Testing multimode fiber OTDR parameter settings

For multimode fiber, set the OTDR to 850nm or 1300nm wavelength, use a pulse width of 5–30 ns for short links, and ensure the refractive index matches the fiber type.Key OTDR Settings for Multimode Fiber1. Wavelength: Multimode fibers are typically tested at 850nm and 1300nm. The 850nm wavelength is commonly used for shorter distances, while 1300nm can be used for slightly longer multimode runs . 2. Pulse Width:For short multimode links (under 2 km), use a pulse width of 5–30 ns.Shorter pulse widths provide higher spatial resolution to detect closely spaced events like connectors or bends, while longer pulses allow testing over longer distances but reduce resolution . 3. Refractive Index: Set the OTDR to the refractive index of the multimode fiber, typically around 1.4818, to ensure accurate distance measurements . 4. Launch and Receive Cables:Use launch and receive reference cables of the same multimode type and core size (50 or 62.5 microns) as the fiber under test.The launch cable eliminates the OTDR dead zone at the start of the fiber, while the receive cable allows accurate measurement of the final connector loss .Ensure connectors are clean and in good condition to avoid measurement errors. 5. Event Detection and Averaging:Adjust event detection thresholds to identify splices, connectors, and bends.Increase averaging time (minimum 45 seconds) to reduce noise and improve accuracy .Use real-time mode to fine-tune pulse width and range if hidden events are suspected. 6. Range and Distance Settings:Set the OTDR range slightly longer than the fiber length to capture the entire link.Avoid measuring too close to reflective events at the start or end, as OTDR settling time can cause nonlinearities .Practical TipsAlways clean connectors and adapters before testing.Use Automode to initially detect the fiber link, then manually adjust settings for higher resolution or longer distance as needed.For short multimode runs (e.g., 300m), prioritize short pulse widths to detect all events accurately .Document OTDR traces for future troubleshooting and comparison. By following these settings, you can accurately measure multimode fiber performance, locate faults, and verify splice and connector quality.