This application example underlines the principal limitation of pure time-domain modeling (TDM) of
large-scale photonic integrated circuits (PICs). It is illustrated with a device composed by several cascaded interleavers
(). Using pure TDM, each PIC
element is described by its own FIR filter. Input signals are filtered sample-by-sample by each PIC element. This technique
is quite accurate within a certain bandwidth; however, it is always accompanied by an intrinsic deterioration near the
edges of the simulated signal bands
(). We overcome this problem
with the novel hybrid time-and-frequency modeling domain (TFDM) approach  where FIR filters are designed not for each
individual passive PIC element but only for compound passive devices
With the TFDM technique, the accumulation of inaccuracies of FIR filters is dramatically improved.
This implies that a larger time step can be used to achieve similar results, and the simulation time can thus be reduced.
This fact is demonstrated in :
similar performances are achieved for a single interleaver and cascaded structure of 15 interleavers.
Keywords: Interleaver, SMATRIX, Time-and-frequency domain, Photonic Integrated Circuits, PICs
Similar demonstrations are available in VPIComponentMaker Photonic Circuits and on the VPIphotonics Forum.
 S. F. Mingaleev, E. Sokolov, C. Arellano, I. Koltchanov, and A. Richter, "Hybrid time-and-frequency-domain approach for modeling photonic integrated circuits", NUSOD, paper ThA4 (2011)