Title:
Technologies for Next-Generation Optical Access Systems
Supervisors:
Principal supervisor: Professor Idelfonso Tafur Monroy, DTU Fotonik
Co-supervisor: Associate Prof. Juan José Vegas Olmos, DTU Fotonik
Evaluation Board:
Associate Professor Andrei Lavrinenko, DTU Fotonik
Professor Knud Erik Skouby, Aalborg Universitet, Denmark
Professor Giovanni Tartarini, University of Bologna, Italy
Master of the Ceremony:
Professor Søren Forchhammer, DTU Fotonik
Abstract:
This thesis expands the state-of-the-art on optical access networks technologies. Two approaches are developed.
First, a novel tunable laser based Wavelength Division Multiplexing (WDM)-Passive Optical Network (PON) system has been analyzed and developed. This system uses a centralized wavelength locker in the Optical Line Terminal (OLT). This enables to omit the wavelength locker in each Optical Network Unit (ONU) and reduces the ONU cost. The centralized wavelength locker analyzes a low-frequency, low modulation amplitude pilot tone modulated onto the ONU bit stream. As wavelength control feedback from the OLT to the ONU, an Auxiliary Management Communication Channel (AMCC) is used to provide all necessary tuning information. The main achievements are in the area of impairments analysis related to the pilot tone, AMCC, and crosstalk effects. The latter possibly occurs during the wavelength tuning process. The achieved results contributed to the standardization of such a system, in the framework of ITU-T study group 15 question 6 recommendation draft G.metro. Furthermore, a novel widely tunable Micro-Electro-Mechanical System (MEMS)-Vertical-Cavity Surface-Emitting laser (VCSEL) has been implemented in this system approach. The high chirp of the laser in combination with an overcompensating Dispersion Compensating Fiber (DCF) enable a wide range of transmission reaches. Furthermore, higher-order modulation formats allowed a transmission of 35 Gbps over 20 km. This demonstrates a future-proof of the G.metro system approach.
Second, a novel approach to match wide bandwidth signals to low bandwidth equipment is introduced. In this thesis, this approach is called signal slicing. A wide bandwidth signal is split into several portions using Digital Signal Processing (DSP) algorithms. Each signal portion is down-converted to baseband and transmitted using a Time Division Multiplexing (TDM) or WDM transmission scheme. A 1 Gbps Non-Return-to-Zero (NRZ) signal is transmitted over up to 25 km using two signal portion with only 500 MHz bandwidth. The number of slices are scaled up to the transmission of a 10 Gbps duobinary signal, split into 10 portions and transmitted over up to 40 km. Power consumption analyzes of signal slicing show a great potential for power savings. In conclusion, the results, presented in this thesis, demonstrate the feasibility of signal slicing and have significantly contributed to the standardization of G.metro. Furthermore, the results also demonstrates the future-proof systems approach of G.metro.