Patent ID: 8755415

Claim:
An optical fibre laser or amplifier comprising an optical fibre and a pump radiation source configured to generate pump radiation which is received through an input end of the optical fibre, the optical fibre comprising a doped core located within cladding which is configured to guide the pump radiation, the doped core being configured to generate or amplify and guide signal radiation when pump radiation passes through it, wherein the optical fibre laser or amplifier further comprises a first reflector configured to reflect pump radiation which has travelled from the input end to an output end of the optical fibre, and further comprises a second reflector configured to selectively reflect a portion of pump radiation which has travelled from the output end to the input end of the optical fibre, wherein a selection of the portion of pump radiation to be reflected by the second reflector depends upon at least one of: a spatial position of the pump radiation, a direction of the pump radiation, and a polarisation of the pump radiation.