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Types and characteristics of optical fibres

Types and characteristics of the optical fibres

G.652 – Standard single-mode fibre

These fibres are widely deployed in the public networks and they represent a large majority of fibres that have been installed.

A single-mode optical fibre with zero-dispersion is a key foundation to the modern optical networks that are the basis of all modern telecommunications, it is classified by ITU-T G.652 standard. This fibre is widely used and optimized for the transmission with the wavelength around 1310 nm. The upper limit of the wavelength L-band is 1625 nm. To test the fibre to macrobending, the mandrel with the radius 30 mm. is used.  

According to the standard the fibres have four categories A, B, C, D.

The fibre G.652. А meets the requirements applicable for informational flows transmission of the level STM 16, - 10 Gbit/s (Ethernet) for the distance up to 40 km., in accordance with G.691 and G.957 recommendations, and also level STM 256, according to G.691.

 

The fibre G.652. B meets the requirements applicable for informational flows transmission of the level STM 64 in accordance with G.691 and G.952 recommendations, and also level STM 256, according to G.691 and G.959.1.

G.652.C and G.652.D fibres enable the data transmission in the wider wavelength range from 1360 to 1530 nm,, they are also characterized by low water peak (LWP) (water peak of the single-mode fibres is located in the wavelength range from 1300 nm to 1550 nm). Other characteristics of the categories C and D are equal to those of G.652.A and G.652.B.

G.652.A/B is equivalent to OS1 (ISO/IEC 11801 classification), G.652.C/D  is equivalent to OS2.

 

When the higher data transmission speed is required and the distance exceeds 40 km., the use of the fibre G.652 leads to the disagreement between the performance efficiency and single-mode fibre standards and as a result, it requires complex endpoint equipment.

G.655 – Single-mode non zero-dispersion shifted fibre (NZDSF)

Single-mode non zero-dispersion shifted fibre is optimized for the transmission of different wavelengths (Wavelength Division Multiplexing WDM and Dense Wavelength Division Multiplexing DWDM). The “Corning” fibre has a double acrylate coating which provides high efficiency and reliability. The outer coating diameter is 245 Mcm.

NZDSF is especially designed for trunk optical fibre lines and global communicational networks, which use DWDM-technology.

The recommendations divide the fibres into three categories – A, B, C, these categories have different polarization mode dispersion coefficients, chromatic dispersion and wavelength range.

Characteristics of the G.655.A optical fibres enable to use them in the single-channel and multi-channel systems with optical amplifiers (recommendations G.691, G.692, G.693) and in optical transport networks (recommendation G.959.1). The operating wavelengths and fibre dispersion of this category limit the input power thus restricting their use in the multi-channel systems.

The optical fibres G.655.B are similar to G.655.A. But depending on the operating wavelengths and dispersion characteristics, the input power can be higher than for G.655.A. The operating distance of 400 km for STM-64 level systems can be provided according to the requirements applied to Polarization Mode Dispersion.

The G.655.C fibres are similar to G.655.B, but more stringent requirements regarding Polarization Mode Dispersion enable to use STM-256 level systems with G.655.C optical fibres (G.959.1 recommendation) either to increase the transmission distance of the STM-64 systems.

G.657 – Bend-insensitive single-mode optical fibre

The bend-insensitive single-mode optical fibreG.657 is widely implemented in the indoor cables installed in the networks of multi-story building, business complexes etc. The fibre G.657.A in it’s optical characteristics is absolutely similar to the standard fibre G.652.D, at the same time the fibre G.657.A has a twice less permitted bending installation radii – 15 mm. The fibre G.657.B is used for short distance connections and has extra low bending losses.

Single-mode optical fibres with low bending losses are designed for the FTTH networks of the multi-story buildings, the advantages of these fibres are revealed in the restricted space. The operating rules for G.657 fibre is almost identical to those of the copper-core cable.

The fibre G.657 is divided into categories A and B, the difference among them is in the core diameter and the minimum bending radius performance.

The core diameter for G.657.A is from 8,6 to 9,5 µm, the core diameter for G.657.B is from 6,3 to 9,5 µm.

 

 

The standards for macrobending losses were significantly tightened since this parameter is crucial for G.657:

Ten turns of the fibre G657.A about the mandrel with the radius 15 mm should not exceed the attenuation coefficient value of 0,25 dB at the wavelength 1550 nm. A single turn of the same fibre about the mandrel with the diameter 10 mm should not exceed the attenuation coefficient value of 0,75 dB, providing that the other parameters are not changed.

Ten turns of the fibre G657.B about the mandrel with the radius 15 mm should not exceed the attenuation coefficient value of 0,03 dB at the wavelength 1550 nm. A single turn of the fibre about the mandrel with the diameter 10 mm should not exceed the attenuation coefficient value of 0,1 dB, about the mandrel with the diameter 7,5 mm should not exceed the attenuation coefficient value of 0,5 dB

 

Recommendation ITU-T G.657.A determines the priority to compatibility with the ITU-T G.652.D fibres with respect to the functionality.

Recommendation ITU-T G.657.B focuses on the bending insensitivity but not on the compliance with the requirements of G.652 standards.

International organization for standardization (ISO) and International Electrotechnical commission (IEC) issued the ISO/IEC 11801 standard  -  “Information Technology – Generic Cabling for Customer Premises”.

The standard determines the structure and requirements for the implementation of the universal cable network as well as requirements for the performance of the individual cable lines.

The standard defines several classes of optical channels/links for Gigabit Ethernet (similar to copper lines categories).

Class

ММ-channel attenuation (dB/km)

SM-channel attenuation (dB/km)

 

850 nm

1300 nm

1310 nm

1.550 nm

OF300

2.55

1.95

1.80

1.80

OF500

3.25

2.25

2.00

2.00

OF2000

8.50

4.50

3.50

3.50

The second edition of the standard defines three classes of the MM-fibres – OM1, OM2, OM3 and one class of the SM-fibres – OS1. These classes differ in the attenuation coefficient and overfilled modal bandwidth.

Fiber class

Core Diameter, µm

Overfilled modal bandwidth, MHz х km

Effective Laser Launch Bandwidth, МГц х км

 

850 nm

1.300 nm

850 nm

OM 1

50 or 62.5

200

500

N/A.

OM 2

50

500

500

N/A.

OM 3

50

1.500

500

2.000

Guidelines for the fibre type selection

All lines within 275 m can work with the protocol 1000Base-Sx. The length within 550 m can be achieved by using 1000Base-Lx protocol combined with the shifted light input (Mode Conditioning).

Channel class

Fast Ethernet

GigaBit Ethernet

10 GigaBit Ethernet

100 Base T

1000 Base SX

1000 Base LX

10GBase-SR/SW

OF300

OM1

OM2

OM1*, OM2*

OM3

OF500

OM1

OM2

OM1*, OM2 *

OS1 (OS2)

OF2000

OM1

OM2 Plus, ОМЗ

OS1 (OS2)

*  Mode Conditioning

Class OM4 MM-fibre is characterized by the minimum overfilled mode bandwidth of 4700 MHz x km at the wavelength 850 nm (Class OM3 shows the minimum overfilled mode bandwidth value 2000 MHz x km)

OM 1 и OM2 – Standard multimode fibres with the core diameters 62,5 µm and 50 µm respectively

Cables, patch cords and pigtails with multimode fibers of the types OM1 62.5 / 125µm and OM2 50 / 125µm have been used for a long time in the SCS for data transmission at high speed and at relatively long distances, which are required in the trunk lines. The most important operating parameters of the MM-fibers are attenuation and overfilled mode bandwidth. Both parameters are determined for wavelengths of 850 nm and 1300 nm, these lengths are used by the largest part of the active network equipment.

OM4 – “laser-optimized” multimode optical fibre with the core diameter 50 µm

This multimode fibre is especially designed for Gigabit and 10 Gigabit Ethernet networks, the only core diameter available is 50 µm.

OM4 type multimode fibre - is now fully corresponds to modern standards for the optical fibers designed for data processing centers and server groups of the next generation. OM4 optical fibre can be used to build more extended lines in the new generation data transmission networks with the highest transmission performance. This fiber is the result of further optimization of OM3 fibre characteristics, making it possible to achieve the data transmission speed of 10 Gb / s over 550 meters. OM4 fibre types are characterized by higher minimal overfilled mode bandwidth of 4700 MHz/km at a wavelength of 850 nm (compared to 2000 MHz/km OM3 type fibre).