Fiber optic cable joint loss testing measures the signal loss at splices or connectors to ensure the network meets design specifications and maintains optimal performance.

Purpose of Joint Loss Testing

Fiber optic joint loss testing evaluates the attenuation introduced by splices or connectors in a fiber optic link. This is critical for verifying that the cable plant meets its loss budget, ensuring reliable data transmission and network performance . Testing also establishes a baseline for future troubleshooting and maintenance .

Equipment Required

• Optical Loss Test Set (OLTS) or Light Source and Power Meter (LSPM) calibrated for the fiber type and wavelength .
• Launch and receive reference cables of the same fiber type and connector type as the cable plant .
• Mating adapters compatible with the connectors.
• Cleaning supplies to ensure connector end faces are free of dirt or debris .

Testing Procedure

1. Warm up the equipment and ensure calibration at the test wavelength (e.g., 850 nm or 1300 nm for multimode, 1310 nm or 1550 nm for singlemode), .
2. Connect the launch cable to the light source and attach it to the fiber under test.
3. Measure the output power at the receive end using the power meter.
4. Calculate insertion loss by comparing the measured power to the reference power, which includes the launch and receive cables .
5. Document results for each splice or connector, noting any values exceeding the expected loss budget .

Expected Loss Values

• Singlemode fusion splices: ~0.15 dB per splice.
• Multimode mechanical splices: ~0.3 dB per splice.
• Connectors: Typically 0.3 dB for adhesive/polish or fusion splice-on connectors; prepolished/mechanical or MPO connectors may be up to 0.75 dB .
• Fiber attenuation: Multimode fiber ~3 dB/km at 850 nm, 1 dB/km at 1300 nm; singlemode fiber ~0.35 dB/km at 1310 nm, 0.25 dB/km at 1550 nm .

Standards and Methods

• OFSTP-14 (double-ended): Includes connectors on both ends of the cable.
• FOTP-171 (single-ended): Includes only the connector attached to the launch cable .
• Bidirectional testing is recommended for higher accuracy, averaging results from both directions .
• OTDR testing can also identify splice losses and faults along the fiber, though insertion loss testing with OLTS/LSPM is more precise for total link loss .

Best Practices

• Clean connectors before and during testing to avoid measurement errors.
• Use a loss budget calculator to estimate acceptable losses for the cable plant.
• Test each segment if measured loss exceeds the expected budget to locate high-loss points .
• Document all results for future reference and troubleshooting . By following these procedures, technicians can ensure that fiber optic joints meet performance requirements, maintain network reliability, and provide a baseline for ongoing maintenance and troubleshooting.