High Power PM Fiber Laser Coupler

Fiber lasers have emerged as a promising technology for future high energy laser (HEL) weapons systems, having demonstrated single mode, CW operation at 10kW power level and high electrical to optical conversion efficiency (>25%). However, commercial fiber lasers are not practical for beam combining to obtain the higher power (100kW) levels required for future weapons systems without sacrificing beam quality. For that, single mode fiber lasers operating with linear polarized output (PM amplifiers) and narrow line width (GHz) need to be developed, ideally in the 1-10kW power range. One of the key “missing” optical elements required for this fiber laser, is the PM coupler used to combine multiple high brightness pump diode modules with the linear polarized signal. Currently this PM coupler technology does not operate robustly at the multiple kW level and must be developed before full scale testing of PM fiber amplifiers at the >1kW can be accomplished. Additional specifications that need to be improved in future PM coupler technology are lower signal insertion loss, to enable counter and bi-directional pumping configurations. This proposal aims to develop an improved multi-kW PM fiber coupler technology and demonstrate their operation in PM fiber amplifiers at 2-3kW, with specifications suitable for future HEL weapons beam combining programs.