Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Air Clad Optical Waveguide - Boundry condition

Please login with a confirmed email address before reporting spam

Hi,
I want to model a bent Air clad wave-guide. I'm using the optics->beam envelope both in 2D and 3D. I'm not sure about my boundary condition.. Do I even need to define one? Is is possible to use the scattering boundary condition, and if so how do I define it as to represent air?
Thanks in advance,
Tom.

1 Reply Last Post 10.07.2014, 14:21 GMT-4
Robert Koslover Certified Consultant

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 10.07.2014, 14:21 GMT-4
Caveats: I don't model a lot of fiber optics and I haven't used the beam-envelope formalism. So I could be wrong about what I say next. OK? Here goes. Anyway, my initial idea would be to include a modest volume of the surrounding medium (in your case, air). This way, the boundary on the fiber optic surface would be handled correctly. After all, in the physical world, there is an evanescent field that extends a little bit outside the cladding. And if you don't allow that to exist in your model, you probably won't have the conditions set right. Finally, to bound the outside air volume, I would use either a scattering boundary condition or PML. Alternatively, I suppose you *might* be able to get away with setting some kind impedance boundary condition on the surface of the fiber, but I wouldn't assume that you could get away with that, unless your careful review of the physics showed it was equivalent to what I described above. I encourage other readers here with more knowledge of simulating optical waveguides or fiber optics to contribute their thoughts.
Caveats: I don't model a lot of fiber optics and I haven't used the beam-envelope formalism. So I could be wrong about what I say next. OK? Here goes. Anyway, my initial idea would be to include a modest volume of the surrounding medium (in your case, air). This way, the boundary on the fiber optic surface would be handled correctly. After all, in the physical world, there is an evanescent field that extends a little bit outside the cladding. And if you don't allow that to exist in your model, you probably won't have the conditions set right. Finally, to bound the outside air volume, I would use either a scattering boundary condition or PML. Alternatively, I suppose you *might* be able to get away with setting some kind impedance boundary condition on the surface of the fiber, but I wouldn't assume that you could get away with that, unless your careful review of the physics showed it was equivalent to what I described above. I encourage other readers here with more knowledge of simulating optical waveguides or fiber optics to contribute their thoughts.

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.