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To measure Return Loss,

some means of isolating the connector part of the reflected signal is required:

a mandrel wrap, index matching gel, or Optical Time Domain Reflectometer (OTDR).


  1. A mandrel wrap is impossible to use with thick cables – Early instruments relied on using a mandrel wrap to choke off further reflections. This referencing works well enough for thin, single-fiber jumpers, but thicker multi-fiber cables cannot be mandrel wrapped tightly enough to be effective.
  2. Gel is difficult with many connector types – Index matching gel works for simple cables, but it’s difficult for complex connectors such as MTP/MPO male or Lemo. Plus, this method is messy and requires cleaning time.
  3. Today, OTDR is the universally preferred method to measure Return Loss – Any sort of cable/connector can be accurately measured using an OTDR, provided the device under test is not too short (~0.5um).


READ THE BLOG: How to Accurately Measure IL/RL


Additional resources from the FOC team include:

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Kathleen Skelton

About Kathleen Skelton

Kathleen Skelton, as FOC's Director of Strategic Marketing, utilizes her expertise in business development, online strategy, market planning, digital best practices, standard operating procedure development, and content management. A graduate of Curry College, she holds degrees in Communications and Education, English and Psychology. Kathleen resides outside of Boston, MA with her husband and four children. Follow @KATHLEENSKELTON