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The History of Optical Transceiver Form Factors

Last year was Pro Optix’s 10th anniversary and when we looked back over the last decade it reminded us of how far we have come in the development of fiber optics and how rapidly technology is changing, with increasing speeds and new form factors being introduced every year now.

This is a far cry from the first GBIC and form factor launched 25 years or so ago, and it is ironic that we still sometimes refer to “Gbics” given the rapid progress and speeds we have today. Back in 2010 our business was founded on 100Mbit and 1G orders and 10G was expensive and limited, but in 2020 800G was launched on OSFP and QSFP-DD, 100G is available over longer distances and WDM has been a key focus over the last few years.

Let’s take a look at the history of optical transceiver form factors and those that are still available and used todayfrom GBIC to SFP-DD…

Form Factors

GBIC Transceiver


GBIC (Gigabit Interface Converter) was one of the first standards released in 1995 by the Small Form Factor Committee (now part of the Storage Networking Industry Association) for flexible hot-swappable transceivers and was revised in 2000. While the GBIC is now all but obsolete technology, people still sometimes refer to transceivers in general as GBICs.

SFP Transceiver Xenpak Transceiver XFP Transceiver


SFP (Small Form-factor Pluggable) transceivers were launched just over 5 years after GBIC as a smaller ”mini” version, but with the same functionality. They largely replaced GBIC, with typical speeds of 1 Gbps for Ethernet and up to 4 Gbps for Fibre Channel. SFP uses different connectors such as LC Duplex, LC Simplex, RJ45, SC Simplex, handling distances up to 160km. The SFP is very much still in demand, selling in large quantities.

Another form factor announced around the same time, included XENPAK which was defined in 2001 via a multisource agreement (MSA) between Agilent Technologies and Agere Systems and adhered to the 10 Gigabit Ethernet (10GbE) standard from the IEEE 802.3 working group. It was closely followed by X2 which was half the size of the XENPAK and launched in 2003 with a 10 Gbps data rate over 10 kilometers. The latest update to the X2 definition was in 2005.

In 2002 the XFP (X Form-factor Pluggable) standard was announced, adopted in 2003 and later updated in 2005. All XFP modules are 10G, the Roman numeral “X” in the abbreviation standing for the “10”. From around 2010 XFP modules were generally used for longer distances especially for DWDM covering distances up to 120km with LC Duplex and Simplex connectors.

SFP+ Transceiver QSFP Transceiver CFP Transceiver


2006 saw the introduction of SFP+ (Enhanced Small Form-factor Pluggable) – an enhanced version of SFP with a higher data rate that brought speeds up to 10 Gbps. SFP+ is supported by many network vendors and is still a dominant industry format with the latest update to the standard in 2013. Data transmission is available at 8 Gbps, 10 Gbps and 16 Gbps. SFP+ can cover distances from 30m to 120km and SFP+ transceivers are available with several different connector types such as LC Duplex, LC Simplex and RJ45.

QSFP (Quad Small Form-factor Pluggable) transceivers are slightly larger than SFP and were also launched in 2006. They have 4 lanes enabling data transmission at 4 times the rate over multi-mode or single-mode fiber at 4 Gbps. They are available to cover distances ranging up to 10km with LC Duplex and MPO-12 connectors.

The CFP (C Form-factor Pluggable) standard was originally designed for 100 Gigabit systems (”C” is the Roman numeral for 100) supporting ultra-high bandwidth networks which formed the backbone of the Internet. Ten 10G lanes or four 25G lanes, support a single 100 Gbps signal (such as 100GbE or OTU4). Alternatively, one or more 40 Gbps signals (such as 40 GbE, OTU3, STM-256/OC-768) can cover distances up to 3000km and above in amplified long-haul systems. Connectors available include LC Duplex and MPO-24.

QSFP+ Transceiver QSFP Transceiver SFP28 Transceiver CFP2 Transceiver


Launched in 2012, the Enhanced Quad Small Form-factor Pluggable QSFP+ is a 4-channel small hot pluggable optical transceiver that supports LC Duplex and MPO-12 fiber connectors. Like QSFP it has larger dimensions than SFP+ optical transceivers and covers distances up to 40km. It is still the dominant form factor for data rates at 40 Gbps.

QSFP28 was also launched in 2014 based on the same technology as QSFP+ and with the same physical dimensions, but using 4 lanes of 25Gbps. QSFP28 is now the standard interface of choice for 100G applications and is available in several different configurations from 100m using multimode to 80km using singlemode. Connectors available are LC Duplex and MPO-12.

With the same physical dimensions as the SFP and SFP+, the SFP28 was designed for speeds of up to 25 Gbps and launched in 2014. SFP28 has a single 28 Gbps channel which is able to transmit 25 Gbps of data plus encoding overhead. Modules are available in either single or multimode fiber connections. SFP28 transceivers only use 1 channel and are available with LC Duplex and Simplex connectors, with a reach of between 100m and 40km.

Since its introduction in 2009 improvements were made to CFP, with the introduction of CFP2 in 2012 and CFP4 in 2014 which allow for higher performance and higher density. CFP2 is half the physical size of the original CFP specification and provides data rates from 100Gbps to 200Gbps, for distances from 10km to 2000km in amplified long-haul systems with LC Duplex connectors. CFP4 is a quarter of the physical size of the original CFP standard, but delivers the same 100 Gbps data rate for distances of up to 10km. It uses LC Duplex connectors, with less than 6 W power usage

CSFP Transceiver QSFP56 Transceiver QSFP-DD Transceiver OSFP Transceiver OSFP Transceiver

2015-to today

In 2018 CSFP (Compact Size SFP) provided an update to bidirectional SFP, with two bi-directional streams of traffic using a SFP port which supports CSFP. CSFP can be used to connect two sites which have bidirectional SFP, halving the number of ports required and reducing power consumption. CSFP supports 2 x 1000Mbps for distances of up to 20km.

QSFP56 was standardized in 2019 doubling the data rate achieved by QSFP28 with a top speed of 200 Gbps. QSFP56 does this either by using parallel fibers and 8 x 25G wavelengths or by taking advantage of PAM4 modulation and an internal multiplexer transmitting 50G over 4 wavelengths. QSFP56 is available in different configurations using OM4 to reach a distance of 100m and OS2 for up to 10km. QSFP56 uses LC or MPO-12 connectors.

Also released in 2019 was the QSFP-DD (Quad Small Form-factor Pluggable Double Density) standard which is backward compatible with other QSFP versions. It enables high-speed solutions via an additional row of contacts which provide an 8 lane electrical. QSFP-DD can obtain data rates of up to 800 Gbps and connect to LC and MPO-16. It also introduced a new connector – the CS connector with 2 x CS Duplex connectors on one transceiver which can be used in breakout applications for 2x100G and 2x200G.

2019 continued to be a busy year for launches, and another form factor using CS connectors, with the introduction of OSFP (Octal Small Form Factor Pluggable) supporting bitrates of 400G and above. It also introduced the new CS connector (along with LC Duplex and MPO-12), which allows 2 x CS Duplex on one transceiver making aggregation possible without the need for MPO. It can cover distances of between 500m and 40km at data rates of 400G and 800G.

SFP-DD (Small Form-factor Pluggable Double Density) is one of the latest multisource agreement standards. SFP-DD is one of the smallest form-factors enabling data centers to double port density and increase data rates. Based on 50G PAM4 signaling it supports 2 channels with up to 100G and will be backward compatible with both SFP+ modules and cables along with new SFP-DD double density products. For use in data centres, the standard offers a cheaper option for high pert density break-out applications. With a data rate of 100G it will eventually be able to support 200G with two 100G PAM4 channels and supports distances of between 500m and 10km.

Whilst GBIC, XENPAK, X2 and XFP are now almost obsolete and form factors of the past, SFP and SFP+ still remain as popular as ever. CWDM transceivers are now offered from 1G to 100G with new wavelengths and distances under development all the time and we can now reach 400G and 800G on QSFP-DD, OSFP and SFP-DD. Form factors are continuously being updated for longer distances, additional wavelengths and higher bitrates. Watch this space for the latest in optical transceiver form factors and developments!

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Learn more about selecting SFP transceivers and applications where they are used >


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