Arrays of Nanoscale-Thick\nITO Hemispherical Shells\nas Saturable Absorbers for Q‑Switched All-Fiber Lasers

We\nreport on the preparation of robust indium tin oxide\n(ITO) hemispherical-shell\narrays (HSAs) with nanoscale thickness of ∼100 nm and their\napplications for passively Q-switched erbium-doped all-fiber lasers\nas saturable absorbers (SAs). The five different-sized ITO HSAs as\nrobust SAs with diameters of 707, 820, 870, 994, and 1100 nm are successfully\nand efficiently fabricated onto the endfaces of commercial single\nmode fiber jumpers by using the nanosphere lithography technology.\nIn the laser measurement, the stable Q-switched laser pulses with\nwavelengths centered at 1.56 μm, 3 dB bandwidths of ∼3.3\nnm, and pulse widths of ∼6.44 μs are successfully obtained\nfor all five different-sized ITO HSAs due to the larger modulation\ndepths of ∼12.8%–16.4%, which is theoretically demonstrated\nto be arising from the excitations of second-order broad transverse-magnetic\nand transverse-electric Mie resonances. In addition, an average output\npower as large as 1.88 mW and single pulse energy as large as 95.46\nnJ are successfully obtained for the ITO HSA SA with a diameter of\n1100 nm. Our results indicate that the nanoscale thick ITO-HSA is\na promising SA for constructing high performance Q-switched all-fiber\nlasers.