SFP modules followed on from GBIC modules and are used in both ethernet and fibre channel switches (and others too), they are usually optical I/O modules although RJ45 copper Ethernet ones are available. Ethernet modules are most commonly 1GB/s but 10GB/s and higher are available.

SFP used for Fibre channel can be 1 or 2GB/s but most common is 4GB/s.

All the optical interfaces are either single or multimode fibre terminated on LC connectors.

Although less common, SFP modules can have an RJ45 socket for copper connectivity.

Another option is Wavelength Division Multiplex SFP which use two different wavelength for Tx and Rx, so only needing one fibre. This example uses SC single mode ( SC == Stick 'n' Click )

As this used two wavelengths, the SFP needs an optical splitter, and will have both a laser and receiver on the two prism ports.

I'm guessing here, but I believe the laser is mounted at the rear with the 3 pins connection to the PCB, and the RX connections are on the side with flexible connection to the PCB.

Close-up of the Prism housing and SC receptacle.

Just a look inside for interest…

Specific to Cisco IOS as SFPs can be found in Fibre Channel SAN switches and other manufacturer's kit.

Inserting a SFP module

router01#
*Nov 30 19:44:22.751: %EHWIC_1GE_SFP_CU-6-SFP_INSERTED: Transceiver module 1000BaseSX SFP is inserted in GigabitEthernet0/0/0 interface.

This is in a Cisco 1921 Gigabit router with a WIC for gigabit copper and and SFP module.

router01#sh inventory 
NAME: "CISCO1921/K9", DESCR: "CISCO1921/K9 chassis, Hw Serial#: FCZ1625C5YF, Hw Revision: 1.0"
PID: CISCO1921/K9      , VID: V04 , SN: FCZ1625C5YF

NAME: "Enhanced High Speed WAN Interface Card-1 Port Gigabit Ethernet SFP/Cu on Slot 0 SubSlot 0", DESCR: "Enhanced High Speed WAN Interfa"
PID: EHWIC-1GE-SFP-CU  , VID: V01, SN: FOC15164VRP

NAME: "1000BASE-SX SFP", DESCR: "1000BASE-SX SFP"
PID:  , VID:    , SN: FNS1007Q4PF