High Order Ribbon Fiber Modes, Simulations, and Experiments for High Power Fiber Amplifiers

Diffraction limited fiber amplifiers in a circular geometry are likely to be limited by nonlinearities to 2 kW for narrowband and 10-36 kW for broadband lasers. We have proposed a ribbon fiber geometry to allow scaling fiber lasers above these limits in which a high order ribbon mode is amplified and converted back to the fundamental mode in free space. Novel methods of illuminating a high order ribbon fiber mode are discussed and compared with modeling and experimental results showing high purity illumination, > 90%. A 10 kW single frequency ribbon fiber amplifier design is presented and BPM simulation results verify the approach.