In this book, semiconductor optical amplifiers (SOAs) are studied with a view to linear and nonlinear applications in next-generation optical networks. Quantum-dot SOAs can be optimized for linear amplification of signals with different modulation formats and multiplexing techniques. Conversely, bulk SOAs can be easily optimized for operation in the nonlinear regime. However, due to the fast carrier recovery times in QD SOAs we also look into nonlinear applications with these devices.

This thesis examines the unique properties of gallium arsenide (GaAs)-based quantum-dot semiconductor optical amplifiers for optical communication networks, introducing readers to their fundamentals, basic parameters and manifold applications. The static and dynamic properties of these amplifiers are discussed extensively in comparison to conventional, non quantum-dot based amplifiers, and their unique advantages are elaborated on, such as the fast carrier dynamics and the decoupling of gain and phase dynamics. In addition to diverse amplification scenarios involving single and multiple high symbol rate amplitude and phase-coded data signals, wide-range wavelength conversion as a key functionality for optical signal processing is investigated and discussed in detail. Furthermore, two novel device concepts are developed and demonstrated that have the potential to significantly simplify network architectures, reducing the investment and maintenance costs as well as the energy consumption of future networks.

Self-coherent receivers are promising candidates for reception of 100 Gbit/s data rates in optical networks. Self-coherent receivers consist of multiple optical delay interferometers (DI) with high-speed photodiodes attached to the outputs. By DSP of the photo currents it becomes possible to receive coherently modulated optical signals. Especially promising for 100 Gbit/s networks is the PolMUX DQPSK format, the self-coherent reception of which is described in detail.

Future access networks are converged optical-wireless networks, where fixed-line and wireless services share the same infrastructure. In this book, semiconductor optical amplifiers (SOA) and mm-wave wireless links are investigated, and their use in converged access networks is explored: SOAs compensate losses in the network, and thereby extend the network reach. Millimeter-wave wireless links substitute fiber links when cabling is not economical.

This books focuses on recent break-throughs in the development of a variety of photonic devices, serving distances ranging from mm to many km, together with their electronic counter-parts, e.g. the drivers for lasers, the amplifiers following the detectors and most important, the relevant advanced VLSI circuits. It explains that as a consequence of the increasing dominance of optical interconnects for high performance workstation clusters and supercomputers their complete design has to be revised. This book thus covers for the first time the whole variety of interdependent subjects contributing to green photonics and electronics, serving communication and energy harvesting. Alternative approaches to generate electric power using organic photovoltaic solar cells, inexpensive and again energy efficient in production are summarized. In 2015, the use of the internet consumed 5-6% of the raw electricity production in developed countries. Power consumption increases rapidly and without some transformational change will use, by the middle of the next decade at the latest, the entire electricity production. This apocalyptic outlook led to a redirection of the focus of data center and HPC developers from just increasing bit rates and capacities to energy efficiency. The high speed interconnects are all based on photonic devices. These must and can be energy efficient but they operate in an electronic environment and therefore have to be considered in a wide scope that also requires low energy electronic devices, sophisticated circuit designs and clever architectures. The development of the next generation of high performance exaFLOP computers suffers from the same problem: Their energy consumption based on present device generations is essentially prohibitive.

This book covers the technology of switching or modulating light in semiconductor optical waveguides. Currently a key function for optical communications systems is the conversion of data from an electrical signal to an optical signal for transmission in very low loss optical fibres and the converse process of optical to electrical conversion the O/E/O data conversion. This conversion between electronic and photonic signals imposes an energy consumption overhead on optical communication systems. So many research workers have been attracted to ultrafast all-optical switching of data in different formats. As a way of introduction to all-optical switching in semiconductor waveguides the book covers the electro-optic effect, electroabsorption and electrorefraction; effects that can be used in semiconductor optical modulation devices. But the book focuses on all-optical switching using second and third order optical nonlinearities in AlGaAs optical waveguides. It covers a variety of device configurations including integrated nonlinear couplers and Mach-Zehnder interferometers. Further, it provides design software in suit of Mathematica notebooks that can be used to explore the device design.

Self-coherent receivers are promising candidates for reception of 100 Gbit/s data rates in optical networks. Self-coherent receivers consist of multiple optical delay interferometers (DI) with high-speed photodiodes attached to the outputs. By DSP of the photo currents it becomes possible to receive coherently modulated optical signals. Especially promising for 100 Gbit/s networks is the PolMUX DQPSK format, the self-coherent reception of which is described in detail.

In this book, the first high-speed silicon-organic hybrid (SOH) modulator is demonstrated by exploiting a highly-nonlinear polymer cladding and a silicon waveguide. By using a liquid crystal cladding instead, an ultra-low power phase shifter is obtained. A third type of device is proposed for achieving three-wave mixing on the silicon-organic hybrid (SOH) platform. Finally, new physical constants which describe the optical absorption in charge accumulation/inversion layers in silicon are determined.

Optical communication systems carry the bulk of all data traffic worldwide. This book introduces multi-Terabit/s transmission systems and three key technologies for next generation networks. A software-defined multi-format transmitter, an optical comb source and an optical processing scheme for the fast Fourier transform for Tbit/s signals. Three world records demonstrate the potential: The first single laser 10 Tbit/s and 26 Tbit/s OFDM and the first 32.5 Tbit/s Nyquist WDM experiments.

New Advances in Semiconductors brings together contributions from important researchers around the world on semiconductor materials and their applications. It includes seven chapters in two sections: “Calculations and Simulations in Semiconductors” and “Semiconductor Materials.” The world will emerge different after the social and economic reorganizations caused by the COVID-19 pandemic and will be even more dependent on semiconductors than ever before. New Advances in Semiconductors is a book that brings together the contributions of important researchers around the world and is able to give an idea about the different characteristics of semiconductor materials and their applications. There is a section dedicated to theory, calculations and logic and another dedicated to the development and characterization of semiconductor materials of great future interest. I really hope that this book will help to spread knowledge about this research field to other researchers and students working in this area or even to those interested in starting their more advanced studies.