System performance of coupler and AWG based all-optical OFDM transmission

Abstract

Inevitable growth in higher data rate demands, optical orthogonal frequency division multiplexing (OFDM) becomes a promising technique to reduce inter-symbol interference (ISI) in a dispersive channel. In an OFDM transmission system, an OFDM symbol can be generated by inverse discrete Fourier transform (DFT) and de-multiplexed by forward discrete Fourier transform. However, conventional optical OFDM sys-tem utilizes electrical DFT circuit which limits the processing speed and cost. Therefore, in this thesis, we focus on designing DFT circuit all optically by using optical passive components and the analysis its system performance. In order to produce all-optical DFT, this thesis proposes two methods. The first is a coupler-based DFT circuit method which can be achieved by cascading 2-by-2 directional couplers with phase shifters. The other is a fundamental mode arrayed waveguide grating (AWG) method whose transfer function characteristics has the same effect of DFT. The proposed these two all-optical methods are applied to 100Gbps and 160Gbps optical OFDM systems. Unfortunately, there are always manufacturing errors in loss uniformity and phase caused by wave-guide length deviation in the manufacturing process due to the accuracy limit. Especially, phase errors generate critical crosstalk penalties that degrade the system performance. In this thesis, we design 100 and 160Gbps optical OFDM transmission systems based on the coupler based DFT and the fundamental mode AWG based DFT under existence of the phase errors and study its impact to the system performance.