Physical layer evaluation of OFDM-based access networks

In this paper, we present a physical layer parameter optimization of direct-detection optical OFDM techniques at bitrates of 10Gb/s and 40Gb/s using two types of field modulation transmitters: optical IQ modulator and frequency up-conversion. The performance of these schemes is evaluated for access networks and a comparison with intensity modulation is also presented. Keywords: Orthogonal Frequency Division Multiplexing, OFDM, Passive Optical Network, PON, directdetection. 1. INTRODUCTION The limits of copper-based and wireless access solutions in terms of offered bandwidth (BW) per user and distance reach have positioned optical fibre as the most prominent solution for emerging media-rich hungry BW applications and upcoming cloud-computing. Passive optical networks (PONs) based on time division multiple access (TDMA) are currently an attractive solution for substituting cable-based networks. However, the sensitivity to packet latency becomes a critical issue when scaling to high bitrates [1], [2]. As an alternative, orthogonal frequency division multiplexing (OFDM) PONs have been proposed recently to combine time and frequency division achieving high bitrates and fine BW granularity [2]. OFDM offers many advantages: through the use of high-level modulation formats, the BW of the optoelectronics can be kept low [1]. Since data is sent in parallel, the period of the OFDM symbol is longer than for serial systems at the same bit rate. As a consequence, the inter-symbol interference (ISI) is lower and equalization is simplified [3].