Low cost and integration capabilities will make this material and process the choice of component and subsystem developers.
Yves Raymond Fontayne
Sierra Monolithics Inc.
Although the rapid build-out of the Internet infrastructure over the last several years has led to bandwidth over-capacity in the short term, few doubt that the industry will continue its migration to multi-port 10 Gbit/sec and, not long after that, OC-768 (40-Gbit/sec) applications. Now, a number of factors are spurring the development of 40-Gbit/sec transport equipment, including the completion of key industry standards as well as advances in both process technology and chip architectures that optimize performance while providing reliable, cost-effective, low-power, and feature-rich solutions.
One of the most important industry developments is the availability of silicon germanium (SiGe) bipolar complementary metal-oxide semiconductor (BiCMOS) process technology that solves OC-768 performance challenges while improving cost, power efficiency, and reliability. Because SiGe BiCMOS is essentially CMOS with a few added steps, it is inherently easier to integrate high levels of functionality as compared to alternative high-speed process technologies like CMOS/indium phosphide (InP). For example, serializer/deserializer (SerDes) devices can be created using SiGe BiCMOS that eliminate the need for high-speed proprietary interfaces to perform electrical-to-optical conversion for fiber-optic transmission. Instead, these SiGe BiCMOS-based SerDes devices are able to convert 16 parallel inputs to a high-speed serial stream in a single integrated circuit. This dramatically cuts costs while meeting the performance criteria for OC-768 fiber-optic links.
With SiGe BiCMOS as the process foundation, chip designers can explore a variety of other integration opportunities as well. For instance, the same single-chip SerDes device that eliminates on-chip electrical-to-optical conversion interfaces can also include a pseudo random bit sequence (PRBS) generator and receiver, temperature sensors, and various features that enable critical management functions and real-time diagnostics. The devices also can include such advanced features as adjustable input threshold and adjustable phase for the recovered clock and data, enabling them to be used in both short and long fiber-optic spans with optical amplifiers. Integrated devices have a major advantage in packaging costs and overall performance, and they enable architectures with lower device counts to support applications for both short and long fiber-optic spans.
Another key development is the Optical Internetworking Forum's (OIF) adoption of the SerDes-Framer Interface 5 (SFI-5) specification, which paves the way for system vendors to mix and match chips from different suppliers in their 40-Gbit/sec systems. Created by the OIF's Physical & Link Layer Working Group, the SFI-5 implementation agreement is part of a series of agreements that address the interfaces for packet and cell transfer in 40-Gbit/sec applications like OC-768 ATM and packet-over-SONET/SDH. It specifies an interface between the SerDes component, the forward-error-correction (FEC) processor, and framer devices within the physical layer, addressing aggregate data bandwidths of OC-768, STM-256, OTN OUT-3, as well as other applications at the 40-Gbit/s data rate. Because SFI-5's availability will ensure interoperability between complementary products, it is expected to accelerate the development of industry-standard 40-Gbit/sec transponders and fuel the economies of scale that are considered to be a key success factor for 40-Gbit/sec transmission.
All indications are that 40-Gbit/sec equipment will be deployed first in short-reach applications of less than 2 km. Many system suppliers are gearing up for 40 Gbits/sec and are expected to have such capability in their boxes by 2003. Companies like Sierra Monolithics are engaged with many customers designing and prototyping OC-768 short-reach transponders, test equipment, optical packet switching, core routers, and long-haul transport equipment. A few carriers have already completed successful 40-Gbit/sec trials, and with continued bandwidth growth, one can predict a turnaround in the industry in 2004. At that time, real 40-Gbit/sec carrier deployments are expected to begin.
As OEMs continue developing high-end OC-768 optical communication systems, they require a high level of performance in solutions that are optimized for reliability, low cost, power efficiency, and rich functional integration. SiGe BiCMOS provides the process technology platform necessary to deliver those capabilities.
Yves Raymond Fontayne is director of sales & marketing at Sierra Monolithics Inc. (Redondo Beach, CA).