Discussion Forum

Hello,

I am new to COMSOL and doing some initial tests to get familiar with the Wave Optics model. One of my intial tests is trying to determine the coupling efficiency from an SMF-28 fiber to a slab dielectric waveguide. I am using the EWBE physics and was able to succesfully get the beam envelope for the fiber alone, then fiber dispersing into air, and now I have added the waveguide but I am getting an error when trying to run the study. I used the tapered waveguide and the fiber to fiber coupling from the COMSOL learning center as guides.

My general approach was to define three domains in the simulation. In each one I am using EWBE to find the phase value psi, and I gave separate definitions in each of the three domains. I have PML around the 3 sides that don't include the input port. I am using an input numeric port and and output domain backed slit port. In between the fiber-air and air-waveguide domains I have transition boundary conditions. My study uses two boundary mode analysis steps for each of the ports and then a frequency domain step to solve for the field overall.

I am including the MPH file and the output error log. The error log is very difficult to parse, so I don't really know where the source of the error is. COMSOL version 6.1 and running on an M1 mac with Sonoma 14.4.1 if that is of any relevance.

As a side note, my next step is to try and optimize the thickness of the waveguide to maximize coupling, so if anyone has good tips on using the Optimization Module with the EWBE physics that would be appreciated.

Thanks, Jack