OTDR Return Loss Measurements
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NPL produces a range of artefacts used to calibrate an OTDR’s return loss scale. The artefacts are based on a length of single-mode fibre with a custom made reflector at the end with a known return loss value.
Artefacts have been developed for calibrating OTDRs, they are not suitable for calibrating return loss test sets or return loss meters.
The return loss artefacts are based on a length of single-mode fibre with a reflector at the end with a known return loss.Artefacts with return loss values in the range -30 dB to -50 dB are usually supplied, others are available on request. We may also be able to calibrate customer supplied return loss and backreflectance standards on request.
Measurements are made at nominal wavelengths of 1310 nm and 1550 nm. Typical fibre lengths are 1 km for a -30 dB artefact and 0.5 km for a -50 dB artefact.
A copy of a typical Calibration Certificate is available to download.| Measurement Range | Typical Uncertainties | |
| 2.2 km fibre | Optical length @ 1310 and 1550 nm | ± 0.1 m |
| 13 km fibre | Optical length @ 1310 and 1550 nm Attenuation coefficient uniformity @ 1310 and 1550 nm |
± 0.3 m ± 0.009 dB/km (each end) ± 0.006 dB/km (average of both ends) |
Optical return loss is defined as the ratio of the reflected signal to the incident signal immediately prior to the end reflecting artefact. The incident signal immediately prior to the end reflecting artefact is obtained by measuring the fibre backscatter signal and assuming the backscatter coefficient as given in the certificate.
This renders the artefacts only suitable to calibrate equipment that uses a similar measuring technique for example OTDRs. Provided the OTDRs backscatter parameter is set to that shown in the certificate, the return loss displayed by the OTDR is directly comparable to the return loss values shown in the certificate since both measurements will be making the same assumptions.