This paper reviews the progress in active fibers suitable for power scaling, highlighting the advances in fiber design that
will enable the control of nonlinearities such as SRS and SBS in high power fiber lasers, as well as making feasible a
practical high power three-level system.
The thermal degradation of double clad optical fiber coatings is known to be the prime limiting factor for the operation
of high power CW fiber lasers. In this paper, we conduct a study of thermal effects in high power CW fiber lasers. A
particular focus is put on heating at the splice points and in the doped fiber due to the quantum defect in 100-W class
CW fiber lasers. A theoretical model and experimental measurements taken with a high resolution IR camera on 125 to
400 μm diameter fibers are presented. Thermal contact resistance between the fiber and its heat sink are considered in
the conduction heat transfer model and measured for different geometries. Proper designs for cooling apparatus are
proposed and optimization of the active fiber is discussed. Some predictions for power scaling and temperature
management of fiber lasers to kW power level are also described.
We present results on a high-power, high-energy cladding-pumped fibre Raman laser. We first discuss fibre
requirements and give a design rule. Then, experimentally, a pulsed cladding-pumped Raman fibre laser is demonstrated
with up to 210 μJ high-brightness pulses. The fibre delivers pulses at the Stokes wavelength of 1112 nm, of 500 ns
duration and 420 W peak power, with M2 = 1.8. The linewidth is 6.5 nm without any wavelength selection. Our result is
the highest reported energy and peak power from any fibre Raman source and illustrates the power scalability capability
of such devices.
Master oscillator power amplifier (MOPA) is becoming the obvious choice in order to develop some high power single
frequency laser sources. Its simplicity, reliability, robustness have already allowed the demonstration of some
tremendous increase of the output power. In this paper we will report our latest results in the development of high power
single frequency, single mode and single polarization MOPA systems. We were able to obtain an output power as higher
as 500 W with still keeping the narrow linewidth proprieties of the source.
Multi-wavelength sources are very attractive for optical telecommunication applications. Recently, several proposals have been made to use a frequency-shifting element inside a fiber laser ring cavity to realize a continuous wave (CW) multi-wavelength source operating at room temperature. In this type of laser, the frequency shift, introduced by an acousto-optic device, prevents the single frequency emission expected from the usual homogenous gain broadening behaviour of erbium-doped fiber. However, it has been previously observed that these sources can emit pulsed or CW radiation. In this paper, we describe the different emission regimes and we experimentally examine the impact of several key parameters on the optimization of the CW emission. To this end, a temporal characterization of the laser output was performed as a function of the cavity length, the number of simultaneously lasing wavelengths, the cavity loss, the erbium doped fiber length and the pump power. We found that an important parameter was the optical intensity circulating in the cavity. Indeed, the accumulated nonlinear phase shift and the amplifier saturation level are directly related to the intra-cavity laser field. By increasing the cavity loss or the number of wavelengths, the CW emission can be favoured over the mode-locked emission regime.