In the state-of-the-art, the access and metro portions of the network are provided by separate systems. As bandwidths grow, this traditional approach of separate access and metro networks will become prohibitively expensive:
- from a capex viewpoint due to the large number of network elements and interfaces to interconnect them;
- from an opex viewpoint due to network design complexity, large number of network elements, large footprint and high electrical power consumption.
A new generation of photonic communication system, which integrates access and metro into one system, has recently attracted the interest of the research community and network operators. These architectures offer the potential to reduce bandwidth transport costs by eliminating the costs of the electronic interface between the access and the outer core/metro back-haul network. In order to achieve this for European national geographies requires a reach of ~100 km from the customer to the ~100 major service nodes in a typical network. The ~100 km reach is necessary to enable full coverage and to allow the option of dual parenting for resilience.
The deployment of point-to-point fibre from each customer to the service node up to ~100 km away would be prohibitively expensive. These architectures, usually called long-reach passive optical networks (PONs) or Super-PONs, will therefore use multi-wavelength, high split PONs to make efficient use of fibre. While the first generations of PONs are now standardized and commercially available, the most advanced of these (GPON and GE-PON) typically offer 2.4 Gbit/s or 1 Gbit/s downstream and ~1 Gbit/s upstream, shared between 32 customers via passive optical splitters and a time-division multiple access (TDMA) protocol, over a reach of up to 20 km. These new architectures aim at a new generation of PON with features totally beyond the capability of today`s PONs:
- bandwidth per customer of up to 10 Gbit/s downstream and 10 Gbit/s upstream each 10 Gbit/s wavelength is shared by up to 512 customers
- significant use of DWDM to provide further fibre efficiency in the metro with up to 32 wavelengths each carrying 10 Gbit/s; the project will therefore take a hybrid WDM/TDMA approach
- all-optical reach of 100 km using optical amplifiers
- no use of optical-electrical-optical conversions at intermediate locations.
In this seminar we will review some of the technical challenges in the physical layer of long-reach PONs and the solutions proposed to overcome them. Our latest experimental and modelling results, obtained also within the IST project PIEMAN (Photonic Integrated Extended Metro and Access Network), will be presented.