Broadband amplified spontaneous emission fibre source near 2 μm using resonant in-band pumping

Broadband amplified spontaneous emission (ASE) at a peak wavelength of 1.85 μm from Tm:Ho-doped silica fibre sources is reported, using in-band pumping from a Yb:Er co-doped fibre laser operating at 1.61 μm. A maximum total output power from both ends of greater than 80 mW with slope efficiency > 14% has been achieved. An ASE bandwidth at FWHM of near 70 nm was measured from the forward signal for the output power from 2-40 mW. The total fluorescence spectral width is > 200 nm. This broadband ASE source has potential applications in optical metrology, fibre sensors, loss and dispersion tests on optical fibres, spectroscopy and medical imaging, including optical coherence tomography. A review of different pumping schemes in generating ASE around 1.9 μm in the Tm-doped fibre is given. Also the nature of three-level ASE and in-band pumping of Tm:Ho-doped silica fibre are also discussed. The results in this paper confirm that in-band pumped Tm-silica fibre is a route to achieve high power broadband output around 1.8 μm.