Propagation Simulation Modules

Zone and FAST

Zone and FAST (Flexible Algorithm Selection Technology) are related techniques that simulate the propagation of light in user-specified calculation windows, which may be at any location and any angle in the design. The module can combine multiple zones (that use different simulation settings or algorithms) in a single simulation run.

A simulation zone behaves just like any other layout element; its ports can be placed anywhere in a design. Its parameters determine the simulation settings; for example, the algorithm to use (BPM or FDTD) and the spatial and temporal grid size. If two simulation zones touch, or overlap each other, they are combined in a single simulation, in which the end field of one simulation zone is passed into the next zone automatically. Non-touching zones can also be linked by means of linked mode launchers, whose amplitude and phase can be modified values from a simulation in a previous zone.


The ability to perform a propagation simulation at any location on a design allows for true simulation of the structure as it will be in the final chip, eliminating the need to create a layout for only the part that you want to simulate and thus avoiding errors.

Some components can be challenging or time consuming to simulate when they need small simulation step sizes or need to take reflections into account. The FAST technology optimizes simulation times by using lightweight tools such as BPM where possible, and only using more time-consuming simulations when absolutely necessary.


Any propagation simulation will use zones, whether it be 2D FDTD, BEP, BPM, or 3D BPM. Linked mode launchers are especially useful in AWGs, where the star couplers have their own simulation zones, but the connecting waveguides are modeled as pure phase and amplitude modifiers. The FAST technology is restricted to 2D BPM and FDTD, but will greatly improve simulation speeds of complex components with many variations in their layouts.


  • Zones define simulation method and parameters in any part of a design, at any angle
  • FAST combines 2D BPM and FDTD in a single simulation run
  • Only forward transfer from one zone to the next; no backward propagation back into a previous zone

Figure 1: Layout with different simulation zones: FDTD simulations in the photonic crystals
and the Y-junctions, BPM everywhere else.