Lumerical Fdtd Tutorial -

A typical simulation in Lumerical FDTD follows a structured workflow. We will illustrate this using a canonical example: calculating the transmission and reflection spectra of a photonic crystal slab.

Step 1: Defining the Simulation Region. The simulation begins by setting up the FDTD region, a rectangular volume where the field evolution is computed. The user defines its size in the x, y, and z dimensions. Crucially, boundary conditions must be assigned. For an open structure radiating into free space, perfectly matched layers (PML) are applied at the boundaries to absorb outgoing waves without spurious reflections. For periodic structures like gratings or photonic crystals, periodic or Bloch boundary conditions are more appropriate. In our example, we use PML in the vertical (z) direction and periodic boundaries laterally (x, y) to model an infinite slab.

Step 2: Adding Materials and Structures. Lumerical provides a comprehensive material database (e.g., Si, SiO₂, Au, Ag) with wavelength-dependent refractive indices (n, k). Users can also define custom materials using models like Lorentz or Drude for dispersive media. The photonic crystal slab—a layer of silicon with a periodic array of air holes—is constructed using primitive geometric objects (rectangles, cylinders) from the layout editor. Boolean operations and parameter sweeps allow for complex, parameterized designs. lumerical fdtd tutorial

Step 3: Configuring the Source. An excitation source injects light into the simulation. Common choices include:

Step 4: Placing Monitors and Analysis Groups. Monitors record field data. Key types include: A typical simulation in Lumerical FDTD follows a

Step 5: Mesh Settings. The FDTD solution's accuracy is governed by the mesh. The default uniform mesh is often insufficient. Users typically employ a conformal mesh that refines near material interfaces. The "mesh override" region allows local refinement in critical areas (e.g., inside the air holes). A standard rule of thumb is a mesh step of at least ( \lambda / 20 ) at the highest frequency of interest. Lumerical also supports a non-uniform mesh to balance speed and accuracy.

Step 6: Running the Simulation and Analyzing Results. After checking for warnings (e.g., insufficient PML thickness, mesh too coarse), the simulation is executed. For 3D problems, this can be memory-intensive. Lumerical leverages parallel computing (multi-core CPU, GPU acceleration). Once completed, results are viewed in the visualizer. We can plot ( T(\lambda) ) and ( R(\lambda) ) versus wavelength, observe the photonic bandgap as a dip in transmission, and visualize the field profile at resonant wavelengths. Step 4: Placing Monitors and Analysis Groups

If you want your simulation to be accepted in a peer-reviewed journal or a product tape-out, follow this checklist:

Lumerical FDTD is not merely a black-box solver; it is an interactive environment that demands the user translate physical intuition into a set of numerical choices—mesh size, boundary conditions, source shape, and monitor placement. Mastering this tool requires both theoretical knowledge of the FDTD method and practical experience with its workflow. By following a disciplined approach—defining the region, constructing the geometry, configuring sources and monitors, refining the mesh, and rigorously testing convergence—a researcher can confidently simulate complex light-matter interactions. From designing meta-lenses and photonic crystals to simulating plasmonic waveguides and solar cells, Lumerical FDTD remains an indispensable bridge between the abstract equations of electromagnetism and the tangible devices of the future.