10 Gigabit Ethernet (10GE, or 10GbE) is a group of computer networking technologies for transmitting Ethernet frames at a rate of 10 gigabits per second. Unlike previous Ethernet standards, 10GE defines only full duplex point-to-point links which are generally connected by network switches. Both copper cabling and fiber cabling can be used for 10GbE. Currently, 10GBASE-SR, 10GBASE-LR, 10GBASE-ER, 10GBASE-LX4, 10GBASE-LRM and 10GBASE-ZR are six common fiber cabling technologies for 10GbE, each with different performance capabilities. BASE refers to baseband, meaning that this is an unfiltered line not requiring a digital modulation scheme. In this post, these six kinds of fiber optics will be introduced.
SR stands for short reach. 10GBASE-SR is the original multi-mode optics specification, and is still by far the most commonly used. 10GBASE-SR uses the lowest cost optics (850nm) to support 10GbE transmission over standard multi-mode fiber. The SR standard also supports up to 300 meters using the new 2000MHz/km multi-mode fiber (laser optimized). 10GBASE-SR transmitter is implemented with a VCSEL which is low cost and low power. 10GBASE-SR delivers the lowest cost, lowest power and smallest form factor optical modules. The following picture shows an XFP and an SFP+ transceiver for 10GBASE-SR.
LR stands for long reach. 10GBASE-LR uses higher cost optics (1310nm) than SR and requires more complex alignment of the optics to support single-mode fiber up to 10 km. 10GBASE-LR can reach up to 10km over single-mode fiber. There is no minimum distance for LR, either, so it is suitable for short connections over single-mode fiber as well.
ER stands for extended reach. 10GBASE-ER is a port type for single-mode fiber and uses 1550nm lasers to support 10GbE transmission over single-mode fiber. 10GBASE-ER has a reach of 40 kilometers over engineered links and 30 km over standard links. For 40km, the fiber-optic connection must be an engineered link. Due to the laser power, attenuation is required for links less than 20km long. The 10GBASE-ER transmitter is implemented with an externally modulated laser (EML).
LX4 stands for short reach. 10GBASE-LX4 standard was developed to overcome the distance limitations of SR optics. 10GBASE-LX4 is a port type for multi-mode fiber and single-mode fiber. It uses four separate laser sources, each operating at a different wavelength. 10GBASE-LX4 supports traditional FDDI (fiber distributed data interface) grade multi-mode fiber for distances up to 300 meters using coarse wavelength division multiplexing (CWDM), which lowers the transmission rate of each wavelength. The LX4 standard also supports single-mode fiber for up to 10 km. LX4 is more expensive than both SR and LR because it requires four times the optical and electrical circuitry in addition to optical multiplexers.
LRM stands for long reach multi-mode. 10GBASE-LRM, as the replacement to LX4, will reach up to 220m over standard multi-mode fiber, but without the complexity of the LX4 optics. Instead, a single laser operating at 1310nm is used. This allows LRM optics to be packaged in XFP and SFP+ form factors, like SFP+ transceiver JD093B branded by HP. Using a technology called EDC (electronic dispersion compensation), 10GBASE-LRM can provide a long distance solution based on multi-mode fiber and operates with a single wavelength.
10GBASE-ZR optics can reach up to 80km over single-mode fiber. Due to the very high transmit power, significant attenuation is needed for shorter links. Use of ZR optics should be preceded with an optical power test of the fiber span in question to ensure a problem-free deployment. Interestingly, 10GBASE-ZR is actually not an IEEE standard, though most vendors offer a ZR option.
Different 10GbE fiber cabling technologies have different optical interface standards. Over the years of 10 Gigabit Ethernet’s existence, there have been numerous different form factors to meet different standards. XENPAK, X2, XFP and SFP+ are currently four popular kinds of modules in the market. Several major brands, like Cisco, HP, Juniper, and Finisar, they manufacture these types of optical transceiver modules for 10GbE with high quality. For example, FTLX1471D3BCL SFP+ and FTLX1412D3BCL XFP branded by Finisar are for 10GBASE-LR, and Cisco XFP-10G-MM-SR and Cisco SFP-10G-SR-X are for 10GBASE-SR. Before you choose a transceiver for your 10GbE fiber cabling system, you should get to know more about them and make the proper decision.