ULMA Fiber Laser Harnesses for High Intensity Ultrafast Lasers

Optical Engines Inc will develop the required technologies and components or a monolithic fiber amplifier harness based on Ultra Large Mode Area (ULMA) gain fibers, i.e., fibers who core size is greater than 55um in diameter. These types of ULMA fibers are required for achieving multi mj per pulse operation in Chirped Pulse Fiber Amplifiers (CPA) with reduced fiber non linearities needed for low femtosecond (fs) operation and hundreds of Watts of average power. To date these ULMA fibers such as Photonic Crystal Fiber (PCF) Rod fibers and Chiral Coupled Core (3C) fibers have only been used in architectures where the signal and pump are coupled via free space optical means. For higher average powers, robustness, reliability, and reduced size and cost in large count parallel fiber amplifier systems, a monolithic system is absolutely necessary. ULMA type fibers are especially challenging because by their very nature they are weakly guiding and thus very sensitive to any micro bending and other stresses that might come about during the use of these fibers to create monolithic components such as combiners and mode adapters. Optical Engines has the unique capabilities and expertise to create these low stress monolithic devices for fully integrated fiber amplifier harnesses based on ULMA fibers. These laser amplifier harness components will utilize Optical Engines Patented Etched Air Taper fiber pump combiner technology, as well as our ultra-low stress fiber bundling technology. This technology has been utilized in directed energy systems with pump efficiencies of over 99% and signal efficiencies of over 96% have been demonstrated in commercially available co pumped devices; reliably operating at over 2.5kW of pump power for over 5 years. These technologies have also been combined to create low loss high beam quality combiners based on 55um core 3C passive and gain fibers. The ultra-low stress bundling technology allows for 6+1, 9+1 and even 18+1 count bundles with virtually no modal distortion of the signal beam in the ULMA fiber and efficient coupling from the gain fiber to the output fiber in a counter pumped combiner. The fiber amplifier harness will contain an input mode adapter, the ULMA gain fiber, the pump signal counter pumped combiner and a delivery fiber/ AR coated end cap. The low stress bundling techniques and optimized Etched Air tapers and splices will also be developed. While several types of ULMA fiber exist, in this phase 1 program OEI will focus on the 85um 3C fiber as supplied by the University of Michigan and nLight. And while OEI has perfected processes for developing monolithic components based on 55um ULMA 3C fiber, the 85um core 3C fiber is expected to be much more sensitive to micro bending and much more challenging to create these components. In order to test these amplifier harnesses, Optical Engines will continue its close collaboration with Professor Almantas Galvanaskaus at the University of Michigan to develop the appropriate testing structures to create realistic test scenarios.