High-Speed Optical Backplane Using Ruggedized Transceivers

An optical backplane designer will have to work closely with the manufacturers of high speed transceivers to adapt their products to the VPX format and the military aviation environment. The backplane would interface directly with these modified transceivers. Bascom Hunter has spoken with Coherent Corp., a US based leader in optical networking. Coherent’s 400G ZR+ transceiver uses dense wavelength division multiplexing (tunable within the 1530–1565 nm optical “C-band”) to achieve a max data rate of 400 Gbps. It features a high-efficiency indium phosphide modulator and receiver combined with a built-in tunable laser that delivers high optical output power. Bascom Hunter envisions a modified version of this type of transceiver designed to mount on a VPX card through a rugged high speed connector fed by multiple wires on the card itself. We believe that these transceivers, while conceptually part of the “optical backplane” would have to be physically mounted on the VPX cards in a form factor. This would allow high data rate signals to be converted to an optical format as close as possible to their sources and destinations. This minimal distance is important, since copper traces, wires, and connectors are lossy for the high frequencies which would be involved here. The fiber outputs of these transceivers would plug into an MT connector on the surface of a standard VPX backplane which faces the cards. On the other side of the standard backplane would be a matching MT connector connected to an optical fiber, such that when a card is pushed into the connector on the reverse, the two corresponding optical cores are mated and optical signals coupled between them.   In the space within the VPX chassis on the other side of the electronic backplane, the additional backplane would be mounted. Physically it might be made of a printed circuit board material like FR4, with optical fibers permanently attached to it (in a manner designed to accommodate any differences in thermal expansion). The input/output ends of the fibers on the backplane, with their MT connectors, would mate with the transceiver connectors from the cards through the MT modules on the conventional backplane. Fiber taps and monitors, and optical inputs and outputs to other systems, could be accommodated adjacent to the fibers as needed – these can be very low profile. The fibers would be fixed in the appropriate positions to implement the desired network architecture, and connectors would couple to the transceivers for each card slot through MT mating sleeves on the conventional backplane. In this way backwards compatibility is preserved. Devices which do not need high data rates could communicate over the conventional backplane. Those which do need high data rates could be designed to accommodate a transceiver which would plug into a mating the sleeve on the conventional backplane, and thus be connected to the optical backplane on the other side.