The development of communications technology is rapidly changing, optical fiber communications in single-core optical fiber transmission capacity also doubled every 3 to 5 years in the rapid growth of the speed, but the main types of optical fibers for communications and optical fibers of the main transmission index for many years without major changes, for example, the current widespread use of G.652.D optical fibers, the use of which has been nearly 20 years of history.
In recent years, a new type of G.654.E optical fibre has started to be used in some long-distance trunk lines, and has achieved better results. So, what is G.654.E optical fibre and will G.654.E optical fibre replace the traditional G.652.D optical fibre?
History of G.654 fibre
In the mid-1980s, in order to meet the demand for long-distance communications over submarine cables, a pure quartz-core single-mode optical fibre was developed for use at 1550 nm wavelengths, where the attenuation was more than 10 % lower than that of G.652 fibres. This fibre was defined as G.654 fibre, which was then called ‘1550nm single-mode fibre with minimal attenuation’.
In the 1990s, WDM technology began to be used in submarine optical communication systems, WDM technology allows a single optical fibre to simultaneously transmit dozens or even hundreds of optical channels, and with the use of fibre amplifiers, high-power multi-wavelength optical signals are coupled into a single optical fibre, aggregated at a small interface, the optical fibre began to show non-linear characteristics. Due to the nonlinear effect of the optical fibre, when the incoming optical power exceeds a certain value, the transmission performance of the system will gradually decrease with the increase of the incoming optical power, as shown in Figure 1.
Fig. 1 Effect of fibre ingress power on system performance
The nonlinear effect of the optical fibre is related to the optical power density of the fibre core, and when the incoming optical power is unchanged, by increasing the effective area of the fibre and decreasing the optical power density of the core, the impact of the nonlinear effect on the transmission performance can be reduced. Therefore, G.654 optical fibres begin to increase the effective area.
The increase in the effective area of the fibre will lead to an increase in the cut-off wavelength, but the increase in the cut-off wavelength must be controlled so as not to affect the use of the fibre in the C-band (1530 nm to 1565 nm); therefore, the cut-off wavelength of the G.654 fibre is set at 1530 nm. in 2000, the ITU, when revising the G.654 optical fibre standard, changed the name to ‘Cut-off wavelength shifted single mode fibre’.
By now, G.654 optical fibre has two characteristics: low attenuation and large effective area. After that, the G.654 optical fibre used for submarine cable communication is also mainly optimized around the attenuation and effective area, and gradually developed into four subcategories of A/B/C/D.
Characteristics of G.654.E optical fibre
The type of optical fibre in the land trunk transmission line is dominated by G.652.D. With the single carrier rate of the WDM system exceeding 100G, the non-linear effect of the optical fibre on the transmission performance is more and more serious, and the researchers naturally want to transplant the G.654 optical fibre for use in the land long-distance trunk transmission system.
Relative to submarine use, terrestrial G.654 optical fibre macro-bend loss requirements are much more stringent (macro-bend loss and G.652.D consistent), while the effective area of the fibre, attenuation indicators than the submarine with the requirements of a wide range, so that the formation of G.654.E fibre standards. The main transmission metrics for the various subclasses of G.654 optical fibre differ as shown in Table 1.
Table 1 Key transmission metrics for different subclasses of G.654 fibre
Advantages and disadvantages of G.654.E over G.652.D
- Advantages of G.654.E optical fibre
For single-carrier ultra 100G WDM systems, as the single-carrier rate increases, the OSNR tolerance of the system is required to be higher. OSNR is related to the incoming optical power, the attenuation of the optical discharge section, etc. The large effective area and low attenuation characteristics of G.654.E optical fibre can effectively improve the OSNR.
The typical value of attenuation of G.654.E fibre is about 0.02dB/km lower than that of G.652.D fibre, and the attenuation of an 80km-long optical amplification section using G.654.E fibre is about 1.6dB lower than that of G.652.D fibre.
Since the location of optical put stations in the land trunk transmission system is often determined, the enhancement of the optical power of the incoming fibre and the reduction of the fibre attenuation do not significantly reduce the number of optical put stations. In the case that the setup of optical repeater stations remains basically unchanged, the OSNR of G.654.E fibre can be improved by about 3dB compared with G.652 fibre.
- Disadvantages of G.654.E optical fibre
The cut-off wavelength of G.654.E optical fibre is 1530nm, which limits the use of G.654.E optical fibre at wavelengths below 1530nm. Currently, the ultra 100G systems in metro networks using non-coherent technology mostly work near the 1310nm wavelength (O-band), such as the core layer and aggregation layer systems for 5G backhaul, so G.654.E fibre is not suitable for use in metro networks.
The market size of G.654.E optical fibre is far from being comparable to that of G.652.D optical fibre, which also leads to the high price of G.654.E optical fibre. Currently, the unit price of G.654.E bare fibre is about 5 to 10 times that of G.652.D fibre.
Usage scenarios for G.654.E optical fibre
At present, the operators in the inter-provincial and intra-provincial trunk cable construction, the use of G.654.E optical fibre cable length of nearly 15,000 km, the use of the effect of the above analysis is basically consistent. This is enough to show that the necessity of using G.654.E optical fibre in inter-provincial trunk lines.
Compared with inter-provincial trunk lines, the single carrier rate of intra-provincial trunk lines is usually lower, the number of optical amplification segments in the multiplexing section is much lower, and the system’s tolerance requirement for OSNR is correspondingly lower, so the necessity of adopting G.654.E optical fibre in the provincial trunk lines is not high, and it is recommended that G.652.D low-loss optical fibre is used (the unit price of bare fibre is about 1.5 times of that of ordinary G.652.D). However, if G.654.E optical fibre is not applied to the provincial trunk line, subject to the scale effect, the high price of the situation is difficult to change.
In metropolitan area networks, some optical transmission systems use wavelengths within the cut-off wavelength range of G.654.E fibre, so G.654.E fibre is not suitable for use in metropolitan transmission.
Conclusion
Ultra-low loss, large effective area G.654.E fibre can significantly improve transmission performance at 100G, 200G, 400G and higher rates. In the coming years, the new G.654.E fibre is expected to capture a larger application market as data centre interconnections (DCI), metro networks and other long-haul fibre networks continue to be deployed on a large scale.
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