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:



Have questions about this FOC Tip?

Contact FOC with questions at: (800) 473-4237 / 508-992-6464 or email: and we will respond ASAP. 







English English Español Español