Built-In Test Capability for WDM Avionic Systems

Wavelength Division Multiplex (WDM) enabled fiber-optic payload integration networks incorporating both 10Gbps digital and 2-40GHz analog/RF links, utilizing either passive star couplers or active wavelength selective switches for signal distribution, have been proposed and demonstrated. Several vendors have produced, and even qualified, MIL-DTL-38999/31 connectors incorporating fiber-optic termini, and these too have been successfully used in system-level demonstrations. Still, MIL-STD-1760 fiber-optic interfaces have yet to be adopted. Currently, the primary limitation to the utilization of these interfaces is the absence of the ability to characterize the quality of the optical link during or prior to operation. The physical connector resides in one of the harshest avionic environments imaginable, where it is subject to thermal and mechanical shock, vibration, altitude and humidity cycling, as well as contamination by dirt/dust and exhaust gasses. Furthermore, aircraft maintenance and upgrade operations potentially expose the unprotected fiber terminations directly to the surrounding environment, also resulting in contamination that reduces link performance. It therefore becomes necessary for the optical transceivers installed within the payload integration network to incorporate a Built-In Test (BIT) capability that can characterize the connector performance prior to, and ideally continuously throughout link operation, as well as perform overall fiber optic network health monitoring.