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Is SFP fiber or copper?
Knowledge Base + 2023.12.07

SFP (Small Form-factor Pluggable) modules can support both fiber and copper connections. Depending on the specific SFP module, it can be used for connecting devices using either fiber optic cables or copper cables.

Some SFP modules, such as GLC-BX-D and GLC-BX-U, support digital optical monitoring, which lets end users monitor the performance of SFPs in real time, tracking metrics, such as temperature, optical output power, optical input power, transceiver supply voltage and laser bias current.

SFP ports vs. RJ45 ports

While SFP and SFP+ modules are relatively inexpensive, 1 Gb and 10 Gb connections are more expensive than RJ45 connections. RJ45 uses copper cables, which are generally less expensive than fiber. Also, RJ45 ports are typically built into switches so customers don't need to purchase additional parts.

The decision of where to use an RJ45 port or an SFP port on a switch depends on the distance between the connection endpoints.The decision of where to use an RJ45 port or an SFP port on a switch depends on the distance between the connection endpoints. If the endpoints are close enough to use copper, then using RJ45 is less expensive. If the distance is great enough to require fiber, then teams should use SFP ports. Fiber is also a better choice where cables must run side by side for a distance that makes cross-talk between copper cables an issue.

Combo SFP ports on a switch offer support for both SFP and RJ45 ports using a single interface. Users can't use both ports simultaneously, however, as only one type will work at a time. These combo ports enable IT teams to choose a connection type that best matches application, network, cost or distance requirements.

SFP types and updates

Vendors have continued to update SFP specifications to support higher rates and additional interconnect types. SFP28 supports 25 Gbps over both multimode and single-mode fiber. BiDi SFPs support bidirectional communication over a single fiber. While other SFP types require two fibers -- one to send and one to receive -- BiDi SFPs use different wavelengths with one wavelength for sending data and the other for receiving.

Compact SFPs support two bidirectional links using the same interface module -- two fibers are used with each carrying bidirectional traffic. Quad SFP (QSFP) modules support four fibers carrying Ethernet, FC or InfiniBand. Most available QSFP modules can support up to 200 Gbps. Both octal SFP and QSPF double density have recently become available and extend data rates to 400 Gbps.

Currently, 400 Gbps is the highest rate available in commercially available products, although work is underway to develop standards and products that support 800 Gbps. SFP technology has demonstrated the ability to evolve as demands increase and will likely continue to evolve to support higher rates.


       1.25G SFP 1550nm 120KM

What is SFP Connector?

SFP connector or SFP plug is another name of SFP as SFP (small form-factor pluggable) is a compact and hot-pluggable interface connector. The SFP connector module functions as the intercommunication media between the network devices and cables to achieve photoelectric and electro-to-optical conversion. SFP interface is commonly used in SFP port network equipment such as Ethernet switches, firewalls, routers, network interface cards (NICs) for both data communication and telecommunication applications.


Figure: the optical interface of the 1000BASE-SX SFP connector module is located at the side of the dust cap. Once unplug the cap, will you see the optical interface.

According to transmission media, there are SFP copper connectors and SFP fiber connectors. Copper SFP uses an RJ45 SFP connector interface, whereas fiber SFP uses SFP lc connector, SFP sc connector, and SFP MTP/MPO connector interface as typical ones. According to the SFP forms, different SFP form factors often utilize corresponding SFP connectors.

The table below shows the SFP connector interface types for different SFP types.

SFP TypesMediaConnector
100 Mbit/s SFP
LC, RJ45
1 Gbit/s SFP
Fiber, copper
1 Gbit/s cSFP
10 Gbit/s SFP+
Fiber, copper, DAC
LC, RJ45
25 Gbit/s SFP28
Fiber, DAC
50 Gbit/s SFP56
Fiber, DAC
4 Gbit/s QSFP

40 Gbit/s QSFP+
Fiber, DAC
50 Gbit/s QSFP28
Fiber, DAC
100 Gbit/s QSFP28
Fiber, DAC
200 Gbit/s QSFP56
Fiber, DAC
400 Gbit/s QSFP-DD
Fiber, DAC

What Type of Connector is Used with an SFP Port?

SFP ports are frequently found in Ethernet network switches. These switches with 1G SFP ports as the major functional switch ports are called gigabit SFP switches.

SFP port on SFP switch supports both SFP copper connector and SFP fiber connector while RJ45 port can only take copper SFP module RJ45 connector. SFP connector types that 1G SFP port can take are RJ45 SFP connector, SFP lc connector, SFP sc connector.

FAQs about SFP Transceiver

Can We Use SFP Hardware in SFP+ Slots?

In many cases, the SFP+ port accepts SFP optics, but the speed will be down to 1G instead of 10G. However, SFP+ optics can not be plugged into the SFP port, because SFP+ does not support speed under 1G. In addition, almost all SFP+ ports on Cisco switches can support SFPs, but many SFP+ ports of Brocade switch only support SFP+ optics.

Can I use a 1000base-LX sfp for 1000base-SX fiber?

Generally, they are not interchangeable. 1000Base SX and LX are two optics standards with different operation wavelengths.1000Base LX SFP transceiver usually operates at 1310nm and uses single-mode fiber to connect, while 1000Base-SX usually is 850nm SFP and works with multimode fiber.

Can you aggregate multiple SFP ports?

Of course, you can. Link aggregation provides benefits like increased bandwidth, redundancy, and load-balancing. That will ensure that one link can immediately switch to a second available link when it fails. Therefore, aggregation on SFP ports is critical for enterprise networks where performance and security are more important. But note that, before connecting the SFP ports, please make sure that the switches have been configured for link aggregation. Otherwise, it will cause network loops.