Thulium doped ZBLAN fibre ring-cavity amplifier

The development of single mode low loss transmission optical fibres at wavelengths lower then 1.55 mum and new semiconductor laser technologies around 1.49 mum makes the wavelength region of Tm amplifiers particularly interesting for expanding the bandwidth in long-haul telecommunication optical system. Single wavelength pumped thulium amplifiers still have poor efficiency caused by the self-terminating nature of the amplifying transition. Here, we have developed a scheme to enhance the efficiency by combining an amplifier at 1.49 mum with a ring laser cavity at 1.88 mum. The supporting laser oscillation at 1.88 mum in the all-fibre low-loss ring cavity decreases the population of the terminating level of the 1.49 mum transition, reducing the bottleneck effect