Learning Forum

[Ruzan Sokhoyan]

Hello,

I am interested in extracting the phase of light reflected from a periodic nanophotonic structure using RCWA. When using FDTD I extract the phase by placing a point monitor far away from the structure (above the plane wave source) where I have a propagating plane wave. However, in the case of RCWA, I never have a propagating plane wave above the structure. It looks like that in RCWA, I have a standing wave above the resonant structure (in reflection).

 

What would be an appropriate method to extract the phase of the reflected light in RCWA? And, in general, how can I extract the complex reflection amplitude in RCWA.

 

Thank you!

 

 

[Guilin Sun]

You can use script to get grating characterization. and the result:

gc=getresult("RCWA","grating_characterization");

Rss=gc.Rss;

etc

are actually the amplitude results, S parameters similar to Fresnel coefficients. They are complex and has the phase you need.

https://optics.ansys.com/hc/en-us/articles/12959229278611-RCWA-Solver-Simulation-Object

 

[Ruzan Sokhoyan]

Thank you very much. This is helpful. 

I have a follow-up question. In my case the illumination is normal and the light also reflects normally. How does software assign s and p polarizations in cases like this?

 

Thank you!

[Guilin Sun]

This is really a good question! In textbooks s and p polarization has a plane of incidence. In simulaiton it is 3D, it can be confusing to define which one is the incident plane. Usually I suggest to check, if you will have angled incidence, which plane it will be? usually it is in xz plane. thus you can take xz plane as the incident plane. 

However in normal incidence, it really does not matter since there is only two states of polarization. If the structure is not rotationarily symmetric, you can DEFINE which plane is the incident plane. But according to our definition, it is xz plane. Please refer to this article:

https://optics.ansys.com/hc/en-us/articles/360034394294-Understanding-direction-unit-vector-coordinates-in-far-field-projections

since we assume phi =zero when only the illumination has an angle.