Amplificadores de fibra em redes óticas transparentes e dinâmicas

Doutoramento em Engenharia EletrotécnicaIn this thesis a study of optical fiber amplifiers in the context of transparent and dynamic optical networks is performed. We propose and validate a simplified model to estimate the gain profile and amplified spontaneous emission (ASE) noise of broadband counterpumped Raman fiber amplifiers (RFAs). The proposed model requires very low computational resources and it is suitable to be used in network planning tools. Based on the proposed model, we also present an algorithm to design flat gain counter-pumped RFAs for the extended C-band with low computational requirements. We experimentally verify that the pump-reflecting RFA presents a higher transient response due to channels add/drop, when compared to the conventional counter-pumped RFA. This makes this amplifier configuration unsuitable for transparent and dynamic optical networks. To mitigate the transient response due to channel add/drop, a pumpcontrolled gain-locked system based on the monitorization of the reflected pump power is proposed and validated numerically and experimentally. Following this approach, an efficient low-cost RFA suitable for dynamic optical networks is proposed. The dependence of the dynamical response of erbium-doped fiber amplifiers (EDFAs) on the pump wavelength, pump power, and temperature due to spectral hole burning (SHB) and site dependent pumping (SDP) is experimentally investigated. A dependence of the dynamic response on the pump wavelength, for amplifiers pumped around 1480 nm, is shown. In order to explain this dependence, the impact of SDP on the performance of EDFAs pumped at wavelengths around 1480 nm is investigated, both experimentally and numerically. As a result, an improved model incorporating the SDP effect for twolevel EDFAs is derived and experimentally validated.Nesta tese é feito um estudo sobre amplificadores de fibra ótica no contexto de redes óticas transparentes e dinâmicas. Propomos e validamos um modelo simplificado para estimar o perfil do ganho e do ruído de emissão espontânea amplificada (ASE), para amplificadores de Raman (RFAs) contra propagantes. O modelo proposto requer baixos recursos computacionais e é adequado para ser usado em ferramentas de planeamento da rede. Com base no modelo proposto, apresentamos também um algoritmo com requisitos computacionais baixos para desenhar RFAs contra propagantes com ganho constante para a banda C estendida. Verificamos experimentalmente que um RFA contra propagante com reflexo da potência da bomba devido à adição/remoção de canais apresenta uma resposta transiente mais elevada, quando comparado com um RFA contra propagante convencional. Isto torna esta configuração inadequada para redes óticas transparentes e dinâmicas. Para mitigar a resposta transitória devido à adição/remoção de canais, um sistema de controlo do ganho baseado na monitorização da potência da bomba refletida é proposto e validado numérica e experimentalmente. Seguindo esta abordagem, um RFA contra propagante eficiente e de baixo custo adequado para redes óticas dinâmicas é proposto. A dependência da resposta dinâmica dos amplificadores de fibra dopada com érbio (EDFAs) em função do comprimento de onda da bomba, da potência da bomba e da temperatura devido ao spectral hole burning (SHB) e site dependent pumping (SDP) é investigada experimentalmente. Nos resultados obtidos é mostrada a dependência da resposta dinâmica em função do comprimento de onda da bomba, para amplificadores bombeados em torno de 1480 nm. Para explicar esta dependência, o impacto do SDP no desempenho de EDFAs bombeados em comprimentos de onda em torno de 1480 nm é investigado, tanto experimental como numericamente. Como resultado, um modelo mais completo, incorporando o efeito SDP para EDFAs de dois níveis é derivado e validado experimentalmente

Fabrication and characterisation of tellurite planar waveguides

Tellurite glasses, which contain Tellurium dioxide as the main component, have some remarkable optical properties which are well recognised and exploited in the bulk optics and fibre fields. They include a high acousto-optic figure of merit, wide mid infrared transparency, the highest optical nonlinearity amongst oxides, and excellent rare earth hosting, etc. Despite these attractive properties, until now, no one has succeeded in fabricating low loss planar waveguides in these materials. This work develops high quality optical planar waveguides in Tellurium dioxide for the first time. The project investigates the materials science for optical Tellurium dioxide films and discovers an appropriate waveguide fabrication method. The thin films have been fabricated by reactive radio frequency magnetron sputtering using a Tellurium target in an oxygen and argon atmosphere. Propagation losses at 1550nm in the planar films are 0.1dB/cm or lower in stoichiometric composition. The properties of films have been also found to be stable with thermal annealing up to 300 degree Celsius. Plasma etching of tellurite glasses has been systematically studied. High quality etching of Tellurium dioxide and chalcogenide glass films has been demonstrated with a Methane/Hydrogen/Argon gas mixture. As a result, a fabrication recipe which produces low loss (0.1dB/cm) planar waveguides has been discovered. The nonlinear coefficient of the sputtered TeO2 has been characterised by self-phase modulation (SPM) experiments and the second order nonlinear coefficient has been measured to be around 25 times that of silica. Significant signal conversion, -4dB, has achieved with large bandwidth of 30nm in the four-wave mixing (FWM) experiment pumped at 1550nm in a slightly normal dispersion waveguide. Erbium doped Tellurium oxide thin films have also been fabricated by co-sputtering of Erbium and Tellurium targets into an Oxygen and Argon atmosphere. The obtained films have been found to have good properties for Erbium doped waveguide amplifiers. The Erbium concentration can be controlled within the range of interest with Erbium/Tellurium ratios ranging from 0.1% to 3% or more. The 1.5 micrometre photoluminescence properties of the films are excellent with effective bandwidth of more that 60nm and intrinsic lifetime of order of 3ms. Despite the fact that there was OH contamination in the films, single mode Erbium doped waveguide amplifiers with high internal gain have been successfully obtained. The 1480nm pumped amplifier achieved internal gain from below 1520nm to beyond 1600nm. The peak gain of 2.8dB/cm and 40nm 3dB gain bandwidth have been accomplished. These results are a major stepping stone towards ""system-on-chip"" optical applications for telecom and mid infrared optics given the multifunctional nature of tellurite materials. -- provided by Candidate

Devices for satellite-assisted quantum networks

Quantum networks, quantum nodes interconnected by quantum channels, offer powerful means of secure communications and quantum computations. They are crucial elements in a broad area of quantum technologies including quantum simulations and metrologies. In particular, quantum links with satellites take the network into a global or greater scale, extending the capability of transmitting information. It also provides experimental platforms of testing quantum physics in a relativistic regime. The realization of satellite-assisted quantum networks requires devices that are interfaced with quantum optical channels to satellites. This thesis discusses the development of four essential devices, three of which are in line with Canada's Quantum Encryption and Science Satellite (QEYSSat) mission. First, polarization-entangled photon sources are developed to transmit one of the paired photons over ground-based fiber-optic networks and the other over ground-to-satellite free-space links. A practical and versatile interferometric scheme is designed and demonstrated, which allows constructing highly non-degenerate sources with only conventional polarization optics. A method of directly producing entangled photon-pairs from optical fibers without interferometers is studied with thorough numerical analysis to show feasibility of experimental demonstration. An entangled photon source for the QEYSSat mission is conceptually designed, and several key parameters to fulfill a set of performance requirements are theoretically studied and experimentally verified. Secondly, this thesis presents two characterization platforms for optical components that are designed and implemented for the QEYSSat mission. One is to precisely measure transmitted wavefronts of large optics including telescopes. A proof-of-principle experiment is conducted with accurate modelling of measurement apparatus via three-dimensional raytracing, and quantitative agreement between the experiment and simulations validates our methodology. The other provides polarization characterizations for a variety of optical components including lenses, mirrors, and telescopes with consistent precision. A detailed description of subsystems including calibrations and test procedures is provided. Polarization-test results of several components for the QEYSSat are discussed. Third, quantum frequency transducers are developed for single-photon quantum key distributions with QEYSSat links. The devices are designed to translate the wavelength of single-photons emitted from quantum dot single-photon sources to QEYSSat channel wavelength via four-wave mixing Bragg-scattering process. Two optical media are concerned: a silicon nitride ring resonator and a photonic crystal fiber. Thorough numerical simulations are performed to estimate the device performance for both cases. A proof-of-principle demonstration of the frequency translation is conducted with a commercial photonic crystal fiber. Finally, a quantum simulator, serving as a quantum node in satellite-assisted quantum networks, is designed in a silicon nitride nanophotonic platform with cesium atoms. The designed photonic structure tailors electromagnetic vacuum such that photon-mediated forces between atoms causes collective motions mediating site-selective SU(2) spin-spin interactions. A coherent spin-exchange rate between atoms and collective dissipation rate of atoms are precisely estimated via finite-element time domain simulations. Furthermore, two schemes of trapping atoms in the vicinity of the designed structure are studied with calculations of potential energies and phonon tunneling rates. Experimental progress toward realization of the proposed system is summarized. The presented research activities of designing, analyzing, and implementing devices demonstrates the readiness of satellite-assisted quantum networks. This work contributes to creating quantum channels by entanglements with interfaces of various quantum systems in line with a broader scope of establishing a global quantum internet and quantum space exploration

EUROSENSORS XVII : book of abstracts

Fundação Calouste Gulbenkien (FCG).Fundação para a Ciência e a Tecnologia (FCT)