COst-effective COhereNt ultra-dense-WDM-PON for lambda-To-the-user access

The COCONUT proposal aims at the definition, study and realization of a new fully scalable optical access network significantly extending the network dimensions in terms of bandwidth utilization, reach and number of accommodated users. The envisioned access network evolves from the almost-commercial WDM-PON architecture to the realisation of the Ultra-Dense WDM solutions, opening the way to the “wavelength-to-the-user” concept. The key enabling technology will be a new cost-effective coherent detection scheme. This will allow for the first time to leverage from well known concepts to implement really cheap, yet effective, coherent terminals suitable for mass deployment. Although conceptually complex, these terminals must be compatible with the cost levels typical of low-cost consumer electronics, thus affordable to the end-users. Therefore COCONUT can drive the realization of flexible and bandwidth-efficient next-generation networks, compatible with the existing PON infrastructures. As a result, high speed connections will be available to the common users, thus opening the way to a huge potential of application and socioeconomical developments.

Project Objectives

1. 1. One order of magnitude increase in spectral efficiency, both optical and electrical domains, by means of low-cost homodyne detection, leading to enhanced user bandwidth granularity, with or without TDMA multiplexing.

2. Low power consumption ONUs, with a targeted reduction with respect to the state-of-the-art FTTH systems. The reduction is expected to come mainly from higher ONU bandwidth efficiency, and lower electronic requirements, like for example serving every user with the 1G Ethernet LAN standard. If the goal for guarantied bandwidth per user is nowadays about 100 Mbit/s, the next step will be 1Gbit/s; for example current PCs are nowadays including a 10/100/1000 MbE interface, thus 1 GbE can be considered a very practical goal here. The energy consumption of the designed COCONUT network will be estimated considering high volume projections of the relevant constitutive elements in typical FTTH deployment cases, and compared with the alternative solutions for analogous PON user distribution and high bandwidth delivery. Our main goal in COCONUT is an energy efficient solution in relevant applications, for the mid/long term deployments of broadband FTTH.

3. As a stretched goal, COCONUT also targets the delivery of 10Gbit/s to cope with the mobile data traffic increase; back hauling of digital radio LTE antenna sites traffic.

4. Transparency and independency among channels, in terms of coding, protocol and bit rate when required, thus avoiding the complex synchronization and ranging of current
   PONs. 

5. Strategies for the use of gridless COCONUT channel allocation, with ultra-low optical channel spacing (as low as few GHz), the use of coherent transmission in combination with digital signal processing and high resolution fast optical spectrum analysis. Elastic flexible optical spectrum management, firstly led by the ONU natural operating wavelength, and secondly finely tuned by the OLT controller. This elasticity adapts to the central wavelength requirements and to the flexible bandwidth demands.
6. The fact that the already deployed PON infrastructure can be reused without extra effort (i.e. power splitter based infrastructure). Extending reach beyond 100 Km, with and without optical reach-extenders, and maximum scalability in terms of number of users and wavelengths. The concept can be easily extended to a wider fibre band, maximizing the number of served users base to several hundreds, as the total fibre bandwidth can be used (40 nm = 50,000 GHz in C-band, or even wider towards other bands). 
7. Low cost integrated ONU optics with newly adapted key devices for the function of phase modulation and phase/polarization scrambling.
8. Mitigation strategies of the main limiting impairment effects: the laser’s phase noise, polarization control, amplifiers ASE noise, crosstalk, etc. 
9. Analysis of TDMA to be applied compatibly with UD-WDM in a practical way, for increased granularity and wavelength collision transitory.