1000BASE-SX is a fiber optic gigabit Ethernet standard for operation over multi-mode fiber using a 770 to 860 nanometer, near infrared (NIR) light wavelength.

The standard specifies a distance capability between 220 meters (62.5/125 µm fiber with low modal bandwidth) and 550 meters (50/100 µm fiber with high modal bandwidth). In practice, with good quality fibre and terminations, 1000BASE-SX will usually work over significantly longer distances.

This standard is highly popular for intra-building links in large office buildings, co-location facilities and carrier neutral internet exchanges.

Optical power specifications of SX interface: Minimum output power = -9.5 dBm. Minimum receive sensitivity = -17 dBm.