Multipath interference (MPI) plays a major role in optical communication links, especially in fiber-to-the-x passive optical network (FTTx PON) architecture, where a splitter-based distribution causes reflections from each splitter. Isolators can help mitigate this problem, but they are not very suitable for passive networks due to their insertion loss.
Accurate modeling of MPI is crucial in order to understand system penalties. However, MPI modeling is complex because of bidirectional interactions between a large number of reflections from multiple sources, which often propagate through nonlinear components, such as fibers. A frequency-domain approach, like the one described in Ref. , calculates power spectral density of MPI to be used in a way similar to the relative intensity noise (RIN). A time-domain approach, like the one described in Ref. , models MPI as “sum of signals” with Monte Carlo estimations on amplitude and phase to calculate the signal at the receiver.
OptSim Circuit™ uses time- and frequency-domain methods to model bidirectional optical and electrical signal propagation and feedback. It can model MPI in a natural and intuitive way without any linear filter type assumptions. The OptSim Circuit’s bidirectional fiber model includes both bidirectional optical signal propagation and Rayleigh backscattering, the two main causes of MPI.
Here is an example showing how to take advantage of OptSim Circuit’s bi-directional propagation capabilities to model MPI.