A passion for the metro | Fiber systems

Panelists from Polimi, CTTC, TUE and Carlos III University of Madrid give their point of view on the future multi Tb / S metro network

The Passion project was set up to create a platform based on photonic technologies that will support the development of the future metropolitan communications network. Funded by the European Horizon 2020 program, its objective is to provide innovative transmission, detection and routing solutions, and a new network architecture to ensure a transmission rate of more than 100Tb / s per link and a switching capacity. of more than 1Pb / s per node. .

In a recent webcast, four panelists discussed the project’s work in developing innovative photonic devices, as well as a fiber-optic network infrastructure for the future metro network.

Module behavior
Pierpaolo Boffi, associate professor at Politecnico Di Milano (Polimi) revealed how the group developed a VCSEL-based transmitter module (TX) for multi-terabit metro networks. He explained, “The Passion approach is based on the expectation of low cost, energy efficient and directly modulated sources such as VCSELs, and their cost advantages are well known. Today, multi-mode GaAs VCSELs are widely used by ISPs for data communications. ‘

The VCSELs used for this project are however indium phosphide (InP), which can operate in a single mode and is characterized by C-band emission. These types of VCSELs can be modulated directly with a multi-level modulation format. such as PAM4, or a multicarrier modulation format such as DMT. “DMT is a very promising modulation format,” he said, “because it can increase the transmission rate of VCSEL. We demonstrate a capacity of over 50 Gb / s per VCSEL. ‘

40 VCSELs covering the C band have been integrated into a single ASIC silicon photonic platform to achieve 2 Tb / s for the transmitter module, considering a capacity of 50 Gb / s per VCSEL. “This 2TB / s module is the cornerstone of the Passion approach,” said Boffi. “We achieved low loss and low crosstalk through SOI coupling between the silicon substrate and the waveguide, exploring a reflective mirror greater than 45 ° to maximize the coupling between the VCSEL emission and the waveguide. ‘silicon waves. “

The modular approach meant that several identical TX modules could be used to build a super-module to increase capacity. “By combining four of these identical modules,” said Boffi, “we can achieve a super-module with 160 wavelength-division multiplexing (WDM) channels corresponding to 160 VCSEL with a granularity of 25 GHz. To realize a transmitter, we have activated the capacity of 8Tb / s and we can also exploit the multiplexing by division of polarization by combining the outputs of two identical super modules to reach 16Tb / s. ‘

Building blocks
Svaluto Moreolo, Principal Investigator at the Catalan Telecommunications Technology Center (CTTC) discussed the group’s work in producing a variable bandwidth / bit rate transceiver (S-BVT). “As Pierpaolo said in her previous speech,” she explained, “the approach we use is modular. It is important to use the building blocks of Passion technologies and devices, and that it This is a paid and license-based module activation.

The S-BVT uses a modular architecture controlled by a software-defined network (SDN), with directly modulated (DM) VCSELs. On the receiver side, coherent receivers were selected with tunable local oscillators. It has full digital signal processing (DSP) and spectral manipulation, said Moreolo, “to the DSP that can be applied and also considering the different contribution of the streams generated using different wavelengths. VCSEL operating mode “.

Adaptive multicarrier modulation (MCM) can be used at DMT / OFDM with a power load, allowing a subwavelength at the MCM subcarriers to help optimize capacity. The target capacity per stream was 50 Gb / s with VCSELs above 18 GHz. Moreolo added that an SDN controller will be used to program and configure the multi-terabit connection in metro networks, and it is through this that the S-BVT will be configured.

On the knots
Nicola Calabretta from Eindhoven University of Technology (TUE) discussed Passion modular network nodes based on integrated photonic switches. He explained, “Next generation networks, especially metro networks, are shifting their network density from 5G to 6G, and will therefore require extreme device densities, higher volume and dynamic traffic, higher data rates. very high data, lower latency and lower power efficiency. ” A large number of nodes are required for this interconnectivity and these are divided into an aggregation layer and a core layer.

Looking at next generation networks with edge computing nodes, there are attributes like telecom and data convergence for a metro access node, especially at the edge node level. It will also need varying bandwidths to cope with dynamic traffic. Its latency sensitivity means it should be fast switching and a large amount of nodes are needed for scalability. Passing through the central node of the metro, there is more static aggregate traffic, Calabretta said, so the speed range is not that critical. “But the capacity will be several hundred terabits per second”, which reiterates the demand for a modular and paid solution. Since the metropolitan core nodes have such a capacity, the group used multi-core fiber, which enters the node and goes through pulse spacing modulation (PSM) to a space switch. Calabretta explained, “The space switch has two functions, one is to direct traffic as it passes to the exit, but some of the traffic will be dropped, in a direction to the aggregation and disaggregation switch. In this case, the programmability allows us to redirect some of that traffic. We are trying to merge the traffic that needs to go in the same direction because at the next node a bypass photonic space switch allows us to send a signal directly to the express port and ensure very low losses. ‘

Keep it simple
Looking at the metro access node, Calabretta reiterated the need for simplicity and low cost. “We used a simple two-degree ROADM for add / remove multiplexing, which is capable of dynamically adding or removing traffic. The difference is that we use a solid state optical amplifier as the key part for fast operation. ‘ The modular and integrated photonic wavelength selective switches (WSS) were to be designed and built in accordance with the aforementioned specifications, one based on hybrid photonic integration and photonics over silicon (SiPh) and InP, and the other as a fully monolithic integrated WSS InP. Hybrid WSS has been found useful to exploit co-integration with high performance passive (de-) multiplexer in SiPh and InP semiconductor optical amplifiers for on-chip switching and amplification. Monolithic WSS, on the other hand, provided lossless operation, offering potential applications for edge computing interconnect and intra-data center networks.

The results
David Larrabeiti, professor at Carlos III University in Madrid, explained how the metro network exploits Passion technologies from an operator’s point of view, moving away from the traditional approach, which uses a proliferation of transmitters- receivers in Internet / WDM protocol. “SBVT Passion offers a different point of view,” he said. “We have a device that can simultaneously make connections to different nodes at the same time. Just with one transceiver, you can do it all. Basically what you get is a network made up of the ROADM Passion and you can interconnect the edge with an all-optical connection. It is very interesting in terms of cost.

Larrabeiti gave deployment cost scenarios. The first is with 600 Gb / s per HL4 node and a 15% CAGR. In this case, while the traffic increases by 15 percent each year, the capex increases by 7.8 and 7.4 percent for two classic IPs on WDM with grooming and bypassing respectively. The Passion solution, hoverver, only increases the capex at a rate of 4%. The other scenario is with 150 Gbps per HL4 node and a 40% CAGR.

In this case, the Passion solution only increases the capex at a rate of 7.6%, compared to the two classic IP on WDM, which see an increase of 15.2 and 13.72% respectively. “In conclusion,” said Larrabeiti, “Passion SBVT technology is an ideal new concept for exploiting the hierarchical nature of traffic in the metro network. 90% of the traffic goes from the periphery to the heart of the metropolitan networks. The license-based pay-as-you-grow system provides operational savings and there are potential global deployment savings for operators of over 40 percent.

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