Unequal bit error probability in coherent QPSK fiber-optic systems using phase modulator based transmitters

We report on the occurrence of unequal bit error probability in a coherent quadrature phase shift keying (QPSK) fiber optic system. The bit error rates (BER) of two QPSK bits are derived individually based on the developed system model, and they turn out to differ by more than an order of magnitude for a phase modulator based transmitter. The phenomenon, previously unreported, arises because such a transmitter introduces a controlled form of inter-symbol-interference (ISI), and the receiver low-pass filters affect this ISI differently for the two bits. The optimum bandwidth of the receiver low-pass filter is obtained from the analytic derivation, which is about 0.7 times the symbol rate. We propose two simple system modifications, one in the transmitter and one in the receiver, to compensate for the phenomenon and equalize the two BER\u27s. Those modifications improve the system performance by about 2~dB without adding any extra hardware

Unequal bit error probability in coherent QPSK fiber-optic systems using phase modulator based transmitters

We report on the occurrence of unequal bit error probability in a coherent quadrature phase shift keying (QPSK) fiber optic system. The bit error rates (BER) of two QPSK bits are derived individually based on the developed system model, and they turn out to differ by more than an order of magnitude for a phase modulator based transmitter. The phenomenon, previously unreported, arises because such a transmitter introduces a controlled form of inter-symbol-interference (ISI), and the receiver low-pass filters affect this ISI differently for the two bits. The optimum bandwidth of the receiver low-pass filter is obtained from the analytic derivation, which is about 0.7 times the symbol rate. We propose two simple system modifications, one in the transmitter and one in the receiver, to compensate for the phenomenon and equalize the two BER\u27s. Those modifications improve the system performance by about 2~dB without adding any extra hardware

Power-efficient modulation formats in coherent transmission systems

Coherent optical transmission systems have a four-dimensional (4-D) signal space (two quadratures in two polarizations). These four dimensions can be used to create modulation formats that have a better power efficiency (higher sensitivity) than the conventional binary phase shift keying/quadrature phase shift keying (BPSK/QPSK) signals. Several examples are given, with some emphasis on a 24-level format and an 8-level format, including descriptions of how they can be realized and expressions for their symbol and bit error probabilities. These formats are, respectively, an extension and a subset of the commonly used 16-level dual-polarization QPSK format. Sphere packing simulations in 2, 3, and 4 dimensions, up to 32 levels, are used to verify their optimality. The numerical results, as the number of levels increases, are shown to agree with lattice-theoretical results. Finally, we point out that the use of these constellations will lead to improved fundamental sensitivity limits for optical communication systems, and they may also be relevant as a way of reducing power demands and/or nonlinear influence. \ua9 2009, IEEE. All rights reserved

Fiber Optics

Optical fibers in metrology, telecommunications, sensors, manufacturing, and health science have gained massive research interest. The number of applications is increasing at a fast pace. This book aims to present a collection of recent advances in fiber optics, addressing both fundamental and industrial applications. It covers the current progress and latest breakthroughs in emergent applications of fiber optics. The book includes five chapters on recent developments in optical fiber communications and fiber sensors, as well as the design, simulation, and fabrication of novel fiber concepts

Silicon-organic hybrid (SOH) electro-optic modulators for high-speed and power-efficient communications

Silicon-organic hybrid (SOH) modulators add a highly efficient nonlinear organic electro-optic cladding material to the silicon photonic platform, thereby enabling efficient electro-optic modulation. In this book, the application potential of SOH modulators is investigated. Proof-of-principle experiments show that they can be used for high-speed communications at symbol rates up to 100 GBd and operated directly from a field-programmable gate array (FPGA) without additional driver amplifiers

Real-time Digital Signal Processing for Software-defined Optical Transmitters and Receivers

A software-defined optical Tx is designed and demonstrated generating signals with various formats and pulse-shapes in real-time. Special pulse-shapes such as OFDM or Nyquist signaling were utilized resulting in a highly efficient usage of the available fiber channel bandwidth. This was achieved by parallel data processing with high-end FPGAs. Furthermore, highly efficient Rx algorithms for carrier and timing recovery as well as for polarization demultiplexing were developed and investigated

Nonlinear impairments and mitigation technologies for the next generation fiber-wireless mobile fronthaul networks

The proliferation of Internet-connected mobile devices and video-intensive services are driving the growth of mobile data traffic in an explosive way. The last mile of access networks, mobile fronthaul (MFH) networks, have become the data rate bottleneck of user experience. The objective of this research are two-fold. For analog MFH, nonlinear interferences among multiple bands of mobile signals in a multi-RAT multi-service radio-over-fiber (RoF)-based MFH system are investigated for the first time. The nonlinear impairments of both single-carrier and multi-carrier signals are investigated, and it is experimentally demonstrated that inter-channel interferences play a more important role in the performance degradation of analog MFH than the nonlinear distortions of each individual signal. A digital predistortion technique was also presented to linearize the analog MFH links. On the other hand, for digital MFH, we experimentally demonstrate a novel digitization interface based on delta-sigma modulation to replace the state-of-the-art common public radio interface (CPRI). Compared with CPRI, it provides improved spectral efficiency and enhanced fronthaul capacity, and can accommodate both 4G-LTE and 5G mobile services.Ph.D

Modulação e conversão de formatos óticos avançados

Doutoramento em Engenharia ElectrotécnicaOver the years, the increased search and exchange of information lead to an increase of traffic intensity in todays optical communication networks. Coherent communications, using the amplitude and phase of the signal, reappears as one of the transmission techniques to increase the spectral efficiency and throughput of optical channels. In this context, this work present a study on format conversion of modulated signals using MZI-SOAs, based exclusively on all- optical techniques through wavelength conversion. This approach, when applied in interconnection nodes between optical networks with different bit rates and modulation formats, allow a better efficiency and scalability of the network. We start with an experimental characterization of the static and dynamic properties of the MZI-SOA. Then, we propose a semi-analytical model to describe the evolution of phase and amplitude at the output of the MZI-SOA. The model’s coefficients are obtained using a multi-objective genetic algorithm. We validate the model experimentally, by exploring the dependency of the optical signal with the operational parameters of the MZI-SOA. We also propose an all-optical technique for the conversion of amplitude modulation signals to a continuous phase modulation format. Finally, we study the potential of MZI-SOAs for the conversion of amplitude signals to QPSK and QAM signals. We show the dependency of the conversion process with the operational parameters deviation from the optimal values. The technique is experimentally validated for QPSK modulation.Nos últimos anos, a crescente procura e troca de informação tem levado ao aumento de tráfego nas redes de comunicação óticas atuais. As comunicações coerentes, com recurso à amplitude e fase do sinal, ressurgem como uma das técnicas de transmissão capazes de aumentar a eficiência espectral e o rendimento dos canais óticos. Nesse âmbito, este trabalho apresenta um estudo sobre a conversão de formatos de modulação de sinais, usando técnicas exclusivamente no domínio ótico, através de conversão de comprimento de onda, com base no MZI-SOA. Esta técnica, aplicada em nós óticos que interligam redes óticas com débitos binários distintos, permite uma maior escalabilidade e eficiência da rede. A tese começa por apresentar uma caracterização experimental detalhada das propriedades estáticas e dinâmicas do MZI-SOA. É depois proposto um modelo semi-analítico que descreve a evolução da amplitude e fase do sinal ótico à saída do MZI-SOA. Os coeficientes do modelo são obtidos recorrendo a um algoritmo genético multiobjectivo. O modelo é validado experimentalmente, explorando a dependência do sinal ótico com os parâmetros operacionais do MZI- SOA. Segue-se a proposta de uma técnica de conversão de formato de modulação de amplitude para modulação de fase contínua. Finalmente, é feito um estudo das potencialidades do MZI-SOA para conversão de formato de modulação de amplitude para modulação QPSK e QAM. Mostra-se a dependência da constelação do sinal com o desvio dos parâmetros operacionais, em torno do valor ótimo. A técnica é validada experimentalmente para modulação QPSK

Advanced optical modulation and format conversion

Tese de Doutoramento em Engenharia Eletrotécnica apresentada à Universidade de Aveiro.Nos últimos anos, a crescente procura e troca de informação tem levado ao aumento de tráfego nas redes de comunicação óticas actuais. As comunicações coerentes, com recurso à amplitude e fase do sinal, ressurgem como uma das técnicas de transmissão capazes de aumentar a eficiência espectral e o rendimento dos canais óticos. Nesse âmbito, este trabalho apresenta um estudo sobre a conversão de formatos de modulação de sinais, usando técnicas exclusivamente no domínio ótico, através de conversão de comprimento de onda, com base no MZI-SOA. Esta técnica, aplicada em nós óticos que interligam redes óticas com débitos binàrios distintos, permite uma maior escalabilidade e eficiência da rede. A tese começa por apresentar uma caracterização experimental detalhada das propriedades estáticas e dinámicas do MZI-SOA. É depois proposto um modelo semi-analítico que descreve a evolução da amplitude e fase do sinal ótico à saída do MZI-SOA. Os coeficientes do modelo são obtidos recorrendo a um algoritmo genético multiobjectivo. O modelo é validado experimentalmente, explorando a dependência do sinal ótico com os parâmetros operacionais do MZISOA. Segue-se a proposta de uma técnica de conversão de formato de modulação de amplitude para modulação de fase contínua. Finalmente, é feito um estudo das potencialidades do MZI-SOA para conversão de formato de modulação de amplitude para modulação QPSK e QAM. Mostra-se a depedência da constelação do sinal com o desvio dos parâmetros operacionais, em torno do valor ótimo. A técnica é validada experimentalmente para modulação QPSK.ABSTRACT: Over the years, the increased search and exchange of information lead to an increase of traffic intensity in todays optical communication networks. Coherent communications, using the amplitude and phase of the signal, reappears as one of the transmission techniques to increase the spectral efficiency and throughput of optical channels. In this context, this work present a study on format conversion of modulated signals using MZI-SOAs, based exclusively on alloptical techniques through wavelength conversion. This approach, when applied in interconnection nodes between optical networks with different bit rates and modulation formats, allow a better efficiency and scalability of the network. We start with an experimental characterization of the static and dynamic properties of the MZI-SOA. Then, we propose a semi-analytical model to describe the evolution of phase and amplitude at the output of the MZI-SOA. The model’s coefficients are obtained using a multi-objective genetic algorithm. We validate the model experimentally, by exploring the dependency of the optical signal with the operational parameters of the MZI-SOA. We also propose an all-optical technique for the conversion of amplitude modulation signals to a continuous phase modulation format. Finally, we study the potential of MZI-SOAs for the conversion of amplitude signals to QPSK and QAM signals. We show the dependency of the conversion process with the operational parameters deviation from the optimal values. The technique is experimentally validated for QPSK modulation.Apoio financeiro da Fundação para a Ciência e Tecnologia — FCT através da bolsa SFRH / PROTEC / 50015 / 2009

Silicon-organic hybrid devices for high-speed electro-optic signal processing

Among the various elements of the silicon photonics platform, electro-optic IQ modulators play an important role. In this book, silicon-organic hybrid (SOH) integration is used to realize electro-optic IQ modulators for complex signal processing. Leveraging the high nonlinearity of organic materials, SOH IQ modulators provide low energy consumption for high-speed data transmission and frequency shifting. Furthermore, the device design is adapted for commercial foundry processes