To Investigate and Develop a Reduced cost, completely monolithic high energy ultrafast fiber amplifier based on microstructured fiber and counter pumping

The DOE has expressed considerable interest in the potential use of a coherently combined array consisting of a very large number of ultrafast (sub picosecond) fiber lasers. In order for this approach to be successful, significant increases in per pulse energies and average power as well as significant reductions in cost and size must be realized. In order to meet this challenge Optical Engines Inc will develop a completely monolithic (all fiber), low cost counter pumped Photonic Crystal Fiber (PCF) ultrafast amplifier for coherently combined fiber arrays. This all fiber amplifier will be less than 20% of the cost of existing approaches through the complete removal of all free space optics resulting in a device that is significantly more robust and reliable , affording a factor of 10 increase in amplifier array packing density. It is expected that the fiber to fiber spacing in the array can be as low as 1.5mm. This amplifier will utilize Optical Engines Patented Etched Air Taper fiber pump combiner technology. This technology has been utilized in directed energy systems with pump efficiencies of over 99% and signal efficiencies of over 96% that have been demonstrated in commercially available co pumped devices; reliably operating at over 2.5kW of pump power for over 2 years. For the phase 1 program, in order to achieve superior performance in a counter pumped architecture, several iterations will be required to create a fiber bundle that is of ultra low stress on the LMA output fiber to insure no mode distortions on the signal core. Low loss cleaves and splices will need to be developed at the high peak power output side of the amplifier. High damage threshold, low back reflection end caps will also be developed. Finally a means for preventing any scattered signal light from going into the pump fibers and damaging the pump diodes will also be developed. The necessary mode adapters and pump dumps for the input side of the amplifier will also be developed. The use of fiber coiling for mode control and near diffraction limited operation will be developed as well. In order to test these amplifiers, Optical Engines will work with KM Labs of Boulder Colorado, one of the leading firms in the development of ultrafast lasers. Seed lasers will pulse widths of less than 100 fs will be used to test the amplifier. Since the counter pumped amplifier will be in a 9+1:1 configuration, pump ports are available for multi diode pumping and also signal monitoring for phase control. Commercial applications for these ultrafast fiber lasers have been developing rapidly in scientific, medical and industrial markets. An ultrafast amplifier as the one proposed for this program will serve to accelerate the adoption of these lasers through improved performance and reduced cost. Key Words; Ultra Fast Fiber lasers, fiber amplifiers, photonic crystal fibers, etched air taper combiners