Coupling efficiency of circular grating coupler



I’m using 3D FDTD to optimize a circular grating coupler. The efficiency should be determined by the power coupled to a SM fiber through the microscope objective. I guess I need to find an overlap of the farfield projection to the gaussian mode. Could you suggest what would be the easiest way to estimate it?
Thanks in advance,


Hi Arina,

An approach you can use would be to use a script to calculate the image of the field through the objective from the result of your FDTD simulation. This approach is used in the Imaging example.

Then, you could use this as a source in a second simulation, where you couple this into the fibre. The coupling efficiency can be obtained with a mode expansion monitor.

I hope this helps!


Thank you! Yes, it works. The only one question: I need to tilt the image plane as if I had a mirror. From the farfield projection I know under which angle the beam is coming out, but how to implement it. Maybe you have already an example? Thanks, Irina


Hi Irina,

I don’t think it is really necessary to tilt the image. I would assume it is to fit an experimental setup? As it shouldn’t modify the image itself so, at least for a start, I wouldn’t take this into consideration.