A 7+1 to 1 pump/signal combiner with single-mode (SM) polarization maintaining (PM) 15 μm mode-field-diameter
(MFD) signal feed-through is demonstrated. The combiner is designed for pulse amplification in an active Yb-doped airclad
fiber operated in backward pumped configuration. Signal coupling through the device is realized by a
microstructured taper element allowing single-mode guidance and constant MFD at a taper ratio of 3.4.
We designed a high output power double cladding erbium-ytterbium fibre amplifier that showed no amplified
spontaneous emission (ASE) at 1.0 &mgr;m using a quasi singlemode fibre. The reduction of the amplified stimulated
emission (ASE) at 1.0 &mgr;m was found to be the combination of fibre design and temperature effect in the core. A 10W
output double cladding Er-Yb amplifier with a core/cladding fibre diameter of 10/125 &mgr;m was realized with a seed signal
of 1.4 W at 1563 nm and with counter-propagating pump power of 35 W at 976 nm without any significant ASE
generation at 1.0 &mgr;m. The fibre also exhibits singlemode behaviour with M2 <1.1 and a high slope efficiency of 30%.
The fibre was designed to minimize ASE at 1.0 &mgr;m by heavily doping the fibre and using the appropriate ratio between
Yb3+ and Er3+ ions. By incorporating into our model the core temperature increase coming from the quantum defect of
the Er-Yb system, we can also predict a raise in the absorption cross-section of the ytterbium ions around 1060 nm
yielding to an increase of the 1 &mgr;m ASE threshold from 14 W to 35 W pump power, which allowed us to reach a 10 W
output power at 1563 nm instead of 5 W normally predicted by the theory. These results show potential power scaling of
the output power or double cladding erbium ytterbium amplifier using quasi singlemode core erbium ytterbium fibre
avoiding the need of large core dimension that degrades the beam quality.
We have developed a single-frequency thulium doped silica fiber laser with a Distributed FeedBack (DFB) cavity operating at a wavelength of 1735 nm. The laser cavity is 5 cm long formed by a UV-written Bragg grating with a phase shift and is pumped by a Ti:Sapphire laser at 790 nm. The laser operates in a single-polarization mode and is tunable over a few nanometers. To the best of our knowledge, this represents the first short cavity, single frequency fiber laser using thulium as the amplifying medium. The lasing wavelength is among the lowest demonstrated in a thulium-doped fiber laser and it falls in an attractive near-to-mid infrared wavelength region only offered by few sources. Single-frequency DFB fiber lasers are compact and stable optical sources, which offer low-noise coherent output with ultra-narrow-linewidth. Typical applications for DFB fiber lasers are as sources for coherent sensing, spectroscopy and several high-end applications. Using optical fiber doped with erbium and/or ytterbium these sources provide emission within the wavelength bands of 980 - 1200 nm and 1525 - 1620 nm. A thulium doped DFB laser opens a new broad wavelength range from 1.7 μm - 2.0 μm, depending on co-dopants. This wavelength range is especially interesting for use in gas sensors, frequency mixing and as a source for eye-safe LIDAR applications.