"In recent years, high-speed low-cost modulators have attracted immense research interest to fulfill the ever-increasing intra-data center traffic. Silicon photonics is a mature platform compatible to the complementary metal-oxide-semiconductor fabrication processes, and it has a low cost for large volume integration. Intensity-modulation/direct-detection systems do not need a local oscillator or complicated digital signal processing (DSP), thus they are favored over coherent systems for intra-data center applications. Currently, four-level pulse amplitude modulation (PAM-4) has been accepted for the next generation 400G Ethernet.In this thesis, two silicon photonic PAM-4 modulators are reported for the next generation intra-data center optical communication systems. They are the dual microring modulators (MRMs) assisted Mach-Zehnder interferometer (MZI) and the dual-drive Michelson interferometric modulator (MIM). Three operating principles of generating PAM-4 optical signals based on the two proposed modulators are investigated. First, by driving the dual MRMs with differential 4-level radio-frequency (RF) signals, low-chirp PAM-4 is achieved. Successful PAM-4 transmission at 92 Gb/s over 1 km of standard single mode fiber (SSMF) and at 40 Gb/s over 20 km of SSMF without chromatic dispersion compensation are presented. Second, based on the resonances overlap of the two microrings and modulation of only one MRM, PAM-4 with large optical modulation amplitudes and extinction ratios are realized. 80 Gb/s PAM-4 transmission over 2 km of SSMF is successfully achieved. Third, dual-drive operation with independent binary RF signals generates PAM-4 optical signals without implementing digital-to-analog converter or DSP, which reduces the power consumption in the optical transmission link. PAM-4 transmission over 2 km of SSMF at 50 Gb/s using the dual MRMs assisted MZI and at 56 Gb/s using the dual-drive MIM are both presented. All the measured bit error rates of PAM-4 transmission based on these three operating principles are below the hard-decision forward-error correction threshold of 3.8 × 10-3." --

"The ever increasing internet traffic driven by the constant spread of cloud services offered by data centers and the increasing demand for higher bandwidth driven by web-based media applications and services have increased the need for faster and inexpensive short reach optic solutions. With the commercialization and deployment of 100 Gb/s technologies, and the development of 400 Gb/s systems, there is a clear need for inexpensive and power efficient building blocks. Currently 100 Gb/s transmission of Ethernet frames over single mode fiber (SMF) is realized using a four color wavelength division multiplexing (WDM) setting in a 4 × 25 Gb/s format. However, it is widely agreed that the 400 Gb/s systems will be realized using 4 × 100 Gb/s configuration, which necessitates the need for a single wavelength operation at 100 Gb/s. To achieve higher data rate transmission, advance optical modulation formats together with polarization and wavelength division multiplexing are required. Pulse amplitude modulation (PAM) enables higher spectral efficiency by using multi-level amplitudes. Using PAM-4 modulation format doubles the spectral efficiency of the optical link. Recently PAM generation has been demonstrated using Silicon Photonics (SiP) intensity modulators. In this thesis, we present a 4.2 mm long, 35 GHz bandwidth single drive series push pull silicon travelling wave Mach-Zehnder modulator (TW-MZM) based on lateral PN junction operating near 1550 nm wavelength. A bit-rate of 112 Gb/s is achieved using PAM-4 modulation scheme at 56 Gbaud after 2 km of single mode fiber (SMF) below the hard decision pre forward error correction (Pre-FEC) threshold of 3.8 × 10-3 to provide a final bit error rate under 10-15. To the best of our knowledge this modulator surpasses the highest bandwidth reported for a SiP modulator by 5 GHz. " --

"Global internet traffic has been growing exponentially in the past several years. This increase is fueled by video streaming services (e.g. Netflix, YouTube), cloud-based storages (e.g. Dropbox, google drive), and machine-to-machine (e.g. Internet of Things) applications. Since 2008 most Internet traffic has originated or been terminated in datacenters and the datacenter traffic is forecasted to grow three-fold in the next five years to reach 20.6 zettabytes by 2021. On-Off-Keying (OOK) has been the main modulation format employed in short reach optical interconnects. The simplicity of the transmitter and receiver architectures have been an important factor in the success of OOK for short reach optical links. Recently deployed, 100 Gb/s systems utilize OOK modulation in 4 × 25 Gb/s configuration. However, as we move towards 400 Gb/s and 1 Tb/s systems, OOK requires a proportional increase in the bandwidth. Hence, a more efficient modulation format is required to avoid such complexity. Silicon photonics (SiP) has recently become a popular choice for datacenter interconnects. Taking advantage of years of complementary metal oxide semiconductor research and development, SiP provides a low cost and high yield platform for datacenter optical interconnects. In this thesis, 3 different SiP Mach-Zehnder modulator (MZM) structures to generate higher order modulation formats are presented. First, the feasibility of utilizing coherent transmission systems as opposed to intensity modulation/direct detection systems for 400 Gb/s and 1 Tb/s systems are discussed and an Inphase-Quadrature modulator is presented. We discuss the advantages and disadvantages of using coherent systems for short reach applications. Next, we investigate and compare the performance advantages of generating 4-level Pulse Amplitude Modulation (PAM-4) using various structures of MZM optically, instead of generating PAM-4 in the electrical domain using digital to analog convertors (DACs) for 400 Gb/s systems. The two variants of optical-DACs are a Dual Parallel Mach-Zehnder modulator (DP-MZM) with one series push pull travelling wave MZM on each arm and a single MZM having two electrodes in series that we name Multi-Electrode MZM (ME-MZM). We present the optical design of the modulators and investigate the effects of non-linearities of the MZM transfer function and PN junction phase-shifters on performance of the PAM-4 generation. Then, the DC, small signal and large signal characterization of each modulator are presented. We parametrically examine the transmission performance of each modulator and present an optimized modulator design for optical generation and transmission of 112 Gb/s PAM-4 without using digital signal processing." --

"In recent years, the amount of traffic within data centers has increased to a point where electrical interconnects are being replaced by optical interconnects and pluggable modules. Silicon photonics, which uses the existing CMOS fabrication capabilities to develop integrated photonics, offers the ability to make compact devices in high volume with relatively better yield. This makes it a highly desired platform to develop optical transceivers and components for modern data centers. As such, it has recently reached the production phase of the technology development cycle. This thesis studies several devices that are applicablein leading data centers. A detailed analysis and characterization of a silicon Michelson modulator with short 500 um phase shifters and a low VpiLpi of 0.72 V-cm under reverse bias is presented. The optical modulation of reverse biased p-n and forward biased p-i-n junctions is investigated. For reverse bias operation, it is demonstrated that bandwidth can be increased with lower impedance drivers and the driver impedance limits the bitrate achievable. Furthermore, forward bias operation with pre-emphasized signals is shown to have clean eye diagrams up to 40 Gbps. Energy consumption is estimated for all cases of studies and their trade-offs are explained.The work on modulators is further developed by studying series push-pull traveling wave Mach-Zehnder modulators. Measurements of electrodes is compared with simulation validating the methods of increasing impedance and microwave effective index with T-shaped electrodes. Moreover, designs with two and three level implants are compared and it is concluded with measurements that a two level doping design is as good as the design with three level implants, thus reducing the number of masks and processing steps required. Another variation of modulators is the dual-drive modulators. Here, the spacing between electrodes can lead to coupling, which results in different responses depending on whether the modulator is driven single-endedly or differentially. The electro-optic frequency response of a four-port traveling-wave dual-drive modulator with relatively weak coupling amongst the electrodes is measured. It is shown that the electro-optic frequency response of the Mach-Zehnder modulator can be predicted with a 2x2 cascaded matrix model if the Mach-Zehnder modulator is symmetric and differentially driven. In recent years, the increase in data transfers has demanded that more bits be transmitted and received in a given bandwidth. The design and characterization of a silicon-on-insulator traveling-wave multi-electrode Mach-Zehnder modulator is reported in this thesis. This 2-bit electro-optic digital-to-analog converter is formed by dividing a series push-pull Mach-Zehnder modulator into two segments, one for each bit, thus allowing for PAM-4 modulation without using a digital-to-analog converter. The device is operated at speeds up to 50 Gbaud and thus generating 100 Gbps on a single wavelength without signal processing at the transmitter or the receiver. The pre-forward error correction bit error rate is estimated to be lower than the hard-decision forward error correction threshold of 3.8e-3 over 1 km of standard single-mode fiber.Another component that is crucial in optical networks is the optical switch. The optical switch has numerous applications in protection and restoration as well as in certain modern data center architectures. A 4x4 fully non-blocking crossbar switch fabric based on interferometric thermal phase shifters is developed and reported in this thesis. Here, heating is achieved using resistive elements around the silicon waveguide. Switching times of 5 us and 36 mW power consumption in an individual switching element is measured. As a proof of concept, the quality in degradation of switching is demonstrated by routing an input signal to some of the outputs of the switch." --

SOH (silicon-organic hybrid) elektrooptische Modulatoren kombinieren Siliziumphotonik mit organischen elektro-optischen Materialien. Dieses Buch befasst sich mit Aspekten, die speziell für den Einsatz von SOH-Modulatoren in praktischen optischen Hochgeschwindigkeitskommunikationssystemen relevant sind, wie z. B. Aufbau- und Verbindungstechnik, Modellierung und die Implementierung effizienter Modulationsformate für IM/DD-Formate. - Silicon-organic hybrid (SOH) electro-optic modulators combining silicon photonic structures with organic EO materials are investigated. This book addresses aspects that are specifically relevant for the use of SOH modulators in practical high-speed optical communication systems such as packaging, modelling of the device, and the implementation of efficient intensity-modulation/direct-detection (IM/DD) modulation formats.

"This thesis covers three topics of optical communications. First, we address long-haul fiberoptic coherent systems and propose a solution to two specific problems: polarization recovery and fiber nonlinearity. Second, we study silicon photonic devices for passive all-optical signal processing and active optical signal modulation enabling dense integration of photonics with advanced microelectronics. Finally, we address the need for faster short-reach transceivers in intra- and inter-data center networks by proposing novel modulation formats, digital signal processing algorithms, and transceiver architectures for Stokes vector modulation and demodulation. The thesis covers a large range of optical transmission distances, from long-haul to chip-scale photonics including short-reach optics for data center networks, all enabled by digital signal processing at both the transmitter and receiver. In the case of long-haul fiber-optic coherent systems, we propose a blind and fast algorithm allowing recovering the state of polarization of any Dual-Polarization square M-ary Quadrature Amplitude Modulation (DP-MQAM) format. The algorithm allows a significant reduction of the convergence time for any polarization orientation at the receiver compared to the traditional blind derotation method. We also propose a complex modulation format being a power constrained version of the Dual-Polarization-8QAM format and we analytically and experimentally demonstrate greater tolerance to nonlinear effects. For chip-scale photonic devices, the thesis contains a thorough study of wavelength multicasting using the parametric process of four-wave-mixing in a silicon-on-insulator photonic waveguide where we demonstrate a 1-to-6 multicast of a 16QAM signal and study the impact on performance of the input and output fiber-chip couplers. We also characterize the performance of the first silicon Mach-Zehnder intensity modulator enabling 112 Gb/s using 8-level intensity modulation for CMOS integrated interconnects. Finally, for optical communications targeting data center applications covering the range of 0.5 to 10 km, we present novel transceivers, modulation formats, and digital signal processing schemes for next generation single wavelength high-speed pluggables. We demonstrate the first transmission of 112 Gb/s over 10 km of single mode fiber in a silicon photonics modulator using 4-level pulse amplitude modulation (PAM), compliant with IEEE©'s new physical specifications of 56 Gbaud signaling and PAM-4 format. The thesis also reports the first demonstration of a 300 Gb/s transceiver enabled by digital to analog and analog to digital converters and novel digital signal processing algorithms where we modulate 6 bits of information per symbol on a single laser source and demodulate with a direct detection Stokes-vector receiver.We conclude this thesis with a summary of the research presented and possible future research to follow those addressed in this work." --

"Global IP traffic will continue to grow in the foreseeable future. Different applications are driving demand for increased capacity such as cloud based services, video streaming services, and big data.Since 2008, most Internet traffic has originated or terminated in datacenters. As a result, datacenters have experienced unprecedented traffic increases, where datacenter traffic will reach more than 20.6 zettabytes by 2021, i.e., 3-fold increase since 2016. In response to demands to support capacity increases, there are significant worldwide research and commercialization efforts that are being directed toward developing high speed intra- and inter-datacenter optical interconnects (DCIs). Different material platforms are used to build optical transceivers including the silicon photonics (SiP) platform. The SiP platform has the potential to build compact, high yield, high performance, and low cost complementary metal oxide semiconductor (CMOS) compatible transceivers. In this thesis, we explore devices and circuits for optical DCIs. This thesis can be divided into three parts. In the first part, we develop and demonstrate passive and active SiP components which are essential in photonic integrated circuits (PICs) for optical transceivers. The first device is a 3-dB beam splitter based on multi-mode interference (MMI), where we present the device design and wafer-scale experimental results. Then, we include subwavelength gratings into an asymmetric MMI to enable compact, large bandwidth, and different splitting ratios. Using cascaded MMIs, we design a C-band polarization beam splitter for coherent PICs, where we demonstrate the advantages of using a cascaded MMI design in improving the device extinction ratio. Next, we present the detailed design and experimental results of a high yield and low insertion loss polarization splitter and rotator. Different variations of this design are demonstrated aiming at different performance metrics and operating bands. Finally, we present a variable optical attenuator based on a Mach-Zehnder interferometer structure where a substrate undercut is added to the design to enable low power consumption. In the second part, we present PICs for 200 Gb/s and 400 Gb/s intra-datacenter optical interconnects. First, a 4-lane SiP transmitter is demonstrated based on four parallel Mach-Zehnder modulators (MZMs). The crosstalk between the four MZMs is studied using small-signal and large-signal modulation. Driving the four MZMs simultaneously, 400 Gb/s aggregate rate can be achieved using relatively low voltage swing and simple digital signal processing (DSP). Then, we explore 200 Gb/s transmitters based on dual parallel multi-electrode MZMs (MEMZMs) to generate the PAM4 signal optically which results in a better signal to noise ratio compared to the electrical generation. Finally, we exploit the other polarization dimension by demonstrating a dual-polarization transmitter in a stokes vector direct detection experiment. More than 200 Gb/s can be achieved using this transmitter which doubles the capacity used for a classical intensity modulation/direct detection system and renders a better scalable approach for bitrates beyond 400 Gb/s. In the last part, we report system-level demonstrations targeting DCI applications. First, we present a single wavelength and polarization PAM4 transmission experiment using state of the art digital-to-analog converters (DACs), analog-to-digital converters (ADCs), and a lithium niobate MZM. Then, we present the first demonstration of a 400 Gb/s transmitter optical sub-assembly (TOSA) on the coarse wavelength division multiplexing (CWDM) grid. The TOSA performance is studied versus several parameters. Results show that we can achieve more than 600 Gb/s over 20 km of single mode fiber (SMF) without optical amplification"--

Bandwidth demand in optical communication systems is continually growing. Data rate values in the order of several hundreds of TBps are expected in the near future. In order to cope with those expectations silicon based technologies are believed to be the best suited. Its naturally compatibility with CMOS easily enables the electronics and photonics co-integration. In the short-term the way increase data rates in next generation optical communication systems goes through using advanced modulation format and increase symbol rates. In the long-term view, new multiplexing techniques will be required. In this sense, mode division multiplexing is nowadays an attractive approach under consideration.In this Thesis work, the way to implement these new optical communication schemes is studied from the transmitter point of view. It includes, on a first part the modeling, design and characterization of silicon modulators. And in a second part, it includes the proposition, design and characterization of novel mode handling devices for mode division multiplexing.A new way of modeling silicon modulators has been developed. This new model permits to reduce the computation time of modulator analysis up to two orders of magnitude, while maintaining a good level of accuracy. Using the model, modulators based on lateral PN junctions and interdigitated PN junctions were designed to work in the O-Band of optical communications. Characterization work has been performed on these modulators with good results. Wide-open OOK (On Off Keying) eye diagrams with 10 dB extinction ratio were obtained at 10GBps. Furthermore, BPSK (Binary Phase Shift Keying) modulation was also demonstrated at 10GBps.New kind of mode converters and multiplexers, intended to work as mode division multiplexing subsystems have been proposed, designed, fabricated and characterized. Measured results show broad bandwidth operation with high extinction ratio.

This book introduces the reader to the optical switching technology for its application to data centers. In addition, it takes a picture of the status of the technology and system architecture evolution and of the research in the area of optical switching in data center. The book is organized in four parts: the first part is focused on the system aspects of optical switching in intra-data center networking, the second part is dedicated to describing the recently demonstrated optical switching networks, the third part deals with the latest technologies developed to enable optical switching and, finally, the fourth part of the book outlines the future prospects and trends.

"This book discusses the principles and the latest progress of silicon optical modulators as cutting-edge integrated photonic devices on silicon-photonic platforms, which play key roles in modern optical communications with low power consumption, small footprints, and low manufacturing costs. Silicon Mach-Zehnder optical modulators are emphasized as the principal small-footprint optical modulator because of its superior performance in high-speed optical modulation at operational temperatures beyond 100 degrees Celsius without power-consuming thermo-electric cooling in spectral bands over 100 nm"--