Abstract
Over the last few years there has been increasing interest in power-scaling of fibre-based sources operating in the eyesafe two-micron wavelength regime driven by a range of applications. Much of this interest has focussed on Tm-doped silica fibres which offer wide spectral coverage from ~1.7 μm to −2.1 μm [1], a range of pump wavelengths and the potential to be scaled to very high powers [2]. By contrast, far less attention has been directed towards Ho-doped silica fibres which also offer a very wide range of emission wavelengths extending well beyond 2.1 μm. However, scaling the output power from Ho-doped silica fibres is hindered by the fact that there is no absorption band that coincides with the emission wavelengths available from high-power (near-infrared) commercially available diode pump sources. One solution to this problem is to add Tm to the core to act as a sensitiser. In this way pump light from high-power laser diodes at ~0.8 μm is absorbed by the Tm ions and the Ho ions in-directly excited by energy-transfer from the Tm ions. Using this approach, Jackson et al. recently reported 83 W of output from a cladding-pumped Tm,Ho co-doped fibre laser [2]. Co-doping with Tm however leads to very strong energy-transfer-upconversion and hence a reduction in the effective upper-state lifetime. The net result is additional heat loading leading, lower efficiency and limited flexibility in mode of operation. An alternative approach is to use a high-power cladding-pumped Tm fibre laser to pump a Ho-doped fibre laser avoiding the need for co-doping with Tm [4]. This has the attraction a very low quantum defect pumping scheme can be employed in the Ho fibre laser allowing very high lasing efficiencies to be achieved and offering the potential to be scaled to very high power levels. In this paper, we report preliminary results for a Ho silica fibre laser operating at 2090 nm in-band pumped by a cladding-pumped Tm doped fibre laser at 1980 nm.
© 2009 IEEE
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