High Power Etched Air Taper Combiner Technology for Next Generation Monolithic Fiber Amplifiers

Optical Engines productized and ruggedized product line of patented etched air taper combiners has been operating in the field for over 5 years at pump power levels over 2kW. These pump/signal combiners have a pump efficiency of over 99%. At power levels much greater than 2kW, excessive heating and damage occurs not in the combiner itself but rather in the passive fiber that links the combiner to the amplifier gain fiber. This heating is due to the very high acceptance NA of the etched Air Taper that allows scattered light to leak into the plastic cladding of the passive transition fiber. In this effort we propose to add NA limiting mode stripping to limit the NA of the Air Taper to under .46NA to eliminate the light leaking into the cladding. We propose to investigate 3 different methods to remove this scattered light before it enters the passive transition fiber. Each of these methods will be tested to 3kW of pump with the goal of extending this performance to over 6kW in the Phase II effort. Approved for Public Release | 18-MDA-9817 (23 Oct 18)