560  W all fiber and polarization-maintaining amplifier with narrow linewidth and near-diffraction-limited beam quality

Abstract

We present a narrow linewidth, all-fiber polarization-maintained amplifier chain seeded by a phase-modulated single-frequency laser, which is a narrow linewidth. Different from previous phase-modulation techniques, the phase-modulation signal is generated by simply imposing an excited signal to an acoustic-optical driven source. Theoretical simulation results show that this method can suppress stimulated Brillouin scattering (SBS) to a better degree, and the output power can be boosted to about 1.2 kW in terms of the SBS threshold. By amplifying the phase-modulated seed based on master-oscillator power-amplification configuration in experiments, a 560 W output laser is achieved with slope efficiency of 87.2% and linewidth of <5 GHz. Further power scaling is limited by mode instability instead of an SBS effect. At maximal output power, the beam quality (M² factor) and polarization extinction ratio is measured to be within 1.3 and 14 dB, respectively.

Seeding High Brightness Fiber Amplifiers With Multi-Phase Coded Signal Modulation for SBS Effect Management

“…And the self-phase modulation and cross-phase modulation between the signal light and the Stokes light are also taken into consideration. The normalized amplitudes of the laser light (A S ), the Stokes light (A B ), and the phonon field (Q) satisfy the following equations [40].…”

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

“…where J n (m) is the first kind of Bessel function, Ω=2 πf m . Therefore, the spectral power exhibits a series of sidebands with integer multiples of p. The broadened linewidth of the sinusoidal modulated signal depends on the modulation depth m d and modulation frequency f m [10].…”

“…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].…”

A 2 kW, 8 GHz-Linewidth Yb-Doped Polarization-Maintained Fiber Laser with Quasi-Flat-Top Pseudo Random Binary Sequence Phase Modulation for SBS Suppression

“…In the last few years, many researchers made great progress in the power scaling of the narrow-linewidth fiber amplifiers using PM fibers. In 2015, a 560 W fiber amplifier with a linewidth of <5 GHz was reported, which used a phase-modulated seed source from an acoustic-optical driven source [34]. An 818 W PM fiber amplifier with a linewidth of <7 GHz was demonstrated based on the PRBS phase modulation in 2019 [22].…”