189 kW all-fiberized and polarization-maintained amplifiers with narrow linewidth and near-diffraction-limited beam quality

Abstract

In this manuscript, we demonstrate high power, all-fiberized and polarization-maintained amplifiers with narrow linewidth and near-diffraction-limited beam quality by simultaneously suppressing detrimental stimulated Brillouin scattering (SBS) and mode instability (MI) effects. Compared with strictly single frequency amplification, the SBS threshold is scaled up to 12 dB, 15.4 dB, and higher than 18 dB by subsequently using three-stage cascaded phase modulation systems. Output powers of 477 W, 1040 W, and 1890 W are achieved with full widths at half maximums (FWHMs) of within 6 GHz, ~18.5 GHz, and ~45 GHz, respectively. The MI threshold is increased from ~738 W to 1890 W by coiling the active fiber in the main amplifier. Both the polarization extinction ratio (PER) and beam quality (M2 factor) are maintained well during the power scaling process. To the best of our knowledge, this is the first demonstration of all-fiberized amplifiers with narrow linewidth, near linear polarization, and near-diffraction-limited beam quality at 2 kW power-level.

High power all-fiberized and narrow-bandwidth MOPA system by tandem pumping strategy for thermally induced mode instability suppression

“…These approaches mainly include incorporating thermal and longitudinal stress gradients [11][12][13] , using counterpropagating pump [14] , special transverse-designed active fiber [12,15] , multi-longitudinal-mode fiber oscillator [16,17] , filtered super-fluorescent source [10,18] , multi-wavelength injection and laser gain competition [19,20] and applying phase modulation technique [8,9,[20][21][22][23][24][25][26][27][28][29] . Within these SBS management approaches, phase modulation technique is a preferable approach beyond the output power of multikilowatt level [22][23][24][25][26][27][28][29] . As for TMI effect, several potential 2 P. Ma et al suppressing methods had also been proposed and validated by investigating on its physical mechanism [30][31][32][33][34][35][36][37] .…”

“…As for TMI effect, several potential 2 P. Ma et al suppressing methods had also been proposed and validated by investigating on its physical mechanism [30][31][32][33][34][35][36][37] . Generally, TMI effect could be suppressed by optimizing the doping area or imposing external bend loss of higher-order modes for mode selection [23][24][25][26][30][31][32][33] , reducing the core size or numerical aperture (NA) of the active fiber [27,28,31,34] , increase of the seed power [33] , weakening head load by optimizing the injected ratios of co-pumped and counterpumped laser [33,35,36] , decrease of quantum defect and/or pump absorption [33,35,37] . Nowadays, as high as 3 kW and 3.5 kW output powers with narrow bandwidths and near-diffraction-limited beam qualities had been respectively presented by using gold-coated specialty gain fiber [24] and low-NA active fiber [28] , while the configurations are not allfiberized and some bulk space components were employed.…”

Spectral evolution and stimulated Brillouin scattering suppression in phase-modulated fiber amplifier

“…The power scaling of high-power narrow linewidth fiber amplifier is mainly limited by stimulated Brillouin scattering (SBS), which is the lowest threshold nonlinear effect in narrow linewidth CW fiber laser. Early works have reported many techniques to suppress SBS such as phase modulation [5][6][7], novel fiber designs [8], longitudinal thermal gradients [9], and laser gain competition [9]. To date, with the development of phase modulators, phase modulation has been the predominant method to suppress SBS effect in high power narrow linewidth fiber laser.…”

“…Phase modulating to signal on time scales shorter than the phono lifetime can decrease the Brillouin gain and increase the SBS threshold. The prevalent phase modulation seeds consist of sinusoidal [7,10], white noise signal (WNS) [11][12][13], pseudo-random binary sequence (PRBS) [14] and nearly top-hat shaped spectrum seed [15,16]. The theoretical models predicting and comparing the SBS enhancement capacity of sinusoidal, WNS and PRBS phase modulation techniques have been reported [17][18][19].…”

4.05 kW monolithic fiber laser oscillator based on home-made large mode area fiber Bragg gratings

“…The gain fiber is coiled in circles and placed on the heat sink. The inner circles have a minimum diameter of ∼12 cm, and the outer circles have a maximum diameter of ∼16 cm, which could also help increase the threshold of TMI [26,27] . Two cladding light strippers (CLSs) are utilized on the both sides of the OC FBG in the fiber laser oscillator to fully dump the cladding light.…”