Fiber Optic Gigabit Ethernet Standards

Fiber implementations of Gigabit Ethernet are specified in IEEE 802.3z and IEEE 802.3ab and define the common twisted-pair copper 1000BASE-T interface type. Gigabit Ethernet is also refered to as 1000BASE-X. The "X" signifies a physical layer based on the ANSI X3.230 Fibre Channel standard.

IEEE 802.3z Standard

The IEEE 802.3z standard includes 1000BASE-SX transmission over multi-mode fiber (MMF), 1000BASE-LX transmission over single-mode fiber (SMF), and the nearly obsolete 1000BASE-CX for transmission over balanced copper cabling. The standard uses 8B/10B encoding, inflating the line rate by 25%, from 1000 Mbit/s to 1250 Mbit/s. The symbols are then sent using NRZ, as 8B/10B mapping already handles the DC balancing properties of the signal (compare to 1000BASE-T).

1000BASE-SX
1000BASE-SX is a fiber optic gigabit Ethernet standard. It operates over multi-mode fiber using a 850 nanometer, near infrared (NIR) light wavelength. The standard specifies a distance capability between endpoints of 220 m over 62.5/125 µm fibre although in practice, with good quality fibre and terminations, 1000BASE-SX will usually work over significantly longer distances. Modern 50/125 µm fibres can reliably extend the signal to 500 m or more. This standard is highly popular for intra-building links in large office buildings, colocation facilities and carrier neutral internet exchanges. Typical optical power parameters of SX interface: maximum mean output power = -5 dBm; stressed receiver sensitivity = -14 dBm.

1000BASE-LX

1000BASE-LX is a fiber optic gigabit Ethernet standard, using a long wavelength laser (See IEEE 802.3 Clause 38). Signaling speed 1.25±100 ppm GBd, wavelength 1270 to 1355 nm, RMS spectral width (max) 4 nm. Typically, GbE lasers will be specified as having a 1300 or 1310 nm wavelength.

1000BASE-LX is specified to work over a distance of up to 2 km over 9 µm single-mode fiber. In practice it will often operate correctly over a much greater distance. Many manufacturers will guarantee operation up to 10 or 20 km, provided that their equipment is used at both ends of the link. 1000BASE-LX can also run over multi-mode fiber with a maximum segment length of 550 m. For any link distance greater than 300 m, the use of a special launch conditioning patchcord may be required. This launches the laser at a precise offset from the center of the fiber which causes it to spread across the diameter of the fiber core, reducing the effect known as differential mode delay which occurs when the laser couples onto only a small number of available modes in multi-mode fiber.

1000BASE-ZX And 1000BASE-LH
1000BASE-ZX and 1000BASE-LH are non-standard but industry accepted terms to refer to gigabit Ethernet transmission using 1550 nm wavelength to achieve distances of at least 70 km over single-mode fiber.

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