Distributed mode filtering rod fiber amplifier delivering 292W with improved mode stability

Area of Science:

• Laser Physics and Photonics
• Optical Engineering
• Materials Science

Background:

• High-power fiber amplifiers are crucial for various applications, but their output power is limited by mode instabilities.
• Distributed mode filter (DMF) fibers offer potential for controlling multimode propagation and mitigating instabilities.

Purpose of the Study:

• To demonstrate a high-power fiber amplifier utilizing a novel DMF rod fiber.
• To investigate the power scaling capabilities and underlying physics of the DMF rod fiber.
• To enhance output power by operating the fiber in a leaky waveguide regime.

Main Methods:

• A 292W average output power fiber amplifier was constructed using an 85 μm core diameter fiber and a 30 ps mode-locked source at 1032 nm.
• A single mode distributed mode filter (DMF) bandgap rod fiber was employed.
• The rod fiber was operated in a leaky waveguide regime to study its guiding dynamics and power performance.

Main Results:

• Up to 292 Watts of average output power was achieved.
• A 44% power improvement was demonstrated before the onset of mode instabilities by operating in the leaky waveguide regime.
• A distinct bandgap blue-shifting was observed as a function of increased signal power, explained by thermally induced refractive index changes.

Conclusions:

• The DMF rod fiber enables significant power scaling in fiber amplifiers.
• Operating in a leaky waveguide regime effectively suppresses mode instabilities, leading to higher output power.
• Understanding the bandgap blue-shifting mechanism is key to further optimizing high-power fiber amplifier design.