Learning Forum

[Sangmyeong Yu]

The figure above represents a unit cell in periodic structures.

When simulating a broadband source with wavelengths ranging from 350 nm to 800 nm at a specific angle, should I simply set the angle theta as a Bloch boundary condition (BC)?

Do all frequencies in the injection source incident at the same angle?

[Amrita Pati]

Hi Sangmyeong,

The Bloch BCs ideally should be used for single wavelength/narrowband simulations. This is because actual incidence angle which will be used in the simulation will change with change in the frequency (answer to your question). The alternate is to run a series of simulations (sweep) with Bloch BCs for different wavelengths. Alternatively, you can use the BFAST source, but using and attaining convergence with BFAST source can be a bit tricky. You can find more information on this here:

1. Broadband Fixed Angle Source Technique (BFAST)
2. Understanding injection angles in broadband simulations

You may also consider using the RCWA solver for this. RCWA is specifically designed to simulate the interactions of plane wave with periodic structure. And will be much faster than FDTD as it is semi-analytic. You may visit the following page for more information:

1. RCWA - Solver Introduction

Regards,
Amrita