Strange results with transfer matrix (Optics)

[Olioli]

Hi everyone,

I'm trying to study reflection on the rear side of an optical device. I wrote a transfer-matrix code in MATLAB to compute the reflectance. I checked my code by comparing some basic cases with other kind of optical simulations (FTDT with Lumerical). When the incident medium is Air or Dielectric materials, I got relevant results (both transfer matrix or FDTD give the same). When I only have one interface (like Silicon-aluminum), My code gives the same solution than the one obtains with Fresnel coefficients. The problem appears when I introduce thin films between two absorbing medium. For example, Silicon-MgF2-Aluminum interfaces, where silicon is the incident medium and Aluminum the substrate. For some wavelength, the reflectance (so the amount of light reflected in the silicon) is higher than 1, which is of course wrong (no luminescence in transfer matrix code).

I don't know what's wrong with transfer matrix. This problem appears only when the incident and substrate medium are absorbing and a dielectric layer are inserted between them.

 

[eljose79]

Can someone please help me understand what is going on and how I can fix this issue?
Hi there,

It sounds like you have already done some thorough testing and troubleshooting of your code, which is great. One possibility could be that your transfer matrix code is not taking into account the absorption coefficient of the materials, which could lead to higher reflectance values for wavelengths where there is significant absorption. It may be helpful to double check your code and make sure you are incorporating the absorption coefficient correctly.

Another potential issue could be the thickness of your thin film. If the film is too thin, it may not be able to fully absorb the incident light, leading to higher reflectance values. I would suggest varying the thickness of the film and seeing if that affects the results.

It's also worth considering the angle of incidence of the light. If the light is at a high angle of incidence, it may increase the path length through the absorbing materials, leading to higher reflectance values. Again, varying the angle of incidence could help determine if this is a factor in your results.

I hope these suggestions are helpful in troubleshooting your code and resolving the issue. If you continue to have trouble, it may be helpful to consult with other experts in the field or reach out to the developers of the transfer matrix code for further assistance.

Best of luck with your research!