Tutorial on filterless optical networks [Invited]

Abstract

The recent acceleration in fiber-to-the-home deployment worldwide along with the emerging 5G communications are pressuring network operators to enhance their networks to serve these new deployments. Hence, operators are seeking new high-capacity optical-network architectures, while averting excessive capital and operational expenditures. Filterless optical networks (FONs), by replacing costly wavelength selective switches in switching nodes with passive optical power splitters/combiners, currently represent a prominent candidate for cost-effective optical-network deployment. In this tutorial, we provide an overview of the architecture and the design issues of FONs when deployed in core and in metro networks. We also perform a techno-economic study to quantify the economic benefits of FONs, comparing their cost to that of state-of-the-art filtered optical networks, and we discuss how several networking problems such as resource allocation, network slicing, and protection are tackled in the context of FONs. Finally, we present our vision of how research on FONs will evolve in the coming years.

Metropolitan Optical Networks: A Survey on New Architectures and Future Trends

“…However, to change from CWDM to DWDM, it is enough that the provider changes some equipment to support many channels with less granularity [34], [46]. Besides, DWDM is especially used in filterless networks [12], [37], [47]. In WDM networks, in order to meet a connection demand, it is necessary to solve the problem of routing and wavelength assignment (RWA) [48].…”

“…The differences between a converter and optical filter, highlighted in the Subsection II-B2 is that, while an OEO signal converter transforms an optical signal to an electronic one, as a way to regenerate it, and then converts it back into an optical signal so that it is possible to activate a laser transmitter capable of emitting at the desired wavelength [5], [8], [63], an optical filter is a device that allows the selection and passage of a specific portion of the spectrum while blocking the unselected part [12], [64]. A scheme of transceiver is shown in the Figure 4.…”

“…In [12], [89], the main restrictions for using filterless architectures are highlighted, for example: (i) is the range of the transmission system used that will decide the maximum distance between the root and a leaf, in the case of tree topology, or the maximum distance between the two ends in the case of chain topologies; (ii) as the transmission is of the broadcast-and-select type among all nodes, the capacity of the system limits the maximum number of wavelengths per fiber; (iii) wavelength reuse limit in the "drop-and-continue" architecture of the line system, which leads to the accumulation of Amplified Spontaneous Emission (ASE) and creates unfiltered channels. As these problems are more present in long-distance systems, the literature has shown that in the metropolitan network environment, and with the implementation of coherent technology, it has been possible to achieve more efficient and low-cost solutions.…”

“…Filterless Optical networks (FON) are a type of network that does not have filters installed on the switching nodes, thus they can't separate (or block) parts of the transmitted signal. As filters are one of the elements that most increase the cost of the network, this type of solution has been in evidence for the metro scenario, as highlighted in [12]. But the authors point out that removing filters can result, over time, in higher absolute expenses on transponders.…”

“…The recent literature tutorial and surveys proposes various solutions for traffic engineering problem in optical networks [12], [10], [16], [17]. While [10], [16], [17] are more generic and do not focus exclusively on MON, [12] presents a technical-economic analysis and discusses the impacts on FON considering the instantiation of virtual networks, protection and survivability.…”