# FDTD
Editor: Create New Project › FDTD · Python: td.Simulation
An FDTD project solves Maxwell's equations step by step in time on a 3D grid. This is the finite-difference time-domain (FDTD) method. The sources usually send a short pulse of light, the pulse travels through the structures, and the monitors record the fields. One run gives the results for a whole wavelength range.
For the modes of a waveguide cross-section only, use a Mode project. For long waveguide devices, an EME project can be faster. For temperature, use a Heat project.
To start, follow Create Your First Project and choose the FDTD tab. For a complete example, follow Measure Transmission Through a Waveguide. Then set up the parts below, click Check Simulation, and run. If the check or the run shows a problem, see FDTD Troubleshooting.
# Structures
The objects in the simulation. Each structure has a geometry and a medium (material). Add them in Model › Structures. See Structures and Mediums.
# Sources
The sources send light into the simulation. Add them in Setup › Sources. See Sources.
# Monitors
The monitors record the results, for example the power through a plane or the field on a plane. Add them in Setup › Monitors. See Monitors.
# Configuration
The wavelength range, the simulation domain, the run time, the grid, the boundaries and the symmetry. Set them in Setup › Configuration. See Configuration.
# Script Objects
Python code that creates structures, sources or monitors, for shapes or setups that the forms cannot make. See Script Objects.