Learning Forum

[sagar]

Does the optimum diameter of the dielectric waveguide for physical mode formation depend upon FDE simulation area for a particular wavelength of light? I notice for FDE area 1.5 um x 1.5 um, physical modes are started forming when the diameter of the waveguide is 148 nm, and below that no modes are supported. And I changed the area 1.2 um x 1.2 um, the physical modes are started forming at 156 nm and if I increase the area of FDE, modes are started forming more lower diameter. I think it should not depend upon the area of the FDE simulation region. Please explain the reason behind it. Thank you.

[Guilin Sun]

Depending on the understanding of "modes", the result may be different under different boundary conditions. Using Metal BCs will always give you modes since it is metal box filling with some materials.
If PML BCs are used, the FDE solver will calculate all the possible modes including PML materials. While the solver tries to report the propagation modes under PML BCs, if the results are all PML modes then the solver will not report any mode. If this the case, please use large number of trial modes. I would suggest that you use Metal BCs and check if the mode is the propagation mode, or simply the metal box mode. You may need a little more knowledge about the waveguide its self. Please check the mode properties and make sure they are what you need. You may also read more about the FDE solver and its result.