OTDR or Light Source Power Meters? What’s Your Best Bet for Link Loss Measurement Uncertainties?


      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 UncertaintiesReal-life Uncertainties
      LSPM Light source instability
      Light source wavelength
      Multimode launch conditions
      Mating reproducibility
      Reference connector repeatability
      Source drift after referencing
      Reference test jumper
      Presence of couplers in optical test sets (OLTS)
      OTDR 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:

      1. LS power reference
      2. Loss measurement for LSPM
      3. Test other devices under test (DUTs)
      4. iOLM Insertion Loss (IL) measurement
      5. 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!