Testing a Newly Spliced OSP Segment Before Turn-Up
A crew has just completed splicing a 6 km outside-plant segment: 12 fibers, fusion splices at three closures, LC connectors at both ends into patch panels. The customer requires proof of compliance before turn-up. The crew's only tester is a light source/power meter (LSPM) with a 1310/1550 nm source. The splice loss spec is 0.1 dB max per splice; connector loss spec is 0.3 dB max; end-to-end loss budget is 4.0 dB at 1310 nm. The crew reports an end-to-end loss of 3.6 dB at 1310 nm and declares the segment compliant.
1. Is the end-to-end LSPM result sufficient to declare the segment compliant? Why or why not?
Read the worked answer
No. An end-to-end LSPM pass only proves the total loss is within budget; it does not prove each splice and connector meets its individual spec.
- A 3.6 dB total could hide a 0.8 dB bad splice offset by good connectors elsewhere, or a dirty connector masking a marginal splice.
- The customer's spec is per-event (0.1 dB/splice, 0.3 dB/connector), so the test method must resolve individual events.
- The correct tool is an OTDR (bidirectional, averaged) to measure each splice and connector loss and locate any anomaly.
An LSPM result is a useful acceptance check but not a diagnostic one.
2. How should the OTDR test be set up and interpreted to satisfy the spec?
Read the worked answer
Setup:
- Wavelengths: 1310 and 1550 nm.
- Launch/receive cables long enough (≥ 100 m) to move the first connector out of the OTDR dead zone.
- Pulse width chosen to resolve splices (short enough for resolution, long enough for range - typically 100 ns–1 µs for 6 km).
- Bidirectional averaging - splice loss readings are direction-dependent; average both directions for true loss.
- Index of refraction set to the fiber's actual value so distance markers are accurate.
Interpretation:
- Read each splice and each connector event against spec (0.1 dB splice, 0.3 dB connector).
- Flag any reflective event above the connector spec - usually contamination or a bad polish.
- Flag any non-reflective event above the splice spec - usually a poor fusion splice or a bend.
- Confirm total loss agrees with the LSPM result.
3. The OTDR shows one splice at 0.45 dB and a connector at 0.6 dB. What is the disposition?
Read the worked answer
Neither passes spec - both must be corrected before turn-up.
- Splice at 0.45 dB (spec 0.1 dB): re-cleave and re-fuse. Check for a dirty cleaver, misaligned electrodes, or a bad arc. Re-test after re-splicing.
- Connector at 0.6 dB (spec 0.3 dB): inspect the endface with a scope, clean, and re-test. If it persists, replace the connector/patch cord.
Do not accept the segment on the strength of the 3.6 dB total - the per-event failures are exactly what the OTDR was run to catch. Document the re-test results and the corrected values in the as-built package.