**Description**
This work covers the historical development of Built-In-Test (BIT) for fiber optic interconnect links for aerospace applications using Optical Time Domain Reflectometry (OTDR) equipped transceivers. The original failure modes found that installed fiber optic links must be disconnected before diagnosis could begin, often resulting in “no fault found” (NFF) conclusion. In fact, the observed root cause was that most (85%) of the fiber optic link defects were produced by contamination of the connector end faces.  In March of 2006, a fiber optics workshop was held with roughly sixty experts from system and component manufacturers to discuss the difficulties of fiber optic test in aerospace platforms. During this meeting it was hypothesized that Optical Time Domain Reflectometry (OTDR) was feasible using an optical transceiver transmit pulse as a stimulus. The time delay and amplitude of received reflections would correlate with the position and severity of link defects, respectively.  The concept was demonstrated by Boeing in 2007. The Naval Air Systems Command followed with a trade study, executed by Penn State and Harris Corporation. That study compared OTDR techniques that could possibly be miniaturized enough to be useful in identification of cable defects in aerospace platforms. Subsequent SBIR and STTR projects supported the development of compliant optical transceivers that include normal transceiver operation and along with OTDR testing. Therefore disconnection of a link for troubleshooting purposes would no longer be necessary. These projects were executed by Ultra Communications (since acquired by Samtec Corporation), which developed a prototype OTDR transceiver for use with multimode fiber. These multimode transceivers are now available. A single mode version of the OTDR transceiver is under development.

**Author(s) - ranked in descending order of contribution / as it should appear when published**
John Mazurowski



Built-In-Test for Fiber Optic Links

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