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IBM researchers demonstrate 'world's fastest' optical chipset

26 Mar 2007

Prototype 160 Gbit/s technology points to new era of data sharing and "instant" movie downloads.

This week scientists from IBM will reveal a prototype optical transceiver chipset capable of reaching speeds of 160 Gbit/s – at least eight times faster than existing commercially available devices.

The transceiver, which is making its debut at the Optical Fiber Conference (OFC) in Anaheim, California, is fast enough to reduce the download time for a typical high-definition feature-length film to just 1 s compared to the usual 30 min or more for the best connectivity available today. IBM says that the development will transform how data is accessed, shared and used across the web.

This is the first time that such high-speed communications management has been achieved in a single, integrated transceiver chip. The chip is intended to be coupled with optical printed circuit board (OPCB) employing waveguides for computing-intensive applications.

To achieve this new level of integration, the IBM researchers built an optical transceiver with driver and receiver integrated circuits in standard CMOS technology, used for most chips today. They then added other necessary optical components made of III-V materials, such as indium phosphide and gallium arsenide, producing a single integrated package measuring 3.25 × 5.25 mm.

"This compact design provides both a high number of communications channels as well as very high speeds per channel," said Marc Taubenblatt, senior manager of Optical Communications at IBM's TJ Watson Research Center in Yorktown Heights, New York. "This results in an amount of information transmitted per unit area of card space taken up by the chipset that is the highest ever achieved."

The transceiver IC was fabricated in the standard IBM CMOS8RF 0.13 µm technology, and consists of 16 independent laser-diode driver circuits and 16 receiver-amplifier circuits arrayed in two separate 4 × 4 blocks with a 250 × 350 µm pitch.

The electrical I/O for the transceiver is provided on the perimeter of the IC through 100 µm diameter pads on a 200 µm pitch, which is compatible with current high-volume industrial flip-chip attachments such as the IBM C-4 process.

The transceiver is designed to be used in conjunction with 985 nm optoelectronic devices including vertical cavity surface emitting lasers (VCSEL) and photodiodes. The 985 nm wavelength allows the optical signals to pass through the substrates of the OE chips and through integrated lenses on the back side of the chips.

Its integrated lenses facilitate optical coupling and ease the packaging alignment tolerances. The flip-chip attachment of the OE devices to the CMOS transceiver chip uses high-temperature gold-tin solder.

The transceiver chipset is designed to enable low-cost optics by its being attached to an optical printed circuit board employing densely-spaced polymer waveguide channels based on economical, mass assembly CMOS processes.

"This level of integration is unprecedented," Taubenblatt added. "Getting the channels in the device as closely packed as possible, but also doing that in a way that complements regular CMOS manufacturing techniques: that is what has enabled us to achieve 160 Gbit/s bi-directional communications."

"By comparison, the best commercial transceivers already available, such as the POP4 modules that will handle four channels of 5 Gbit/s each, give a total of around 20 Gbit/s, which means that the IBM chipset is effectively eight times faster."

Other commercial alternatives are available from several companies, including Emcore and Avago. Taubenblatt says that the IBM chip's key advantages lie in its single chip-like assembly whereas the POP4 MSA design is based on a combination of separate III-V chips and OE chips.

POP4 is a multi-source agreement providing a common specification for four-channel, pluggable, parallel fibre optic transceivers. These transceivers support applications such as next-generation scalable switch-router backplane interconnections in conjunction with 10 Gbit/s very short reach (VSR) physical layer interfaces.

Each module contains a transmitter and receiver section with four channels, each operating at up to 2.7 Gbit/s. The aggregate full duplex bandwidth of the module is 10.8 Gbit/s. VCSEL source technology is employed to transmit data up to 300 m over industry standard multimode fibre.

Market opportunity

Media developments such as High-definition TV and almost-instant movie downloads are driving the demand for higher-speed transceivers. In particular, the new IBM development is intended for short-link applications of a few hundred metres or fewer, rather than hundreds of kilometres.

The chip is still in the prototype stage. Although the relatively economical CMOS technology at the heart of the chips will ultimately make these high-speed chips widely affordable, the company is in the early stages of exploring plans for use in commercial products.

"There is certainly room for growth in the core optical network, and the new chipset could support that," Taubenblatt said. "Ultimately, it's a serious possibility to provide 100 Gbit/s services to the home. We are seeing a tremendous increase in growth due to the usual quad-play developments, especially mushrooming content on the Internet.

"One could say that this 160 Gbit/s chip anticipates an all-fibre-optical communications network. The other side of the equation is that if customers [increasingly] wish to do video-on-demand functions then the bandwidth needs to be that much greater."

The work was partially funded by the US government's Defense Advanced Research Project Agency through the Chip to Chip Optical Interconnects (C2OI) program.

• The report on this work, "160 Gbit/s, 16-channel full-duplex, single-chip CMOS optical transceiver," by C L Schow, F E Doany, O Liboiron-Ladouceur, C Baks, D M Kuchta, L Schares, R John, and J A Kash of IBM's TJ Watson Research Center will be presented on Thursday, 29 March, at OFC in Anaheim, California.

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