Effect of non-optimal filtering on the performance of FSK/IM transmission schemes

Optical label switching is a technique for more effective use of the processing speed of electronic IP routers. In this technique IP packets are accompanied by small optical labels, which the node uses for routing and forwarding decisions. In each node only the label is recovered, processed electronically and a new label is reinserted, while the payload remains in the optical domain. One method for labelling IP packets is orthogonal FSK/IM modulation, where the payload is ‘Intensity Modulated’ (IM) and the label is ‘Frequency Modulated’ (FSK). Transmission through optical filters, i.e. multiplexers and passive AWG routers can cause signal degradation. When a combined FSK/IM signal is not well filtered, the two FSK tones will induce intensity fluctuations, which can result in FSK to IM conversion. In this paper, we show simulation and experimental results of how the combined FSK/IM scheme performs with respect to signal degradation due to laser nominal wavelength detuning and optical filter misalignments. Further we show analytical results on the relation between required optical filter bandwidth and frequency deviation.