Resumen de New generation ftth onu and olt design for upstream transmission in wdm pon including optimized combination of electronics and optics
Mireia Esther Omella Cancer
This research is developed in the context of the Next Generation of Passive Optical Networks (NG-PON) for Fibre to the Home (FTTH) network. In this thesis, several techniques are proposed in order to increase the network capacity, dealing with the main optical impairments present in PON with minimum infrastructure, and with the goals of wavelength transparency and cost effectiveness. The main issues in this work are the photodetection process over chromatic dispersion (CD) and ASE noise impairments, the mitigation strategies for Rayleigh Backscattering (RB) effect and the WDM-PON RSOA-based ONUs, with their limitations of bandwidth and chirp. Regarding photodetection, a novel module which performs the mathematical function SQRT has demonstrated its linearizing capability at partially compensating the square-law of the photon to electron conversion process after reception. Improvements in RoF systems in terms of harmonics level reduction and in digital transmissions with linear FFE equalizers have been achieved. Also, the complexity requirements in MLSE receivers are reduced after the SQRT module. This module has been implemented electronically, first, by using the intrinsic non-linearity of the schottky diodes, on a microstrip circuit. After that, a MMIC chip has been designed and experimentally tested. But the SQRT module is also useful for other applications as downstream cancellation in the upstream signal in bidirectional transmissions, and to reduce the amplitude differences of the different packets in burst mode receivers, relaxing the adjustment requirements for the following limiting amplifiers. The statistics of the received signals in optically amplified (ASE dominant) systems have been also studied. The optimum function, capable of recovering the Gaussian distribution after detection, has been obtained. For systems working at FEC limit, like with MLSE, the improvement over SQRT is small, validating the good performance of the SQRT module. RB effect has been mitigated by using wavelength shifting at the ONU premises. Several wavelength shifter devices have been proposed for the first time, based in 2 and 3 arms capable of translating (in several GHz) the wavelength that comes from the OLT to avoid the overlap between the upstream signal and the RB, while maintaining the signal in the same AWG channel. These devices are less complex than the recently proposed 4-arm structures and require simpler signals than the sawtooth that is necessary for a 1-arm phase modulator. Experimental validation of the WS technique for RB mitigation has been performed, first with a commercial dual arm MZM and after by using a RSOA with a low duty square signal with improvements of 5 to 7dB in tolerance to RB. The new standards that have just been approved (XG-PON, 10G-EPON) propose the upgrading of the network towards symmetrical 10G/10G operation. However, RSOA’s bandwidth and chirp still limit the performance at these bit rates. The first 10Gb/s transmission in real time and with low BER (10-9) using a RSOA as an intensity modulator has been reported by using some of the techniques presented in this thesis: duobinary transmission and detuned optical filtering plus DFE-FFE equalization. Other techniques proposed and experimentally tested are the phase adjustment with a programmable optical filter and the direct detection together with MLSE equalization.
