Efficient side pumping of high-ower fiber lasers using doubly grooved binary metallic diffraction gratings

A metallic binary grating with two grooves per period, defined by different linewidths and the same depth, is applied to side-pumping high power fiber lasers for the first time. This kind of doubly grooved metallic grating can be fabricated directly on inner clad of double-clad fiber and so that it can be used for high-power laser pumping. By combining a gradient algorithm (quasi-Newton methods) and micro- genetic algorithm, the grating is optimized and the maximum coupling efficiencies of 94.77% and 77.27% for TM and TE polarization waves respectively are demonstrated. Meanwhile, the fabrication-error and the minimum feature size of grating are also analyzed.