Long exposure to pump and signal light creates color centers in heavily doped ytterbium fiber, adding broadband absorption that is strongest in the visible but extends to the laser wavelength. Output power sinks over hundreds to thousands of hours and the fiber heats more. Fiber makers suppress it with aluminum, phosphorus or cerium codoping and qualify fibers with accelerated tests.
That amp lost 12 percent in 800 hours with the same pump current, that's photodarkening, the new fiber batch isn't cerium codoped.
Also heard as
- photo-darkening
Related terms
Fiber laser
A laser whose gain medium is an optical fiber with a rare-earth-doped core, pumped by diodes.
Double-clad fiber
Fiber with a small doped core for the laser light inside a much larger inner cladding that guides multimode pump light.
Slope efficiency
The rate at which laser output power rises per unit of extra pump power above threshold.