What two core components are necessary for a fiber to function as an active laser medium?

Answer

A waveguide (the fiber itself) and a gain medium (doped material)

The fiber requires the physical structure to confine light (the waveguide) and a material doped with rare-earth ions (the gain medium) to amplify that light.

What two core components are necessary for a fiber to function as an active laser medium?
inventionlaserfiber