An all-fiber ultrafast laser system was demonstrated by utilizing polarization-maintaining fibers and polarization-maintaining fiber components. The central wavelength of the system was 1064 nm. A passively mode-locked fiber laser, a pulse selector, and subsequent fiber amplifiers realized micro joule pulse energy with tunable repetition rate and alterable pulse number in a single pulse string. In addition, an application of this laser system was carried out on dicing of 110 μm thick sapphire wafer. Experimental results showed that the pulse energy, the pulse number in a single pulse string, and the beam quality significantly affected the ablation performance. Up to 99.58% yield rate was achieved by using 100 kHz repetition rate, 7 pulses in a pulse string, 97% beam circularity, 0.37 W average power, and 600 mm/s dicing speed.