Broadband Receiver Electronic Circuits for Fiber-Optical Communication Systems

The exponential growth of internet traffic drives datacenters to constantly improve their capacity. As the copper based network infrastructure is being replaced by fiber-optical interconnects, new industrial standards for higher datarates are required. Several research and industrial organizations are aiming towards 400 Gb Ethernet and beyond, which brings new challenges to the field of high-speed broadband electronic circuit design. Replacing OOK with higher M-ary modulation formats and using higher datarates increases network capacity but at the cost of power. With datacenters rapidly becoming significant energy consumers on the global scale, the energy efficiency of the optical interconnect transceivers takes a primary role in the development of novel systems. There are several additional challenges unique in the design of a broadband shortreach fiber-optical receiver system. The sensitivity of the receiver depends on the noise performance of the PD and the electronics. The overall system noise must be optimized for the specific application, modulation scheme, PD and VCSEL characteristics. The topology of the transimpedance amplifier affects the noise and frequency response of the PD, so the system must be optimized as a whole. Most state-of-the-art receivers are built on high-end semiconductor SiGe and InP technologies. However, there are still several design decisions to be made in order to get low noise, high energy efficiency and adequate bandwidth. In order to overcome the frequency limitations of the optoelectronic components, bandwidth enhancement and channel equalization techniques are used. In this work several different blocks of a receiver system are designed and characterized. A broadband, 50 GHz bandwidth CB-based TIA and a tunable gain equalizer are designed in a 130 nm SiGe BiCMOS process. An ultra-broadband traveling wave amplifier is presented, based on a 250 nm InP DHBT technology demonstrating a 207 GHz bandwidth. Two TIA front-end topologies with 133 GHz bandwidth, a CB and a CE with shunt-shunt feedback, based on a 130 nm InP DHBT technology are designed and compared

Wideband integrated circuits for optical communication systems

The exponential growth of internet traffic drives datacenters to constantly improvetheir capacity. Several research and industrial organizations are aiming towardsTbps Ethernet and beyond, which brings new challenges to the field of high-speedbroadband electronic circuit design. With datacenters rapidly becoming significantenergy consumers on the global scale, the energy efficiency of the optical interconnecttransceivers takes a primary role in the development of novel systems. Furthermore,wideband optical links are finding application inside very high throughput satellite(V/HTS) payloads used in the ever-expanding cloud of telecommunication satellites,enabled by the maturity of the existing fiber based optical links and the hightechnology readiness level of radiation hardened integrated circuit processes. Thereare several additional challenges unique in the design of a wideband optical system.The overall system noise must be optimized for the specific application, modulationscheme, PD and laser characteristics. Most state-of-the-art wideband circuits are builton high-end semiconductor SiGe and InP technologies. However, each technologydemands specific design decisions to be made in order to get low noise, high energyefficiency and adequate bandwidth. In order to overcome the frequency limitationsof the optoelectronic components, bandwidth enhancement and channel equalizationtechniques are used. In this work various blocks of optical communication systems aredesigned attempting to tackle some of the aforementioned challenges. Two TIA front-end topologies with 133 GHz bandwidth, a CB and a CE with shunt-shunt feedback,are designed and measured, utilizing a state-of-the-art 130 nm InP DHBT technology.A modular equalizer block built in 130 nm SiGe HBT technology is presented. Threeultra-wideband traveling wave amplifiers, a 4-cell, a single cell and a matrix single-stage, are designed in a 250 nm InP DHBT process to test the limits of distributedamplification. A differential VCSEL driver circuit is designed and integrated in a4x 28 Gbps transceiver system for intra-satellite optical communications based in arad-hard 130nm SiGe process

High speed optical coherence microscopy with autofocus adjustment and a miniaturized endoscopic imaging probe

Optical coherence microscopy (OCM) is a promising technique for high resolution cellular imaging in human tissues. An OCM system for high-speed en face cellular resolution imaging was developed at 1060 nm wavelength at frame rates up to 5 Hz with resolutions of < 4 µm axial and < 2 µm transverse. The system utilized a novel polarization compensation method to combat wavelength dependent source polarization and achieve broadband electro-optic phase modulation compatible with ultrahigh axial resolution. In addition, the system incorporated an auto-focusing feature that enables precise, near real-time alignment of the confocal and coherence gates in tissue, allowing user-friendly optimization of image quality during the imaging procedure. Ex vivo cellular images of human esophagus, colon, and cervix as well as in vivo results from human skin are presented. Finally, the system design is demonstrated with a miniaturized piezoelectric fiber-scanning probe which can be adapted for laparoscopic and endoscopic imaging applications.National Institutes of Health (U.S.) (R01-CA75289-13)National Institutes of Health (U.S.) R01-EY11289-25United States. Air Force Office of Scientific Research (FA9550-07-1-0101)United States. Air Force Office of Scientific Research (FA9550-07-1-0014)Max Planck Society for the Advancement of ScienceNational Institutes of Health (U.S.) (Fellowship) (F31 EB005978

Optimizing the limit of detection of waveguide-based interferometric biosensor devices

Waveguide-based photonic sensors provide a unique combination of high sensitivity, compact size and label-free, multiplexed operation. Interferometric configurations furthermore enable a simple, fixed-wavelength read-out making them particularly suitable for low-cost diagnostic and monitoring devices. Their limit of detection, i.e., the lowest analyte concentration that can be reliably observed, mainly depends on the sensors response to small refractive index changes, and the noise in the read-out system. While enhancements in the sensors response have been extensively studied, noise optimization has received much less attention. Here we show that order-of-magnitude enhancements in the limit of detection can be achieved through systematic noise reduction, and demonstrate a limit of detection of ~10 RIU with a silicon nitride sensor operating at telecom wavelengths

An integrated CMOS optical receiver with clock and data recovery Circuit

Traditional implementations of optical receivers are designed to operate with external photodetectors or require integration in a hybrid technology. By integrating a CMOS photodetector monolithically with an optical receiver, it can lead to the advantage of speed performance and cost. This dissertation describes the implementation of a photodetector in CMOS technology and the design of an optical receiver front-end and a clock and data recovery system. The CMOS detector converts the light input into an electrical signal, which is then amplified by the receiver front-end. The recovery system subsequently processes the amplified signal to extract the clock signal and retime the data. An inductive peaking methodology has been used extensively in the front-end. It allows the accomplishment of a necessary gain to compensate for an underperformed responsivity from the photodetector. The recovery circuits based on a nonlinear circuit technique were designed to detect the timing information contained in the data input. The clock and data recovery system consists of two units viz. a frequency-locked loop and a phase-locked loop. The frequency-locked loop adjusts the oscillator’s frequency to the vicinity of data rate before phase locking takes place. The phase-locked loop detects the relative locations between the data transition and the clock edge. It then synchronises the input data to the clock signal generated by the oscillator. A system level simulation was performed and it was found to function correctly and to comply with the gigabit fibre channel specification.Dissertation (MEng (Micro-Electronics))--University of Pretoria, 2007.Electrical, Electronic and Computer Engineeringunrestricte

Design of event-driven automatic gain control and high-speed data path for multichannel optical receiver arrays

The internet has become the ubiquitous tool that has transformed the lives of all of us. New broadband applications in the field of entertainment, commerce, industry, healthcare and social interactions demand increasingly higher data rates and quality of the networks and ICT infrastructure. In addition, high definition video streaming and cloud services will continue to push the demand for bandwidth. These applications are reshaping the internet into a content-centric network. The challenge is to transform the telecom optical networks and data centers such that they can be scaled efficiently, at low cost. Furthermore, from both an environmental and economic perspective, this scaling should go hand in hand with reduced power consumption. This stems from the desire to reduce CO2 emission and to reduce network operating costs while offering the same service level as today. In the current architecture of the internet, end-users connect to the public network using the access network of an internet service provider (ISP). Today, this access network either reuses the legacy copper or coaxial network or uses passive optical network (PON) technologies, among which the PON is the most energy efficient and provides the highest data rates. Traffic from the access network is aggregated with Ethernet switches and routed to the core network through the provider edge routers, with broadband network gateways (BNGs) to regulate access and usage. These regional links are collectively called the metro network. Data centers connect to the core network using their own dedicated gateway router. The problem of increasing data rates, while reducing the economic and environmental impact, has attracted considerable attention. The research described in this work has been performed in the context of two projects part of the European Union Seventh Framework Programme (FP7), which both aim for higher data rates and tight integration while keeping power consumption low. Mirage targets data center applications while C3PO focuses on medium-reach networks, such as the metro network. Specifically, this research considers two aspects of the high-speed optical receivers used in the communication networks: increasing dynamic range of a linear receiver for multilevel modulation through automatic gain control (AGC) and integration of multiple channels on a single chip with a small area footprint. The data centers of today are high-density computing facilities that provide storage, processing and software as a service to the end-user. They are comprised of gateway routers, a local area network, servers and storage. All of this is organized in racks. The largest units contain over 100 000 servers. The major challenges regarding data centers are scalability and keeping up with increasing amounts of traffic while reducing power consumption (of the devices as well as the associated cooling) and keeping cost minimal. Presently, racks are primarily interconnected with active optical cables (AOCs) which employ signal rates up to 25 Gb/s per lane with non-return-to-zero (NRZ) modulation. A number of technological developments can be employed in AOCs of the future to provide terabit-capacity optical interconnects over longer distances. One such innovation is the use of multilevel modulation formats, which are more bandwidth-efficient than traditional NRZ modulation. Multilevel modulation requires a linear amplifier as front-end of the optical receiver. The greater part of this dissertation discusses the design and implementation of an AGC system for the data path of a linear transimpedance amplifier (TIA). The metro network is the intermediate regional network between the access and core network of the internet architecture, with link lengths up to 500 km. It is estimated that in the near future metro-traffic will increase massively. This growth is attributed mainly to increasing traffic from content delivery networks (CDNs) and data centers, which bypass the core network and directly connect to the metro network. Internet video growth is the major reason for traffic increase. This evolution demands increasingly higher data rates. Today, dense wavelength division multiplexing (DWDM) is widely recognized as being necessary to provide data capacity scalability for future optical networks, as it allows for much higher combined data rates over a single fiber. At the receiver, each wavelength of the demultiplexed incoming light is coupled to a photo diode in a photo diode array which is connected to a dedicated lane of a multichannel receiver. The high number of channels requires small physical channel spacing and tight integration of the diode array with the receiver. In addition, active cooling should be avoided, such that power consumption per receiver lane must be kept low in order not to exceed thermal operation limits. The second component of this work presents the development of an integrated four-channel receiver, targeting 4 × 25 Gb/s data rate, with low power consumption and small footprint to support tight integration with a p-i-n photo diode array with a 250 μm channel pitch. Chapter 1 discusses the impact of increasing data rates and the desire to reduce power consumption on the design of the optical receiver component, in wide metropolitan area networks as well as in short-reach point-to-point links in data centers. In addition, some aspects of integrated analog circuit design are highlighted: the design flow, transistor hand models, a software design tool. Also, an overview of the process technology is given. Chapter 2 provides essential optical receiver concepts, which are required to understand the remainder of the work. Fundamentals of feedback AGC systems are discussed in the first part of Chapter 3. A basic system model is presented in the continuous-time domain, in which the variable gain amplifier (VGA) constitutes the multistage datapath of a linear optical receiver. To enable reliable reception of multilevel modulation formats, the VGA requires controlled frequency response and in particular limited time-domain overshoot across the gain range. It is argued that this control is hard to achieve with fully analog building blocks. Therefore, an event-driven approach is proposed as an extension of the continuous-time system. Both the structural and behavioral aspects are discussed. The result is a system model of a quantized AGC loop, upon which the system-level design, presented in Chapter 4, is based. In turn, Chapter 5 discusses the detailed implementation of the various building blocks on the circuit level and presents experimental results that confirm the feasibility of the proposed approach. Chapter 6 discusses the design and implementation of a 4 × 25 Gb/s optical receiver array for NRZ modulation with a small area footprint. The focus lies on the input stages and techniques to extend bandwidth and dynamic range are presented. Measurement results for NRZ and optical duobinary (ODB) modulation are presented, as well as the influence of crosstalk on the performance. Finally, Chapter 7 provides an overview of the foremost conclusions of the presented research and includes suggestions for future research. Two appendices are included. Appendix A gives an overview of the general network theorem (GNT), which is used throughout this work and which has been implemented numerically. The results from Appendix B, the analysis of a two-stage opamp compensated with capacitance multipliers, were used to design a building block for the AGC system

A single-event transient tolerant optical receiver

Fiber optical communication systems have attained significant importance in space applications e.g. Satellites, Space stations, etc. The systems have remarkably lightweight characteristics, less frequency dependent loss, and provide high-speed data transmission in a power-efficient way. Satellites and space stations are exposed to a higher level of radiation due to energetic particles in space. Fiber optical links mainly consist of integrated semiconductor devices. When integrated circuits are exposed to radiation such as in space applications, they are influenced by high-energy ionizing particles. This radiation causes malfunctioning of electronic devices and reduces their life span. It also generates transmission errors which are classified as single-event transients (SETs), single event upsets, and single event latch-up, and also causes total ionization dose effects. This thesis proposes a radiation tolerant (SET tolerant) optical receiver using triple modular redundancy (TMR) in which a conventional receiver is split into three identical sub-receivers in parallel. Majority voting is performed at the outputs after the received analog signal has been thresholded. To investigate the effectiveness of the proposed design, a conventional optical receiver is taken as a reference design, and its performance is compared with the proposed TMR-based radiation tolerant optical receiver. The proposed receiver uses an impedance scaling technique so that its overall power dissipation, gain, and bandwidth are the same as the reference design while providing SET tolerance. The proposed receiver removes SET errors with the limitation that only one subreceiver experiences a SET in a given unit interval. By applying the impedance scaling technique, the proposed receiver is robust to SET errors with no increase in overall power dissipation but at the sensitivity cost of 0.8 dB

Développement d'une architecture de communication sans fil pour les réseaux de capteurs dans le domaine aérospatial

Les travaux de cette thèse s'inscrivent dans le cadre du développement des réseaux de capteurs sans fil pour le domaine aérospatial. Les applications concernées sont la mesure de température et des contraintes mécaniques sur les ailes d'avion en vol d'essai ainsi que sur la structure des satellites. Ces mesures sont effectuées en temps réel et sans perte de données. Nos travaux de recherches se focalisent sur le développement d'une architecture de communication sans fil qui permet de répondre aux besoins des ces applications en terme de faible coût, faible consommation et haut débit. Nous avons développé une architecture à conversion directe avec l'utilisation de deux voies différentielles I et Q. Cette architecture exploite la bande de fréquence UWB 6–8.5 GHz autorisée en Europe. Nous nous sommes concentrés en particulier sur la conception des mélangeurs de fréquence qui demandent une bande passante très importante en valeur relative (10–510 MHz) sur l'entrée de mélangeur rehausseur de fréquence et sur la sortie de mélangeur abaisseur de fréquence. La conception de l'amplificateur faible bruit est moins délicate car son besoin en bande passante relative est moins important. Une nouvelle topologie de mélangeur a été conçue pour répondre au besoin en largeur de bande. Nous avons pris soins à ce que le mélangeur d'émission ait une perte de conversion nulle pour attaquer directement l'antenne sans passer par un amplificateur de puissance et réduire la puissance de contrôle à 3d Bm pour diminuer la consommation de l'oscillateur contrôlé en tension (VCO). De cette manière, la chaine d'émission se réduit à deux mélangeurs I et Q basse consommation. Cette architecture d'émission laisse plus de marge en terme de consommation pour la conception de la chaine de réception. Les différents blocs RF ont été développés en technologie CMOS 130 nm, permettant d'atteindre de bonnes performances avec un coût minimum. Les mesures effectuées valident le fonctionnement des circuits développés.The context of this thesis is the development of wireless sensor networks for aerospace applications. The concerned aerospace applications are the temperature and mechanical stress measurement, on the aircraft wings for flight test and on the satellite structures. Note that these measurements must be made in real time without data loss. Our researches are focused on developing wireless communication architecture. This architecture should meet the specific needs of these applications in term of low cost, low power consumption and high data rate. The RF front-end architecture developed in this thesis uses the UWB frequency band from 6 GHz up to 8.5 GHz approved in Europe. The RF transceiver is based on a direct conversion architecture that uses two differential channels I and Q. Our work is focused on the design of frequency mixers. These mixers require a very important relative frequency bandwidth (10–510 MHz), in the input of the up-conversion mixer and in the output of down-conversion mixer. The design of the low noise amplifier (LNA) is less sensitive because its relative bandwidth requirement is less important. A new topology of mixer was designed to meet the need for bandwidth with zero conversion loss to directly connect the antenna without using power amplifier and reduce the control power to -3 dBm to reduce consumption of the Voltage Controlled Oscillator (VCO). In this way, the transmitter is reduced to two low consumption mixers. This architecture leaves more flexibility in terms of power consumption for the design of the receiver. The RF blocks have been developed in CMOS 130 nm; this technology allows us to achieve good performance with minimum cost. The measurements validate the operation of the developed circuits