# Optical Technology for NFV Converged Networks
## 6 Conclusions  
The evolution to 5G and beyond promotes novel technologies for the network such as SDN and NFV that allow a decoupling between the hardware resources and the services. This paradigm enables the digitalization of the network and facilitates the creation of services. The low latency requirements of the E2E services has enabled the replacement of big data centers located in regional area with smaller ones located near the access. Hence the access network is evolving in a converged network to support 5G mobile transport, fixed access, and vertical services. This network is typically named as Xhaul. A higher level of automation is required in all segments of the network, which is evolving to a converged network, able to support all service types. These will include the Xhaul segment and will be managed as \"one network\". Optics is the promising technology to meet the requirements of high bandwidth and low latency of 5G and beyond and offer a high level of automation suitable for SDN and NFV paradigm. However, due to the high capillarity of the equipment used in the Xhaul segment, the cost and the size of the optical nodes needs to be reduced, with respect to the case of the metro network segment. Integrated silicon photonics is a promising technology to achieve the cost and power consumption targets in the access segment. This technology was born for data center applications and has now reached a maturity level such to be suitable for telecom applications. De facto the SDN and NFV paradigm for Xhaul represents a concrete business case to push the use of integrated silicon photonics and accelerate the necessary investments to assess its use in the telecom segment. In this paper two main reference architectures for RAN access network are considered: PON and ring topology. Concrete technology solutions based on integrated silicon photonics are described for each architecture, that enable the realization of key optical components such as tunable transceivers and ROADMs with reduced cost and size. Overall, two network scenarios have been considered, such as WDM overlay PON and rings. For DWDM over PON, the use of silicon photonics is essential to realize pluggable transceivers, fully tunable both in transmission and receiver directions. For DWDM ring, the integrated silicon photonics is the key technology to realize a pluggable ROADM supporting 20 bidirectional channels. The main challenges are to realize such equipment have been discussed such as: size, power consumption, and cost to support 20 channels, and be integrable in a suitable form factor. Moreover, for the ROADM the open issue is the use of SOAs which can limit the number of channels.  
The technical analysis carried out in the paper demonstrates the applicability of integrated silicon photonics in telecom applications and highlights the main challenges to be addressed.  
P.I., A.B. ([PERSON]), A.B. ([PERSON]), S.M., M.R., V.S. and F.C.: Writing--original draft, review & editing. All authors have read and agreed to the published version of the manuscript.  
This work has been partially supported by European Commission H2020 5 GPPP 5 Growth project (Grant 856709).  
Not applicable.  
We kindly acknowledge [PERSON] for providing valuable information on the temperature management of the mini-ROADM prototype.  
The authors declare no conflict of interest.