A real-time implementation of a coherent optical pluggable module using digital sub-carrier (DSC) multiplexing has recently been demonstrated. Whilst these modules can support traditional point-to-point (P2P) applications, similar to e.g., 400ZR(+) – with at least the same performance, it is the point-to-multi-point (P2MP) functionality that differentiates their capabilities from a single-carrier implementation. The superior performance of coherent transmission and its insensitivity to link effects, in combination with P2MP capability, allows for new network architectures and can dramatically simplify how metro and access networks are designed. The enabling engine is the DSP ASIC, which generates and demodulates the sub-carriers in the digital domain and furthermore, handles P2MP operation-related aspects. Within the DSP, most of the functional blocks are equivalent to its single-carrier counterpart – even the DSP functionality and algorithms are very similar. Just a few additional mechanisms inside the DSP are needed to process DSCs. This paper details the related DSP design and discusses the requirements on the DSP algorithms that accommodate the low per sub-carrier symbol rate and the operation on intermediate digital carriers.

Coherent optical transmission systems using digital sub-carriers are ideal for point-to-multi-point applications. Many functional blocks are similar to the ones of single-channel processors. But, several aspects, specific to digital sub-carriers and point-to-multi-point, need consideration in the DSP implementation.

Metro aggregation is one of the fastest growing segments in telecommunications in terms of data traffic. At the intersection of core and access, where coherent modules compete with direct detection technology, high capacity must be provided at low cost and low power, with enhanced scalability and flexibility. Real-life Telecom Italia Mobile metro aggregation networks are examined and their design and planning optimized. The analysis is supported by techno-economics, which compares two coherent solutions: traditional point-to-point (P2P) and digital subcarrier (DSC)-based coherent modules for P2P and point-to-multipoint transmission. We demonstrate that the greater flexibility of DSC-based coherent modules leads to significant cost savings over a three-phase network deployment.

The various topologies, traffic patterns and cost targets of optical networks have prevented the deployment of end-to-end solutions across multi-domains, and the optimization of the network as a whole. The consequent limitations in flexibility, scalability, and adaptability of optical networks will become increasingly important with new applications, such as 5G/6G. Coherent transceivers based on digital subcarrier multiplexing (DSCM) are proposed to address these current constraints. In particular, DSCM allows (i) the design of high-capacity point-to-point (P2P) and -multipoint (P2MP) optical networks; (ii) simplified aggregation with passive optics; and (iii) connections between low- and high-speed transceivers. Furthermore, DSCM-based networks reduce the number of opto-electro-opto stages, halve the number of bookended transceivers, and provide a better match for existing hub-and-spoke (H&S) traffic patterns in fast-growing and dynamic access/metro segments. A DSCM-based transceiver will pave the way for the deployment of next-generation flexible, adaptable, and scalable software-configurable optical networks. Key steps and elements to realize this solution are laid out, and promising applications outlined. The first real-time experimental results of coherent P2MP transceivers are presented.

Point-to-multipoint (P2MP) optical coherent transceivers, which take advantage of digital subcarrier multiplexing, can greatly simplify design, planning and operations in next-generation high-capacity metro aggregation networks.In this paper, we investigate their utilization over two complex network scenarios: urban/industrial and suburban/rural. We provide evidence that with P2MP technology, it is possible to achieve a 32% Capital Expenditure (CAPEX) savings compared to the use of traditional point-to-point (P2P) transceivers, and 41% in the case of increased aggregation in a short-term scenario.

We propose combining point-to-multipoint coherent transceivers with a hybrid ROADM/filterless line system to enable a flatter IP-architecture for cost-effectively scaling metro-core/access networks. Considering various traffic and link engineering scenarios, we show CAPEX savings exceeding 40%. © 2022 The Author(s)

Coherent technology can be operated with independent digital subcarriers to realize point-to-point and point-to-multipoint optical networks. Enabled by configurable software management, it creates a simple, scalable, low-cost solution, compatible across network, vendors, and generations. © 2022 The Author(s)

We report a live-network demonstration of coherent point-to-multipoint technology for mobile fronthaul applications with total transmission capacity up to 100 Gbps per radio unit and 400 Gbps per hub. We show significant network simplification enabled by coherent technology and Nyquist subcarriers.

A paradigm shift in optical communication networks is proposed, with the introduction of a new ecosystem of devices and components with the capability of transforming current point-to-point optical networks (with their entailed, limiting, electrical aggregation) into flexible, scalable and cost-effective point-to-multipoint networks. In the new architecture, which better aligns with the hub-and-spoke traffic patterns observed in today's metro and access network segments, interoperability across a variety of transceivers operating at different speeds is achieved using individually routed, digitally generated subcarriers. The first comprehensive demonstration of the technical feasibility of the proposed point-to-multipoint architecture based on digital subcarrier multiplexing is presented, along with the remarkable cost savings and simplification of the network it enables.

A coherent MODEM is implemented with FEC payload and checksum distributed between two PM-QPSK optical channels spaced at 200 GHz. Real-time experiments verify PDL and PMD penalties are 40-50% higher without FEC gain sharing.

We present a 500 Gb/s, PM-QPSK Photonic Integrated Circuit (PIC) based MODEM, software configurable into 250 Gb/s TCM mode, as a flexible optical network building block, operating over a 6000 km link with flex ROADMs.

We demonstrate 100-Gbps tunable transmitter (Tx) and receiver (Rx) photonic integrated circuits (PICs) with minimal performance penalties over a 150 GHz tuning range.