Arrays of Nanoscale-Thick ITO Hemispherical Shells as Saturable Absorbers for Q-Switched All-Fiber Lasers

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