OPTICAL TRANSCEIVERS IN FIBER NETWORKS

Fiber optic networks evolved in late 20th century to cater the increasing demands of bandwidth and to allow faster communication networks. Fiber optic Transceivers use a laser as light source which transfer signals through one or more glass strands (fibers). Optical Transceivers have several advantages over the copper/electrical wire communication such as increased communication distance, more bandwidth and higher data rates. Apart from the enormous advantages that optical Transceivers offers, a few extra measures need to be taken as well, to ensure a reliable and robust network, which includes taking care of fiber bends, coupling, splicing and the use of appropriate Transceivers to communicate over the fiber optic network. Fiber optic Transceivers are available in various types and form-factors and evolved from the Gigabit Interface Converter, commonly referred to as GBIC, over Small Form-Factor Pluggable, commonly referred to as SFP up to the C Form-Factor Pluggable, commonly referred to as CFP.

 

All of the above mentioned Transceivers provide the interface for the fiber optic to be terminated on the communication equipment (like a switch or router). The choice of the Transceiver depends on various factors which include:

 

• Length of the communication link

• Type of fiber optic cable being used, i.e., single-mode or multi-mode

• Type of slot on the communication equipment

• Bandwidth of the communication link

 

Let us dig deeper into the evolution of the fiber optic Transceivers in the sections ahead.

 

GIGABIT INTERFACE CONVERTER (GBIC) TRANSCEIVER

The GBIC Transceiver was first introduced and standardized in 1990 by the Small Form-Factor Committee (SFF Committee). The primary reason to develop such a Transceiver was to enable the use of fiber optic cables to connect two or more communication devices and allow more bandwidth and longer distance direct links. GBIC Transceivers usually provide up to 1Gbps duplex bandwidth over a single link, although it has been tested for speeds up to 2.5Gbps.

 

GBIC Transceivers commonly use the SC connector to terminate the fiber optic cable. GBIC Transceivers are also available for 1000BASE-T to terminate the common twisted pair copper cables. One of the main features of GBIC is that it is hot-swappable, i.e., one does not need to power off the communication equipment to insert or remove the GBIC. This allows the communication network to be always-on despite new links being added on it.

 

The dimensions of the GBIC Transceiver as defined by the SFF Committee standard document are 57.15mm x 12.01mm x 30.48mm (L x H x W). The GBIC slot in the communication equipment is also designed keeping the mentioned dimensions in view.

 

SMALL FORM-FACTOR PLUGGABLE (SFP) TRANSCEIVER

SFP Transceivers were the next step in the development of fiber optic Transceivers, this one was also developed as a standard by the SFF Committee in 2001. A SFP Transceiver is much smaller in size as compared to its predecessor. The size of the SFP slot in a communication equipment is somewhat comparable to the normal electrical Ethernet port. Dimensions given in the SFF Committee standard document are given in the following table:

 

Transceiver width, front 13.7 mm

Transceiver height, front 8.6 mm

Transceiver width, rear 13,4 mm

Transceiver height, rear 8,5 mm

Transceiver overall length 56,5 mm

 

It is necessary to mention here that several variants of SFPs have been developed to support higher bandwidth using the similar form-factor. In between SFP+, XFP, XENPAK, X2 are Transceivers that supports 10Gbps duplex link, QSFP Transceivers support up to 40Gbps links with a little larger size than the SFP and SFP+.

 

C FORM-FACTOR PLUGGABLE (CFP) TRANSCEIVER

To meet the ever-growing demand for higher speed communications, engineers started working on developing a Transceiver that could support 100Gbps and higher bandwidths. In 2009, CFP MSA came out with a new standardized Transceiver called CFP which could support 100Gbps traffic. A CFP module has the dimensions of 144.8mm x 82mm x 13.6mm (LxWxH).

 

A CFP Transceiver supports up to 10km link length on single-mode optical fiber cables and up to 150m on laser optimized multi-mode optical fiber cables. Variants of CFP Transceivers have also been developed as standards, CFP2 supports up to 100Gbps with a smaller form-factor and CFP4 supports up to 100Gbps with form-factor similar to QSFP Transceivers.

 

CONCLUSION

In light of the above mentioned details about the advancement and development of the fiber optic Transceivers, it is imperative that the trend of faster communication speeds and smaller form-factors will continue in future. Today, every other person has a smart-phone, a tablet PC, a laptop and a desktop computer which all connect to some kind of network, even the wrist watches and televisions connect to internet these days. This enormous growth in the internet’s traffic has produced the need for this development which we are seeing today in fiber optic networks. It is in near future that the current technology we have might not be enough to support the demands of the next generation smart devices, so the development and research is continuing at an even faster pace to cope up with the advancement in technology.