Analytical study on the stimulated Raman scattering threshold in distributed-pumped fiber amplifiers

Area of Science:

• Optics and Photonics
• Laser Physics
• Fiber Optics

Background:

• Distributed-pumped fiber amplifiers are crucial for high-power laser systems.
• Stimulated Raman scattering (SRS) is a significant nonlinear effect limiting amplifier performance.
• Understanding SRS thresholds is essential for optimizing amplifier design and efficiency.

Purpose of the Study:

• To analytically investigate the stimulated Raman scattering (SRS) threshold in distributed-pumped fiber amplifiers.
• To develop a formula for predicting SRS thresholds.
• To systematically study the impact of pumping schemes on SRS suppression.

Main Methods:

• Analytical study based on the rate-equation model.
• Derivation of an SRS threshold formula.
• Numerical verification of the derived formula.
• Systematic investigation of pumping scheme effects.

Main Results:

• An accurate SRS threshold formula was derived and validated with numerical results.
• Optimized SRS suppression is achieved by strategically combining counter-pumped and bi-directional-pumped sub-amplifiers.
• For single-directional pumping, counter-pumping the first sub-amplifier is recommended for optimal SRS suppression.
• The influence of the number of sub-amplifiers on the SRS threshold was analyzed.

Conclusions:

• The derived SRS threshold formula provides valuable insights for designing distributed-pumped fiber lasers and amplifiers.
• Strategic pumping schemes are critical for mitigating SRS and enhancing amplifier performance.
• The findings offer practical guidance for optimizing fiber amplifier design to minimize nonlinear effects.