Made available in DSpace on 2016-03-15T19:37:49Z (GMT). No. of bitstreams: 1 Lucia Akemi Saito -EE2006.pdf: 2213180 bytes, checksum: d5a6d162d17171e2b4cf99c0fa4797ce (MD5) Previous issue date: 2006-08-02 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Most of researches about Raman amplifier had been made in C and L bands (1530-1625 nm), which is possible to found more data of Raman efficiency gain and the requirements for design is consolidated. The first issue that should be considered when the amplifier is to use in another band, like our project (O-band) is to consider the decrease of effective area and wavelength in the calculation of Raman efficiency, not only the pump wavelength. We have two configuration types: for the first one, the gain is obtained in the transmission fiber and for the second that is demonstrated in this work, we need special fibers as DSF, DCF and Raman fiber to amplifier the signals. Note that the amplification can be obtained in any band of optical spectrum, which depends on the pump wavelength that is used for made it. Our studies demonstrated that the discrete Raman amplifier that was made of Raman fiber of OFS Fitel Denmark was more efficient in short wavelengths and has more improvement when it was working in O-band. In spite of the higher attenuation, we can have higher Raman gain efficiency (CR) because the effective area (Aeff) decreased in short wavelengths. The characteristics of Raman fiber were studied when we found the Raman gain efficiency peak of 3.9 (W.km)-1 for a pump laser of 1240 nm wavelength. For this case, the gain of O-band amplifier was about 50 % higher when we compared with the C-band. For a CWDM system, we need to design a multi-pump amplifier. It is necessary four pump lasers to amplifier a bandwidth of 70 nm and six pump lasers to cover all O-band. The gain value depends on the pump power and if we want a good result, we should verify the total power of channels in the input of amplifier to avoid the device saturation. In addition, the noise figure of Raman amplifier was studied and then we found results that demonstrated higher noise values in short wavelengths specially, when we need to locate some pump lasers between signal wavelengths. / A maior parte das pesquisas realizadas sobre amplificadores Raman tem seus estudos centrados nas bandas C (1530 a 1565 nm) e L (1565 a 1625 nm), regiões onde os dados de eficiência de ganho Raman e a parametrização dos amplificadores têm seus estudos consolidados. Um ponto importante para ser considerado quando se deseja trabalhar numa banda diferente, como no caso a banda O (1260 a 1360 nm), é que a alteração não é apenas no comprimento de onda do laser de bombeio. Deve-se considerar o decréscimo da área efetiva e do comprimento de onda que influenciará diretamente no valor da eficiência e conseqüentemente no próprio ganho do amplificador Raman. Alguns amplificadores Raman utilizam a própria fibra de transmissão e outros têm como meio de amplificação fibras especiais como DSF, DCF ou a própria fibra Raman como é demonstrado neste trabalho. Sabe-se, no entanto, que a amplificação Raman pode ocorrer em qualquer banda do espectro óptico sendo necessário para a sua montagem, apenas alterar o comprimento de onda do laser de geração do efeito. Este trabalho demonstrou que o Amplificador Raman Discreto utilizando a fibra Raman da OFS Fitel Denmark é mais eficiente em comprimentos de onda menores e com melhor aproveitamento na região compreendida pela banda O . Nossos estudos demonstraram que apesar do aumento da atenuação nesta região, pode-se obter maior Eficiência de Ganho Raman (CR) devido ao decréscimo da Área Efetiva (Aeff) em comprimentos de onda curtos. A variação das características da fibra Raman para a banda O foram analisadas sendo encontrado um pico de Eficiência de Ganho Raman de 3,9 (W.km)-1 para um laser de bombeio de 1240 nm resultando em torno de 50 % a mais de Ganho no amplificador quando comparado com a banda C . Analisando o amplificador utilizando múltiplos lasers de bombeio, verificou-se que para uma aplicação em sistema CWDM seriam necessários 4 lasers para amplificação numa faixa de 70 nm e 6 lasers para cobrir toda a banda O sendo que a magnitude de amplificação depende diretamente da potência destes lasers devendo-se observar a potência total dos canais na entrada para evitar a saturação do dispositivo. Foi analisada a figura de ruído do amplificador Raman sendo encontrados valores mais altos em comprimentos de onda curtos e de maior magnitude quando há lasers de bombeio entre os comprimentos de onda de sinal.

Made available in DSpace on 2016-03-15T19:37:35Z (GMT). No. of bitstreams: 1 David Steinberg.pdf: 1201176 bytes, checksum: 38de6b0554611de53adf67ca19a556a1 (MD5) Previous issue date: 2011-01-28 / In this work, the O-band discrete Raman amplifier gain bandwidth optimization using genetic algorithm of a commercial simulator is carried out. The main objective of the study was to optimize the wide Raman amplifier gain bandwidth obtaining values of gain variation less than 0.5 dB. Using a fiber DCF (Dispersion Compensating Fiber) as Raman amplifier medium, the pump number was varied and the gain variation for each pump configuration has been verified. For a fixed 70 nm (1275-1345 nm) bandwidth consisting of 62 signal frequencies points, the results were generated for one, two, three, four, five, six, seven and eight backward pumps, which with the last one it was obtained the best result of 0.35 dB gain variation. In addition to this analysis, it was also found the Raman amplifier noise figure for this band and made a brief comparison with the conventional profile bands. / Neste trabalho a otimização da largura de banda de ganho de um amplificador Raman discreto na banda "O" utilizando algoritmo genético de um simulador comercial foi realizada. O objetivo principal do trabalho foi otimizar a maior largura de banda de ganho do amplificador Raman obtendo valores de variação de ganho menores que 0.5 dB. Utilizando uma fibra DCF (Dispersion Compensating Fiber) como meio de ganho do amplificador Raman, o número de bombeio foi variado e a variação de ganho para cada configuração de bombeio foi verificada. Para uma largura de banda fixa em 70 nm (1275-1345 nm) compreendendo 62 pontos de freqüências de sinal, foram gerados resultados para um, dois, três, quatro, cinco, seis, sete e oito bombeios contrapropagantes sendo que com esta última configuração foi obtido o melhor resultado de variação de ganho de 0.35 dB. Além desta análise, também foi verificado o perfil da figura de ruído do amplificador Raman nesta banda e feita uma breve comparação com o perfil em bandas convencionais.

Made available in DSpace on 2016-03-15T19:38:55Z (GMT). No. of bitstreams: 1 DAVID STEINBERG.pdf: 3031041 bytes, checksum: e320f0c21b75ca5bdd5a63f93fa6dd1d (MD5) Previous issue date: 2015-08-27 / Fundo Mackenzie de Pesquisa / In this thesis, for the first time we present results of passively-mode-locking O-band Raman fiber laser operating at 1310 nm by using carbon nanotubes as saturable absorber. The first results were obtained for an experimental setup based on single mode fiber (SMF) with laser operating near zero fiber dispersion at 1310 nm at anomalous regime. In this same configuration, a study of pulse duration shortening in terms of intracavity dispersion management with dispersion shifted fiber lengths (DSF) was performed. Replacing the SMF by a highly doped germanium fiber as gain medium of Raman fiber laser, operation was shifted to normal dispersion regime and passive mode-locking was also generated. In this laser, a study of pulse duration shortening in terms of gain medium length reduction was performed and the picosecond pulse regime of the laser could be estimated. We also present a brief comparison between the two dispersion regimes of the Raman fiber laser and passive mode-locking results obtained with different diameters of carbon nanotubes as saturable absorbers. / Nesta tese, apresentamos pela primeira vez resultados do acoplamento passivo de modos em um laser Raman à fibra operando em 1310 nm na banda O, utilizando nanotubos de carbono como absorvedor saturável. Os primeiros resultados foram obtidos de uma configuração experimental baseada totalmente em fibra monomodo padrão (SMF) com o laser operando próximo ao zero de dispersão da fibra em 1310 nm, porém em regime anômalo. Nesta mesma configuração, um estudo do encurtamento da duração do pulso em função do gerenciamento da dispersão intracavidade com comprimentos de fibra de dispersão deslocada (DSF) foi realizado. Substituindo a SMF por uma fibra altamente dopada com germânio como meio do ganho do laser Raman, a operação do laser foi deslocada para o regime de dispersão normal e o regime de acoplamento passivo de modos também foi gerado. Neste laser, um estudo do encurtamento da duração do pulso em função da redução do comprimento do meio de ganho foi realizado e a operação do acoplamento passivo de modos do laser em regime de picossegundos pôde ser estimada. Também apresentamos uma breve comparação entre os dois regimes de dispersão do laser Raman à fibra e resultados do acoplamento passivo de modos obtidos com diferentes diâmetros de nanotubos de carbono como absorvedores saturáveis.

In this project, the performance aspects of a new early generation 1310 nm Sampled-Grating Distributed Bragg Reflector (SG-DBR) semiconductor laser are investigated. SG-DBR lasers are ideal for Source Swept Optical Coherence Tomography (SS-OCT), a Fourier-Domain based approach for OCT, necessitating a tunable wavelength source. Three internal sections control the frequency output for tuning, along with two amplifiers for amplitude control. These O-band SG-DBR devices are now being produced in research quantities. SG-DBR lasers have been produced at 1550 and 1600 nm for some times. Fundamental questions regarding the performance of the 1310 nm devices must be quantified. Standard metrics including the laser linewidth, amplitude modulation and frequency modulation responses are characterized. The intrinsic electrical parasitics of the laser diode segments and packaging are also investigated. In addition, testing fixture including a Thermal Electric Cooler (TEC) controller is for the characterization task. Measurements of these key metrics are essential to the enhancement of future devices, aiding in the optimization of more mature products.

Semiconductor quantum dots (QDs) are well established as sub-Poissonian sources of entangled photon pairs. To improve the utility of a QD light source, it would be advantageous to extend their emission further into the near infrared, into the low absorption wavelength windows utilised in long-haul optical telecommunication. Initial experiments succeeded in interfering O-band (1260—1360 nm) photons from an InAs/GaAs QD with dissimilar photons from a laser, an important mechanism for quantum teleportation. Interference visibilities as high as 60 ± 6 % were recorded, surpassing the 50 % threshold imposed by classical electrodynamics. Later, polarisation-entanglement of a similar QD was observed, with pairs of telecom-wavelength photons from the radiative cascade of the biexciton state exhibiting fidelities of 92.0 ± 0.2 % to the Bell state. Subsequently, an O-band telecom-wavelength quantum relay was realised. Again using an InAs/GaAs QD device, this represents the first implementation of a sub-Poissonian telecom-wavelength quantum relay, to the best knowledge of the author. The relay proved capable of implementing the famous four-state BB84 protocol, with a mean teleportation fidelity as high as 94.5 ± 2.2 %, which would contribute 0.385 secure bits per teleported qubit. After characterisation by way of quantum process tomography, the performance of the relay was also evaluated to be capable of implementing a six-state QKD protocol. In an effort to further extend the emitted light from a QD into the telecom C-band (1530—1565 nm), alternative material systems were investigated. InAs QDs on a substrate of InP were shown to emit much more readily in the fibre-telecom O- and C-bands than their InAs/GaAs counterparts, largely due to the reduced lattice mismatch between the QD and substrate for InAs/InP (~3 %) compared to InAs/GaAs (~7 %). Additionally, to minimize the fine structure splitting (FSS) of the exciton level, which deteriorates the observed polarisation-entanglement, a new mode of dot growth was investigated. Known as droplet epitaxy (D-E), QDs grown in this mode showed a fourfold reduction in the FSS compared to dots grown in the Stranski-Krastanow mode. This improvement would allow observation of polarisation-entanglement in the telecom C-band. In subsequent work performed by colleagues at the Toshiba Cambridge Research Labs, these D-E QDs were embedded in a p-i-n doped optical cavity, processed with electrical contacts, and found to emit entangled pairs of photons under electrical excitation. The work of this thesis provides considerable technological advances to the field of entangled-light sources, that in the near future may allow for deterministic quantum repeaters operating at megahertz rates, and in the further future could facilitate the distribution of coherent multipartite states across a distributed quantum network.