UC San Diego

The work in this thesis introduces a variety of techniques that can be used to improve the performance of previous state of the art passive optical networks (PONs). These networks will be of increasing importance as increasing bandwidth demand drives the penetration of optical fiber into access networks. PONs require novel design techniques due to their bidirectional nature and tight cost requirements. In this thesis improvements are proposed in three categories: filtering of bidirectional noise; novel modulation techniques; and use of non-traditional low cost devices (specifically vertical cavity surface emitting lasers (VCSELs)). High pass filtering (HPF) is shown to reduce the impact of bidirectional Rayleigh noise, which is dominant in PONs. It is demonstrated that under certain circumstances Rayleigh noise immunity is improved by up to 10 dB with proper selection of an HPF. A model to predict the effects of baseline wander caused by HPF is developed and experimentally validated. This model is combined with an existing Rayleigh noise model, which is experimentally validated. This model is extended to predict the performance of a bidirectional on-off keyed (OOK) PON and experimentally verified. Three methods are investigated to improve the ONU modulator. First it is shown that transmitter pre-distortion can provide a doubling of the non-equalized datarate of a low modulation bandwidth ONU modulator. Next a four level intensity modulation format is demonstrated. It is shown that while this method is possible, it provides no improvement over OOK modulation. A novel method for modulating the orthogonal phases of an intensity modulated microwave subcarrier, similar to quadrature amplitude modulation (QAM), is demonstrated. Significant performance improvement is realized with this scheme. Finally the use of a VCSEL in PONs is evaluated. It is predicted that using a VCSEL as central office (CO) laser will offer minor benefits and some moderate challenges. Use of a vertical cavity semiconductor optical amplifier (VCSOA) as an ONU modulator is prevented by a dispersive nonlinearity. This nonlinearity leads to bistability. First demonstration of butterfly bistability in a 1550 nm VCSOA and record low power bistability are demonstrated