Contributions to optimal detection in OTDM and OCDMA optical receivers
Recent developments in optical communication systems have increased the performance of optical networks. Low attenuation fiber optics, high spectral purity lasers and optical amplifiers, among others, are systems that have allowed to transport terabits per second across thousands of kilometers, in a...
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| Formato: | tesis doctoral |
| Fecha de publicación: | 2016 |
| País: | España |
| Recursos: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/98139 |
| Acesso em linha: | https://hdl.handle.net/2117/98139 https://dx.doi.org/10.5821/dissertation-2117-98139 |
| Access Level: | acceso abierto |
| Palavra-chave: | Radiofreqüència Comunicacions òptiques Àrees temàtiques de la UPC::Enginyeria de la telecomunicació |
| Resumo: | Recent developments in optical communication systems have increased the performance of optical networks. Low attenuation fiber optics, high spectral purity lasers and optical amplifiers, among others, are systems that have allowed to transport terabits per second across thousands of kilometers, in a more reliable, secure and efficient manner, compared to radiofrequency (RF) systems. New optical access network technologies such as EPON and GPON are also providing Gbit/s connectivity to customers in both the enterprise and consumer markets. This transport capacity provides enough data for the growing demand of new communication services. The main goal of the researchers in optical networks is to provide higher-speed data transmission by exploiting the intrinsically fast behavior of the optical domain. Optical signal processing is a key technology for constructing flexible and ultra high-speed photonic networks. In this context, it will be possible to build ultra-high speed, simple and reliable optical networks, at low operational expenses, regardless of the format of the information. Before these technologies enter into commercial operation, some obstacles should be removed, such as the problem of obtaining extremely precise synchronization of the network without any optical-electrical conversion. Also, a synchronization-related problem appear at the receiver for some systems such as OTDM and OCDMA, where even the fastest photo-detectors are not able to separate the data of the desired user from the signals of the adjacent users. This means that detection of ultrashort pulses in the presence of the multiple access interference (MAI) is key in these systems. Therefore, it is vital to apply an all-optical signal processing on the received optical signal before the photo-detection. In most of the ultra-high-speed light-wave communication systems, it is an effective technique to use an optical time gating at the receiver side in order to extract the desired user's signal from the received signal. This approach requires an optical clock recovery procedure. But by increasing the data rate in optical networks the accuracy of the optical clock recovery decreases because of increasing jitter and MAI and consequently the system performance is degraded. Currently the only approach is to use a clock signal that has the same pulse-width as the data, and when the jitter is large, this technique fails to properly capture the main part of the data signal and collects more interference instead, so these techniques have to lower the data-rate to avoid large BERs. Our contributions can achieve larger signal to noise ratio versus the fixed pulse-width clock. The main goal of this work is to discuss the characteristics of the current transmission technologies, including OTDM and OCDMA, providing a detailed analytical model and proposing a solution for improving the performance of optical receivers. We use a nonlinear media (Four Wave Mixing) as a combiner in the receivers. We have modeled analytically the relationship between the input and the output of the nonlinear media systems in these techniques using nonlinear Schrödinger equations. Then, we solved these equations by Volterra series. Our aim is to develop analytical models of the response of the optical receiver, and validate them with simulations. Also we consider the effect of variation of the bandwidth of the clock in the performance of receivers with presence of jitter. We obtain the optimum value of the clock's bandwidth and confirm that theory and simulation results coincide. Using our proposed technique, the data-rate of the optical systems can be increased and we can achieve a lower BER for the same jitter. The goal of these efforts is the improvement of the overall performance of the network, in terms of transmission speed, bit error rate (BER), reliability and cost. The results could be applied to next-generation optical networks, in both the backbone and access scenarios. |
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