 Optical amplifier

An optical amplifier is a device that amplifies an optical signal directly, without the need to convert it to an electrical signal first. It is a key component in fiber optic communication systems and is used to boost the strength of light signals over long distances, where signal attenuation can occur.

These are closely related to lasers, as they do a similar basic job: take a DC source as input and amplify light. Lasers just happen to use the input voltage to also generate the incoming light.