Fiber types

Fibers are classified as multimode fibers and single-mode fibers.

  • Multimode fibers

    Multimode fibers (MMFs) have thicker fiber cores and can transport light in multiple modes. However, the intermodal dispersion is greater and worsens as the transmission distance increases.

    Multimode fibers can be classified into multiple grades according to their diameters and modal bandwidth. For more information, see Table 2. The modal bandwidth of a multimode fiber is determined by the expression of the maximum modulation frequency pulse that can pass a fiber × the fiber length. The modal bandwidth is a comprehensive index reflecting the optical characteristics of a multimode fiber.

    International Telecommunication Union (ITU) defines multimode fiber types in its G series standards. The commonly used multimode fiber is defined in the ITU G.651 standard. The G.651-compliant fiber transmits light at the wavelength range 800 nm to 900 nm or 1200 nm to 1350 nm.

    Table 3: Multimode fiber grades
    Fiber mode Fiber grade Fiber diameter (μm) Modal bandwidth at 850 nm (MHz*km)
    Multimode fiber OM1 62.5/125 200
    OM2 50/125 500
    OM3 50/125 2000
    OM4 50/125 4700

    Other factors that influence the transmission distance of multimode fibers include interface type, central wavelength, and fiber grade. The modal bandwidth values shown above are for the fiber grades listed. There are multimode fibers that have different modal bandwidth characteristics and do not necessarily match the OM1 - OM4 grades.

    Table 4: Multimode fiber specifications
    Interface types Central wavelength (nm) Fiber grade Transmission distance
    1000BASE-SX 850 OM1 < 275 m (902.23 ft)
    OM2 < 550 m (1804.46 ft)
    10GBASE-SR 850 OM1 < 33 m (108.27 ft)
    OM2 < 82 m (269.03 ft)
    OM3 < 300 m (984.25 ft)
    OM4 < 400m (1312.34 ft)
    10GBASE-LRM 1 1310 OM1 < 220 m (721.78 ft)
    OM2 < 220 m (721.78 ft)
    OM3 < 220 m (721.78 ft)
    OM4 < 220 m (721.78 ft)
    SMF <300m (987.25 ft)
    1

    LRM technology requires a PHY behind the SFP port. Not all 10G SFP (or higher) can support the use of a 10G LRM transceiver. Check the compatibility chart for your switch series to see if 10G LRM is supported.

  • Single-mode fibers

    Single-mode fibers (SMFs) have a small core size, typically 9 μm or 10 μm, and can transmit light in only one mode. Single-mode fibers suffer little intermodal dispersion and are suitable for long-haul communication. Single-mode fibers transmit light at the central wavelength of 1310 nm or 1550 nm.

    Telecommunication Industries Alliance (TIA)/Electronic Industries Alliance (EIA) defines that single-mode fibers use yellow outer jackets with the mark "SM".

    ITU defines single-mode fiber types in its G series standards. The most commonly used single-mode fibers are defined in ITU G.652 and G.655 standards. The following table describes features of the G.652 and G.655-compliant fibers.

    Table 5: Features of G.652- and G.655-compliant fibers
    Single-mode fiber type Wavelength (nm) Features Applications
    G.652-compliant fiber (standard single-mode fiber)

    1260 to 1360

    1530 to 1565

    		Zero dispersion at 1310 nm Connecting transceiver modules with a central wavelength of 1310 nm or 1550 nm.
    G.655-compliant fiber (non-zero dispersion shifted fiber) 1530 to 1565 Near-zero dispersion around 1550 nm For 1550 nm wavelength-division multiplexing (WDM) transmissions.