Søren Agger

Emission and absorption cross section of thulium doped silica fibers

A thorough investigation of the emission and absorption spectra of the (3F4,3H6) band in thulium doped silica fibers has been performed. All the basic parameters of thulium in silica have been extracted with the purpose of further analysis in laser and amplifier simulations. The experimental methods used to obtain the scaled cross sections have been carefully selected in order to avoid problems associated with calibrated measurements and knowledge of the radiative lifetime. The values of the absorption cross sections agree well with previously reported values, however the peak emission to peak absorption cross section ratios are found to be significantly below 1. Also confinement factors and thulium concentrations are estimated from the results.

10W ASE-free single-mode high-power double-cladding Er3+-Yb3+ amplifier

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.

Comments on "Dynamical noise in single-mode distributed feedback fiber lasers"

The comments given here refer to the two excellent and complete papers by Foster (see ibid., vol.40, no.7, p.884, 2004 and ibid., vol.40, no.9, p.1283, 2004). After closely studying the papers, we have found a couple of issues that require comments in order to understand and use the model. Despite this, one should honor the achievements in the papers in which Foster establishes an accurate analytical model for a DFB fiber laser. The comments relate to a gain parameter and the noise arising from pump power fluctuations and something that affects the noise equations, which we believe to be a small misprint

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

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.

Novel design method for generalized lattice filters

A new design method for wide-band gain equalizers using cascaded MZIs is proposed. The method achieves a given accuracy with fewer stages than previously described methods. Furthermore, the method is capable of minimizing PDL.