Beyond economic considerations, what are the critical, top-level
performance factors on which DOFS systems are judged? Two factors stand
Range describes the maximum length of fiber over which
the measurement system remains capable of delivering useful metrology –
essentially the sensitivity. The boundary conditions for detection range
are related to the dynamic range of the specific measurement approach
used, the fiber attenuation constant as well as the probe pulse width and
illumination signal power. Such diversity of variables leads to
significant differences in implementations and capabilities.
Resolution determines how closely spaced each measurement
point along the fiber can be. For a given fiber length this is wholly
determined by the probe pulse width. Shorter pulses lead to finer spatial
resolution at the cost of reduced photon energy and hence dynamic range;
attaining an optimal pulse width for a certain application becomes a
question of engineering tradeoffs.
Some DOFS systems (e.g. Brillouin optical time domain reflectometry -
BOTDR) are specifically designed to maximize detection range up to and
beyond 100 km. Equally, some industrial applications may only need a few
tens of meters range, but centimeter precise spatial resolution.