ECE 4006 Capstone Design Gbps Optoelectronic Link Design Group 2 Members Allen Duncan Curtis Grens Kenny Haulk Chris Lambrecht Nassisa Geda Techane Instructors Professor Martin A Brooke Ph D Professor Nan Marie Jokerst Ph D Georgia Institute of Technology School of Electrical and Computer Engineering Spring 2003 0 Table of Contents I Abstract 2 II Introduction 3 III Background i The Optical Gigabit Ethernet 3 ii The Learning Receiver Board 5 IV Project Overview i Goals 6 ii Design Constraints 7 V Managerial Issues i Group Management 8 ii The Financial Budget 9 iii Vendor Relations and Parts Ordering 10 VI Optical Link Budget i The VCSEL 11 ii The SC Connectorized and Unconnectorized PDs 12 VII Transceiver Design i Schematic Design 14 ii PCB Layout Design 15 VIII Results i Baseline Tests 18 ii Standards Compliance Tests 19 iii Alignment Tolerance 23 IX Conclusions 25 References 27 Appendix A The Financial Budget and Parts Ordered in Detail 28 A1 Appendix B An Updated GANTT Chart 29 B1 1 I Abstract The latest Ethernet evolution uses optical communication devices to transfer data at up to 10 Gbps This project attempts to harness optical Ethernet technology to design build and test a transceiver board capable of transmitting and receiving data at a rate of 1 25 Gbps while adhering to the IEEE 802 3z standard and the IEC eye safety power constraints First background information on optical Ethernet was researched to determine the boundaries of the design Also to become familiar with soldering surface mount parts and the laboratory equipment a learning receiver board was built and tested Next an optical link budget was calculated to characterize the performance of the optical components of the design A schematic and PCB layout of the optoelectronic transceiver were then designed The PCB design was optimized to prevent typical design pitfalls such as excessive cross talk high frequency signal reflection poor part placement and inefficient spacing Finally parts were ordered and one operable board was assembled and tested successfully The results of these baseline receiver sensitivity and alignment tolerance tests verified that the transceiver design and assembly were functionally successful and compliant with the IEEE 802 3z standard The ultimate goal of this project was to provide the lowest cost fully functional optical Ethernet transceiver board 2 II Introduction In the today s fast paced world people are relying increasingly on rapid communication from one point to another Computer and other electronic communication devices have become smaller and faster providing people with improved portability and connectivity In the past several years we have moved from depending on telephone cables to make all our communications to new optical fibers that transmit information to its destination at the speed of light while consuming less power over longer distances For this reason it is obvious why the telecommunications industry has looked more towards using optical systems to meet their communication needs One of such systems is the class of Ethernet known as the optical gigabit Ethernet which has been of great interest in the areas of research and development ever since the IEEE standardized the 1 Gbit per second 1 Gbps optical Ethernet systems in 1998 As recent advances have pushed the transmission speed of these systems up to 10 Gbps and beyond optical fibers are emerging as a worthy competitor of traditional copper in the realm of gigabit Ethernet 1 Thus engineers in this field are compelled to learn more about the tenets and intricacies of optical communication systems To that end the primary goals of this senior design team are to conduct background research on the technologies associated with the optical gigabit Ethernet to design and fabricate a working transmitter receiver transceiver optoelectronic module This optoelectronic transceiver module must comply with the IEEE Standard 802 3z the industry standard for optical Ethernet systems 2 III Background i The Optical Gigabit Ethernet Ethernet was invented in 1976 to solve the problems of networking local computer workstations Fundamentally the Ethernet works by sensing a carrier signal before transmitting a signal onto a transmission bus When two devices such as computers or printers send a message at the same time a collision is likely to occur in which case both devices stop transmitting and then retransmit after some amount of time Bob Metcalfe one of the original 3 inventors of Ethernet drew the diagram in Figure 1 to show the first Ethernet design This original concept has evolved through the years to the present 10 Gbps Ethernet which transmits and receives information at a rate of 10 Gigabits per second one thousand times faster than the original Ethernet which operated at a rate of 10 Mbps 3 Figure 1 Drawing of the original Ethernet system 3 At the heart of the Ethernet technology is the transceiver which is the optoelectronic transmitter receiver module Figure 2 shows a block diagram of a simplified transceiver module as used in optical Ethernet applications As shown in Figure 2 an electrical signal enters the transceiver module at a rate of 1 25Gbps for instance as in this design This signal is then converted to an optical one by the vertical cavity surface emitting laser VCSEL On the receiver front end the photodiode PD senses the incoming optical signal and converts it to an electrical signal The optical fiber that links the two optical ends of the transceiver can be either single mode or multimode depending on the network layer design Most importantly the choice of the physical media of transmission dictates the electrical and optical design parameters of the transceiver For this reason the transceiver is also called the physical medium dependent PMD module of the Ethernet 4 Electrical Signal Mux IN Electrical Signal OUT Optical Transmitter Fiber OUT VCSEL Demux Optical Receiver Fiber IN Photodiode Figure 2 A simplified block diagram for an electro optical Ethernet 4 The IEEE 802 3 is the official Ethernet standard around the world 3 In less than three decades Ethernet has moved from a crawling data transmission rate of 10 Mbps through copper wires to a sprinting rate of 10 Gbps through optical fibers Lately the IEEE committees that oversee the development of the optical gigabit Ethernet have set up two standards in order to facilitate the smooth implementation of optical Ethernet systems In 1998 the IEEE 802 3z committee