Hi there, I'm new to modelling with comsol. I would like to ask if it is possible for comsol to output linearly polarized (LP) modes? I tried modelling a simple single mode fiber with an enlarged core so that it becomes multimode, but it seems like I can only get the exact modes (TE, TM and HE) individually for the higher order modes. Am I missing some other settings? Thanks!
Hello Li,
In COMSOL, obtain LP modes directly can be a bit tricky since the software typically calculates the exact modes like TE, TM, and hybrid modes (HE, EH). However, LP modes are approximations of these exact modes, particularly in weakly guiding fibers where the core and cladding refractive indices are very close to each other.
Basically, after solving for the eigenmodes to obtain the exact modes (TE, TM, HE, EH), use the mode analysis feature to inspect the electric field distributions. To approximate LP modes, you need to combine the exact modes, as LP modes can be represented by superpositions of these exact modes. For instance, LP11 modes can be approximated by combining HE21 and TE01 modes, considering their similar propagation constants.
Then, create expressions to linearly combine the electric fields of the calculated modes. For example, to approximate an LP01 mode, use the fields of the HE11 mode directly. For higher-order LP modes, linearly combine HE and EH modes with appropriate phase adjustments. Use the Global Evaluation feature under Derived Values in the Results section to create expressions for combining the modes, such as E_x = a*E_HE21_x + b*E_TE01_x and E_y = a*E_HE21_y + b*E_TE01_y.
This work can also be used as reference: https://www.comsol.com/paper/analysis-of-linearly-polarized-modes-10480
Best Regards,
Marcos.
Thank you very much for your reply. Is it necessary to normalize the electric field and then superimpose it when calculating Ex or Ey in LP mode. Because the TE01 mode field intensity I obtained is much greater than that of HE21, the electric field distribution map of the TE01 mode is still maintained after superposition. Or how to obtain the values of a and b in the equation of E E_x = a*E_HE21_x + b*E_TE01_x.@Marcos Moura
Hi, with COMSOL it's too hard to calculate and finally you can't have a accurate answer.
There is a code "BPM-matlab" that you can get it from github and it's so easy for calculate fibers and other optical module and it calculate LP modes.
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