Solution‐Processible Multi‐component Cyclometalated Iridium Phosphors for High‐Efficiency Orange‐Emitting OLEDs and Their Potential Use as White Light Sources

The synthesis and photophysical studies of several multifunctional phosphorescent iridium(III) cyclometalated complexes consisting of the hole‐transporting carbazole and fluorene‐based 2‐phenylpyridine moieties are reported. All of them are isolated as thermally and morphological stable amorphous solids. Extension of the π‐conjugation through incorporation of electron‐pushing carbazole units to the fluorene fragment leads to bathochromic shifts in the emission profile, increases the highest occupied molecular orbital levels and improves the charge balance in the resulting complexes because of the propensity of the carbazole unit to facilitate hole transport. These iridium‐based triplet emitters give a strong orange phosphorescence light at room temperature with relatively short lifetimes in the solution phase. The photo‐ and electroluminescence properties of these phosphorescent carbazolylfluorene‐functionalized metalated complexes have been studied in terms of the coordinating position of carbazole to the fluorene unit. Organic light‐emitting diodes (OLEDs) using these complexes as the solution‐processed emissive layers have been fabricated which show very high efficiencies even without the need for the typical hole‐transporting layer. These orange‐emitting devices can produce a maximum current efficiency of ～ 30 cd A^–1 corresponding to an external quantum efficiency of ～ 10 % ph/el (photons per electron) and a power efficiency of ～ 14 lm W^–1. The homoleptic iridium phosphors generally outperform the heteroleptic counterparts in device performance. The potential of exploiting these orange phosphor dyes in the realization of white OLEDs is also discussed.     

On teletraffic applications to OBS

We provide teletraffic models for loss probability evaluation of optical burst switching (OBS). We show that the popular Engset formula is not exact for OBS modeling and demonstrate that in certain cases it is not appropriate. A new exact model is provided. The various models are compared using numerical results for various OBS alternatives with and without burst segmentation.     

Optical transmission characteristics of fiber ring resonators

We present the results of an experimental investigation of the transfer characteristics of a fiber ring resonator for various values of the resonator finesse. In particular, we measure the spectral dependence of the intensity transmission and the induced phase shift in the undercoupled, critically coupled, and overcoupled regimes. We also demonstrate tunable optical (true time) group delay via a fiber ring resonator and show that a high finesse is unnecessary. Our laboratory results are in excellent agreement with theoretical predictions.     

FULL-RCMA: a high utilization EPON

This paper proposes an alternate solution for Ethernet passive optical networks. Our solution uses a novel protocol named full utilization local loop request contention multiple-access protocol to efficiently provide communications in passive optical networks. We study the physical layer implementation, as well as medium access control (MAC) layer protocol performance to illustrate the feasibility and benefit of our solution. The performance studies show that the MAC protocol is capable of offering 95% channel utilization under heavy load conditions. The performance results also indicate that delivery of multimedia traffic with a high quality-of-service can be achieved with our solution.     

Efficient visualization of large routing topologies

As the Internet grows in size and complexity, network managers face a significant challenge in trying to understand the behaviour of routing protocols in large networks. In this paper, we present a tool called VLNT (visualizing large network topologies), which helps network managers to analyse complex routing topologies. A key contribution of our system is a novel hybrid layout algorithm, which significantly reduces the computation time required to layout large network topologies in comparison to conventional layout approaches. In addition our algorithm includes a novel termination criterion that avoids unnecessary iterations when optimizing the network layout. We demonstrate how the visualization features of VLNT can be used to analyse and improve BGP routing topologies, and provide examples using real‐life routing data. Copyright © 2004 John Wiley & Sons, Ltd.     

Gain-enhanced compact broadband microstrip antenna

With the loading of a high-permittivity superstrate layer and a 1 Ω chip resistor, a compact rectangular microstrip antenna with enhanced gain and wider bandwidth can be implemented. With the antenna size reduced to be ~6% that of a conventional patch antenna, the proposed structure can have an operating bandwidth of more than six times that of a conventional patch antenna, with an almost equal antenna gain level. Details of the experimental results are presented and discussed     

Modified planar inverted F antenna

The design of a modified planar inverted F antenna (PIFA) which is more compact (antenna length <λ₀/8 and antenna height <0.01 λ₀) and has a much wider antenna bandwidth (greater than 10 times that of a simple PIFA) is demonstrated. The reduction in antenna length is achieved by meandering the radiating patch, while the enhanced bandwidth with low antenna height is obtained using a chip-resistor load in place of the shorting post. A typical design of the modified PIFA in the 800 MHz band has been implemented, and experimental results are presented and discussed     

Single-feed dual-band circularly polarised microstrip antenna

A novel technique for obtaining dual-band circular polarisation (CP) radiation of a single-feed circular microstrip antenna is proposed and demonstrated. By embedding two pairs of arc-shaped slots of proper lengths close to the boundary of a circular patch, and protruding one of the arc-shaped slots with a narrow slot, the circular microstrip antenna can perform dual-band CP radiation using a single probe feed. Details of the antenna design and experimental results are presented     

Small slot-coupled circularly-polarised microstrip antenna withmodified cross-slot and bent tuning-stub

A novel design of small slot-coupled circularly-polarised circular microstrip antenna with a modified cross-slot cut in the patch and a bent tuning-stub aligned along the patch boundary is proposed and experimentally studied. Results show that, for fixed circular polarisation (CP) operation, the antenna proposed can have an antenna size reduction of ~80%, as compared to a regular-size CP design. The significant size reduction of the proposed antenna is due to the novel modified cross-slot cut in the patch, and CP operation is obtained using a bent tuning-stub incorporating a properly oriented coupling-slot in the ground plane of the microstrip feed line     

Circularly polarised microstrip antenna with a tuning stub

A simple circular polarisation (CP) design of microstrip antennas using a tuning stub is proposed and studied. It is also demonstrated that, by applying this CP design method to a circular microstrip patch with a cross slot having equal slot lengths, a compact circularly-polarised microstrip antenna can easily be implemented, with much more relaxed manufacturing tolerances as compared to the case of using a cross slot of unequal slot lengths. Details of the antenna designs are described, and experimental results are presented and discussed