Simultaneous spectrum and coherent combining by active phasing dual two-tone all-fiber MOPA chains

Area of Science:

• Optics and Photonics
• Laser Physics
• Fiber Lasers

Background:

• High-power fiber lasers require advanced beam combining techniques.
• Stimulated Brillouin scattering (SBS) is a major challenge in fiber amplifiers.
• Maintaining phase coherence during amplification and combining is difficult.

Purpose of the Study:

• To develop a method for simultaneous spectral and coherent combining of fiber laser amplifiers.
• To achieve robust suppression of stimulated Brillouin scattering.
• To demonstrate stable in-phase combining with active phase control.

Main Methods:

• Utilizing spectrally combined single-frequency seed lasers in a master oscillator power amplifier (MOPA) configuration.
• Employing active phasing for coherent combining of spectrally combined amplifiers.
• Implementing an all-fiber power amplifier chain designed for SBS suppression.

Main Results:

• Achieved a total output power of 390 W from two coherently combined MOPA chains.
• Demonstrated a two-fold increase in main lobe power in a closed-loop system compared to an open-loop system.
• Obtained visibility exceeding 75% in long-exposure interference patterns, indicating stable phase control.

Conclusions:

• The proposed MOPA configuration with active phasing enables simultaneous spectral and coherent beam combining.
• The system effectively suppresses stimulated Brillouin scattering and maintains phase stability.
• This technique offers a robust solution for generating high-power, coherent fiber laser beams.