Lumerical VGC question
To Lumerical Support,
I am trying to simulate an apodized VGC grating as shown in the attached paper using 2D-FDTD. I have also attached an FSP file with my current setup as well as the LSF file with the parameters that match the paper (height of my waveguide is 260 nm). I make sure the simulation region size, the mesh setting (8) and the Mode field diameter(10.8 um) of the source also matches the paper. My current result which is shown below shows coupling efficiency of ~73% at wavelength of 1523 nm.
However, there is a mismatch of about 10% coupling efficiency and a small deviation in centre wavelength of about 30 nm. Below is the simulated result from the paper. I cannot figure out why there is a variation in the result if I use the same geometry and same FDTD setting as the paper.
Can you advise me on this issue? Thank you very much for your help.
PS: I double checked the grating structure and it matches the table from the paper on page 7.