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) designation. 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. This was followed with a trade
study that 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 included normal transceiver operation, along with OTDR testing
using transmitted pulses.
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.
