A method of transferring energy in an optical fiber (12) from the fiber's cladding element (16) of the fiber's core element (14) is disclosed. The core element (14) includes an active gain component and an energy migration component, and the cladding element (16), which surrounds the core element (14), includes the energy migration component. The method includes the steps of providing a pump (22) for producting energy and optically coupling the pump with the cladding element (16), such that the energy is absorbed and stored in the cladding element (16) by its energy migration component. A further step includes the active gain component in the core element (14) lasing or providing gain, when the transferring of energy from the cladding element's energy migration component to the core element's energy migration component takes place.