322,901 research outputs found
Next generation optical access networks towards Gigabit/s per user
No full textAt the time of writing this Ph.D. thesis, FSAN (Full Service Access Network) and ITU-T (International Telecommunication Union - Telecommunication Standardization Bureau) working groups are involved in the final definition of the Recommendation G.989, which has recently established that the Next Generation Passive Optical Network (NG-PON2) architecture will be based on Time- and Wavelength-Division Multiplexed PON (TWDM-PON), and it will consist in its first version on four wavelength-stacked XG-PONs using four wavelengths per direction, likely with a very narrow (for PON) spacing of 100 GHz or even 50 GHz. Furthermore, the Optical Distribution Network (ODN) will be splitter-based and passive, like all previous PON standards, avoiding the use of any wavelength selection/filtering and any optical amplification inside the ODN. Moreover, since complete ODN backward compatibility is required, the TWDM-PON must be compliant with the same previous ODN loss classes, i.e. 33 and 35 dB for the extended E1 and E2 classes, respectively, and up to 15 dB of Differential Optical Path Loss (DOPL). One of the few physical layer problems over which FSAN is still working before the final NG-PON2 Recommendation release, is related to the lack of available low-cost tunable lasers with sufficient tuning range and launch power, to be installed at the Optical Network Unit (ONU) side for the upstream signal generation. Indeed, they should have a precision compatible with a 100 GHz wavelength grid, and be able to tune on (at least) four wavelengths, adopting some protection systems during their switch-on time, in order to avoid interferences with other channels (due to the uncontrolled wavelength transmission at the laser power on); moreover, they should operate on a very wide temperature range and they should have a target price compatible with equipment to be installed at the customer premises. Furthermore, in the longer term, if more than four wavelengths will be used (for instance for WDM overly), this issue will be particularly critical. In order to avoid the use of expensive tunable lasers at the ONU, several WDM reflective PON architectures have been proposed in the last ten years, whose key idea is to generate the unmodulated upstream wavelengths at the Central Office, and modulate them in reflection at the ONU side. Unfortunately, most of the reflective WDM-PON architectures proposed in literature seem to be completely incompatible with TWDM-PON for a set of different reasons such as: - most of them require the use of Arrayed Waveguide Gratings (AWG) in the ODN, while most telecom operators believe that backward compatibility in PON is a must, and thus the splitter-based architecture should be maintained also in NG-PON2; - the achievable ODN loss is limited to typically 20-25 dB, due to several spurious effects such as the Rayleigh back-scattering and the low received optical power; - most of them use a dedicated wavelength for each ONU, and do not support burst-mode TDMA in the upstream. The main objective of this Ph.D. project is to try to solve all these issues, proposing a self-coherent, burst-mode, reflective PON architecture that completely satisfies the main requirements defined in the TWDM-PON standard. In order to reach this goal, the activity started in early 2012 in the Photonlab of Istituto Superiore Mario Boella (Turin, Italy), and was supported by the joint group composed by Dipartimento di Elettronica of Politecnico di Torino (Turin, Italy) and Cisco Photonics (Monza, Italy) throughout the entire Ph.D. project. At first, a full characterization of the Reflective Semiconductor Optical Amplifier (RSOA) was performed in order to find the best working parameters that provide the best performance if this device is used as reflective optical modulator at the ONU side. Thanks to this optimization, very good results were obtained using the RSOA in a full upstream self-coherent reflective PON setup, working in continuous mode at 1.25 Gbps. In order to overcome the limit of one dedicated wavelength for each user, the emulated ONU was forced to work in burst-mode, replacing the RSOA with the cascade of a Semiconductor Optical Amplifier (SOA) and a Reflective Electro-Absorption Modulator (REAM). The obtained results demonstrate that this solution, combined with a burst-mode self-coherent detection at the Central Office, supports a 2.5 Gbps TDMA upstream transmission, as required by TWDM-PON standard. The proposed architecture was then finalized by adding two important new features, i.e. the upstream bit rate upgrade to 10 Gbps per wavelength and the use of commercial distributed feedback (DFB) lasers rather than External Cavity Lasers (ECL), showing very good performance. To resume, the work performed during this Ph.D. activity demonstrated that, thanks to the burst mode reflective-ONUs and the burst mode, self-coherent detection at the OLT side, the proposed architecture supports the transmission of N simultaneous upstream signals on each wavelength, working at 2.5 Gbps, over up to 35 dB of ODN loss and more than 15 dB of DOPL. Therefore, most G.989 physical layer specifications are satisfied by this proposal, even without the need for a tunable laser at the ONU side, but only a tunable filter locked on OLT-generated optical wavelength combs. If properly integrated, the reflective ONU structure can be less expensive than the TWDM-PON solution in terms of CAPEX, and have a much simpler wavelength control. The only significant increase in cost in the proposed solution is due to the presence of one coherent receiver per each upstream wavelength, but it is shared among all the users with the same wavelength. The authors of the aforementioned writings hope that this work can contribute to the discussion currently taking place in FSAN and ITU-T on future PON generations, particularly for a future use of DWDM with significantly more than 4 wavelengths on a 50 GHz grid, which is a requirement that would make tunable lasers at ONU even more critical. While the need for more than 4 wavelengths seems really far-fetched for residential PONs, it could likely become more handy if mobile front-hauling for Long Term Evolution (LTE) and LTE-advanced will adopt bit rate hungry Common Public Radio Interface (CPRI) approaches, and it will be supported over PO
Gridless Transmission of Tb/s Super-Channels based on PM-64QAM with 100G Channels over a mixed Fiber Networks
No full textWe present results of transporting different line-rate technologies over a gridless network with flexible spectrum switching nodes. Signal at CP-DQPSK 100Gb/s and CP-64QAM Tb/s super-channel are generated and successfully transported over EDFA+RAMAN fiber link
Final system results from the EU FP7 project FABULOUS
No full textIn the framework of the EU-funded research project 'FABULOUS' we experimentally demonstrate an innovative FDMA-PON architecture whose upstream transmission is based on a reflective Mach-Zehnder modulator, reaching an overall upstream capacity of 32 Gbps per wavelength over 31 dB ODN loss in several previously published experiments targeting 1 Gbps per user and using 16-QAM as a modulation format. In this paper, we focus on the experimental demonstration of the flexibility of our system to a variety of different working conditions, targeting higher bit-rates per user (up to 10 Gbps) and different modulation formats
Single-wavelength full-duplex 10 Gbps reflective PON capable of 31 dB of ODN loss
No full textWe demonstrate a single-wavelength fully-bidirectional and symmetrical 10 Gbps OOK transmission using simple direct-detection in downstream, and self-coherent detection in upstream over a standard 31 dB loss splitter-based PON, relying on wavelength remodulatio
Synergetical use of analytical models and machine-learning for data transport abstraction in open optical networks
No full textThe key-operation to enabling an effective data transport abstraction in open optical line systems (OLS) is the capability to predict the quality of transmission (QoT), that is given by the generalized signal-to-noise ratio (GSNR), including both the effects of the ASE noise and the nonlinear interference (NLI) accumulation. Among the two impairing effects, the estimation of the ASE noise is the most challenging task, because of the spectrally resolved working point of the erbium-doped fiber amplifiers (EDFA) depending on the spectral load, given the overall gain. While, the computation of the NLI is well addressed by mathematical models based on the knowledge of parameters and spectral load of fiber spans. So, the NLI prediction is mainly impaired by the uncertainties on insertion losses an spectral tilting. An accurate and spectrally resolved GSNR estimation enables to optimize the power control and to reliably and automatically deploy lightpaths with minimum margin, consequently maximizing the transmission capacity. We address the potentialities of machine-learning (ML) methods combined with analytic models for the NLI computation to improve the accuracy in the QoT estimation. We also analyze an experimental data-set showing the main uncertainties and addressing the use of ML to predict their effect on the QoT estimation
FULLY WORKING 1GBIT/S ETHERNET TRANSMISSION SYSTEM:FINAL RESULTS FROM THE POF-PLUS EU PROJECT
No full text
Alternative solutions for fronthauling based on DSP-assisted Radio-over-Fiber
No full textWe review alternative solutions for optical fronthauling in next generation fixed-mobile converged architectures that try to solve the problems related to the extremely high bit rates required by current fronthauling implementations based on the so-called digitized Radio over Fiber (as for the CPRI or OBSAI standards). In particular, we present our most recent results on Digital Signal Processing (DSP) assisted Frequency Division Multiplexed (FDM) aggregated radio over fiber solutions. We experimentally show two DSP-based optimization at the transmitter and/or receiver that improves the received Error Vector Magnitude (EVM). Moreover, we discuss on simple spectral estimation of the EVM parameter at the Remote Radio Head (RRH)
Compatibility between coherent reflective burst-mode PON and TWDM-PON physical layers
No full textWe discuss the compatibility between reflective PON architectures and the recently defined ITU-T G.989.1 TWDM-PON. Focusing on the upstream, we experimentally demonstrate that, by using burst-mode coherent detection at OLT, reflective PON can achieve the specification target set for TWDM-PON, without requiring precise wavelength accuracy at ONU. Compared to the companion ECOC 2013 paper, we investigate on the differential optical path loss (DOPL) issue, proposing a simple SOA gain control algorithm to achieve reliable transmission for DOPL up to 17 d
- …
