We present a gallium antimonide-based semiconductor saturable absorber mirror (SESAM) operating at 2 μm wavelength region. GaSb-based material system is the preferred choice for fabricating surface-normal devices operating beyond 2 μm because it enables the use of highly reflective semiconductor reflectors and quantum wells for wide wavelength range. For the purpose of generating short laser pules, the SESAM was carefully designed to attain a large modulation depth. The device was utilised successfully to passively Q-switch a 2 μm Tm3+-/Ho3+ -doped fiber laser, demonstrating record-short Q-switch pulses of about 20 ns.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.