C. W. Tsao

Localized modes in one-dimensional symmetric Thue-Morse quasicrystals

We present occurrence of the strongly localized modes with high transmission in one dimensional symmetric Thue-Morse quasicrystals. This quasicrystal has some interesting properties, including (i) there are strongly localized modes in separated regions which are around odd semi-quarter-wave thickness of the system, (ii) both the frequency of localized mode and the thicknesses of the space layer to appear localized modes are variant for different generation orders of the system, and (iii) the sharpness of the resonant peaks in the transmission spectra increases as the generation order of the system increases.

Strong localization of photonics in symmetric Fibonacci superlattices

Strong localization from the Fabry-Perot-like resonances that occur in symmetric Fibonacci superlattices is presented in this study. When compared with traditional Fabry–Perot resonators, in symmetric Fibonacci superlattices, the middle space is a variant rather than an invariant half-wavelength thickness for each resonance with different orders. In addition, the electric fields of the resonances may be located on both sides of the space layer in the superlattice, which is in contrast to those in a traditional Fabry–Perot resonator. The electric field of the resonances is strongly localized as the generation order increases. Moreover, the group delays of these peaks increase with generation order. More strongly localized modes can be found from the symmetric Fibonacci superlattices than from the traditional Fabry–Perot resonators, which makes the proposed structure an attractive alternative to a wide variety of optoelectronic devices.

Quasi-Bragg conditions in Thue-Morse dielectric multilayers.

The existence of quasi-Bragg conditions (QBCs) in Thue-Morse dielectric multilayers (TMDMs), based on high reflectance and large forbidden gap regions in its transmission spectra, is presented. In contrast to a single traditional Bragg condition (TBC) in periodic bilayers, there are three QBCs in TMDMs. The formula for each of these QBCs is derived. The results show that one of these QBCs just overlaps the TBC. However, a singular point with perfect transmission exists in this QBC at the quarter-wave stack, at which high reflection exists in the periodic bilayers.

Control of Silver Diffusion in Low-Temperature Co-Fired Diopside Glass-Ceramic Microwave Dielectrics

Electrode material for low-temperature co-fired diopside glass-ceramic used for microwave dielectrics was investigated in the present work. Diffusion of silver from the electrode to diopside glass-ceramics degrades the performance of the microwave dielectrics. Two approaches were adopted to resolve the problem of silver diffusion. Firstly, silicon-oxide (SiO2) powder was employed and secondly crystalline phases were chosen to modify the sintering behavior and inhibit silver ions diffusion. Nanoscale amorphous SiO2 powder turns to the quartz phase uniformly in dielectric material during the sintering process, and prevents the silver from diffusion. The chosen crystalline phase mixing into the glass-ceramics enhances crystallinity of the material and inhibits silver diffusion as well. The result provides a method to decrease the diffusivity of silver ions by adding the appropriate amount of SiO2 and appropriate crystalline ceramics in diopside glass-ceramic dielectric materials. Finally, we used IEEE 802.11a 5.8 GHz as target specification to manufacture LTCC antenna and the results show that a good broadband antenna was made using CaMgSi2O6 with 4 wt % silicon oxide.

High-order micro-ring resonator with perfect transmission using symmetrical Fibonacci structures.

A symmetrical Fibonacci micro-ring resonator (SFMR) has been presented to avoid the coupled resonator optical waveguide (CROW) bottle, which is a bottle-shaped distribution for high orders in transmission spectra. The SFMR features three advantages that improve filtering quality compared to that provided by traditional periodic micro-ring resonators. First, sharper resonances are obtained by eliminating the CROW bottle from the mini gaps that appear in the major-band region. Second, peaks with perfect transmission are always obtained without a radius and coupling modulation in the mini-band regions and major-band regions. Third, the full width at half-maximum of the band-edge peak decreases with the increasing generation order.

Microstructural evolution and microwave dielectric properties of MgO-CaO-2SiO 2 material system

Microstructural characteristics and microwave dielectric properties of MgO-CaO-2SiO<inf>2</inf> glass-ceramic system for microwave components were investigated using Rietveld refinement method, transmission electron microscopy and microwave dielectric measurements. Different amount of monoclinic zirconia (m-ZrO<inf>2</inf>) nucleating agent was added into MgO-CaO-2SiO<inf>2</inf> glass system to synthesize and enhance the quality factor (Q×f) of CaMgSi<inf>2</inf>O<inf>6</inf> diopside glass-ceramic for low sintering temperature process (from 850°C to 950°C). Experimental results reveal that the tetragonal (t)-ZrO<inf>2</inf> forms in the amorphous MgO-CaO-2SiO<inf>2</inf> matrix first, and then crystalline CaMgSi<inf>2</inf>O<inf>6</inf> phase is nucleated and grown around the t-ZrO<inf>2</inf> after sintering due to heterogeneous nucleating from 850 °C. Formation of t-ZrO<inf>2</inf> can be attributed to the diffusion of Ca²⁺ and Mg²⁺ into the m-ZrO<inf>2</inf> and led to transformation to a t-ZrO<inf>2</inf>. Rietveld refinement results show that the lowest amorphous content and the highest quality factors due to the CaMgSi<inf>2</inf>O<inf>6</inf> diopside phase formation and crystal growth when the specimens were sintered at 950°C for 2 hrs. Transmission electron microscopic investigations imply that structural and microstructural arrangements influence the microwave dielectric properties remarkably.

Sharp resonance with complete transmission in Thue-Morse microring resonators

We present sharp resonances with complete transmission in the Thue-Morse microring resonator. The quasi-periodic structure attains a better quality of filtering than the traditional periodic structure. This includes the following: (i) the high-Q resonances with complete transmission are obtained in the transmission spectra, (ii) the maximum value of transmittance always remains 1 for an arbitrary proportion of two different radiuses in the major-band regions, and (iii) the complete transmission occurs for arbitrary coupling in the mini-band regions. Moreover, we propose an analytical method to predict the occurrences of resonance peaks in the mini-band regions based on the gap map.