With the great popularity of optical links in the last few years, the main part of them is currently based on modern single-mode fibers. However, both single-mode and multimode fibers are divided into many types/categories that comply with established standards and factory specifications. Basic issues connected with two kinds of optical fibers are brought up in the article Multimode and single mode fiber-optic cables.
The specifications of various types and categories of the fibers are contained in the standards set by international organizations. In addition, there are numerous factory standards/specifications used on local markets.
Terminology and classification
An organization responsible for international standardization in the field of fiber-optic communications is International Electrotechnical Commission Technical Committee 86 (IEC TC86) that has defined the following series of types:
  • Multimode fibers, e.g. A1a, A1b, A1d..., further divided into groups (e.g. A1a.1...),
  • Single-mode fibers, e.g. B1, B4, B6...
However, more popular markings are based on shorts of the fiber kinds:
  • OM - Optical Multimode
  • OS - Optical Singlemode
    The examples are: OM1, OM2, OM3, OM4, OS1, OS2. The specifications defining specific transmission parameters of the fibers will be presented later in the text.
    The OM markings have been widely adopted, in contrast to OS ones. In the case of single-mode optical fibers the more common names are those used by another international organization, the ITU (International Telecommunication Union), specifically by the department dedicated to standardizing telecommunications solutions (ITU-T).
    ITU-T recommendations are are widely known and used.
    "Transmission media and optical systems characteristics" are covered by G.600-G.699 series, optical fibers are described in the G.650-G659 range. Each recommendation is for a specific type of fiber.
    Selected standards and recommendations
    Below there is a summary of selected standards for fiber optics.
    ISO/IEC standards:
    • IEC 60793 parameters of optical fibers and and cables:
      • IEC 60793-2-10 - applicable to multimode optical fiber types A1a, A1b, and A1d
      • IEC 60793-2-50 - applicable to single-mode 9/125 optical fiber types B1.1, B1.2, B1.3, B2, B4, B5
    • IEC 60794-2 - requirements for indoor cables
    • IEC 60794-3 - requirements for outdoor cables
    • ISO/IEC 11801 - specifies general-purpose telecommunication cabling systems (structured cabling), including several classes of optical fiber interconnections (OM1 - OM4, with specified minimum modal bandwidth at 850 nm, and OS1, with attenuation max 1 dB/km)

    The table below presents a simplified summary of multimode fiber types defined by IEC standards
    Type Core diameter [µm]
    Min modal bandwidth [MHz • km]
    OFL* EMB**
    850 nm 1300 nm 850 nm
    OM1 50 or 62.5 200 500 -
    OM2 50 500 500 -
    OM3 50 1500 500 2000
    OM4 50 3500 500 4700
    OFL* – OverFilled Launch - standardized fiber bandwidth measurement method where the source launches light uniformly into all modes of the multimode fiber (LED source).
    EMB** - Effective Modal Bandwidth - effective modal bandwidth of center/offset launch (laser source illuminating a small portion of the fiber core).
    The development of multimode fibers is clearly moving in the direction of fibers that can carry more and more data. OM1 enables 10 Gbps data rate over very short distances (up to 33 meters), while OM4 allows for transmission of a 100 Gbps data stream over a distance up to 150 m. However, looking at the contemporary expansion of single-mode fibers, even OM3 and OM4 types will be rarely used.
    ITU-T recommendations:
    • ITU-T G.650.1 and G.650.2 - definitions and test methods for linear, deterministic attributes of single-mode fibers and cables,
    • ITU-T G.651.1 - characteristics of a 50/125 µm multimode graded index optical fiber cable...,
    • ITU-T G.652 - characteristics of a single-mode optical fiber and cable (9/125 μm, four versions: A, B, C, D),
    • ITU-T G.653 - characteristics of a dispersion-shifted single-mode optical fiber and cable (DS-SMF),
    • ITU-T G.654 - characteristics of cut-off shifted single-mode optical fiber and cable (CS-SMF),
    • ITU-T G.655 - characteristics of non-zero dispersion-shifted single-mode optical fiber and cable (NZDS-SMF),
    • ITU-T G.656 - characteristics of a fiber and cable with Non-Zero Dispersion for Wideband Optical Transport,
    • ITU-T G.657 - characteristics of a bending loss insensitive single mode optical fiber and cable for the access network.
    Such a large number of documents is a result of the rapid development of fiber-optic communication due to the high demand for fast, long-range links. Today, single-mode fibers are generally cheaper than multimode fibers. The future belongs to this kind of fibers and some exceptions may only exist in local systems, because devices operating with single-mode optical fibers are a bit more expensive.
    ITU-T recommendations are much more restrictive (or precise) than the transmission performance categories defined by the IEC (OS1 and OS2). For example, the specifications required by OS2 are fulfilled by G.652.C fiber, which means that G.652D fiber has even better parameters.
    Single-mode fibers most useful for typical applications are those compliant with the following standards:
    G.652 - defines 4 versions (A, B, C, D). The G.652.C and G652.D variants feature a reduced water peak (ZWP - Zero Water Peak), which allows them to be used in the wavelength region between 1310 nm and 1550 nm supporting Coarse Wavelength Division Multiplexed (CWDM) transmission. G.652.D is Standard Single Mode Fiber (SSMF) dedicated for 10 Gbps and 40 Gbps systems (thanks to reduced polarization mode dispersion - PMD). Currently, it is the most popular optical fiber.
    G.655 - defines an optical fiber with performance specified at 1550 nm and 1625 nm with a non-zero chromatic
    dispersion slope in these wavelength regions. This kind of optical fiber can support long-haul systems using Dense Wavelength Division Multiplexed (DWDM) transmission in 1530 nm to 1625 nm wavelength window.
    G.656 - optical fiber dedicated for use in broadband systems using both DWDM and CWDM, intended to operate in 1460 nm to 1625 wavelength window.
    G.657 - defines optical fibers that produce lower levels of attenuation caused by bends. The minimum bending radius has been reduced to 15-5 mm (depending on version). G.657A fiber is compatible with G.652 fibers, G.657.B versions do not provide 100% compatibility with the other fibers, however have unique mechanical characteristics suitable for the most demanding installations.
    How to compare all of the existing standards and recommendations?
    ITU-T recommendations are based on IEC standards, however there may be slight differences in some versions.
    It is worth mentioning about another organization that associates a considerable part of telecommunications industry - Telecommunications Industry Association (TIA). The activity and documents of the organization are best known in the U.S., some standards are published earlier than in Europe.
    Some comparisons:
    Multimode fibers:
    OM1 – 62,5/125 – IEC60793-2-10 A1b – TIA 492-AAAA
    OM2 – 50/125 – IEC60793-2-10 A1a.1 – G.651.1 – TIA 492-AAAB
    OM3 – 50/125 – IEC60793-2-10 A1a.2 – G.651.1 – TIA 492-AAAC
    OM4 – 50/125 – IEC60793-2-10 A1a.3 – TIA 492-AAAD
    Single-mode fibers:
    G.652A, B – 9/125 – IEC60793-2-50 B1.1
    G.652C, D – 9/125 – IEC60793-2-50 B1.3
    G.655 – 9/125 – IEC60793-2-50 B4
    G.657A – 9/125 – IEC60793-2-50 B6_a1
    G.657B – 9/125 – IEC60793-2-50 B6_a2

    Parameters of selected single-mode fibers
    Fiber type
    G.652.C G.652.D G.655 G.657.A (1)
    Detail Value
    Mode field diameter Wavelength 1310 nm 1310 nm 1550 nm 1310 nm
    Range of nominal values 8.6-9.5 μm 8.6-9.5 μm 7-11 μm 8.6-9.5 μm
    Tolerance ±0.6 μm ±0.6 μm ±0.7 μm ±0.4 μm
    Cladding diameter
    Nominal 125.0 μm 125.0 μm 125.0 μm 125.0 μm
    ±0.1 μm ±0.1 μm ±0.1 μm ±0.7 μm
    Core concentricity error Maximum 0.6 μm 0.6 μm 0.8 μm 0.5 μm
    Cladding noncircularity Maximum 1.0% 1.0% 1.0% 1.0%
    Cable cut-off wavelength Maximum 1260 nm 1260 nm 1450 nm 1260 nm
    Macrobend loss Radius 30 mm 30 mm 30 mm 10 mm
    Number of turns
    100 100 100 1
    Maximum at 1550 nm 0.1dB 0.1dB 0.1dB 0.75 dB
    Maximum at 1625 nm - - - 1.5 dB
    Proof stress Minimum 0.69 GPa 0.69 GPa 0.69 GPa 0.69 GPa
    Chromatic dispersion coefficient λ0min 1300 nm 1300 nm - 1300 nm
    λ0max 1324 nm 1324 nm - 1324 nm
    S0max 0.092ps/nm2• km 0.092ps/nm2• km - 0.092ps/nm2• km
    Attenuation coefficient* Maximum at 1310-1625 nm 0.4 dB/km 0.4 dB/km - 0.4 dB/km
    Maximum at 1383±3 nm 0.4 dB/km 0.4 dB/km 0.4 dB/km -
    Maximum at 1550 nm 0.3 dB/km 0.3 dB/km 0.35 dB/km 0.3 dB/km
    Maximum at 1625 nm - - 0.4 dB/km -
    PMD coefficient M 20 sections 20 sections 20 sections 20 sections
    Q 0.01% 0.01% 0.01% 0.01%
    Maximum PMDQ 0.5 ps/√km 0.20 ps/√km 0.20 ps/√km 0.20 ps/√km
    *Attenuation coefficient should be measured only for longer sections of fibers (shouldn't be measured using e.g. patch cords).
    The fiber most commonly used in today's systems is G.652.D, due to its versatility and price. Some standards, such as G.653, quickly ceased to be used, due to application costs and the limitations of the physical properties of the fiber.