This is the Cisco industry standard SFP, which stands for Small Form-Factor Pluggable (part number GLC-SX-MM).  This device plugs into a Gigabit Ethernet port on a variety of Cisco devices (Router, Switches, etc) and is hot-swappable.  The Cisco GLC-SX-MM operates on ordinary multi-mode fiber optic link spans of up to 550 m in length.

This device is currently ON SALE