Gemma Vall-Llosera

Towards ultra-dense wavelength-to-the-user: The approach of the COCONUT project

This paper presents the high-level COCONUT architecture of an optical access network based on coherent technology, supporting ultra-dense Wavelength Division Multiplexing (WDM). The COCONUT network should allow for seamless evolution from present PON architectures, but also support new emerging applications such as mobile back-haul and front-haul. Coherent techniques will hence allow serving a higher number of users, thanks to ultra-dense WDM, and reaching higher power budget, thanks to higher sensitivity. These features should allow for economy of scale and network consolidation. Although coherent solutions are well-developed for core networks, the prohibitive cost of their optical and electronic parts makes them unsuitable for the massive deployment of access networks. To this aim, COCONUT will address realization of coherent transmitter/receivers exploiting low-cost components and simple electronics, so that the cost of typical line terminals would be affordable to the end-users. The paper presents an overview of the target results and key issues that are addressed by the COCONUT partners.

Technologies for Cost-Effective udWDM-PONs

New technologies for ultradense WDM-PON (udWDM-PON), enabled by coherent techniques and low-cost devices, are developed for an efficient utilization of the optical spectrum, revealing that the “Wavelength-to-the-User” concept can be feasible. In this paper, an udWDM-PON with only 6.25-GHz channel spacing is implemented with conventional DFB lasers, for a splitter-based PON infrastructure with 256 ONUs. The results of the analysis of udWDM access network architecture with respect to their associated complexity, cost, and migration scenarios, exhibit the potential for higher aggregate throughput, higher split ratios, and node consolidation, when compared to competing technologies.

COCONUT cost, power consumption and migration analysis: A route towards NG-PON3

The results of the analysis of the COCONUT (“COst-effective COhereNt Ultra-dense-WDM-PON for λ-to-the-user access”) project architectures with respect to their associated cost, power consumption and migration scenarios are presented. COCONUT develops udWDM access with simplified coherent technology to allow for node consolidation, increased number of homes passed, and higher split ratios when compared to standardised technologies. COCONUT can operate in a very narrow spectral band due to the 6.25 - 12.5 GHz wavelength channel spacing and provides increased per user capacity when compared to currently deployed solutions. COCONUT technology shows 80% cost reduction when compared to a conventional coherent receiver. Also in terms of power consumption at 10G, the adopted transceiver solutions compare well to TWDM PON solution, achieving less than 2 W/Gb/s.

Small cell strategy: meeting the indoor challenge

In this work we present an innovative solution to reach good quality of service while using mobile broadband indoors: the fiber radio-dot. This solution consists of a new architectural logical point-to-point optical link that brings the macro layer indoors. This solution provides higher bandwidth, no eavesdropping, frequency reuse, low latency, interference and network management, and cell selection. We tested the solution in the lab achieving an EVM of 0.75 %rms, SFDR of around 95 dBxHz2/3 and an LTE transmission of 75 Mbit/s.

WDM-PON fiber-fault automatic detection and Localization with 1 dB event sensitivity in drop links

Trial of live WDM-PON monitoring based on Optical Time Domain Reflectometry (OTDR) and Optical Transceiver Monitoring (OTM) is presented. The concept of cost-effective, remote and quick operation without drop-line demarcation components is demonstrated.

COCONUT requirements for residential, business and outdoor scenarios

Five basic requirements have been defined for the COCONUT ultra-dense WDM PON architecture: (1) untouched optical distribution network, (2) no active components, (3) no intervention in the outside plan, (4) smooth upgrade from legacy systems, and (5) use of the same technology for point-to-point and point-to-multi-point links. These requirements are analysed with respect to five application scenarios: main remote, small cell backhaul/residential, business, and macro cell backhaul. The low-cost coherent techniques targeted in the project will allow for increased power budget, thus splitting ratio, distance, and a narrower grid that will enable a densification of the network as foreseen with small cell deployments.

A silicon-on-insulator 120° Optical hybrid based on 3× multimode interference coupler

A 120° optical hybrid based on 3× multimode interference coupler is reported. The device exhibits less than 10° phase deviation over 55 nm in the C- and L-band.

Photonics for radio access networks

In this work we analyse radio access networks (RAN) deployments from the capacity and cost points of view. We find that in order to support the new radio (NR) with system bandwidth of 800MHz and reduce the number of fibre connections between NR and baseband units (BBU) one can use dense wavelength division multiplexing (DWDM), pulse amplitude modulation (PAM4) or multicore fibre. We also find that spectrum and site are the most costly factors in a wide-area RAN deployment and we propose optical solutions to cope with this cost: a) advanced antenna solutions to improve uplink and downlink and downlink performance (throughput and coverage) by means of optical beamforming with silicon photonics phase shifters, or microstructural optical fibres; b) reducing footprint by means of silicon photonics; c) increasing capacity per site exploiting ultra dense WDM transceivers, PAM4 transceivers, multicore fibre.

Field-trial of a λ-to-the-user high-budget PON using a novel class of low-cost coherent transceivers and compatible with EPON system operation

COCONUT project demonstrated an innovative DWDM Passive Optical Network implementing the full λ-to-the-user concept in a filterless distribution fiber network. We make use of an innovative class of coherent transceivers that exploit the advantages of coherent detection in terms of sensitivity and channel selectivity in a cost efficient manner. The different transceivers developed target different use case scenarios, showing perfect compatibility with legacy infrastructures installed. In this paper, we report the successful trial of the proposed system in a testbed where 4 different coherent transceivers (plus one legacy E-PON system) ran simultaneously, operating over 14 DWDM channels, in a dark-fiber network in the city of Pisa, delivering real-time and/or test traffic. The testbed demonstrated filterless operations, multi-rate transmission (from 1.25 to 10 Gb/s/λ), high ODN loss (18 – 40 dB) as well as a bi-directional channel monitoring system.