Stimulated Brillouin scattering suppression through laser gain competition: scalability to high power

Abstract

We demonstrate stimulated Brillouin scattering (SBS) suppression in a Yb-doped fiber amplifier by seeding with a combination of broad- and single-frequency laser beams that are separated sufficiently to suppress four-wave mixing and to allow for efficient laser gain competition between the two signals. In the experiment, a monolithic fiber configuration was used. With appropriate selection of seed power ratio, we were able to generate single-frequency 1064 nm light with a slope efficiency of 78% while simultaneously suppressing the backscattered Stokes light. We discuss scalability to high power wherein a large thermal gradient can be induced at the output end of the fiber via quantum defect heating, leading to an SBS suppression factor comparable to counterpumping.

Suppression of stimulated Brillouin scattering in optical fibers using a linearly chirped diode laser

“…If the laser linewidth, ∆ν L , is large compared to the Brillouin linewidth, ∆ν B , the Brillouin gain is given approximately by eff 0 B L / . g g = ∆ ∆ ν ν Techniques to suppress SBS while maintaining fundamental mode operation include increasing the mode area while reducing the numerical aperture [1], increasing L ∆ν via phase modulation [2][3][4], laser gain competition [5], and using highly doped fibers to absorb the pump light in a short length to minimize L. A combination of these techniques has yielded 10 kW from a single-mode fiber master oscillator power amplifier [6]. However, the ~2-THz output bandwidth implies that to coherently combine multiple amplifiers, path lengths will have to be matched to ~10 µm.…”

High-efficiency and high-power single-frequency fiber laser at 1.6 μm based on cascaded energy-transfer pumping

“…Through seeding both SF signal and broadband auxiliary light, the effective length of the amplifier is shortened as the signal experiences a rapid rise at the output end of the active fiber [28]. Moreover, due to gain competition, steep thermal gradients are optically induced near the output end of the fiber, and the SBS threshold is enhanced [28]. The output signal power could be further improved through heightening more pump powers.…”

“…The linewidth of the output laser is tested based on the selfheterodyne method. The measuring device is mainly composed of a Mach-Zehnder interferometer, a 48.8 km fiber delay line, and a 40 MHz fibercoupled acoustic-optic modulator [28][29][30]. According to Fig.…”

Nanoparticle doping for improved Er-doped fiber lasers

“…Some efforts to mitigate this effect have included varying the acoustic refractive index profile in the longitudinal direction, 7 using hole assisted structures, 8 reduction of the overlap of guided optical and acoustic waves, 9 incorporation of materials of lower photoelastic coefficients than SiO 2, 10,11 and by seeding with a combination of broadband and single frequency laser beams. 12 In this work we were interested in investigating whether NP doping might offer an advantage in terms of SBS.…”