Large mode area 8+1 to 1 backward pump signal combiner

We report an 8+1 to 1 pump-signal combiner (PSC) designed for backward pumping with higher-order mode content 19 dB lower than the fundamental mode in the output pigtail. The mode content is measured using the S2 measurement technique. The output beam M2 was near diffraction limited at M2 X of 1.23 and M2 Y of 1.21. The high signal beam quality is attributed to a high-quality taper and low overlap splice loss between the tapered fiber bundle and the output fiber. The combiner output fiber is large mode area with an LP01 mode field diameter of 33 µm at 1064 nm and mode effective area of 854 µm2. The large effective area of the output pigtail is ideal for low nonlinearity and high-power delivery. The additional pump ports allow for lower system weight by eliminating the additional layer of pump combiners (PC) in a PC+PSC tree of combiners and using higher power low brightness pump diode sources.