Finite-Difference Time-Domain (FDTD) is an electromagnetic modeling technique. Until recently, this technique had been used primarily for the cm to meter scales and at microwave frequencies. Now this technique is commonly applied to the nanometer scale and at optical frequencies.

The FDTD method belongs to a general class of differential time domain numerical modeling methods. Maxwell’s (differential form) equations are modified into central-difference equations and discritized. Discritization of space and time makes implementation into software very simple.

The modeling space is defined as a collection of cells which are named Yee Cells. The equations are solved in a leap-frog fashion. That is, the electric field is solved at a given instant in time, then the magnetic field is solved at the next instant in time, and the process is repeated over and over again, and from cell to cell in the direction of propagation.

Explanation of images:

(left center) Focusing lens.

(Right top to bottom) x polarization of focused light, y polarization and z polarization.