Outdoor long-range terahertz (THz) communications often come at the expense of transmission rate. Moreover, the practicability of the single polarization optical/THz link, which is commonly used in the previous long-range THz demonstrations based on photonics, is extremely limited by the following two fatal defects. One is relying on active polarization control, and the other is not supporting the transparent bridging of optical polarization division multiplexed (PDM) signals for mature coherent optical communication networks. In this work, a large-capacity photonics-aided THz wireless communication system based on the outdoor long-range 2 × 2 multiple-input multiple-output (MIMO) links has been successfully demonstrated. We first build the 200-m 2 × 2 MIMO THz wireless links at the 300 GHz band. The cascaded linear and nonlinear equalizers are proposed which can significantly improve the transmission performance of 100- and 200-Gb/s PDM quadrature phase shift keying (QPSK) signals. Then an interesting 2 × 2 MIMO structure which can provide certain diversity reception gain under 200-m long-range wireless delivery using the same polarization scheme is also presented and further compared with the orthogonal polarization scheme. Since each THz receiver simultaneously receives data from both the two THz transmitters for this MIMO links, an improvement over 6 dB in receiving sensitivity and one order of magnitude in bit error ratio performance under low signal-to-noise ratio conditions can be achieved. Finally, based on the proposed cascaded equalizers and novel 2 × 2 MIMO structure, we successfully demonstrate a record-breaking 58-Gbaud (232-Gb/s) PDM-QPSK signal transmission over 200-m 2 × 2 MIMO THz wireless links. This is an important attempt for the photonics-aided THz wireless communication systems to achieve 2 × 2 MIMO transmission over a long wireless distance in the outdoors. Furthermore, attaining over 200 Gb/s at a wireless distance of 200 m also represents a key milestone for the long-range and large-capacity THz wireless communication systems.
We demonstrate the generation of 92 nm (−3 dB bandwidth) flat-topped ultrabroad stimulation emission from a chirped InAs/InP quantum dot (QD) laser. A greatly enhanced bandwidth of the gain spectrum is achieved, which is attributed to the additionally broadened quantum dot energy levels utilizing gradually changed height of QDs in the stacked active layers. The laser exhibits a maximum output power of 0.35 W under pulsed conditions, and the average spectral power density of above 3.8 mW/nm is obtained. The ultrabroad lasing spectrum in the wavelength interval of 1.49–1.61 μm covering S-C-L bands makes such a laser potentially useful as an optical source for various applications being compatible with silica fibers.
We demonstrate improved performance of quantum dot solar cells (QDSCs) by type-II InAs/GaAsSb structure. With a moderate Sb composition of 18% and high quality QDs, a high efficiency of 17.31% under AM1.5 G illumination is achieved, showing an improvement of 11.25% in efficiency relative to type-I InAs/InGaAs QDSC. This improvement can be attributed to a high fill factor (FF) of 72.37% compared to 63% of the latter because the type-II structure effectively suppresses carrier recombination losses in QDs. As Sb composition increases to 24%, the FF maintains at a high level of 72.67%, but the efficiency drops to 17% because the elevation of valence band (VB) in GaAsSb capping layer further enhances the hole confinement. And the confinement reduces external quantum efficiency (EQE) and short-circuit current density (Jsc). These results prove the potential of improving efficiency of QDSCs by type-II structure.
This is the final report of a 3-year project. Emerging electro-optic technologies, including optical signal processing, switching, and data manipulation, require high performance, processable nonlinear optical (NLO) and electro-optic (EO) materials. Aim of this project is to combine physical characterization and materials modelling to guide a rational synthesis of artifically structured materials optimized for NLO and EO applications. New materials consisting of chromophores optimized for the red and near-infrared spectral region, directly attached to optical substrates using covalent bonding of self-assembled mono- and multi-layers have been produced and their NLO response measured. A second strategy, based on construction of multiple heterojunctions of one-dimensional solids, is also being explored. Results of CW and ultrafast optical and Raman spectroscopy of these materials demonstrate the highly polarizable nature of the junctions, confirming the NLO potential of the materials. Overall goal was to develop these synthetic approaches through a combined synthesis, characterization, and theoretical effort where materials modeling, benchmarked by observed physical properties, is used to guide rational synthesis of advanced electronic materials.
We demonstrate significantly enhanced performances of 1.3-μm InAs/GaAs quantum dot (QD) lasers by directly Si-doped QDs. The lasers were grown by molecular beam epitaxy. Following Si doping, the ridge waveguide laser, with uncoated facets, showed a remarkably reduced continuous-wave threshold current density of 71.6 A/cm2 (14.3 A/cm2 per QD layer), compared with 167.3 A/cm2 (33.5 A/cm2 per QD layer) for an undoped device with an identical structure, measured at 20 °C. Moreover, doping improved the single-side slope efficiency from 0.28 to 0.42 W/A. In addition, the Si-doped QD laser exhibited a higher lasing temperature of up to 140 °C compared with 120 °C for the undoped QD laser.
The capacity to specifically destroy cancer cells while avoiding normal tissue is urgently desirable in cancer treatment. Herein, a photothermal-trigger-released system serves as a photoacoustic imaging agent constructed by entrapping diketopyrrolopyrrole-based conjugated polymers and curcumin in a poly(ethylene glycol) (PEG)-protected thermoresponsive liposomal phospholipid bilayer. This lipid nanostructure can improve the bioavailability of hydrophobic agents for photothermal treatment with high efficiency and deliver the anticancer drug curcumin to the tumor site actuated by near-infrared (NIR) irradiation. A significantly enhanced combined therapeutic effect to HepG2 tumor-bearing mice was acquired in contrast to the result of single therapy alone. These liposomes with the capability of photoacoustic imaging, greater EPR-induced accumulation in tumor sites, and hyperthermia ablation for photothermal chemotherapy show potential for photoacoustic imaging-guided photothermal/chemo combined therapeutic applications.
Aiming to achieve InAs quantum dots (QDs) with a long carrier lifetime, the effects of Sb component in cap layers on the band alignment of the InAs/GaAsSb QDs have been studied. InAs QDs with high density and uniformity have been grown by molecular beam epitaxy. With increasing Sb composition, the InAs/GaAsSb QDs exhibit a significant red-shift and broadening photoluminescence (PL). With a high Sb component of 22%, the longest wavelength emission of the InAs/GaAs 0.78 Sb 0.22 QDs occurs at 1.5 μm at room temperature. The power-dependence PL measurements indicate that with a low Sb component of 14%, the InAs/GaAs 0.86 Sb 0.14 QDs have a type-I and a type-II carrier recombination processes, respectively. With a high Sb component of 22%, the InAs/GaAs 0.78 Sb 0.22 QDs have a pure type-II band alignment, with three type-II carrier recombination processes. Extracted from time-resolved PL decay traces, the carrier lifetime of the InAs/GaAs 0.78 Sb 0.22 QDs reaches 16.86 ns, which is much longer than that of the InAs/GaAs 0.86 Sb 0.14 QDs (2.07 ns). These results obtained here are meaningful to realize high conversion efficiency intermediate-band QD solar cells and other opto-electronic device.
This chapter investigates the cost of public debt for firms using a comprehensive sample consisting of 17,368 industrial bond issues from 1970 to 2011. The empirical evidence shows that yield spreads for seasoned bond issues are significantly lower than those for initial bond issues. This seasoning effect is robust across different sample periods, subsamples, and model specifications. On average, the yield spreads for seasoned bond issues are around 50 bps lower than those for initial bond issues. This difference cannot be explained by other bond and firm characteristics. The seasoning effect is more pronounced for firms with higher levels of uncertainty, lower information disclosure quality, and longer time intervals between the first and subsequent issues. Our empirical findings provide supportive evidence for the extant theories that aim to rationalize the information role in determining the cost of capital.
The aim of this article is to advance the discussion of use-misuse cases as a tool for information system security risk assessment during system development. We closely examined the limitations and came up with some basic pointers that needed to be addressed in order to overcome the limitations. We proposed some solutions to these lacks and present a framework and modeling process to achieve the solutions. We illustrate the use of the proposed model on popular e-shop system as a case study. The proposed model is able to allow managers and system developers to share a commonly understand view concerning the potential impact of various information system related threats that make sense to them within their limited resources.
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