Waveguides can be used to transfer light bidirectionally between different circuit elements, and are
commonly used together with waveguide coupler elements to interfere multiple optical signals,
for example in resonant structures and interferometers.
In many applications, it is crucial to capture the time delay associated with propagation,
also called the group delay, to get accurate circuit simulation results.
For example, the free spectral range frequency of a ring resonator is inversely proportional
to the round-trip group delay, and the free spectral range of a Mach Zehnder interferometer
is inversely proportional to the group delay difference between the two arms.
To most accurately capture the group delay of a primitive waveguide element from the
“Waveguides” folder of the Element Library , we recommend using the following Digital
filter settings for the waveguide, which are located in the Numerical properties section
of the waveguide Property View, as is shown here for the Straight Waveguide element.
Set the digital filter to true, the single tap filter to false, the number of taps estimation
to group delay and the fractional delay to true.
For best results, be sure to enter an accurate group index and center frequency in the Waveguide
properties section, for the mode or modes of interest.
When the waveguide is implemented with the recommended settings, the complex transmission
value is accurate at the center frequency of the simulation.
The accuracy of the group delay at the center frequency depends on the delay compensation
and the sample rate.
The accuracy of the frequency dependent complex transmission also depends on these properties.
We'll discuss these further in the Delay compensation and Sample rate units.