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This book focuses on recent research and developments on optical communications. The chapters present different aspects of optical communication systems, comprising high capacity transmission over long distances, coherent and intensity modulated technologies, orthogonal frequency-division multiplexing, ultrafast switching techniques, and photonic integrated devices. Digital signal processing and error correction techniques are also addressed. The content is of interest to graduate students and researchers in optical communications.



Multilevel Pulse Amplitude Modulation Transmissions for Data Center Applications

Four-level pulse amplitude modulation (PAM4) is appearing as an important option for many applications that require optical communications at high data rate for short distances and/or with low complexity, such as Data Center interconnects. In this sense, this chapter aims to evaluate key features requirements for PAM4 transmissions focusing on short-reach DC applications. Therefore, we present a software to emulate PAM4 transmission at a high baud rate (56 GBd) in order to evaluate different configurations and impairments that could affect data transmission in the C-band, namely the digital signal processing (DSP) complexity, bandwidth limitation, chromatic dispersion tolerance, differential group delay (DGD) tolerance, and analog-to-digital converter (ADC) sampling requirements.
Rafael Carvalho Figueiredo, André L. N. Souza, Stenio M. Ranzini, Andrea Chiuchiarelli

Ultrafast Electro-Optical Switches Based on Semiconductor Optical Amplifiers

This chapter presents results from enhanced semiconductor optical amplifiers based switches to be employed on high-performance applications, which demand ultrafast transition times between operational states together with reduced guard times. A discussion on devices performance is accomplished through experimental characterizations of SOAs’ nonlinear properties and its oscillatory behavior. Switching techniques and mounting schemes are presented to improve switches’ dynamic operation, resulting in rise times below 200 ps and guard times of 650 ps. This performance, when combined with an improved energy efficiency, can offer a viable technical solution for switching in high-rates applications, such as Data Centers and supercomputers.
Tiago Sutili, Rafael Carvalho Figueiredo, Bruno Taglietti, Cristiano M. Gallep, Evandro Conforti

Coherent Optical Access Networks

The constant increase in IP traffic, mainly driven by the growth of the number of connected users and the demand for bandwidth per user, has profoundly influenced the evolution of optical communication systems as a whole, including fiber-based access networks, which constitute the last mile of an optical system, directly connecting the edge IP network to the end users. This chapter is devoted to coherent optical access networks. The main intent of the chapter is to analyze different fiber-access technologies, showing the benefits and the main limitations of each of them in assessing the needs for higher bandwidth and higher number of connected users together with the concerns of minimizing the impact on the network cost and complexity. It will be showed that coherent detection offers the highest potential in terms of network efficiency, with recent studies proving its feasibility for the access scenario also in terms of complexity and power consumption.
Andrea Chiuchiarelli, Sandro M. Rossi

High-Capacity Unrepeatered Optical Transmission

In the global telecommunications scenario, a great deal of interest has recently been devoted to taking the internet to country remote communities that are densely populated but in which the challenges imposed by climatic and environmental limitations are not straightforward to overcome. This chapter focuses on high-capacity unrepeatered optical transmission systems to enable high-speed connectivity in hard-to-reach areas. An optimization method for the unrepeatered optical system design is provided and detailed, followed by laboratory demonstrations showing the potential of repeaterless transmission in WDM systems with 400 Gb/s per carrier over distances greater than 400 km.
Sandro M. Rossi, João C. S. S. Januário, José Hélio da C. Júnior, Andrea Chiuchiarelli, André L. N. Souza

Impact of Nonlinear Effects and Mitigation on Coherent Optical Systems

This chapter presents an overview of modeling and mitigation of nonlinear effects on coherent optical systems. The Gaussian Noise (GN) is presented as an efficient method to analyze the nonlinear propagation in an uncompensated link and used to estimate the system performance. In order to compensate for the nonlinear impairments, four digital techniques were investigated: Digital Back-Propagation (DBP), DBP with coupled equations, Volterra series, and Maximum Likelihood Sequence Estimator (MLSE). Different scenarios were used to validate the algorithms. Finally, a nonlinear estimation algorithm based on Steepest Descent Algorithm (SDA) is shown and experimentally validated in an unrepeatered optical system.
Stenio M. Ranzini, Victor E. Parahyba, José Hélio da C. Júnior, Fernando Guiomar, Andrea Carena

High-Order Modulation Formats for Future Optical Communication Systems

Transceivers must evolve to cope with the ever-increasing traffic demand on optical networks. Some of their new features include using high-order modulation formats combined with more complex forward error correcting codes, nonlinear compensation, and probabilistic shaping. Beyond performance enhancement, power consumption is also an issue. This chapter focuses on some simulation results of using supervised phase recovery algorithm for complexity and power consumption reduction and experimental results on probabilistic shaping for performance enhancement.
André L. N. Souza, José Hélio da C. Júnior

Soft-Decision Forward Error Correction in Optical Communications

In order to effectively design good error-correcting codes for a given application, it is important to know how they work, how to assess the reliability of a given implementation and to be aware of the available codes and its features. In this chapter, a background about error correction is given so the reader can grasp the ideas behind error-correcting codes. Derivations about the confidence of error rate estimates are presented. These derivations turn out to be useful in the assessment of a system reliability when it is not possible to simulate enough codewords to observe a considerable number of errors. Finally, a brief historical review is presented and the authors present their view about promising codes for optical communications.
Alexandre Felipe, André L. N. Souza

Challenges Toward a Cost-Effective Implementation of Optical OFDM

We present a review of concepts and challenges to implement the OFDM technique in the all-optical domain so that it may emerge, in a near future, as a technically and economically feasible option to meet, with spectral efficiency and energy saving, the ever-increasing demand of capacity in data transmission systems.
Mônica L. Rocha, Rafael J. L. Ferreira, Diego M. Dourado, Matheus M. Rodrigues, Stenio M. Ranzini, Sandro M. Rossi, Fabio D. Simões, Daniel M. Pataca

Narrow Linewidth and Compact External-Cavity Lasers for Coherent Optical Communications

In this chapter, the activities related to external-cavity laser development executed in CPqD will be presented in detail. The target application is high-speed and high-order modulation formats optical systems for telecom. Using cavity design techniques, a narrow linewidth and high output power laser suitable for manufacturing is presented. It is presented the operation principle of the tunable mirror which is used as channel selector for the external cavity. Experimental results of a fixed-wavelength prototype are presented, showing optical output power above 16 dBm, Side-mode Suppression Ratio (SMSR) of 60 dB, and linewidth around 75 kHz. The cavity shows good stability for long-term high-temperature storage.
Giovanni B. de Farias, Leandro T. Zanvettor, Hening A. de Andrade, João C. S. S. Januário, Mayara E. Bonani, Maria Chiara Ubaldi, Aldo Righetti, Fausto Meli, Giorgio Grasso, Luis H. H. de Carvalho

Photonic Devices for Submarine Optical Amplifiers

In this work, the most recent research and development activities to design a photonic integrated circuit for submarine optical repeaters are reported. These activities are under the scope of a Brazilian project and accomplish the photonic integrated circuit design, fabrication and packaging. The developed technology must have high-reliability in order to target submarine applications. Simulation and experimental results are also presented, to prove the concept of each component inside the integrated photonic circuit.
Uiara Moura, Giovanni B. de Farias, João C. S. S. Januário, Márcio C. Argentato, Sandro M. Rossi

Optical Devices in Silicon Photonics

This chapter describes the development of passive and active components for silicon photonic integrated circuits that were performed in the CPqD. Specifically, the devices studied are polarization splitter and rotator (PSR), optical \(90^{\circ }\) hybrid, modulator, and laser. Each one is explained showing the principle of operation, modeling, and results obtained. These designed devices are compatible with standard manufacturing processes enabling monolithic integration with other devices. In addition, they can be used as building blocks for coherent transceivers and receivers in silicon photonics.
Yesica R. R. Bustamante, Uiara Moura, Henrique F. Santana, Giovanni B. de Farias
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