FIMMWAVE with the complex solver option includes solution for the modes of bent waveguides as their bend radii vary.

Two different ways of using FIMMPROP to study field evolution around bends are (a) field decomposition in terms of the bent wavguide modes which typically have negligible power exchange and just beat, and (b) field decomposition in terms of the modes of the locally straight wavguide at each point around the bend - these typically have significant coupling representing the field moving away from (and possibly back to) the center of the waveguide as it goes around the bend.

FIMMWAVE shows modal symmetries and exploits geometric symmetries.

FIMMPROP is an excellent tool for understanding propagation in tapers and y-junctions providing full Maxwell Equation solutions for both 2D and fully 3D structures.

Furthermore, FIMMPROP reveals the physics of electromagnetic field propagation through tapers between the sudden and adiabatic approximation limits. Kallistos when combined with FIMMPROP can be used to efficiently optimize taper shape to obtain maximum throughput. In the initial third of the taper below, we see propagation within the sudden approximation regime, i.e., although the taper diameter varies significantly, it does so quickly with respect to the inter-modal beatlengths and thus the total field is hardly changed. However, the local modes that go to make up that total field are radically changed, and as these local modes have different phase velocities, this is very important for what happens downstream.

For slow diameter variations, as opposed to the example shown above, the local mode powers are conserved, and thus given only one local modes, the total field evolves as the local modes evolves as a function of diameter.  Starting with several modes entering a section of adiabatic taper, relative phase evolution is important in determining the intensity variation due to inter-modal beating along that taper.

FIMMPROP is fully bidirectional and can accurately solve for resonant propagation in Fabry-Perot cavities. Shown below is (a) the oscillatory resonant solution (DWG) for a gap between two waveguides as the gap length is varied compared with (b) an approximate solution that only takes account of one reflection (FSJ).

Kallistos can be combined with CrystalWave (or FIMMPROP as in the example below) for the optimization of photonic crystal bends.