Comparing EME and FDTD
Choose the right method, save hours on simulations.
EME and FDTD are the industry’s go-to waveguide simulation methods; both as rigorous solutions to Maxwell’s equations. When both methods are applicable and configured correctly there is no reason their result should differ.
So how to pick which method to use?
This page shows pros and cons of each method through their application in common photonic devices.
Finite Difference Time Domain - FDTD
The FDTD method divides photonic devices with a very fine mesh. Maxwell’s equations are then solved along small steps in space and steps in time to evolve fields through the device.
The more fine the mesh, the more accurately the physics of light propagation is modelled.
Runtime is increased the more mesh points there are (larger bounding volume, finer mesh resolution) or if the designer simulates a larger amount of time.
EigenMode Expansion - EME
EME splits photonic devices into multiple cross sections and calculates a set of modes at each cross section; enough modes to act as a basis set to describe the field in that cross section.
To connect the neighbouring mode lists, a scattering matrix is calculated and the full result is a scattering matrix for the entire device.
EME simulations increase in compute time the more modes that are required to form a basis set, the more cross sections needed to be calculated, and for larger cross sectional areas.
Comparing EME and FDTD: Tapers
Examine the benefits of EME for taper simulations
Comparing EME and FDTD: Rings
Compare EME and FDTD for Ring Resonator Simulations
Comparing EME and FDTD: Bends
Comparing EME and FDTD for simulations of waveguide bends
Conclusions
The many benefits of EME such its fast simulations (and the iterative designing this enables) make it Photon Design’s go-to choice for waveguide devices. Where EME is not applicable and on the occasion where it’s preferable, FDTD can fill in the gaps. These occasions include:
- When light cannot be described as a basis set of bound modes (surface grating coupler)
- Where time evolution must be considered (non-linear materials, photonic crystal lasers)