# Sources

Editor: Setup › Sources

A source sends light into the simulation. Its type sets where and how the light starts, for example a guided mode in a waveguide or a plane wave. Its Excitation Signal sets the time shape of the light. The default, a Gaussian Pulse, covers a whole wavelength range in one run.

# Add a Source

Add Source panel with Uniform Current Source, Point Dipole, Gaussian Beam, Astigmatic Gaussian Beam, Mode Source, Plane Wave, TFSF, Custom Field Source and Custom Current Source

Add Source panel

  1. In Setup › Sources, click +.
  2. Click a source type. The editor adds the source. Custom Field Source and Custom Current Source first ask for a data file.
  3. In the source's form, set its position, size, direction and wavelength range.

# How to Choose

If you want to … Use
Send a guided mode into a waveguide Mode Source
Light a periodic structure, such as a grating or a metasurface Plane Wave
Model a focused beam, for example from a fiber Gaussian Beam, or Astigmatic Gaussian Beam for an elliptical beam
Model a small emitter, such as a molecule or a quantum dot Point Dipole
Light a finite object with a plane wave, and see the scattered light outside a box TFSF
Apply a current over a plane or a volume Uniform Current Source
Use fields or currents from your own data Custom Field Source or Custom Current Source

# Common Mistakes

  • The monitors record wavelengths outside the source's range. The check then warns. See FDTD Troubleshooting.
  • A Plane Wave at an angle, with PML on its sides. The check stops with an error. Use Bloch boundaries that match the angle, or an angle of 0.
  • A Plane Wave or Gaussian Beam whose plane crosses more than one medium. The check stops with "Plane must be homogeneous". Move the source plane into one medium.

# Source Time Types

# GaussianPulse

Source time dependence that describes a Gaussian pulse.

See: GaussianPulse

# ContinuousWave

Source time dependence that ramps smoothly to a continuous oscillation.

See: ContinuousWave

# CustomSourceTime

Source time dependence defined by a user-supplied envelope and carrier frequency.

See: CustomSourceTime

# Baseband Source Time Types

Baseband source time types produce time-domain waveforms without a carrier frequency. For a new source, the Source Time selector offers Gaussian Pulse, Continuous Wave, and Custom Source Time. It shows a baseband type only when the source already uses one, for example a source created with the Python interface.

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