Mode competition in high power fiber amplifiers

Area of Science:

• Photonics
• Fiber Optics
• Laser Physics

Background:

• Continuous Wave (CW) fiber amplifiers are crucial for various laser applications.
• Understanding mode competition and gain saturation is key to optimizing amplifier performance.
• Higher-order modes (HOMs) can degrade beam quality if not managed.

Purpose of the Study:

• To investigate the impact of fundamental mode gain saturation on the growth of higher-order modes (HOMs) in Ytterbium-doped fiber amplifiers.
• To analyze polarization-dependent effects of gain saturation on HOMs.
• To quantify these effects in different fiber geometries (straight vs. bent) and doping profiles (full core vs. restricted area).

Main Methods:

• Utilizing a beam propagation model.
• Simulating Ytterbium (Yb3+) doped, Continuous Wave (CW) fiber amplifiers.
• Analyzing the growth of HOMs under strong fundamental mode saturation.

Main Results:

• Gain saturation by the fundamental mode significantly suppresses the growth of HOMs with parallel polarization.
• Conversely, gain saturation enhances the growth of HOMs with perpendicular polarization.
• These effects were quantified in both straight and bent fibers, and for full core and restricted area doping configurations.

Conclusions:

• Fundamental mode saturation in Yb-doped fiber amplifiers exhibits polarization-dependent control over HOM growth.
• This finding is critical for designing advanced fiber amplifiers with tailored beam characteristics.
• The study provides insights into managing mode instability in optical fiber systems.