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Optical fibre

Calibration of optical time domain reflectometers

Using reference artefacts for OTDR calibration

There are many different combinations of measurement settings for optical time domain reflectometers (OTDRs), and it is important that the instrument is calibrated for required measurement settings. The following calibrated reference standards enable calibration of OTDRs to reflect specific customer conditions.

Fibre attenuation standard

NPL manufactures a fibre attenuation standard, which can be easily transported worldwide. The single mode fibre is calibrated for total attenuation (using the cut-back technique) and attenuation coefficient uniformity. Attenuation stability is within ±0.03 dB. Lengths range from 2 km to 15 km with a choice of connectorised or bare fibre ends. Single-mode and multi-mode fibre versions are available.

OTDR distance scale calibration artefact

An NPL artefact based on a recirculating optical delay line can be supplied for generating calibration features along the distance scale of OTDRs. A calibrated 12 km loop with 2 km lead-in fibre will provide features every 6 km out to 40 km, and other lengths can be supplied. Typical uncertainty for single-mode is 0.1-0.3 m and multi-mode is 0.3-0.5 m.

Return loss artefacts

OTDRs can determine the return loss at fibre connectors and splices from the amplitude of reflections and the pulse width. However, OTDRs should be calibrated for the measurement of this parameter. NPL can supply calibrated return loss artefacts at -30 dB, -40 dB and -50 dB.

ODTR calibration fibres

NPL can provide 2.2 km and 13 km lengths of single mode fibre, with FC/PC connectors, calibrated for attenuation coefficient uniformity and optical length.  Typical uncertainties ± 0.1-0.3m; ± 0.009 dB/km.

Chromatic dispersion calibration artefact

NPL provides a single mode or dispersion shifted reference fibre, typically 13 km, calibrated in the 1310 nm and 1550 nm windows.

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