Optical time-domain reflectometers (OTDRs) are widely used to characterize elements on a fiber link, such as connectors and splices, because they can measure attenuation (signal loss), link loss reflectance and location for each element.
However, many operators question the degree of uncertainty of the link loss measurements obtained by an OTDR as opposed to that of a traditional light source power meter (LSPM). Which test equipment is more accurate? What best practices can be implemented to mitigate the degree of measurement uncertainty in each device?
Above all, it’s important to understand that there are a wide variety of theoretical and real-life loss-measurement uncertainties that are caused by LSPMs and OTDRs. Here is an overview:
| ||Theoretical Uncertainties||Real-life Uncertainties
||Light source instability
Light source wavelength
Multimode launch conditions
Reference connector repeatability
|Source drift after referencing
Reference test jumper
Presence of couplers in optical test sets (OLTS)
||Different loss uncertainty definitions
Launch and receive test cord fiber geometry
|OTDR trace noise
Weak backscattering signal after strong reflectance
Quality of trace analysis and event detection robustness
EXFO’s Systems Engineering and Research Team recently carried out a series of rigorous tests to compare the accuracy of an LSPM and OTDR, which was combined with EXFO’s Intelligent Optical Link Mapper (iOLM). The tests generated results for both multimode and singlemode fiber links, proving that very little or virtually no bias were found between the OTDR and LSPM.
Among other specific guidelines, the team came up with five easy steps that can help you comparing both testing methods:
- LS power reference
- Loss measurement for LSPM
- Test other devices under test (DUTs)
- iOLM Insertion Loss (IL) measurement
- Test other DUTs
Our latest app note describes in detail each test that was performed and key learnings. If you’re concerned about link loss measurement uncertainties, download it today!