Ridge waveguide to slab waveguide modal reflection



I am simulating a FP laser structure: A ridge waveguide structure which contains a slab waveguide at one end with a tilted facet. (Slab waveguide is also named passive absorption section is lasers)
I am interested to study the effect of modal reflection (back reflection) into ridgewaveguide due to the increase in the length of slabwaveguide. As the length of slab waveguide increases the modal reflection into the ridge waveguide should decrease (in my opinion?). In have simulated the slabwaveguide length vs modal reflection, but modal reflection doesnt change.
I would like to know that my approch to calculate this parameter is correct?
I have attached the main .lsf file, structure geometry and simulated graph. Main .lsf file: BD_length_vs_reflection.lsf (1.5 KB)
Geometry lsf. file:
tilted_facet_2.lsf (8.3 KB)


Hi @nouman.zia

FDTD definitely can simulate the geometry, and can be used for final tests. Here are a few modifications into your simulations:

  1. Increase the FDTD span in the +z direction so that there is an air gap between your structure and PML.
    Setting about FDTD Region and mesh
  2. Extend your geometry through PML:
  3. Make sure that the injected mode decays at least 5 orders of magnitude before reaching PML:
    Reflection problem form straight and bend silicon waveguides

You can also run these simulations in EME which is was faster. Please visit the link below for an application example:

You can take our online course in EME to learn more on how to use it:
New EME Solver online course now available at Lumerical University!

Please set your simulation file and let me know if you had any further inquiry.