You pick a 1G SFP on two things: what fiber is in the ground and how far it has to go. On multimode in the data center there's 1000BASE-SX up to 550 m. On single-mode you choose 10 km (LX), 40 km (EX) or 80 km (ZX). These are all duplex optics: two fibers per link.
If the port needs to go to copper, there's an RJ45 SFP for 1000BASE-T. Only one fiber between two sites? See 1G BiDi. We code every optic for your platform, from Cisco and Juniper to MikroTik and Ubiquiti.