Bad optical connection resulting in high loss and/or high reflectance

Applies to

All instruments with physical contact optical ports. For example; OTDRs, Light Sources, Switches, and many others.


This guide offers an approach to troubleshooting a bad optical connection, often observed when connecting a jumper/cable to the port of an EXFO optical instrument, however it can also be used for any physical contact fiber-optic connection.

Typical symptoms of a bad optical connection could be;

  • a high insertion loss
  • complete loss of transmission
  • a strong reflection
  • error messages from some instruments
  • loss of dynamic range
  • Inconsistent measurements

Troubleshooting steps

Possible Cause 1: Dirty connector

Proposed Solution: Inspect and Clean

  • Inspect the connector with an inspection probe and clean as required.
  • If an inspection probe is  not available, clean connector using proper method and materials.


Possible Cause 2: Damaged connector

Proposed Solution: 

  • If on inspection there are chips, uncleanable spots, or other major defects, an RMA will be required for Connector replacement.
  • If an inspection probe is not available, then please follow the below steps to further troubleshoot, if connector damage is confirmed, an RMA will be required for Connector replacement.
  • For most EXFO products the -CR (Calibration with connector replacement) service is available. This service will have the connector replaced followed by a complete factory calibration.


Possible Cause 3: A bad or incompatible launch cable or test jumper

Proposed Solution: 

  • If an inspection probe is available, inspect the launch connector, clean if soiled and discard if damaged
  • Try another Test jumper with same fiber and connector type
  • Ensure the launch connector is compatible with the optical port (APC/UPC compatibility)


Possible Cause 4: Damaged EUI or adapter

NOTE: EUI = EXFO Universal Adapter and is the part fitted to the optical ports of your instrument

Proposed Solution: Try another EUI

  • As for any adapter, the EXFO EUI has an internal split sleeve to ensure precise fiber-to-fiber alignment. Should the sleeve be damaged, the poor alignment will result in high loss and/or strong reflections.
  • Try another EUI if available. This is a common part used on many EXFO instruments, so there is a good chance you may have one available
  • Replace the EUI or other adapter as required. This is an accessory available from EXFO