Key Enabling Components for High-Power Fiber Lasers

Three key enabling components are critically needed for advancing highpower fiber lasers. They are the double clad, multicore fibers; high brightnessdiode laser pumps; and optical coupling between the pump and the fiber. Thisproposal is focused on the most neglected component, the coupling between thepump and fiber laser. Material damage thresholds eliminate end pumping as aviable way to achieve multiple kilowatt outputs from a double clad fiber lasersystem. Side pumping the entire surface of a double clad system has not shownpromise due to excessive losses that are artifacts inherent in the design. Theaim of this proposal is to develop a reliable optical coupling technique bydistributing the pump power at various strategic locations along the length ofthe double clad fiber without compromising the fiber integrity. The design ofour proposed coupling scheme takes into account the effective absorption of thefiber cores along the propagation length of the fiber. The pump power from amultimode fiber is injected into the inner cladding at an angle exceeding thecritical angle. With this approach it may be possible to couple several kilowattsof pump power into the fiber without exceeding the material damage threshold.This proposal describes an approach and presents the necessary steps todemonstrate the practicality of our proposed coupling scheme. If the results ofthis Phase I prove successful a Phase II will be proposed to develop a prototypewhich will be delivered to the Air Force for demonstration. High power diode-pumped multicore fiber lasers can be very competitive in the market place as compared to high power diode-pumped solid-state lasers and C02 lasers presently employed byautomotive, aerospace and ship-building industries for precision drilling, high-speed cutting and welding of metals and composition materials.