European Terrestrial Fibre Upgrade Tsunami: G.657a Dethrones G.652.d

During most of my telecom career terrestrial long haul fibre was synonymous with the ITU's G652 standard. This is single mode optical fibre that has zero chromatic dispersion at the 1310 nanometer wavelength and good wavelength performance in the 1260 to 1625 nanometer range. This include the O, E, S and workhorse C bands.

G.652d fibre quickly became the de facto standard for long haul terrestrial fibre optic networks. The G.652 standard was introduced in 1984. Its motivation was a dual purpose optical fibre suitable for data centers and long haul. Most optical equipment for internal data center traffic transmitted in the O band, which ranges from 1260 to 1390 nanometers. But long haul traffic faces significant attenuation as distances grow. This required repeaters, another source of capex and opex expense. It was already known that attenuation or the diminishing of light's intensity was minimized in glass at 1550 nanometers. The versatility of the G.652 standard made it hugely popular. It meant one could build a long haul network using the same fibre from end-to-end. This was important at the time because different commercial fibre products were not always compatible. So the market convergence to the G.652 standard simplified purchasing, drove production economies of scale, and made the large scale fibre optic deployments in the 90s and early 2000 era much easier. It became and still is the single most used type of fibre based on global mileage. The standard also required that manufacturers eliminate the so-called water peak in the E band. All glass contains OH ions. These ions are very good at absorbing light in the E band. So the thinking was that eliminating the water peak would free up the E band for use. However, DWDM has up til now has allowed the C band to do all the work. To sum it up, G.652 fibre is reliable, high performance single mode fibre that works fine for most terrestrial applications regardless of distance. It played a crucial in the wave division multiplexing revolution as it is compatible with 1310 nanometer CWDM, but also perfect for C band DWDM.

However, nothing lasts forever. The smarter terrestrial networks are now migrating from the recent G.652 standard, namely G.652d, to G.657. The G.657 standard was motivated by the rise of fibre to the home (FTTH). These deployments required bending fibre, which induces optical loss. Another factor was that FTTH is only economical for customers if optical regeneration can be avoided or minimized in the Last Mile. So minimizing optical loss is essential. Hence the interest and growing deployment of passive optical last mile networks. The G.657a standard meets all the requirements of G.652d, but has ten times better macro bending performance. A macro bend is any bend whose radius exceeds 1 cm. The more severe bending, the more light leaks out of the optical core.