Gain switching of monolithic 1.3 μm InAs/GaAs quantum dot lasers on silicon

© 1983-2012 IEEE. We report the first demonstration of gain-switched optical pulses generated by continuous-wave 1.3 μm InAs/GaAs quantum dot (QD) broad-area lasers directly grown on silicon. The shortest observed pulses have typical durations between 175 and 200 ps with peak output powers of up to 66 mW. By varying the drive current pulsewidth and amplitude systematically, we find that the peak optical power is maximized through sufficiently long high-amplitude drive pulses, whereas shorter drive pulses with high amplitudes yield the narrowest achievable pulses. A three-level rate equation travelling-wave model is used for the simulation of our results in order to gain a first insight into the underlying physics and the laser parameters responsible for the observed behavior. The simulations indicate that a limited gain from the InAs QDs and a very high gain compression factor are the main factors contributing to the increased pulsewidth. As the optical spectra of the tested broad-area QD laser give a clear evidence of multitransverse-mode operation, the laser's dynamic response could be additionally limited by transversal variations of the gain, carrier density, and photon density over the 50 μm wide laser waveguide

Dynamic Properties of Monolithic 1.3 μm InAs/GaAs Quantum Dot Lasers on Silicon

Small-signal experiments with a 2.5 mm-long quantum dot narrow ridge-waveguide laser on silicon show a modulation bandwidth of 1.6 GHz. For the first time, we report key high-speed parameters such as the differential gain and the gain compression factor

High-Bandwidth Low-Cost High-Speed Optical Fiber Links using Organic Light Emitting Diodes

Record-high 200 Mbps transmission using an OLED with a 31 MHz 3 dB bandwidth using a 3-tap feedforward equaliser is achieved, demonstrating the potential of such devices for use in low-cost polymer optical fiber links.EPSRC Ultra Parallel Visible Light Communication Project (EP/K00042X/1) EPSRC Studentship 146672

Understanding the bandwidth limitations in monolithic 1.3 μm InAs/GaAs quantum dot lasers on silicon

In this paper, we present measurements and simulations of the small-signal modulation response of monolithic continuous-wave 1.3 μm InAs/GaAs quantum dot (QD) narrow ridge-waveguide lasers on a silicon substrate. The 2.5 mm-long lasers investigated demonstrate 3dB modulation bandwidths of 1.6 GHz, D-factors of 0.3 GHz/mA1/2, modulation current efficiencies of 0.4 GHz/mA1/2, and K-factors of 2.4 ns and 3.7 ns. Since the devices under test are not designed for high-speed operation due to their long length and hence long photon lifetime, the modulation response curves are used as a fitting template for numerical simulations with spatiotemporal resolution to gain insight into the underlying laser physics. The obtained parameter set is used to unveil the true potential of the laser material in an optimized device geometry by modeling the small-signal response at different cavity lengths, mirror reflectivities, and for different numbers of QD layers. The simulations predict a maximum 3dB modulation bandwidth of 5 GHz to 7 GHz for a 0.75 mm-long cavity with 99 % and 60 % high-reflection coatings and ten QD layers. Modeling the impact of dislocations on the dynamic performance qualitatively reveals that enhanced non-radiative recombination in the wetting layer leaves the modulation bandwidth of QD lasers on silicon almost unaffected, while dislocation-induced optical loss does not pose a problem, as long as sufficient gain is provided by the QD active region.UK EPSRC Grant, No. EP/J012904/1 & EP/J012815/1 Qualcomm Inc. studentship Royal Academy of Engineering, Reference No. RF201617/16/2

Gain Switching of Monolithic 1.3 μm InAs/GaAs Quantum Dot Lasers on Silicon

We report the first demonstration of gain-switched optical pulses generated by continuous-wave 1.3 μm InAs/GaAs quantum dot (QD) broad-area lasers directly grown on silicon. The shortest observed pulses have typical durations between 175 and 200 ps with peak output powers of up to 66 mW. By varying the drive current pulsewidth and amplitude systematically, we find that the peak optical power is maximized through sufficiently long high-amplitude drive pulses, whereas shorter drive pulses with high amplitudes yield the narrowest achievable pulses. A three-level rate equation travelling-wave model is used for the simulation of our results in order to gain a first insight into the underlying physics and the laser parameters responsible for the observed behavior. The simulations indicate that a limited gain from the InAs QDs and a very high gain compression factor are the main factors contributing to the increased pulsewidth. As the optical spectra of the tested broad-area QD laser give a clear evidence of multitransverse-mode operation, the laser's dynamic response could be additionally limited by transversal variations of the gain, carrier density, and photon density over the 50 μm wide laser waveguide

Small-Signal Modulation and Analysis of Monolithic 1.3μm InAs/GaAs Quantum Dot Lasers on Silicon

The first small-signal modulation experiments with monolithic single transverse mode InAs/GaAs lasers on Si demonstrate a 3dB bandwidth of 1.6 GHz. By fitting the modulation response curves, we extract high-speed laser parameters allowing an insight into the intrinsic laser dynamics

Identification of Colletotrichum species associated with anthracnose disease of coffee in Vietnam

Colletotrichum gloeosporioides, C. acutatum, C. capsici and C. boninense associated with anthracnose disease on coffee (Coffea spp.) in Vietnam were identified based on morphology and DNA analysis. Phylogenetic analysis of DNA sequences from the internal transcribed spacer region of nuclear rDNA and a portion of mitochondrial small subunit rRNA were concordant and allowed good separation of the taxa. We found several Colletotrichum isolates of unknown species and their taxonomic position remains unresolved. The majority of Vietnamese isolates belonged to C. gloeosporioides and they grouped together with the coffee berry disease (CBD) fungus, C. kahawae. However, C. kahawae could be distinguished from the Vietnamese C. gloeosporioides isolates based on ammonium tartrate utilization, growth rate and pathogenictity. C. gloeosporioides isolates were more pathogenic on detached green berries than isolates of the other species, i.e. C. acutatum, C capsici and C. boninense. Some of the C. gloeosporioides isolates produced slightly sunken lesion on green berries resembling CBD symptoms but it did not destroy the bean. We did not find any evidence of the presence of C. kahawae in Vietnam

Effect of continuous positive airway pressure therapy on a large hemangioma complicated with obstructive sleep apnea syndrome: a case report

<p>Abstract</p> <p>Introduction</p> <p>Hemangiomas involving the upper airway can be an uncommon cause of obstructive sleep apnea syndrome.</p> <p>Case presentation</p> <p>A 26-year-old Caucasian man with a known history of a large hemangioma of his head and neck presented with sleep-disordered breathing to the sleep unit of our hospital. Severe obstructive sleep apnea syndrome was revealed on polysomnography. Nasal continuous positive airway pressure was implemented effectively, reducing daytime hypersomnolence and significantly improving sleep parameters. After three years of adherent use, the patient remains in a good condition and the hemangioma is stable.</p> <p>Conclusion</p> <p>Application of continuous positive airway pressure can be an effective treatment for patients with obstructive sleep apnea syndrome complicated with vascular tumors. Periodic follow-up of these patients is necessary, as little is known about the long-term effects of continuous positive airway pressure therapy.</p

Extracellular Matrix Proteomics Reveals Interplay of Aggrecan and Aggrecanases in Vascular Remodeling of Stented Coronary Arteries.

BACKGROUND: Extracellular matrix (ECM) remodeling contributes to in-stent restenosis and thrombosis. Despite its important clinical implications, little is known about ECM changes post-stent implantation. METHODS: Bare-metal and drug-eluting stents were implanted in pig coronary arteries with an overstretch under optical coherence tomography guidance. Stented segments were harvested 1, 3, 7, 14, and 28 days post-stenting for proteomics analysis of the media and neointima. RESULTS: A total of 151 ECM and ECM-associated proteins were identified by mass spectrometry. After stent implantation, proteins involved in regulating calcification were upregulated in the neointima of drug-eluting stents. The earliest changes in the media were proteins involved in inflammation and thrombosis, followed by changes in regulatory ECM proteins. By day 28, basement membrane proteins were reduced in drug-eluting stents in comparison with bare-metal stents. In contrast, the large aggregating proteoglycan aggrecan was increased. Aggrecanases of the ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) family contribute to the catabolism of vascular proteoglycans. An increase in ADAMTS-specific aggrecan fragments was accompanied by a notable shift from ADAMTS1 and ADAMTS5 to ADAMTS4 gene expression after stent implantation. Immunostaining in human stented coronary arteries confirmed the presence of aggrecan and aggrecan fragments, in particular, at the contacts of the stent struts with the artery. Further investigation of aggrecan presence in the human vasculature revealed that aggrecan and aggrecan cleavage were more abundant in human arteries than in human veins. In addition, aggrecan synthesis was induced on grafting a vein into the arterial circulation, suggesting an important role for aggrecan in vascular plasticity. Finally, lack of ADAMTS-5 activity in mice resulted in an accumulation of aggrecan and a dilation of the thoracic aorta, confirming that aggrecanase activity regulates aggrecan abundance in the arterial wall and contributes to vascular remodeling. CONCLUSIONS: Significant differences were identified by proteomics in the ECM of coronary arteries after bare-metal and drug-eluting stent implantation, most notably an upregulation of aggrecan, a major ECM component of cartilaginous tissues that confers resistance to compression. The accumulation of aggrecan coincided with a shift in ADAMTS gene expression. This study provides the first evidence implicating aggrecan and aggrecanases in the vascular injury response after stenting

Short-term efficacy of physical interventions in osteoarthritic knee pain. A systematic review and meta-analysis of randomised placebo-controlled trials.

BACKGROUND: Treatment efficacy of physical agents in osteoarthritis of the knee (OAK) pain has been largely unknown, and this systematic review was aimed at assessing their short-term efficacies for pain relief. METHODS: Systematic review with meta-analysis of efficacy within 1-4 weeks and at follow up at 1-12 weeks after the end of treatment. RESULTS: 36 randomised placebo-controlled trials (RCTs) were identified with 2434 patients where 1391 patients received active treatment. 33 trials satisfied three or more out of five methodological criteria (Jadad scale). The patient sample had a mean age of 65.1 years and mean baseline pain of 62.9 mm on a 100 mm visual analogue scale (VAS). Within 4 weeks of the commencement of treatment manual acupuncture, static magnets and ultrasound therapies did not offer statistically significant short-term pain relief over placebo. Pulsed electromagnetic fields offered a small reduction in pain of 6.9 mm [95% CI: 2.2 to 11.6] (n = 487). Transcutaneous electrical nerve stimulation (TENS, including interferential currents), electro-acupuncture (EA) and low level laser therapy (LLLT) offered clinically relevant pain relieving effects of 18.8 mm [95% CI: 9.6 to 28.1] (n = 414), 21.9 mm [95% CI: 17.3 to 26.5] (n = 73) and 17.7 mm [95% CI: 8.1 to 27.3] (n = 343) on VAS respectively versus placebo control. In a subgroup analysis of trials with assumed optimal doses, short-term efficacy increased to 22.2 mm [95% CI: 18.1 to 26.3] for TENS, and 24.2 mm [95% CI: 17.3 to 31.3] for LLLT on VAS. Follow-up data up to 12 weeks were sparse, but positive effects seemed to persist for at least 4 weeks after the course of LLLT, EA and TENS treatment was stopped. CONCLUSION: TENS, EA and LLLT administered with optimal doses in an intensive 2-4 week treatment regimen, seem to offer clinically relevant short-term pain relief for OAK