780W narrow linewidth all fiber laser with sinusoidal phase modulation

In high power fiber laser, the limiting factor of narrow linewidth output is analyzed. The influence of Stimulated Brillouin scattering effect and sinusoidal phase modulation suppressing method are studied. The linewidth of a single frequency laser is broadened from 1MHz to 2.9 GHz by sinusoidal phase modulation technology. The output power of single frequency laser is 50mW. And through three stage fiber amplified, the central wavelength of 1064.34nm, linewidth of 2.9 GHz and power of 780W are achieved respectively. The optical-optical efficiency is 79%. And the beam quality is M-x(2) = 1.33 and M-y(2) = 1.27. The distributing characteristic of longitudinal mode, under every modulating coefficient, is measured. And the result is the same as theoretical result. The increasing of longitudinal mode number, controlling of longitudinal mode spacing and reducing power spectrum density by sinusoidal phase modulation are proved to be viable. Then Stimulated Brillouin Scattering threshold is increased. Finally, the output power is increased a lot. The output power of this laser is only limited by pump power. If the pump power is increased, the higher power of narrow linewidth fiber laser will be achieved.