Why do I sometimes get unexpected results with Micro-OTDR SFPs in our Lab test setups?

Reflections in an optical link are not a good thing for SFPs. But they make the Micro-OTDR work. Understanding reflections is important for the interpretation of Micro-OTDR test results.

Micro-OTDR SFPs operate in any conventional optical fiber network, but are specified for use with Ultra-Polish (UPC) connectors, which are widely deployed and exhibit a reflectance of -55 dB when connected (see chart below), and -15 dB when open.

SC/PC or LC/PC => A link with multiple connections will show many reflection points.
SC/APC or LC/APC => Will not interfere with Micro-OTDR measurement.
SC/UPC or LC/UPC => Problematic when close to the transmitter.

These are for ideal, very clean connections. Dirt will increase the reflectance significantly.

We assume that UPC connectors are used and clean fiber practices employed – specifically the connection to the SFP itself. Dirt increases the reflected signal – reducing the optical signal to noise ratio (OSNR).

See earlier post regarding the capability of the Micro-OTDR to measure and react to a low OSNR condition.


Michael Hartmann, VP Business Development, Digital Marketing