2.5d photonic crystal slab waveguide sharp bend


#1

Dear Lumerical technical support,

I followed examples from https://kb.lumerical.com/en/diffractive_optics_waveguide_pcbandstructure.html
and design a slab photonic crystal with square lattice. Having modified the script now I scan the entire bandstructure and create find large bandgap at large frequency range.

1.Then I build a line defect photonic crystal waveguide and butt coupler and it works well for 1.5-1.6um.
However it does show transmission oscillation at ~ 1.3um if source bandwidth covers that and at that wavelength there should also be a bandgap. Why this can happen?

2.I am using such photonic crystal waveguide only at 1.5-1.6um and try to create a sharp bend. However a 90 degree bend shows strong reflection and scattering inside lattice and transmission is very low.

However it seems from other software like COMSOl with following link: FEM results did not sow such reflection
http://wsshin.github.io/maxwellfdfd/doc/topic/gallery2d.html

2.5d bend1.lms (432.1 KB)

2.5d straight.lms (430.9 KB)


#2

There can still be some transmission at band gap frequencies if there are relatively few periods of the periodic lattice. As a test, I tried running the straight waveguide case with the original number of periods and double the number of periods and I was able to see the transmission reduce in the range between about 1.15-1.45 um.

I also checked the images from the COMSOL simulation that you linked and it looks like it includes many more periods of the device in both bent and straight cases, so I think that could be the difference. Hopefully this helps!