325 research outputs found
AlGaInN Laser Diode Technology for Systems Applications
Gallium Nitride (GaN) laser diodes fabricated from the AlGaInN material system is an emerging technology that allows laser diodes to be fabricated over a very wide wavelength range from u.v. to the visible, and is a key enabler for the development of new system applications such as (underwater and terrestrial) telecommunications, quantum technologies, display sources and medical instrumentation
Lateral grating DFB AlGaInN laser diodes for optical communications and atomic clocks
AlGaInN laser diode technology is of considerable interest for telecom applications and next generation atomic optical clocks based on Sr (by using 422nm & 461nm) and Rb at 420.2nm.Very narrow linewidths (<1MHz) are required for such applications. We report lateral gratings on AlGaInN ridge waveguide laser diodes to achieve a single wavelength device with a good side mode suppression ratio (SMSR) that is suitable for atomic clock and telecom applications
Free-space and underwater GHz data transmission using AlGaInN laser diode technology
Laser diodes fabricated from the AlGaInN material system is an emerging technology for defence and security applications; in particular for free space laser communication. Conventional underwater communication is done acoustically with very slow data rates, short reach, and vulnurable for interception. AlGaInN blue-green laser diode technology allows the possibility of both airbourne links and underwater telecom that operate at very fast data rates (GHz), long reach (100’s of metres underwater) and can also be quantum encrypted. The latest developments in AlGaInN laser diode technology are reviewed for defence and security applications. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well. Ridge waveguide laser diode structures are fabricated to achieve single mode operation with optical powers of <100mW. Visible light communications at high frequency (up to 2.5 Gbit/s) using a directly modulated 422nm Galliumnitride (GaN) blue laser diode is reported in free-space and underwate
High Speed Visible Light Communication Using Blue GaN Laser Diodes
GaN-based laser diodes have been developed over the last 20 years making them desirable for many security and defence applications, in particular, free space laser communications. Unlike their LED counterparts, laser diodes are not limited by their carrier lifetime which makes them attractive for high speed communication, whether in free space, through fiber or underwater. Gigabit data transmission can be achieved in free space by modulating the visible light from the laser with a pseudo-random bit sequence (PRBS), with recent results approaching 5 Gbit/s error free data transmission. By exploiting the low-loss in the blue part of the spectrum through water, data transmission experiments have also been conducted to show rates of 2.5 Gbit/s underwater. Different water types have been tested to monitor the effect of scattering and to see how this affects the overall transmission rate and distance. This is of great interest for communication with unmanned underwater vehicles (UUV) as the current method using acoustics is much slower and vulnerable to interception. These types of laser diodes can typically reach 50-100 mW of power which increases the length at which the data can be transmitted. This distance could be further improved by making use of high power laser arrays. Highly uniform GaN substrates with low defectivity allow individually addressable laser bars to be fabricated. This could ultimately increase optical power levels to 4 W for a 20-emitter array. Overall, the development of GaN laser diodes will play an important part in free space optical communications and will be vital in the advancement of security and defence applications
AlGaInN laser diode technology for GHz high-speed visible light communication through plastic optical fiber and water
AlGaInN ridge waveguide laser diodes are fabricated to achieve single-mode operation with optical powers up to 100 mW at ∼420 nm∼420 nm for visible free-space, underwater, and plastic optical fiber communication. We report high-frequency operation of AlGaInN laser diodes with data transmission up to 2.5 GHz for free-space and underwater communication and up to 1.38 GHz through 10 m of plastic optical fiber
On the Crystal and Magnetic Behavior of ScFe4Al8 Single Crystal
Nuclear and magnetic properties of the ScFe4Al8 single crystal were found to exhibit unparalleled complexity
of nuclear and magnetic structures. Our previous neutron measurements revealed presence of two modulation
vectors, both along [", ", 0], however with dfferent critical temperatures. Recent experiments forced us to revise
our knowledge of the structural ordering in the sample. So far, the crystal structure of this alloy, being of
ThMn12-type, has never been questioned
Mixed infections with distinct cytomegalovirus glycoprotein B genotypes in Polish pregnant women, fetuses, and newborns
The purpose of this investigation was to describe a distribution of cytomegalovirus (CMV) single and multiple genotypes among infected pregnant women, their fetuses, and newborns coming from Central Poland, as well as congenital cytomegaly outcome. The study involved 278 CMV-seropositive pregnant women, of whom 192 were tested for viral DNAemia. Human cytomegalovirus (HCMV) genotyping was performed for 18 of 34 pregnant women carrying the viral DNA and for 12 of their 15 offspring with confirmed HCMV infections. Anti-HCMV antibodies levels were assessed by chemiluminescence immunoassay (CLIA) and enzyme-linked fluorescence assay (ELFA) tests. Viral DNA loads and genotypes were determined by real-time polymerase chain reaction (PCR) assays for the UL55 gene. In the pregnant women, we identified HCMV gB1, gB2, gB3, and gB4 genotypes. Single gB2, gB3, or gB4 genotypes were observed in 14 (77.8 %) women, while multiple gB1–gB2 or gB2–gB3 genotypes were observed in four (22.2 %). Maternal HCMV genotypes determined the genotypes identified in their fetuses and newborns (p ≤ 0.050). Half of them were infected with single HCMV gB1, gB2, or gB3 genotypes and the other half with multiple gB1–gB2 or gB2–gB3 genotypes. Single and multiple genotypes were observed in both asymptomatic and symptomatic congenital cytomegaly, although no gB3 genotype was identified among asymptomatic cases. In Central Poland, infections with single and multiple HCMV strains occur in pregnant women, as well as in their fetuses and neonates, with both asymptomatic and symptomatic infections. HCMV infections identified in mothers seem to be associated with the viral genotypes in their children
Temperature-dependence of exciton radiative recombination in (Al,Ga)N/GaN quantum wells grown on a-plane GaN substrates
This article presents the dynamics of excitons in a-plane (Al,Ga)N/GaN single quantum wells of various thicknesses grown on bulk GaN substrates. For all quantum well samples, recombination is observed to be predominantly radiative in the low-temperature range. At higher temperatures, the escape of charge carriers from the quantum well to the (Al,Ga)N barriers is accompanied by a reduction in internal quantum efficiency. Based on the temperature-dependence of time-resolved photoluminescence experiments, we also show how the local disorder affects the exciton radiative lifetime at low temperature and the exciton non-radiative lifetime at high temperature.We acknowledge financial support from the Swiss National
Science Foundation through Project No. 129715 and from
the Polish National Science Center (Project DEC-2011/ 03/B/ST3/02647). The work was partially supported by
the European Union within European Regional Development Fund through Innovative Economy Grant No. POIG.01.01.02-00-008/08. P.C. also acknowledges
financing from the European Union Seventh Framework
Program under grant agreement No. 265073
Agricultural harvesting emissions of ice-nucleating particles
Agricultural activities can modify natural ecosystems and change the nature
of the aerosols emitted from those landscapes. The harvesting of crops can
loft plant fragments and soil dust into the atmosphere that can travel long
distances and interact with clouds far from their sources. In this way
harvesting may contribute substantially to ice-nucleating particle (INP)
concentrations, especially in regions where agriculture makes up a large
percentage of land use. However, a full characterization of particles emitted
during harvesting has not been reported. This study characterizes immersion
mode INPs emitted during harvesting of several crops in the High Plains
region of the United States. The Colorado State University Continuous Flow
Diffusion Chamber (CFDC) and the Ice Spectrometer (IS) were utilized to
measure INP concentrations during active harvesting of four crops in Kansas
and Wyoming. Large spikes of INPs were observed during harvesting, with
concentrations over 200 L−1 at −30 °C measured during a
wheat harvest. To differentiate between mineral and organic components, a
novel heating tube method was employed in real time upstream of the CFDC to
deactivate organic INPs in situ. The results indicate that harvesting
produces a complex mixture of organic, soil dust, and mineral components that
varies for different crops. Electron microscopy analysis showed that while
mineral components made up a large proportion of INPs, organic components
comprised over 40 % of measured INPs for certain crops at warm
temperatures. Heating and enzyme post-treatment of aerosol samples collected
for IS processing indicated that bacteria and heat-labile and heat-stable
organics contributed to wheat harvest-produced INPs. These results indicate
that plant material and organic particles are a significant component of
harvest INPs and their impacts on ice formation in clouds and precipitation
on a regional scale should be explored.</p
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