SFP module is the core component in gigabit Ethernet networks. What is an SFP module? This article will give a comprehensive introduction to the SFP module, including SFP meaning, SFP port, SFP types, and how to choose an SFP module. I hope this post will help you fully understand SFP and choose the right SFP modules for your SFP network.
What is an SFP module?
What is SFP? SFP stands for small form-factor pluggable, a hot-pluggable interface device used to convert electrical signals into optical signals in gigabit networking. SFP is an upgraded version of GBIC (Gigabit Interface Converter). Both the GBIC module and SFP module are input/output devices used to link the 1000BASE-X fiber optical or copper network by plugging into a Gigabit Ethernet port of network switch or router devices. The physical appearances and specifications of the GBIC module and SFP module are shown in the following chart.
| Specification | GBIC Module | SFP Module |
| Dimensions (H x W x D) | 0.39 in. x 1.18 in. x 2.56 in.
(1 cm x 3 cm x 6.5 cm) |
0.33 in x 0.53 in x 2.22 in
(8.5 mm x 13.4 mm x 56.5 mm) |
| SFP Connector Type | SC | LC/RJ45 |
GBIC was quite popular in the 1990s. It uses an SC connector and supports hot plug and play. GBIC module can be seen as the first optical transceiver module with a standardized packaging interface. Gigabit switches designed with GBIC interface once occupied a large share of the market. However, SFP was then introduced in 2001, and it greatly improves GBIC in size and adopts an LC or RJ45 connector, only half the size of the GBIC module, so the SFP transceiver module is also known as Mini-GBIC. With the increasing demand for the transmission capacity of the communication network, it is an inevitable trend that network devices need to configure with more ports, then SFP rapidly replaced GBIC modules because it offers much higher port density than GBIC.
The SFP form factor is specified by SFP MSA (multi-source agreement), which has become the reference standard for worldwide optical module manufacturers to develop SFP optical modules. It specifies the design requirements of the SFP transceiver module, including the pin definition, mechanical dimensions, packaging of the gold finger, application circuit and etc.
How the SFP module works
What is the SFP module used for? SFP fiber module is used to complete the electrical-optical/optical-electrical conversion of optical signals. Specifically, the SFP fiber module was inserted in the SFP slot of network devices (switches, routers, NICs, etc.). It converts the electrical signal of the switch or router into an optical signal, then relying on a fiber optic cable, the optical signals are transmitted to the SFP module at the other end. Finally, the receiving end of the SFP fiber module receives the transmitted optical signal and converts it into an electrical signal, and inputs it into the device.
An SFP fiber module is mainly composed of optical components, detector, laser, amplifier, clock data recovery, driver chip, and limiting amplifier. The following figure is the working principle block diagram of an SFP optical module.
SFP Module Working Principle
What is an SFP Port?
The SFP port is a slot configured on network devices that enables SFP modules inserted. The following figure shows the SFP ports on the switch, router, server, and NIC.
SFP ports on the switch, router, server, and NIC
Can an SFP module be inserted in an SFP+ port? and can an SFP+ module be inserted in an SFP port?
SFP+ and SFP modules look exactly the same by sharing with same form factor shape and size. The major difference is SFP+ module improves SFP at speed. SFP+ supports 10Gbit/s while SFP only offers 1Git/s. An SFP module can be plugged into an SFP+ switch port, but the speed will be fixed at 1 Gbps. However, plugging an SFP+ module into an SFP port, the SFP+ module might not work at all. It depends on whether the SFP+ transceiver can negotiate to 1Gbps.
Does an SFP port connect an optical fiber cable or copper cable?
An SFP port can connect both optical fiber cable and copper cable. Which one to choose determines the SFP module type plugged. According to different transmission media (fiber optic cable and copper cable), SFP module types include fiber SFP modules and copper SFP modules. Common fiber SFP modules include 1000BASE-SX, LX, BiDi, CWDM, and DWDM. They use LC connectors and connect single-mode or multimode fiber cables. The copper SFP module is known as 1000BASE-T SFP, it is interfaced with an RJ45 connector and connects a Cat 5e/6/6A Ethernet copper cable.
How to choose an SFP module?
To choose the right SFP module, being aware of what SFP types there are is essential. As above mentioned, according to copper and fiber optic cable transmission media, there are fiber SFP modules and 1000BASE-T copper SFP modules. Then how to choose between them. It must be determined by your actual needs. The following chart list the major specification differences between them helping you determine which SFP type to choose.
| SFP Types | Fiber SFP Module | Copper SFP Module |
| Connector | LC | RJ45 |
| Cable | Multimode fiber cable/single-mode fiber cable | Cat5e/Cat6/Cat6A |
| Max Distance | >100km | 100m |
| Cost | High | Low |
Besides being classified based on different transmission media, SFP modules also can be classified as single-mode SFP and multimode SFP. Multimode SFP modules (1000BASE-SX) operate on multimode fiber cables, whereas single-mode SFP modules (1000BASE-LX, EX, ZX, BiDi, CWDM, DWDM, etc.) operate on single-mode fiber cables. Single-mode fiber cables have a smaller diameter and are suitable for long transmission distances. The common multimode fiber SFP and single-mode SFP module types and their major specifications are shown in the following chart.
| SFP Type | Product No. | Wavelength | Distance | Connector |
| Multimode SFP | 1000BASE-SX | 850nm (OM2) | 550m | Duplex LC |
| Single-mode SFP | 1000BASE-LX/LH | 1310nm | 10km | Duplex LC |
| 1000BASE-EX | 1310nm | 40km | Duplex LC | |
| 1000BASE-ZX | 1550nm | 80km | Duplex LC | |
| 1000BASE-BX20-U | 1310nm | 20km | Simplex LC | |
| 1000BASE-BX20-D | 1490nm | 20km | Simplex LC | |
| 1000BASE-BX40-U | 1310nm | 40km | Simplex LC | |
| 1000BASE-BX40-D | 1550nm | 40km | Simplex LC | |
| 1000BASE-BX80-U | 1490nm | 80km | Simplex LC | |
| 1000BASE-BX80-D | 1550nm | 80km | Simplex LC |
Final words
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