RESUMO
Semiconductor saturable absorber mirror (SESAM) modelocked high pulse repetition rate (≥10 GHz) diode-pumped solid-state lasers are proven as an enabling technology for high data rate coherent communication systems owing to their low noise and high pulse-to-pulse optical phase-coherence. Compared to quantum well, quantum dot (QD)-based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the first 10 GHz pulse repetition rate QD-SESAM modelocked laser at 1.55 µm, exhibiting 2 ps pulse width from an Er-doped glass oscillator (ERGO). The 10 GHz ERGO laser is modelocked with InAs/GaAs QD-SESAM with saturation fluence as low as 9 µJ/cm2.
RESUMO
We report a comparison of different capping materials on the intermixing of modulation p-doped InAs/In(Ga)As quantum dots (QD). QD materials with different caps are shown to exhibit significant difference in their optical properties during the annealing process. The selective area intermixing technique is demonstrated to laterally integrate two and three different QD light emitting devices with a single electrical contact. A spectral bandwidth of 240nm centered at 1188nm is achieved in a device with two sections. By calculating the point spread function for the obtained emission spectra, and applying the Rayleigh criteria for resolution, an axial resolution of 3.5µm is deduced. A three section device realizes a spectral bandwidth of 310nm centered at 1145nm. This corresponds to an axial resolution of 2.4µm. Such a small predicted axial resolution is highly desirable in optical coherence tomography system and other coherence-based systems applications.
Assuntos
Luz , Medições Luminescentes/instrumentação , Nanotecnologia/instrumentação , Pontos Quânticos , Desenho de EquipamentoRESUMO
Different capping of quantum dot (QD) materials is known to produce different degrees of intermixing during a post-growth thermal annealing process. We report a study of the effect of different degrees of intermixing on modulation beryllium doped quantum dot superluminescent light emitting diodes (QD-SLEDs). The intermixed QD-SLEDs show high device performance whilst achieving a large central emission wavelength shift of approximately 100nm compared to the as-grown device. The evolution of the emission spectra and power with drive current suggest a transition from QD-like to QW-like behavior with increasing degree of intermixing. A selective area intermixed QD-SLED is demonstrated, and with optimized differential intermixing, such structures should allow ultra-broadband sources to be realized.
Assuntos
Óptica e Fotônica , Pontos Quânticos , Algoritmos , Berílio/química , Difusão , Eletrônica , Desenho de Equipamento , Luz , Luminescência , Nanotecnologia/métodos , TemperaturaRESUMO
Broadband superluminescent light emitting diodes are realized by a post-growth annealing process, on modulation p-doped multiple InAs/InGaAs/GaAs quantum dot layer structures, under a GaAs proximity cap. The device exhibits a large and flat emission with spectral width up to 132 nm at 2 mW. This is mainly attributed to the reduction of the energy separation between the ground state and the excited state, in addition to the optical quality of the intermixed modulation p-doped quantum dot materials being comparable to that of the as-grown sample.
Assuntos
Arsenicais/química , Gálio/química , Iluminação/instrumentação , Medições Luminescentes/instrumentação , Nanotecnologia/instrumentação , Pontos Quânticos , Desenho de Equipamento , Análise de Falha de Equipamento , Medições Luminescentes/métodos , SemicondutoresRESUMO
This paper considers multiple structural designs for photonic crystal surface emitting lasers operating at key wavelengths. Initially a structure from Williams et al. is modelled, the structure is modified to include an additional GaAs waveguide layer (termed ballast layer) and to include an additional PC layer (termed double decker). These structures are modelled by a combination of coupling calculation and waveguide modelling and are compared to the original structure. We show that both of these schemes give an increase in coupling, but present fabrication challenges. Next, we model standard laser structures operating at key wavelengths (400 nm, 1.3 and 10 µm) where a photonic crystal is located above the active region and explore the effect of increasing thickness of photonic crystal. We find that increasing the thickness increases the coupling coefficient but not true for the full range of thicknesses considered. This study allows a more universal comparison of the use of all-semiconductor, or void containing PCSELs to be conducted and we find that the realisation of all semiconductor PCSELs covering a wide range of material and wavelengths are possible.
RESUMO
We demonstrate a semiconductor PCSEL array that uniquely combines an in-plane waveguide structure with nano-scale patterned PCSEL elements. This novel geometry allows two-dimensional electronically controllable coherent coupling of remote vertically emitting lasers. Mutual coherence of the PCSEL elements is verified through the demonstration of a two-dimensional Young's Slits experiment. In addition to allowing the all-electronic control of the interference pattern, this type of device offers new routes to power and brightness scaling in semiconductor lasers, and opportunities for all-electronic beam steering.
RESUMO
During the period July 1983 to June 1985, 76 submissions of material from feral pigeons were received. Five separate submissions resulted in the isolation of an avian paramyxovirus type 1 (A/PMV-1) variant indistinguishable from the virus responsible for the 1058 disease outbreaks confirmed in racing pigeons up to the end of 1984. In addition 11 separate submissions of pigeon sera had haemagglutination inhibition titres of log(2)4 or greater to A/PMV-1 antigen. Feral pigeons from six sites widely distributed throughout England had evidence of A/PMV-1 infection.
Assuntos
Doenças das Aves/epidemiologia , Columbidae/sangue , Paramyxoviridae/isolamento & purificação , Infecções por Respirovirus/veterinária , Animais , Doenças das Aves/transmissão , Aves , Inglaterra , Infecções por Respirovirus/transmissão , Sorotipagem , País de GalesRESUMO
Botulism was diagnosed clinically in grazing cattle on three closely sited dairy farms. The evidence suggests that the source of the toxin was poultry carcases containing types C and D Clostridium botulinum. These organism were also found in the alimentary tract of affected animals. Silage is suspected as having acted as a vehicle for the organisms and, or, toxins in cases which occurred later in housed cattle on one of the farms.
Assuntos
Criação de Animais Domésticos , Botulismo/veterinária , Doenças dos Bovinos/etiologia , Infecções por Clostridium/veterinária , Contaminação de Alimentos , Esterco , Animais , Toxinas Botulínicas/análise , Botulismo/etiologia , Bovinos , Infecções por Clostridium/etiologia , Sistema Digestório/microbiologia , FemininoRESUMO
A large outbreak of suspected botulism occurred on a dairy farm. The affected animals were listless and showed signs ranging from hindlimb unsteadiness to lateral recumbency, although the most common presentation was sternal recumbency with an apparent hindlimb weakness when stimulated to rise. Postmortem examinations revealed no conclusive gross pathology or histopathology. The affected cattle were found to have neutrophilia and hyperglycaemia with no other consistent haematological or biochemical abnormalities. The combination of clinical signs, disease epidemiology and the ruling out of other differential diagnoses strongly supported a diagnosis of unconfirmed botulism; however, the source of toxin was not demonstrated. Botulism is a severe disease in human beings and there are uncertainties about the pharmacokinetics and pharmacodynamics of Clostridium botulinum toxins. In such circumstances, a precautionary approach to food safety is essential. Restrictions were placed on the movement of livestock and sale of milk from the farm premises until 14 days after the onset of the last clinical case.
Assuntos
Botulismo/veterinária , Bovinos , Clostridium botulinum/patogenicidade , Surtos de Doenças , Contaminação de Alimentos , Saúde Pública , Agricultura , Animais , Botulismo/epidemiologia , Botulismo/transmissão , Diagnóstico Diferencial , Feminino , Humanos , Leite/microbiologiaAssuntos
Surtos de Doenças , Doenças do Cão/transmissão , Infecções por Escherichia coli/transmissão , Escherichia coli O157/isolamento & purificação , Zoonoses/transmissão , Adulto , Animais , Criança , Surtos de Doenças/veterinária , Doenças do Cão/microbiologia , Cães , Infecções por Escherichia coli/epidemiologia , Fezes/microbiologia , Humanos , Toxina Shiga II , Toxinas Shiga/isolamento & purificação , Reino Unido/epidemiologia , Zoonoses/epidemiologia , Zoonoses/microbiologiaRESUMO
During the decade to 1999, the incidence of human infections with the zoonotic pathogen verocytotoxin-producing Escherichia coli O157 (VTEC O157) increased in England and Wales. This paper describes the results of a survey of 75 farms to determine the prevalence of faecal excretion of VTEC O157 by cattle, its primary reservoir host, in England and Wales. Faecal samples were collected from 4663 cattle between June and December 1999. The prevalence of excretion by individual cattle was 4.2 per cent (95 per cent confidence interval [CI] 2.0 to 6.4) and 10.3 per cent (95 per cent CI 5.8 to 14.8) among animals in infected herds. The within-herd prevalence on positive farms ranged from 1.1 to 51.4 per cent. At least one positive animal was identified on 29 (38.7 per cent; 95 per cent CI 28.1 to 50.4) of the farms, including dairy, suckler and fattening herds. The prevalence of excretion was least in the calves under two months of age, peaked in the calves aged between two and six months and declined thereafter. The phage types identified most widely were 4, 34 and 2, which were each found on six of the 29 positive farms.
Assuntos
Doenças dos Bovinos/epidemiologia , Infecções por Escherichia coli/veterinária , Escherichia coli O157/isolamento & purificação , Animais , Tipagem de Bacteriófagos/veterinária , Bovinos , Doenças dos Bovinos/microbiologia , DNA Bacteriano/análise , Inglaterra/epidemiologia , Infecções por Escherichia coli/epidemiologia , Escherichia coli O157/classificação , Fezes/microbiologia , Feminino , Masculino , Reação em Cadeia da Polimerase/veterinária , Prevalência , Distribuição Aleatória , Estações do Ano , Toxinas Shiga/análise , Inquéritos e Questionários , País de Gales/epidemiologiaAssuntos
Doenças dos Bovinos/microbiologia , Doenças dos Genitais Femininos/veterinária , Infecções por Bactérias Gram-Positivas/veterinária , Complicações Infecciosas na Gravidez/microbiologia , Streptococcaceae/isolamento & purificação , Animais , Bovinos , Inglaterra , Feminino , Doenças dos Genitais Femininos/microbiologia , Infecções por Bactérias Gram-Positivas/microbiologia , Humanos , Gravidez , País de Gales , Zoonoses/microbiologiaAssuntos
Doença da Fronteira/epidemiologia , Doença da Fronteira/prevenção & controle , Vírus da Doença da Fronteira/isolamento & purificação , Doenças dos Bovinos/epidemiologia , Doenças dos Bovinos/prevenção & controle , Animais , Doença da Fronteira/sangue , Doença da Fronteira/etiologia , Vírus da Doença da Fronteira/genética , Bovinos , Doenças dos Bovinos/sangue , Doenças dos Bovinos/etiologia , DNA Viral/análise , Vírus da Diarreia Viral Bovina/isolamento & purificação , Inglaterra/epidemiologia , Feminino , Programas de Rastreamento/veterinária , Reação em Cadeia da Polimerase/veterinária , País de Gales/epidemiologiaRESUMO
High pulse repetition rate (≥ 10â GHz) diode-pumped solid-state lasers, modelocked using semiconductor saturable absorber mirrors (SESAMs) are emerging as an enabling technology for high data rate coherent communication systems owing to their low noise and pulse-to-pulse optical phase-coherence. Quantum dot (QD) based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the development of an epitaxial process for the realization of high optical quality 1.55 µm In(Ga)As QDs on GaAs substrates, their incorporation into a SESAM, and the realization of the first 10â GHz repetition rate QD-SESAM modelocked laser at 1.55 µm, exhibiting â¼2â ps pulse width from an Er-doped glass oscillator (ERGO). With a high areal dot density and strong light emission, this QD structure is a very promising candidate for many other applications, such as laser diodes, optical amplifiers, non-linear and photonic crystal based devices.
RESUMO
Scanning surveillance by the Veterinary Laboratories Agency revealed the emergence of suspected botulism in ruminants in 2003, presented as flaccid paralysis. From 2003 to 2009, 168 cattle and 19 sheep incidents were recorded, with mortality between 5 and 80 per cent. All sheep incidents and 95 per cent of cattle incidents had proximity to broiler litter. From July 2006, the gut contents collected from 74 affected cattle and 10 affected sheep were tested for Clostridium botulinum toxins using mice bioassays and for organisms by culture. Type D toxin was identified in 32 per cent of cattle and 18 per cent of sheep samples. C botulinum type D organisms were identified in 40 per cent of cattle and 30 per cent of sheep samples, but broth from one sample reacted with C and D antisera. Type C botulism has previously been reported more commonly than type D in the UK and has been associated with the use of poultry litter as fertiliser, bedding or feed. The almost exclusive association with C botulinum type D toxins or organisms in the gut contents in this survey suggests a change in the source or epidemiology of botulism in the UK. The source of C botulinum type D was uncertain. Broilers may carry C botulinum type D in their gut flora subclinically. The emergence of a new type D strain, or changes in broiler husbandry and nutrition, medication and other enteric infections may have affected colonisation with C botulinum. Further investigation of poultry and farm environments for sources of type D awaits the development of tests for C botulinum toxins that do not require the use of mice.