Crossbar links aircraft optics to electrical readouts

17 Jun 2002

The ability to monitor fibre optic signals in avionics is becoming increasingly important with the advent of fly-by-light systems. But to handle the read-outs on board an aircraft requires that the optical signals be converted to low-speed electronic signals.

Heriot-Watt University, in collaboration with Imperial College, London, BAE Systems and DERA, Malvern, has come up with STAR (System for Transparent Avionics Routing). It interconnects multimode fibre ribbons via a crossbar consisting of a detector array, a VLSI switch matrix and a VCSEL array to reintroduce signals into the optical fibre ribbon.

The philosophy behind the architecture of STAR is not to have any off-board high-speed signals. The switch requirements include a slow switching speed of microseconds of many high speed (2.5Gbit/s) channels.

Key to the conversion from optical to electrical signals are optical waveguides which route light from the input fibre ribbon to the detectors and from the VCSELs to the output fibre ribbon. The waveguides have turning mirrors written on their ends to reflect the light out of the plane of the ribbon into the detectors and reflect light from the VCSELs into the guides. The guides mediate between the linear channel spacing of the fibres and the 2D array geometry of the VCSELs and receivers.

The detector and VCSEL arrays contact the waveguide substrate by the simple mechanical compression of metal-coated polymer bumps.

The 45-degree mirrors bend the light out of the plane of the guide and into the detectors and launch light from the VCSELs into the guides.

"We believe that our technique for creating 45-degree mirrors is unique," said Frank Tooley of Heriot-Watt. "It allows top-emitting VCSELs and detectors to be placed very close to the waveguides whereas conventional 45-degree mirrors need the light propagating through the substrate of the waveguide platform."

The detector arrays are supplied by DERA, the VCSEL arrays from CSEM in Switzerland and the crossbar switch implemented on silicon germanium at Imperial.

Story courtesy of Opto and Laser Europe magazine