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

Abstract

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.

Roadmap of optical communications

“…The main challenge is to scale down the typical high cost of this technology, explained in section 6, by means of integrated optics, new signal processing, and statistical wavelength multiplexing [126][127][128]; 50 dB of power budget and 6.25 GHz channel spacing have recently been demonstrated without significant increase of the transceiver complexity.…”

Coherent ultra dense wavelength division multiplexing passive optical networks

“…Coherent technology with advanced modulation formats and Nyquist pulse shaping, has demonstrated several technical highlights, such as excellent spectral efficiency with high aggregated capacity, easier network upgrade and future-proof solution for flexible bandwidth next generation optical access networks (NG-OAN) [3][4][5][6]. Therefore, it may be a natural next step towards network efficiency [7,8].…”

DQPSK Directly Phase Modulated DFB for Flexible Coherent UDWDM-PONs

“…FTER the decision of the full service access network (FSAN) committee for a time and wavelength division multiplexing (TWDM) as the second stage of the next generation passive optical networks (NG-PON2) standard, ultra-dense WDM (UDWDM) appears as a candidate for upcoming access network generations [1][2][3]. Though coherent UDWDM offers high sensitivity and coexistence with current PON deployments, the potential high cost and device complexity has limited its attractiveness to operators.…”

“…The result was a signal with either 0º and 180º variations (DPSK) or 0º, 90º, 180º, 270º phases (DQPSK). The ONUs had DFB lasers with 4 MHz linewidth whose wavelength was tuned through temperature for flexible grid operation [1]. The optical signals from the ONUs were joined with a 3 dB coupler and sent through single mode fiber (SMF) with 0 dBm total launched power.…”