Single-frequency thulium-doped silica DFB fiber laser at 1735 nm

Abstract

We have developed a single-frequency thulium doped silica fiber laser with a Distributed FeedBack (DFB) cavity operating at a wavelength of 1735 <i>nm</i>. The laser cavity is 5 <i>cm</i> long formed by a UV-written Bragg grating with a phase shift and is pumped by a Ti:Sapphire laser at 790 <i>nm</i>. 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 <i>nm</i> and 1525 - 1620 <i>nm</i>. A thulium doped DFB laser opens a new broad wavelength range from 1.7 <i>&mu;m </i>- 2.0 <i>&mu;m</i>, 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.