Learning Forum

[Saar Poplinger]

Hi, I want to simulate a "nonlinear diffraction grating" in Lumerical FDTD. It's basically a diffraction grating with a chi2 material, a plane wave source (with an angled incidence) in a fundamental frequency and I'd like to measure its reflected and transmitted grating orders in the far field for the second harmonic frequency.

I've tried to simulate a unit cell w/ Bloch BCs with no success (doesn't return the correct grating orders in the corresponding angles).

Is there a way to perform this simulation (whether with Bloch BC, RCWA solver or any other way) in FDTD?

[Trevor O'Loughlin]

Hi Saar,

Bloch BCs are set to a single wavevector, so a change in frequency will have an angle offset.  Since you are looking at different frequencies, I think this is why the grating orders are not in the corresponding angles.  This should have some more information to help you: Bloch BCs in broadband sweeps over angle of incidence – Ansys Optics

 

Likewise, since you are looking for a generated response, you might need to be careful about the input field and make sure that you are not including your second harmonic frequency in your input.  This page might be helpful in this regard: Harmonic generation with a chi2 material – Ansys Optics