High-Speed Electro-Optical Components for Integrated Transmitter and Receiver in Optical Communication

Background

By the end of the 20^th century and the beginning of the 21^st, telecommunication and information technology started to strongly influence the community. Today, all areas of society, politics, and economics make use of the possibilities offered by these technologies and as an example, the influence on economic processes is enormous. Also private users take more and more advantage of mobile communication and Internet. As the new techiques have come to play a key role in all social areas and in the lives of people, the requirements on the telecommunication technologies have changed dramatically.

In today's metro and core networks 10Gbit/s transmission systems with a total number of 80 wavelength channels in the core (dense wavelength division multiplexing systems, DWDM) and 16 wavelength channels in the metro area (coarse WDM) are established. Until the year 2001 the speed of development of optical SDH/SONET*, transmission systems was enormous, from below 1Gbit/s to 2.5Gbit/s and today's 10Gbit/s. At that time, all major system vendors promised to provide systems with a data rate of 40Gbit/s per channel soon. To be prepared for the next steps, many research projects envisaging 160Gbit/s transmission were started, among them the very successful IST projects FASHION and TOPRATE, but with the downturn of the communication industry the innovation nearly stopped. Suddenly, the best performing system with over a hundred wavelengths bridging a distance of several thousand of kilometers was of no interest, but a cheap system just satisfying short-term requirements.

Recently the situation has become more relaxed again. Some operators now ask for an option to deploy 40Gbit/s systems, although no larger installation of this bit rate has been performed so far. Another topic from the past is also under strong discussion and has high chances to become realized during the next years: Automatically Switched Optical Network (ASON) in combination with Generalized Multi Protocol Label Switching (GMPLS) seems to be a very promising solution to reduce network costs, capital expenditure (CAPEX) as well as operational expenditures (OPEX).

At the same time the Ethernet technology has expanded from local area networks (LAN) into the metro area networks where it won the race against the ATM-technology (ATM=Asynchronous Transfer Mode). Today Ethernet is the definite standard in the local and metro area offering the best cost-benefit relation. Its evolution is an impressive success story up to now, with bitrates of 10Mbit/s in year 1990, 100Mbit/s in 1994, 1Gbit/s in 1998, and recently 10Gbit/s in 2002.

It is now visible that technological advances in the area of high bandwidth optical transmission and high-speed electronics will allow climbing to the next Ethernet speed level of 100Gbit/s within the next few years. It may also be expected that the Ethernet will utilize these technological advances and enter the core networks. Especially the fact that the share of packet based data transport is rapidly growing and that voice traffic is already possible in packet switched networks as "Voice-over-IP" (VoIP) paves the ground for the Ethernet also in the central area of the data network. The figure below shows the intrusion of Ethernet into the Metro and Core parts of the network.

The packet data connection and IP is still a purely electrical technology, especially the switching, but to transport these packets at data rates of 10Gbit/s today or even 100Gbit/s in the future, there is no alternative to the optical domain. The optical single mode fiber provides the unique solution to transport such high data rates over long distances. Transmission experiments have been demonstrated in which 160Gbit/s signals were submitted error-free over several hundred kilometers of deployed fiber. However, to convert these high data rates between the electrical and the optical domain, sophisticated optical multiplexing and demultiplexing technologies have been applied.

In order to make 100Gbit/s Ethernet or also higher data rate TDM technologies economically interesting, cost efficient electro-optical and opto-electrical components have to be provided. Within the project HECTO high-speed components for conversion in both directions will be developed. In order to achieve both high-performance and cost-efficient components, these converters will be developed as integrated devices. In the transmitter and the receiver, the converters will be accompanied by high-speed integrated electronic circuits, which also will be developed within this project.

Finally, the goal of the project is not only to provide individual converters in both directions, but to develop both components in tight cooperation. Therefore, dedicated system experiments are planned to investigate the proper interaction between the transmitter (electro-optical converter) and the receiver (opto-electrical converter). This enables the consortium to demonstrate that these components can be integrated into a high-speed transmission system. Finally, field experiments are planned to verify the applicability under real conditions.

*⁾  SDH=Synchronous Digital Hierarchy is the international standard published by the International Telecommunications Union, ITU; SONET= Synchronous Optical NETwork is the United States version of the standard published by the American National Standards Institute, ANSI.