Neste trabalho são apresentadas a preparação e investigação das propriedades luminescentes dos sistemas vítreos PbO-GeO2 e PbO-GeO2-Ga2O3 dopados com íons de érbio e contendo nanopartículas (NPs) metálicas de prata, ouro e cobre, para aplicações em dispositivos fotônicos. Estes vidros apresentam larga janela de transmissão (400-4500nm), alto índice de refração (~1,9) e baixa energia de fônon (700cm-1). Com a finalidade de verificar a nucleação das nanopartículas metálicas, foram realizadas análises por Microscopia Eletrônica de Transmissão que indicaram a presença de nanopartículas metálicas, cristalinas, aproximadamente esféricas e com tamanho médio entre 2 e 10nm. As medidas de absorção óptica evidenciaram a incorporação dos íons de Er3+ na forma trivalente e a presença de bandas de absorção relacionadas à ressonância dos plasmons superficiais, localizadas em aproximadamente 470nm (no caso das NPs de prata) e em torno de 800nm (no caso das NPS de cobre). As medidas de emissão foram realizadas através da excitação das amostras com laser cw de 980nm e potência de 80mW. Foram medidas bandas de emissão associadas à conversão ascendente de freqüências do Er3+ em 530, 550 e 670nm devidas às transições 2H11/2->4I15/2, 4S3/2->4I15/2 e 4F9/2->4I15/2 respectivamente. Nas amostras contendo NPs de prata, para concentrações de 1,0 e 2,0% de AgNO3, foi observado aumento significativo da emissão da luz verde (530 e 550nm) com o crescimento do tempo de tratamento térmico, quando comparadas com a emissão em 670nm. Para as amostras com NPs de ouro, com concentrações de 0,5 e 1,0% de Au2O3 verificamos um aumento maior da emissão em 670nm quando comparada com as emissões em 530 e 550nm. Para amostras com NPs de cobre, as emissões associadas à conversão ascendente de freqüências do Er3+ foram igualmente afetadas pela presença das NPs e possuem intensidade significativamente inferior as dos casos anteriores. O estudo da variação da intensidade de fluorescência com a potência do laser de excitação nos permitiu concluir que dois fótons participam do processo de conversão ascendente de freqüências na presença e na ausência de NPs metálicas. Os aumentos ocorridos na luminescência são provavelmente causados pelo aumento do campo local nas proximidades dos íons de terras-raras devido ao tamanho observado para as NPs (2-10nm). Portanto, a presença das NPs metálicas desempenha papel fundamental no aumento e/ou diminuição da luminescência da conversão ascendente de freqüências dos íons de Er3+, conferindo aos vidros propriedades novas que são bastante interessantes para aplicações em dispositivos fotônicos. / This work presents the preparation and investigation of the luminescent properties of PbO-GeO2 and PbO-GeO2-Ga2O3 vitreous systems, doped with Erbium ions and containing silver, gold and copper metallic nanoparticles (NPs), for applications in photonic devices. These glasses have a large transmission window (400-4500nm), high refractive index (~1,9) and low phonon energy (700cm-1). Transmission Electronic Microscopy analysis were performed, to verify the metallic NPs nucleation. This analysis indicated that the NPs are metallic and crystalline, approximately spherical, with average size between 2 and 10nm. Optical Absorption measurements showed the Er3+ ions incorporation are in trivalent form and the presence of the absorption bands related to the surface plasmon resonance (SPR) centered around 470nm (for silver NPs) and around 800nm (for copper NPs). Emission measurements were performed pumping the samples with a cw laser (980nm; 80mW). Bands associated to Er3+ frequency upconversion centered around 530, 550 and 670nm were observed due to the transitions 2H11/2 -> 4I15/2, 4S3/2 -> 4I15/2 e 4F9/2 -> 4I15/2, respectively. For the samples containing silver NPs, for 1,0 and 2,0% of AgNO3, it was observed a higher enhancement of the green emission (530 and 550nm), with the increasing of the annealing time, when compared to the emission at 670nm. The samples with 0,5 and 1,0% of Au2O3 showed higher enhancement of the emission centered at 670nm, when compared to the emissions at 530 and 550nm. For the samples with copper NPs, the Er3+ emissions were uniformly affected by the presence of the NPs, and have lower intensity than the other ones. The study of the variation of the fluorescence intensity with the pump laser power indicated that two photons are involved in the frequency upconversion process in the presence and in the absence of the metallic NPs. The observed enhancements in the luminescence are probably due to the local field enhancement in the proximities of the rare-earth ions, due to the small size observed for the NPs (2-10nm). Thus, the presence of metallic NPs plays an important role in the enhancement and/or quenching of the Er3+ frequency upconversion, given new properties to glasses which are of great interest for application in photonic devices.

Neste trabalho são apresentadas a preparação e investigação das propriedades luminescentes dos sistemas vítreos PbO-GeO2 e PbO-GeO2-Ga2O3 dopados com íons de érbio e contendo nanopartículas (NPs) metálicas de prata, ouro e cobre, para aplicações em dispositivos fotônicos. Estes vidros apresentam larga janela de transmissão (400-4500nm), alto índice de refração (~1,9) e baixa energia de fônon (700cm-1). Com a finalidade de verificar a nucleação das nanopartículas metálicas, foram realizadas análises por Microscopia Eletrônica de Transmissão que indicaram a presença de nanopartículas metálicas, cristalinas, aproximadamente esféricas e com tamanho médio entre 2 e 10nm. As medidas de absorção óptica evidenciaram a incorporação dos íons de Er3+ na forma trivalente e a presença de bandas de absorção relacionadas à ressonância dos plasmons superficiais, localizadas em aproximadamente 470nm (no caso das NPs de prata) e em torno de 800nm (no caso das NPS de cobre). As medidas de emissão foram realizadas através da excitação das amostras com laser cw de 980nm e potência de 80mW. Foram medidas bandas de emissão associadas à conversão ascendente de freqüências do Er3+ em 530, 550 e 670nm devidas às transições 2H11/2->4I15/2, 4S3/2->4I15/2 e 4F9/2->4I15/2 respectivamente. Nas amostras contendo NPs de prata, para concentrações de 1,0 e 2,0% de AgNO3, foi observado aumento significativo da emissão da luz verde (530 e 550nm) com o crescimento do tempo de tratamento térmico, quando comparadas com a emissão em 670nm. Para as amostras com NPs de ouro, com concentrações de 0,5 e 1,0% de Au2O3 verificamos um aumento maior da emissão em 670nm quando comparada com as emissões em 530 e 550nm. Para amostras com NPs de cobre, as emissões associadas à conversão ascendente de freqüências do Er3+ foram igualmente afetadas pela presença das NPs e possuem intensidade significativamente inferior as dos casos anteriores. O estudo da variação da intensidade de fluorescência com a potência do laser de excitação nos permitiu concluir que dois fótons participam do processo de conversão ascendente de freqüências na presença e na ausência de NPs metálicas. Os aumentos ocorridos na luminescência são provavelmente causados pelo aumento do campo local nas proximidades dos íons de terras-raras devido ao tamanho observado para as NPs (2-10nm). Portanto, a presença das NPs metálicas desempenha papel fundamental no aumento e/ou diminuição da luminescência da conversão ascendente de freqüências dos íons de Er3+, conferindo aos vidros propriedades novas que são bastante interessantes para aplicações em dispositivos fotônicos. / This work presents the preparation and investigation of the luminescent properties of PbO-GeO2 and PbO-GeO2-Ga2O3 vitreous systems, doped with Erbium ions and containing silver, gold and copper metallic nanoparticles (NPs), for applications in photonic devices. These glasses have a large transmission window (400-4500nm), high refractive index (~1,9) and low phonon energy (700cm-1). Transmission Electronic Microscopy analysis were performed, to verify the metallic NPs nucleation. This analysis indicated that the NPs are metallic and crystalline, approximately spherical, with average size between 2 and 10nm. Optical Absorption measurements showed the Er3+ ions incorporation are in trivalent form and the presence of the absorption bands related to the surface plasmon resonance (SPR) centered around 470nm (for silver NPs) and around 800nm (for copper NPs). Emission measurements were performed pumping the samples with a cw laser (980nm; 80mW). Bands associated to Er3+ frequency upconversion centered around 530, 550 and 670nm were observed due to the transitions 2H11/2 -> 4I15/2, 4S3/2 -> 4I15/2 e 4F9/2 -> 4I15/2, respectively. For the samples containing silver NPs, for 1,0 and 2,0% of AgNO3, it was observed a higher enhancement of the green emission (530 and 550nm), with the increasing of the annealing time, when compared to the emission at 670nm. The samples with 0,5 and 1,0% of Au2O3 showed higher enhancement of the emission centered at 670nm, when compared to the emissions at 530 and 550nm. For the samples with copper NPs, the Er3+ emissions were uniformly affected by the presence of the NPs, and have lower intensity than the other ones. The study of the variation of the fluorescence intensity with the pump laser power indicated that two photons are involved in the frequency upconversion process in the presence and in the absence of the metallic NPs. The observed enhancements in the luminescence are probably due to the local field enhancement in the proximities of the rare-earth ions, due to the small size observed for the NPs (2-10nm). Thus, the presence of metallic NPs plays an important role in the enhancement and/or quenching of the Er3+ frequency upconversion, given new properties to glasses which are of great interest for application in photonic devices.

The Quantum Cascade Laser (QCL)-based terahertz-over-fibre (ToF) concept combines the strength of QCLs as ultra-wide bandwidth, high speed data sources, with the mature optical fibre technology. In this thesis, for the first time, by fusing multiple technologies, digitally selected, electronically-switchable ToF concept is experimentally demonstrated. Furthermore, the digital mode selection principle and electronic tuning mechanism provided by novel aperiodic distributed feedback (ADFB) multi-band filters are presented. For the development of electronically tunable ADFB lasers, a range of bound-to-continuum and chirped superlattice terahertz (THz) QCLs are measured across the frequency range 2.9 – 4.5 THz. The availability of these active materials allowed rapid assessments of the optimum design parameters for subsequent measurements. First, a range of photonic lattice-engineered lasers operating at 4.4 THz are characterized and key design parameters identified. Following this initial development, full electrical and spectral characterization of ADFB lasers operating at 2.9 THz are presented. The novelty of this work lies in the first-ever successful demonstration of discretely tunable QCLs, operating at six distinct THz frequencies. The ADFB technology was experimentally applied using various device geometries and gain dynamics. Toward this aim, results are presented for a Y coupled QCL architecture, showing that complex on-chip signal manipulation can be extended into the THz regime. In addition, it is demonstrated that ADFB technology provides broadband multi-channel optical filtering for the entire gain bandwidth. It is shown that discrete, purely electronic, tuning of simultaneous dual colour output can be achieved. Multi band optical filter functions derived from ADFB gratings possess highly nonlinear dispersion across the filter bandwidth and are found to modify the gain-induced, driving current-dependent continuous mode tuning. This thesis, therefore, presents a systematic experimental analysis of the dispersion engineered continuous fine-tuning in THz QCLs. In the final two chapters, the thesis presents, for the first time, transmission of tunable THz signals over standard single-mode optical fibre by up converting 2.9 THz QCL radiation via intra-cavity nonlinear mixing with an optical fibre-injected near-infrared (NIR) carrier in the 1.3 µm band. Discrete and continuous tuning technologies, as developed in chapters 3 – 5, are now successfully transferred to THz sidebands on the NIR carrier, extracted via a butt coupled single mode fibre and recorded using an optical spectrum analyzer. The major novel outcome of this thesis is the first demonstration of electronically tunable phase-matched points in a THz plasmon waveguide. The key breakthrough is the experimental confirmation of the photonic band-gap engineering of group velocity of THz signals – as both ‘fast’ and ‘slow’ switchable side bands are observed. Such novel nonlinear up-conversion of spectrally flexible THz signals may open up new possibilities for ultrafast THz telecom frameworks.