Optical attenuators reduce te optical energy emitted from the light source. They are mainly used to align the optical power of a transmitter to the receivers sensitivity. Another reason for an optical attenuator is the reduction of optical power for test or measurement purposes. The attenuator can be built into a patch cord or as a male-female adaptor.
A variable optical attenuator can be used for adaptive power optimization there the necessary attenuation varies. It is also used for test purposes. The attenuation can be controlled manually (mechanically) or electrically.