Custom Integrated Circuits

Contains table of contents for Part III, table of contents for Section 1 and reports on eleven research projects.IBM CorporationMIT School of EngineeringNational Science Foundation Grant MIP 94-23221Defense Advanced Research Projects Agency/U.S. Army Intelligence Center Contract DABT63-94-C-0053Mitsubishi CorporationNational Science Foundation Young Investigator Award Fellowship MIP 92-58376Joint Industry Program on Offshore Structure AnalysisAnalog DevicesDefense Advanced Research Projects AgencyCadence Design SystemsMAFET ConsortiumConsortium for Superconducting ElectronicsNational Defense Science and Engineering Graduate FellowshipDigital Equipment CorporationMIT Lincoln LaboratorySemiconductor Research CorporationMultiuniversity Research IntiativeNational Science Foundatio

Custom Integrated Circuits

Contains reports on nine research projects.Analog Devices, Inc.International Business Machines CorporationJoint Services Electronics Program Contract DAAL03-89-C-0001U.S. Air Force - Office of Scientific Research Contract AFOSR 86-0164BDuPont CorporationNational Science Foundation Grant MIP 88-14612U.S. Navy - Office of Naval Research Contract N00014-87-K-0825American Telephone and TelegraphDigital Equipment CorporationNational Science Foundation Grant MIP 88-5876

High-speed low-power modulator driver arrays for medium-reach optical networks

The internet is becoming the ubiquitous tool that is changing the lives of so many citizens across the world. Commerce, government, industry, healthcare and social interactions are all increasingly using internet applications to improve and facilitate communications. This is especially true for videoenabled applications, which currently demand much higher data rates and quality from data networks. High definition TV streaming services are emerging and these again will significantly push the demand for widely deployed, high-bandwidth services. The current access passive optical networks (PONs) use a single wavelength for downstream transmission and a separate one for upstream transmission. Incorporating wavelength-division multiplexing (WDM) in a PON allows for much higher bandwidths in both directions. While WDM technologies have been successfully deployed for many years in metro and core networks, in access networks they are not commonly used yet. This is mainly due to the high costs associated with deploying entire WDM access networks. However, the present optical networks cannot be simply and cost-effectively scaled to provide the capacity for tomorrow’s users. As an effect there is a strong need for new WDM access components which are compact, cost-competitive and mass-manufacturable. Increasing the number of wavelengths for WDM-PON automatically leads to an increase in the number of single pluggable transceivers, which brings substantial design challenges and additional costs. The multitude of TXs and RXs for different wavelength channels increases the total footprint considerably. Photonic integration of transceivers into arrays will significantly reduce the footprint and cost. However, the total power consumption of an array device is an issue. To avoid the use of a thermoelectric cooler, the integration density of components is severely limited by the heat dissipating capabilities offered by their package. As a result the WDM-PON philosophy necessitates the reduction of the transceiver’s power dissipation. From this plea it is apparent that the main technology challenges for realizing future-proof optical (access) networks are reducing active component power consumption, shrinking form factors and lowering assembly costs. In this perspective an over 100 Gb/s throughput component, composed of 10 channels at 11.3 Gb/s per wavelength channel would be a great contribution to the expansion of customer bandwidth. It can provide increased line rates to the end users at speeds of 10 Gb/s per wavelength. As RXs typically consume much less power than externally modulated TXs, they can relatively easily be integrated into an array. Mainly high speed optical transmitters have significant power consumptions and the heat generation caused by power dissipation forms a critical obstacle in the development of a 10-channel transmitter, which again underlines the importance of power reduction. Alongside the introduction of WDM in access networks, also inter-office point-to-point connections in data center environments could benefit from the WDM philosophy. As data center operators often suffer from fiber scarcity or do not own their fiber infrastructure, WDM technologies are essential to deliver reach and capacity extension for these scenarios. Interdata center communication also benefits from cost-, footprint- and energyefficient components operating at high speed to maximize the throughput. As an effect integrated over 100 Gb/s transceivers, such as 4 channels at 28 Gb/s, are highly desirable. The research described in this dissertation was partly funded by the European FP7 ICT project C3PO (Colourless and Coolerless Components for low Power Optical Networks) and the UGent special research fund. The C3PO project aimed to develop a new generation of green Si-photonic compatible components with record low power consumption, that can enable bandwidth growth and constrain the total cost. C3PO envisioned building high-capacity access networks employing reflective photonic components. To achieve this, cost-competitive reflective transmitters based on electroabsorption modulators (EAM) needed to be closely integrated into arrays. A multi-wavelength optical source provides the required wavelength channels for both downstream and upstream signals in the WDM-PON. Chapter 1 gives a short overview of a PON and describes the main implementations of a WDM-PON access network. It introduces integrated low power transmitter arrays for a cost-effective architecture of WDM-PONs and inter-data center communication. Chapter 2 compares different optical transmitters and gives a short overview of their most important characteristics. External modulation through both Mach-Zehnder modulators (MZMs) and EAMs is described. It shows that EAMs are the best choice for low power transmitter array integration, thanks to their lower drive voltage and smaller form factor, compared to MZMs. To achieve a reduced consumption, the electronic modulator driver topology is studied in chapter 3. The challenge in designing modulator drivers is the need to deliver very large currents in combination with high voltage swings. Four distinct output configurations are compared and techniques to reduce the power consumption of the drivers are described. Chapter 5 presents duobinary (DB), a modulation scheme that is gaining interest in today’s optical transmission. As the required bandwidth is about half that of NRZ, it softens the constraints on the transmitter bandwidth. Thanks to its narrow optical spectrum, it has an improved tolerance to dispersion in long haul single mode links and it can improve the spectral efficiency in WDM architectures. For optical DB a precoder is necessary to assure the received signal is equal to the original binary signal. The conducted research that resulted in this dissertation produced 2 low power EAM driver arrays: A 10-channel 113 Gb/s modulator driver array with state-of-the art ultra-low power consumption. A 2-channel 56 Gb/s duobinary driver array with a differential output with low power consumption. Both designs are elaborately analyzed in chapter 4 and 6 respectively. To the best of our knowledge the 10-channel EAM driver array is the first in its kind, while achieving the lowest power consumption for an EAM driver so far reported, 50% below the state of the art in power consumption. The 2-channel EAM driver array is the fastest modulator driver including on-chip duobinary encoding and precoding reported so far. The final chapter provides an overview of the foremost conclusions from the presented research. It is concluded with suggestions for further research