Fiber tail measurement involves using a tail cord in OTDR testing to accurately account for the first and last connectors in a fiber link, ensuring precise loss and reflectance readings.

Purpose of Fiber Tail Measurement

In fiber optic testing, particularly with an Optical Time-Domain Reflectometer (OTDR), the first and last connectors of a fiber link can distort measurements if not properly accounted for. A tail cord is a short fiber segment attached to the far end of the fiber under test, complementing the launch cord at the near end. This setup allows the OTDR to measure the loss and reflectance of the entire link, including the first and last connectors, while providing sufficient backscatter for accurate readings .

How to Measure and Compensate

1. Select Matching Fiber Types: Ensure the tail cord has the same fiber type as the launch cord and the fiber under test to avoid measurement errors .
2. Set Launch Compensation: On the OTDR, use the launch/tail cord compensation function. This removes the lengths of the launch and tail fibers from the final measurement, so the reported link length and loss reflect only the installed fiber .
3. Clean and Inspect Connectors: Before testing, clean and inspect all connectors on the launch cord, tail cord, and fiber under test to prevent contamination from affecting results .
4. Run OTDR Test: Connect the setup as Launch + Fiber + Tail. The OTDR will detect the end of the launch cord and the start of the tail cord, allowing accurate measurement of the fiber link in between .
5. Manual Entry Option: If the OTDR cannot detect low-reflectance connectors (e.g., APC connectors), manually enter the lengths of the launch and tail cords to ensure correct compensation .

Best Practices

• Use factory-terminated pigtails for tail cords to ensure low insertion loss and high return loss .
• For bi-directional averaging, perform OTDR tests from both ends of the fiber, using the tail cord in each direction, and process the results in software like LinkWare PC .
• Always document the compensated lengths and test results to maintain a performance baseline for future troubleshooting . By following these procedures, fiber tail measurement ensures accurate characterization of the fiber link, including connector and splice losses, while eliminating errors caused by the launch and tail segments themselves .