Real-Time Definite Sequence Modulation Based Spectral Broadening Scheme for High-Power Narrow-Linewidth Fiber Laser

High-power narrow-linewidth continuous fiber lasers have wide applications in the fields of power synthesis, nonlinear frequency conversion, and industrial processing. The output power of kW or even MW can be achieved by adopting spectral synthesis. However, in the power amplification process, the nonlinear effect represented by the stimulated Brillouin scattering (SBS) effect limits the further increase of the laser power. And the accompanying self-pulsing effect poses a threat to the safety of the laser system. A high-order phase modulation scheme using a definite time sequence has been proposed to realize the controllable spectral broadening of the seed source, so as to suppress the SBS effect and improve the output power in the amplification stage. In this paper, we demonstrate a real-time definite time sequence generation scheme by using an integrated field-programmable gate array (FPGA) and digital-to-analog converter (DAC). Combined with a single-stage phase modulator, the broadened bandwidth up to 30 GHz and controllable spectral shape can be achieved by adjusting the output waveform of the DAC directly. The generation principles and waveform control methods of real-time sequence are introduced in detail. Proven by a master oscillator power amplifier (MOPA) structure, the laser output power has increased by 30% under the extended bandwidth of 10 GHz compared to the cascaded white noise modulation case. This scheme provides a compact real-time control module for spectral broadening, which lays the foundation for implementing low-cost, compact, and standardized high-power narrow-linewidth fiber lasers.