Germain Guiraud

Gain dynamics of clad-pumped Yb-fiber amplifier and intensity noise control

Gain dynamics study provides an attractive method to understand the intensity noise behavior in fiber amplifiers. Here, the gain dynamics of a medium power (5 W) clad-pumped Yb-fiber amplifier is experimentally evaluated by measuring the frequency domain transfer functions for the input seed and pump lasers from 10 Hz to 1 MHz. We study gain dynamic behavior of the fiber amplifier in the presence of significant residual pump power (compared to the seed power), showing that the seed transfer function is strongly saturated at low Fourier frequencies while the pump power modulation transfer function is nearly unaffected. The characterization of relative intensity noise (RIN) of the fiber amplifier is well explained by the gain dynamics analysis. Finally, a 600 kHz bandwidth feedback loop using an acoustic-optical modulator (AOM) controlling the seed intensity is successfully demonstrated to suppress the broadband laser intensity noise. A maximum noise reduction of about 30 dB is achieved leading to a RIN of -152 dBc/Hz (~1 kHz-10 MHz) at 2.5 W output power.

Multi-100W class, fully integrated, monolithic ytterbium-doped photonic-crystal fiber amplifier module

We report a high performance, fully monolithic 40 μm core, Yb-doped photonic crystal fiber amplifier module. The developed fused combiner allows us to couple 6 pumps of 50 W at 976 nm and 5 W of signal at 1064 nm in the PCF amplifier. We then produced up to 210 W of average power at 1064 nm which is the highest power ever delivered by a fully monolithic PCF amplifier. The module is entirely thermally controlled in a rugged package, and has run more than 25 days at > 100W average power with an excellent peak to peak power stability < 1%.

200-W single frequency laser based on short active double clad tapered fiber

High power single frequency lasers are very attractive for a wide range of applications such as nonlinear conversion, gravitational wave sensing or atom trapping. Power scaling in single frequency regime is a challenging domain of research. In fact, nonlinear effect as stimulated Brillouin scattering (SBS) is the primary power limitation in single frequency amplifiers. To mitigate SBS, different well-known techniques has been improved. These techniques allow generation of several hundred of watts [1]. Large mode area (LMA) fibers, transverse acoustically tailored fibers [2], coherent beam combining and also tapered fiber [3] seem to be serious candidates to continue the power scaling. We have demonstrated the generation of stable 200W output power with nearly diffraction limited output, and narrow linewidth (Δν<30kHz) by using a tapered Yb-doped fiber which allow an adiabatic transition from a small purely single mode input to a large core output.

Gain dynamics and intensity noise suppression of a clad-pumped Yb-fiber amplifier

Low intensity noise laser sources are a fundamental prerequisite for demanding fundamental research such as interferometric gravitational-wave detection (GWD) [1], precision spectroscopy, LIDAR, and ultra-cold atom/molecular optical lattices. Besides, high power lasers with low intensity noise also attract great interest in the industry applications. Direct pump current control is the simplest method to suppress the laser intensity noise. However, the modulation of high current multi-mode pump diodes is not straightforward and achieving wide feedback control bandwidth beyond 200 kHz is challenging. For the laser sources used in GWD, the intensity noise could be suppressed down to −140 dBc/Hz (1 kHz-10 kHz) for an output power of 160 W. However, this approach requires a quite complex setup and the feedback bandwidth is limited to ∼10 kHz [1].

120W single frequency laser based on short active double clad tapered fiber

High-power single-frequency lasers are very attractive for a wide range of applications such as nonlinear conversion, gravitational wave detection, atom trapping or LIDAR. Power scaling in single-frequency regime is a challenging domain of research. In fact, nonlinear effect such as stimulated Brillouin scattering (SBS) is the primary power limitation in single-frequency amplifiers. To mitigate SBS, different well-known techniques have been improved: temperature or strain gradient, gain competition. These techniques allow generation of several hundred of watts [1]. Large mode area (LMA) fibers, transverse acoustically tailored fibers [2], coherent beam combining and also tapered fiber [3] seem to be serious candidates to continue the power scaling. The main goal is to reduce optical densities by using large effective area, leading to an increase of the SBS threshold. By adiabatic transition from few microns to several tens of microns, tapered fibers allow to increase the core diameter fibers while keeping a single mode emission. We report on the generation of stable 120W optical power with diffraction limited output, and narrow linewidth (Δν<30 kHz).