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With the huge popularisation of fibre optic links over the past few years, modern single-mode fibres have become increasingly common. However, among both single-mode and multimode fibres, there is a range of standards that distinguish them from each other. The basics of fibre modality issues are presented in the library: "Single-mode and multimode fibre - an introduction ".
The differences between fibres are described in standards established by international organisations. In addition, there are manufacturers' company standards on the subject. These are often regarded as binding in local markets.
Terminology and classification
An organization responsible for international standardisation 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 optical fibres - e.g. A1a, A1b, A1d... subdivided into additional groups (e.g. A1a.1...)
- single-mode optical fibres - e.g. B1, B4, B6...
More popular, however, have become the designations for optical fibres that specify their transmission performance categories:
- Category OM - Optical Multimode - for multimode optical fibres
- Category OS - Optical Singlemode - for single-mode fibres
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.
While the IEC naming of multimode fibres (OM...) has been widely adopted, OS names are rarely seen. For single-mode fibre optics, the names used by another international organisation, the ITU (International Telecommunication Union), are more common, with the division dealing with the standardisation of solutions in telecommunications (ITU-T).
ITU-T recommendations are are widely known and used.
In the case of optical fibres, the appropriate group for describing standards on the characteristics of transmission media and photonic networks is G. For recommendations on optical fibre cables and related topics, the range G.650-G659 is provided. Each recommendation refers to a different type of fibre, hence the names of the fibre types are directly derived from the recommendation number.
Selected standards and recommendations
Below there is a summary of selected standards for fiber optics.
ISO/IEC standards:
- IEC 60793 - a standard discussing the parameters of optical fibres, in particular the standards can be distinguished here:
- IEC 60793-2-10 (concerns 50/125 A1a and 62.5/125 A1b multimode fibres)
- IEC 60793-2-50 (applicable to 9/125 single-mode fibre types B1.1, B1.2, B1.3, B2, B4, B5)
- IEC 60794-2 - requirements for equipment for indoor applications
- IEC 60794-3 - requirements for outdoor equipment
- ISO/IEC 11801 - structured cabling for public buildings. Among other things, the standard defines transmission channels and specifies the attenuation per channel expressed in dB for single-mode and multimode fibre categories. The ISO/IEC standard also defines the properties of optical fibres: maximum attenuation and minimum bandwidth defining the cable capacity.
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)
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 - the recommendations concern definitions and ways to test the characteristics of single-mode fibres and cables
- ITU-T G.651.1 - the recommendation concerns the characteristics of 50/125 μm multimode fibre
- ITU-T G.652 - Recommendation applies to 9/125 μm singlemode fibre characteristics, distinguishes 4 fibre versions - A, B, C, D
- ITU-T G.653 - recommendation concerns dispersion-shifted single-mode optical fibre DS-SMF characteristics
- ITU-T G.654 - Recommendation applies to characteristics of cut-off-shifted single-mode optical fibre CS-SMF
- ITU-T G.655 - Recommendation applies to non-zero dispersion-shifted single-mode optical fibre characteristics (so-called non-zero dispersion-shifted single-mode optical fibre NZDS-SMF)
- ITU-T G.656 - recommendation concerns the characteristics of non-zero dispersion single-mode optical fibres dedicated to data transmission using the widest possible bandwidth of the optical spectrum
- ITU-T G.657 - recommendation concerns characteristics of single-mode fibres with reduced bending radius. We distinguish between type A and type B fibres
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.
The ITU-T recommendations are far more restrictive than the transmission performance categories defined by the IEC - OS1 or OS2. For example, G.652.C fibre already meets OS2 (this category cannot be met by fibres complying with G.652A B).
Among the single-mode fibre standards, it is worth focusing on:
G.652 - the standard defines 4 versions of fibre - A, B, C and D. At the moment, the most popular fibre is G.652.D. The other standards have slightly worse wavelength specific attenuation values and polarisation dispersion coefficient PMD. G.652.D is a standard fibre (so-called Standard Single Mode Fiber SSMF), with reduced impact of -OH ion action (ZWP Zero Water Peak), dedicated to 10 Gbps and 40 Gbps systems (due to reduced impact of polarisation dispersion).
G.655 - a fibre dedicated to systems using DWDM in the 3rd transmission window. Non-zero chromatic dispersion coefficient in the whole operating band eliminates non-linear effects having a negative impact on information transmission.
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 - often referred to as improved G.652.D. G.657 fibre - is available in several versions. The main advantage of the fibre is its increased mechanical resistance - the minimum bending radius of this fibre is 7.5-15 mm (depending on the version). Version G.657.A is compatible and can be combined with fibre G.652. Version G.657.B does not provide 100% compatibility with other fibres and therefore cannot be combined with them. However, the mechanical characteristics allow this fibre to be used in very demanding installations.
How to compare all of the existing standards and recommendations?
ITU-T recommendations are based on IEC standards. However, it is not always possible to put an equal signbetween the names of different fibres resulting from documents of different organisations.
It is worth mentioning about another organisation 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) | |
| Attribute | 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 |
| Tolerance | ±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.
