This video is taken from the FDE 100 course on Lumerical University.

## Transcript

As we saw in the previous unit, the FDE solver calculates the mode profiles and the propagation

constant on a cross section of the straight waveguide.

For bent waveguides, the solver calculates the modes for an infinite bend.

The calculation is similar to straight waveguides, but in cylindrical coordinate.

Note the bending radius must be greater than or equal to half of the simulation region

width.

The bent orientation angle can be set in the FDE analysis window.

The angle is defined with respect to the plane formed by the direction of propagation and

the horizontal axis.

In the case of a helical waveguide, the solver takes a cross section of the waveguide, extrudes

that cross section in the propagation direction and twists each point in space around the

origin of the global coordinates, creating a helical structure in the propagation direction.

The relationship between the helical coordinate (X, Y, Z) and the Cartesian coordinate (x,

y, z) is given here, where α is the torsion of the waveguide.

In the next unit we will discuss the overlap and power coupling calculations that are available

in the overlap analysis tool.