This sanitized bidirectional OTDR test report example shows how a 5.452 km G.652.D single-mode link was documented and how its reported attenuation can be checked arithmetically. It is published as an engineering case study, not as a blanket product guarantee or an independently accredited laboratory certificate.
Test setup
| Field | Recorded value | Engineering relevance |
|---|---|---|
| Fiber/link | G.652.D single-mode, core 12 | Defines the single-mode fiber family and tested path. |
| Instrument | EXFO MAX-730C | Model recorded in the source document; calibration evidence was not independently checked. |
| Wavelength | 1550 nm | A wavelength commonly used to assess attenuation and bend-sensitive events in single-mode plant. |
| Index of refraction | 1.4682 | Affects the OTDR distance calculation and should match the tested fiber specification. |
| Backscatter coefficient | -79.5 dB | Used by the instrument when estimating event loss from backscatter levels. |
| Pulse / averaging | 30 ns / 15 s | Balances spatial resolution, dynamic range and trace noise. |
| Environment | 24°C; 55% RH | Records the test conditions for traceability. |
Reported link results
| Measurement | Result |
|---|---|
| Link length | 5.4520 km |
| Direction A→B total loss | 1.21 dB |
| Direction B→A total loss | 1.11 dB |
| Bidirectional average total loss | 1.16 dB |
| Reported fiber attenuation | 0.198 dB/km |
Event table and bidirectional averaging
| Event | Distance | A→B | B→A | Bidirectional average |
|---|---|---|---|---|
| Link start | 0.0000 km | Reflectance -48.5 dB | — | |
| Fusion splice 1 | 1.8540 km | 0.09 dB | -0.03 dB | 0.03 dB |
| Fusion splice 2 | 3.6120 km | 0.02 dB | 0.08 dB | 0.05 dB |
| Link end | 5.4520 km | Reflectance -46.2 dB | — | |
The -0.03 dB reading does not mean the splice created optical power. OTDRs infer event loss from backscatter. When two fibers have different backscatter characteristics, the same splice can appear as a “gainer” in one direction and a larger loss in the other. Testing both directions and averaging the two readings gives the more representative splice estimate: (0.09 + -0.03) / 2 = 0.03 dB. EXFO explains this gainer/loser behavior and recommends bidirectional averaging for accurate splice-loss characterization.
Reproducing the attenuation calculation
1. Average total loss: (1.21 + 1.11) / 2 = 1.16 dB
2. Average splice loss: 0.03 + 0.05 = 0.08 dB
3. Estimated fiber-only loss: 1.16 – 0.08 = 1.08 dB
4. Estimated fiber attenuation: 1.08 / 5.452 = 0.198 dB/km
As a useful cross-check, dividing the unadjusted average link loss by length gives a gross coefficient of 1.16 / 5.452 = 0.213 dB/km. The difference between 0.213 dB/km and 0.198 dB/km is explained by removing the two averaged splice losses before calculating fiber-only attenuation.
Applicable standards and the corrected reference
- ITU-T G.652 defines characteristics of a single-mode optical fibre and cable and is the relevant fiber-family reference for G.652.D.
- IEC 61280-4-2:2024 addresses attenuation and optical return-loss measurement of installed single-mode cabling.
- IEC TR 62316:2026 covers interpreting OTDR backscatter traces for single-mode optical fibres, including apparent gainers and losers.
- EXFO’s OTDR gainer application note explains why bidirectional averaging is required.
Reference correction: IEC 61280-4-1 is for installed multimode cabling. Because this case records a G.652.D single-mode link, IEC 61280-4-2 is the appropriate primary installed-cabling measurement reference.
How buyers can use this case
A useful purchase or acceptance specification should state the fiber identity, test wavelength, launch and receive conditions, instrument settings, link direction, event-loss limits, total-loss limit, required raw-file format and traceability fields. A screenshot or summary table alone does not replace the original trace when a project requires audit-ready evidence.
Continue with the fiber optic installation testing guide, compare an optical power meter with an OTDR, review our quality assurance policy, or prepare a commercial requirement on the fiber optic cable manufacturer page.
