Learning Forum

[vision]

Recently encountered several questions while studying the case "Antireflective circular polarizers in OLED display", hoping to get answers:

 

1. I noticed that when calculating the transmission and reflection coefficients, there are the following four lines of code. After reviewing some basic knowledge, I think this should be calculating the coefficient between the energy flow transmittance and amplitude transmittance. According to the formula, it should be n2cosθ2/n1cosθ1. Why is the calculation method here sqrt(n2^2-n1^2*cosθ1^2)/n1cosθ1?

 

 

2. In practice, we need to use dispersive materials to calculate the reflectance spectra under different angles of incidence, so we used RCWA to build the corresponding model, and used the refractive index in the official website to basically reproduce the anti-reflective phenomenon, but I feel that there is still a discrepancy between the calculation results and the json file obtained from the case study by using STACK, so can you help us to check if there is any problem in the model?

 

 

3. How to get more realistic and high resolution simulation results when completing calculations with RCWA and importing the json into speos, how can I adjust the model to get better simulation results when these colored noise can always be seen in the current simulation results?

 

my results use rcwa：

reference results use stackrt solved:

 

[Guilin Sun]

 

A1： it is the same as n2cosθ2/n1cosθ1. However it uses theta1 instead of theta2. You can deduct this formula with only theta1 with Snell’s law.

A2: Stack function can deal with dispersive material. Please refer to this: https://optics.ansys.com/hc/en-us/articles/360034406254-stackrt-Script-command

for RCWA, it is designed for periodic nano structure, and you may need to test how many k vectors are to be used in general.

For planar structure like thin films, in principle both should give the same result, with minor difference due to the fact: STACK is analytical without meshing whereas RCWA is semianalytical which needs meshing. The difference might be from meshing.

A3: I guess you uploaded the wrong images. 

RCWA needs converging tests for mesh and k vectors in general, provided that the material model is exactly the same. Please note that STACK uses FDTD fitted material data. RCWA is frequency-domain solver so it might simply use the material raw data if you do not set the fit: