Types Of Fibers:single-mode Optical Fibres

Types of fibers:Single-mode optical fibres:
The ITU-T first single-mode optical fibre and cable: The first single-mode optical fibre was specified in Recommendation ITU-T G.652, Characteristics of a single-mode optical fibre and cable, and for this reason, the ITU-T G.652 fibres are often called, “standard single-mode fibres”. These fibres were the first to be widely deployed in the public network and they represent a large majority of fibres that have been installed. The agreements that led to the first publication of Recommendation ITU-T G.652 formed a key foundation to the modern optical networks that are the basis of all modern telecommunications.
Recommendation ITU-T G.652 describes the geometrical, mechanical, and transmission attributes of a single-mode optical fibre and cable which has zero-dispersion wavelength around 1 310 nm. This fibre was originally optimized for use in the 1 310 nm wavelength region, but can also be used in the 1 550 nm region.
Recommendation ITU-T G.652 was first created in 1984; several revisions have been intended to maintain the continuing commercial success of this fibre in the evolving world of high-performance optical transmission systems.
Over the years, parameters have been added to Recommendation ITU-T G.652 and the requirements have been made more stringent to meet the changes in market and technological demands, and in manufacturing capability. An example is the addition of a requirement for attenuation at 1 550 nm in 1988. In that year, the chromatic dispersion parameters and requirements were also defined.
Some other examples include the addition of low water peak fibres (LWP) with negligible sensitivity to hydrogen exposure and the addition of requirements for PMD. However at the advent of these new capabilities and perceived needs, there was a consensus that some applications would need these attributes
for advanced technologies, bit rates, and transmission distances; however, there were also applications that would not need these capabilities. Therefore, some options had to be maintained.
For this reason, it was agreed to create different categories of ITU-T G.652 fibres. At the present time there are four categories, A, B, C, and D, which are distinguished on the PMDQ link design value specification and whether the fibre is LWP or not, i.e. water peak is specified (LWP) or it is not specified (WPNS), as shown in Table 1.

Table 1 – ITU-T G.652 fibre categories

A non-normative Appendix in Rec. ITU-T G.652 gives representative values of attenuation and chromatic dispersion, which can be taken as the basis for the design of concatenated optical fibre links in accordance with the guidelines outlined in Supplement 39 to the ITU-T G-series Recommendations. The same Appendix gives an indication of the maximum link length at various channel bit rates allowed by different values of Polarization Mode Dispersion (PMDQ).
Category A of ITU-T G.657 (see § 9.2.6) is aligned with all the ITU-T G.652.D values, but has more stringent bend loss requirements.

A dispersion-shifted single-mode optical fibre and cable: The characteristics of a dispersion-shifted single-mode optical fibre and cable are described in Recommendation ITU-T G.653. This fibre has a nominal zero-dispersion wavelength close to 1 550 nm and a dispersion coefficient that is monotonically increasing with wavelength. This fibre was initially developed for use in single-channel high bit rate and long distance transmission in the 1 550 nm region (where the attenuation coefficient is smallest) by shifting the zero-dispersion wavelength of the ITU-T G.652 fibre to around 1 550 nm. This fibre is optimized for use in the 1 550 nm region, but may also be used at around 1 310 nm subject to the constraints outlined in the Recommendation. Some provisions are made to support transmission at higher wavelengths up to 1 625 nm and lower wavelengths down to 1 460 nm.
This was the second Recommendation for single-mode fibre and cable, and it was first created in 1988. The current version contains two categories, A and B, that are distinguished on the PMDQ link design value specification, the description of the chromatic dispersion coefficient, the geometrical parameters and the
macrobending loss specifications.
ITU-T G.653.A fibre is the base category for a dispersion-shifted single-mode optical fibre and cable, and retains the original “box-type” specification for the dispersion coefficient. The zero-dispersion wavelength is within the operating wavelength range from 1 525 nm to 1 575 nm, so that it performs very well for singlechannel systems (e.g. ITU-T G.957, ITU-T G.691 and ITU-T G.693 systems), but non-linear effects are deleterious in dense wavelength division multiplexing (DWDM) systems with an equal channel spacing in the 1 550 nm wavelength region. However, this category is also suitable for multichannel systems (e.g. ITU-T G.692 and ITU-T G.977 systems) with unequal channel spacing in the 1 550 nm wavelength region (for more detail on unequal channel spacing see Recommendation ITU-T G.692). The ITU-T G.653.A fibre is used for multichannel systems with equal channel spacing within the operating wavelength range from 1 565 nm to 1 625 nm where the chromatic dispersion has non-zero values (e.g. ITU-T G.698.1 and ITU-T G.698.2 systems).
Many submarine applications can utilize this category. For some submarine applications, the full optimization can lead to choosing different limits than are found here. One example could be to allow cable cut-off wavelength to values as high as 1 500 nm.

ITU-T G.653.B fibre attributes are similar to those of ITU-T G.653.A fibre, but the more stringent PMD requirement allows STM-64 systems to lengths longer than 400 km and ITU-T G.959.1 NRZ 40G applications. This category defines the chromatic dispersion coefficient requirements as a pair of bounding curves vs. wavelength for wavelengths from 1 460 nm to 1 625 nm. This category may support coarse wavelength division multiplexing applications which do not have significant non-linear impairments.