Kingfisher's novel Optical Power Leveler product is used to stabilise receiver power in an optical transmission system. Used instead of a fixed optical attenuator, it dynamically adjusts it's attenuation to keep the output power at a steady level, so it can compensate for varying laser power level and cable attenuation. Mounted on a standard DIN rail, and requiring only a 12 - 48V DC power supply, it is reliable and easy to use. It is set up locally, and doesn't need a telemetry link. It is particularly useful to resolve issues with SDN or "white box" optical networks. 

Optical Power Leveler