- Monitors (Optical)
- Symmetric and anti-symmetric BCs
- Spectral averaging (details on total and partial spectral averaging which can be set under the "Spectral averaging and apodization" tab for frequency domain field monitors)
- Apodization (details on apodization settings which can be set under the "Spectral averaging and apodization" tab for frequency domain field monitors)
In the previous unit, we saw a list of the different types of available monitors.
Some basic properties of monitors are shared between several monitor types, so we’ll
start by going through these common settings and general tips for using monitors.
Monitors can be added from the “Monitors” drop-down menu in the top toolbar.
The global properties window can also be opened from this menu.
Global properties are used by all monitors frequency domain monitors by default.
In the global properties edit window, under the main tab, you can set the wavelength or
frequency range over which to record data, as well as the number of data points to record
over the specified range.
By default the data points are spaced evenly over the frequency range, but you can also
choose to record data at points evenly spaced wavelength instead.
In the Advanced tab, you can set the desired sampling rate in time.
By default this is set to the Nyquist limit based on the frequency range of the source.
For linear simulations, this sampling rate does not need to be adjusted, however if running
nonlinear simulations where you want to measure fields at higher frequencies than the source
frequency range, the sampling rate can be increased to get accurate frequency domain
There are other common settings that only apply to some monitor types.
This is a frequency domain power monitor.
Under the general tab, one of the common monitor settings is the simulation type.
Under the drop down menu you can specify whether the monitor should record data if the simulation
region geometry is 2D, 3D, or both.
By default, this is set to “All”, so the monitor will always record data regardless
of the simulation region.
You can also choose to override the global monitor settings.
Under the Geometry tab, you can set the monitor type which sets the monitor orientation and
The available options may vary depending on the monitor type, but for this monitor you
can choose to set the monitor to a point monitor to record data at a single point in space,
a 1D linear monitor along the x, y, or z-axis directions, a 2D surface monitor with the
surface normal to the x, y, or z directions, or a 3D monitor which records data over a
The monitor position and spans can be set, and below that, down sampling can be set,
which allows you to reduce the amount of data recorded by the monitor.
For example, if down sample x is set to 2, this means that data will be averaged over
every 2 mesh cells along the x-direction, reducing the amount of data recorded, and
memory required by half.
A setting of 1 means no spatial down sampling is applied.
Under the "Data to record" tab, you can set which field components to record.
These include E and H field components, Poynting vector components, and "output power" which
is the net power flowing through the monitor which can be calculated by integrating the
real part of the Poynting vector normal to the monitor surface.
Under the "Advanced" tab, you can select the spatial interpolation options, and set the
sampling rate in time.
Click OK to accept the settings and you can see the yellow outline of the edges of the
monitor in the CAD.
Monitors are always represented in yellow in the CAD view.
Here is some general information and tips to keep in mind when setting up monitors.
FDTD Solutions is a time-domain solver, so frequency domain monitor results are obtained
by applying a Fourier transform to the time signal.
To review the details, see the FDTD algorithm section of the course.
If symmetry is used in the simulation region boundary conditions, monitor data will be
unfolded according to the specified symmetry to give the full field profile.
However, any monitors that are contained completely within the shaded side of the simulation region
will not record any data.
Monitors can extend outside of the simulation region, and monitor results are automatically
truncated at the boundaries of the simulation region by default, although it is possible
to set the monitor to record data within the PML absorbing boundary region.
Any monitors located outside of the simulation region will not record any data.
Adding monitors to a simulation does not increase the time it takes to run the simulation, except
when using a movie monitor since the movie monitor will save data and generate the movie
file as the simulation is running.
Adding monitors will increase the memory required to run the simulation, as well as the size
of the saved file after running the simulation.
To make sure that your system has enough memory to run the simulation, you can generate a
You can reduce memory requirements by using 2D or 1D monitors instead of 3D monitors,
recording fewer frequency points, using spatial down sampling, or selecting fewer field components
to record in the "Data to record" tab.
For example, if you are only interested in getting the transmission through a monitor
you can choose not to record the E and H field components and only record "output power".
Additional information about advanced monitor settings such as partial spectral averaging
and apodization can be found in the links listed below.