Tm3+-doped ZBLAN fibre amplifier at 1.49 [micro sign]m with co-operative lasing at 1.88 [micro sign]m

The limiting effect of the self-terminating 3H4-3F4 transition on the gain of a thulium ZBLAN fibre amplifier has been reduced by the integration of a fibre ring cavity into the amplifier. The ring cavity allows co-operative laser oscillation at 1.88 µm, enhancing the obtainable gain. A gain of 11 dB was observed at 1.49 µm for a 4 m fibre length.