Electronic Design

40-Gbit Optical Active Cable Reaches 300 m

In addition to power consumption, of course, interconnects represent one of the biggest problems facing data centers today. Massive bundles of wire cables transport data between servers and other equipment. Most of this wiring is Cat5e or Cat6 Ethernet twisted-pair and InfiniBand cable.

Not only are these cables fat and heavy, they also block airflow and add to the system's overall weight. More importantly, their upper data speed has topped out for the distances that need to be covered. Luxtera's Blazar fiber-optic cables, though, could solve these problems.

The Blazar ribbon cables comprise four single-mode fibers that collectively can carry data as far as 300 m at a rate up to 42 Gbits/s (see the figure). Each cable transmits parallel data at 10.5 Gbits/s. Also, each end of the cable includes Luxtera's unique single-chip CMOS optics module, which includes a 1550-nm continuous-wave (CW) distributed-feedback (DFB) laser, photo detectors, modulators, transceiver circuits, and passive light cavities.

These modules achieve such rates without electronic dispersion compensation. Also, they greatly minimize light loss in connectors because the fiber is permanently attached to the chip and the transceivers. Power consumption is 2.2 W per connector at 40 Gbits/s.

The cable assembly is thinner, lighter, and more flexible than copper cables, so racks can be more fully populated. Its smaller size increases airflow and can improve cooling or reduce cooling costs when used throughout an installation. Its fiber also reduces electromagnetic interference and eliminates ground loops that are a pain in large installations. And, its longer reach means larger cluster servers spaced farther apart.

This cable uses quad small-form-factor pluggable (QSFP) Multi-Source Agreement (MSA) connectors and an SFP+ compliant electrical interface. Hot-pluggable and field-replaceable, they're being adopted for InfiniBand for the quad-data-rate (QDR) standard. The single-data-rate (SDR) and double-data-rate (DDR) Infini- Band standards specify CX-4 electrical connectors that cannot support the 10- Gbit/s transmission paths.

So with full InfiniBand compatibility, Luxtera is addressing the rapidly growing market for InfiniBand connections in switches, servers, and routers. The Blazar optical active cables (OAC) are available in lengths from 1 to 300 m. Samples will be available later in the fourth quarter with production quantities available in 2008.

Luxtera Inc. www.luxtera.com

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