Beam combinable, kilowatt, all-fiber amplifier based on phase-modulated laser gain competition

Area of Science:

• Fiber laser technology
• Nonlinear optics

Background:

• High-power fiber amplifiers are crucial for various applications.
• Stimulated Brillouin scattering (SBS) limits power scaling in narrow-linewidth fiber lasers.
• Maintaining narrow linewidths at high power is challenging.

Purpose of the Study:

• To achieve 1 kW output power from a monolithic Ytterbium-doped fiber amplifier.
• To suppress stimulated Brillouin scattering (SBS) in a dual-signal seeded amplifier.
• To investigate power scaling while maintaining narrow spectral linewidth and good beam quality.

Main Methods:

• Utilized a dual-signal seed (1038 nm and 1064 nm) with optimized power ratio.
• Implemented phase modulation with a pseudo-random bit sequence (2.5 GHz clock rate).
• Integrated laser gain competition with phase modulation to manage nonlinear effects.

Main Results:

• Achieved 1 kW output power with predominantly the longer wavelength signal.
• Successfully suppressed SBS using the combined technique.
• Measured near-diffraction-limited beam quality (M² ≈ 1).
• Demonstrated 90% coherent beam combination efficiency without spectral broadening.

Conclusions:

• The developed technique effectively scales power in narrow-linewidth Yb-doped fiber amplifiers.
• This method offers a significant reduction in spectral linewidth compared to commercial alternatives.
• The results pave the way for more efficient high-power fiber laser systems.