Fdtd comsol
![fdtd comsol fdtd comsol](https://kavli.berkeley.edu/sites/default/files/styles/panopoly_image_original/public/comsol.jpg)
Modal solutions offer another approach to waveguide design problems. Typical FD-BPM applications include WDM devices, switches, modulators, multimode interference devices, passive splitters, and design of standard and specialty fiber. The paraxial approximation enables BPM to analyze much longer structures (on the millimeter and centimeter scale) than would be reasonable for analysis with FDTD. Finite-difference BPM can still solve some high-index-contrast problems and some problems with significant power off-axis, but the further one strays from safe cases the more is left to the skill and judgment of the user. Other beam-propagation methods exist, but the finite-difference version is most commonly used commercially.
#Fdtd comsol software
The approaches include parallel processing features in the software and, most recently, dedicated hardware to boost single system processing speeds.įor light propagating through a low-index-contrast waveguide or optical fiber, where it is appropriate to use the paraxial approximation, a finite-difference beam-propagation method (FD-BPM) can be used, which retains the finite difference grid in transverse directions but assumes a slowly varying envelope in the axial or propagation direction. Different vendors take significantly different approaches to optimize the performance of their software in solving problems that require clustering. One source interviewed for this article offered an example of clustering on more than 1000 processors on West Grid, Western Canada’s largest supercomputer, for an almost 1000× improvement in computation speed. The upper limit for using the FDTD approach without clustering computers is about 10 wavelengths. So a three-dimensional design problem with feature sizes on the order of one wavelength would require about 10,000 grid points, and the need to calculate the field for every grid point rapidly renders FDTD impractical for large devices. In practice, FDTD needs to have about 15 to 20 grid points per wavelength in every direction, depending on the application and accuracy required. The primary limitation of FDTD is that it is computation intensive. In addition, all sorts of optical materials can be used with FDTD algorithms-a crucial factor because of the increasingly complex materials being incorporated into photonic component and system designs (see figure).
![fdtd comsol fdtd comsol](https://congshanwan.github.io/images/fig_meep.png)
Typical applications for optical software based on an FDTD algorithm include design of photonic-bandgap structures for photonic crystals, ring resonators, wavelength-scale object scattering (such as surface-plasmon effects), gratings and other diffractive structures, high-index-contrast waveguides, biosensing devices, and nano- and microlithography. The FDTD technique is a discrete representation of Maxwell’s equations on a grid that is exact in the limit that the grid spacing goes to zero, so in principle FDTD can be used to solve any optical problem without approximation. In this article, we look at a few algorithms commonly used in commercially available photonic-design software: finite-difference time-domain (FDTD) method, the finite-difference beam-propagation method (FD-BPM), and a couple of mode-solving methods.
#Fdtd comsol series
Part I of this series was published in September (see ). When the physical features of an optical system shrink to within an order of magnitude of the wavelength of light, physical-optics software must be used for system design, because the assumptions necessary for a geometrical optics or ray-tracing approach no longer hold.