solid immersion lens combining with a conical probe and a highly efficient solid immersion lens-probe system
(2004-04-01)
Chau, YF
;
Yang, TJ
;
Tsai, DP
;
電子物理學系
;
Department of Electrophysics
A solid immersion lens (SIL) combined with near-field probes which are the conic dielectric probe and the local metallic coating on the SIL probe is designed for optical recording by means of a three-dimensional rather than two-dimensional finite difference time domain method to gain more insight in the near-field distribution. Our computation model is realistic to match the real SIL-probe system. The optical properties of near-field distributions between the SIL probe and recording layers are investigated. A promising idea for fabricating a type of the SIL-probe system is proposed. Results of our designation of an optimal SIL-probe system can achieve higher performance (in terms of high throughput and low reflection of the light beam) for optical data storage and microscopy than the conventional metal NSOM probe or SIL used alone. (C) 2004 American Institute of Physics.
Significantly enhanced coupling efficiency in 2D photonic crystal waveguides by using cabin-side-like tapered structures at two terminals
(2004-08-15)
Chau, YF
;
Yang, TJ
;
Gu, BY
;
電子物理學系
;
Department of Electrophysics
We report that using a cabin-side-like tapered structure, containing only one pair of defects, can markedly enhance the coupling efficiency at the entrance and exit terminals of planar photonic crystal waveguides (PPCWGs). The PPCWGs are composed of circular dielectric rods set in 2D triangular lattices. By means of simulations, we find that the transmission efficiency reaches up to 90%. Moreover, the suggested structures possess other advantages, such as the shortness of the taper, the ease of fabrication, and its low cost. It is anticipated that the proposed structures might be feasibly be applicable to the integrated optical circuits compatibility.