When testing a fiber using and OTDR, how can the technician determine the correct IOR for the fiber.

Question: When testing a fiber using and OTDR, how can the technician determine the correct IOR for the fiber in order to set the proper parameters on the test set to ensure the measurements will be accurate?

Answer: The index of refraction (IOR) can be found on the specification sheets for the fiber in question. This does actually vary by a small amount from batch to batch, and is usually marked on the original spool from the factory. As a baseline set of numbers, (based on Corning SMF28e, and Infinicor Multimode fibers) singlemode IOR should be set at 1.4682 for 1550nm and 1.4677 for 1310nm , 1.496 (850nm) or 1.491 (1300nm) for 62.5/125 multimode and 1.481 (850nm) or 1.476 (1300nm) for 50/125.