One uses four fibers each way at 2.5 Gbits/second, with an 850-nanometer vertical-cavity surface-emitting laser (VCSEL). The other uses an 850-nm VCSEL for the transmitter and a PIN photodiode for the receiver.

"Providing the lowest-cost interface specifications for different applications has been the focus of the Physical and Link Layer Working Group," said Adam Dunstan, president of the Optical Internetworking Forum (OIF). The choice of the new specifications, along with two earlier short-reach interfaces for OC-192, "reflects the different maturity levels of the technology and the differing needs of carriers," he said.

The four-fiber spec, designated OIF-VSR-03.0 (or VSR-3), transmits OC-192 data over 300 meters of multimode ribbon fiber cable with a 50-micron core. The interface calls for four 2.5-Gbit/s VCSELs in each direction on a single 12-fiber ribbon (with four unused fibers).

Fibre Channel, Infiniband

The four-fiber solution leverages the low-cost parallel-fiber VCSEL base technology now being deployed in many optical backplane applications for digital cross-connect systems, terabit routers and terabit switches. Four-fiber solutions are also being specified in the ANSI Fibre Channel standard and by the Infiniband consortium. The OIF's solution will map the OC-192 frame onto the parallel optical link with no bandwidth expansion and no overwriting of the Sonet overhead bytes.

The goal of the second new OIF interface spec, OIF-VSR-04.0 (VSR-4), is to transmit a Sonet/SDH OC-192 data stream over 50-micron multimode fiber at up to 85 meters, or up to 300 meters with 2-GHz high-bandwidth multimode fiber. VSR-4 uses a single 850-nm VCSEL for the transmitter optical element and a single PIN photodiode for the receiver. A similar 10-Gbit/s serial 850-nm optical interface is under consideration by the IEEE 802.3ae group for the 10 Gigabit Ethernet standard.

Earlier this year the same OIF working group approved VSR-1, an OC-192 interface for parallel optics, and VSR-2, a serial 1,310-nm interface. Interfaces on both sides of OC-192 framers have also been specified, and work on OC-768 VSR and framer interfaces is under way. Specs are on view at www.oiforum.com/public/technical.html.