Mode Adapting Etched Air Taper Fiber Optic Pump Combiner

ABSTRACT: The Etched Air Taper Combiner as fist proposed by the US Air Force Academy has the advantages in that the input fiber bundle, the combining section, and the output to the gain fiber can be individually improved and optimized and then the components are spliced together to create the finished device. Pump efficiencies of over 96% and power handling capabilities of 1.5kW have been demonstrated as well as both co and counter pumped designs. When the input and output signal core fibers are the same a 99% signal core efficiency has been demonstrated. The problem arises when transitioning from a LMA SIF type fiber to a PCF type fiber involving large core transition. Past efforts have relied on a step transition between the two fibers. In this proposal a continuous mode adapter between a 20um LMA fiber and a 40um PCF core will be developed and demonstrated. In the Phase 2 program this mode adapter will be built into a multiple copies of a finished high power, ruggedized combiner for delivery to the Air Force for integration and testing. BENEFIT: To enable the development of MOPA based directed energy systems by providing low loss fiber optic pump combiners with optical signal feed throughput that allow for the low loss, low scatter transition from LMA to PCF type fibers.