Re: Different results of PhC waveguides by using triangular lattice and rectangular lattice

On Nov 23, 2009, at 9:11 PM, JiangjunZheng wrote:
> In the meep tourial, there is a 2d exmaple of PhC waveguide. I  
> modified it for W1 PhC slab waveguide. It works well. But problems  
> come when it is applied for waveguides of different width, for  
> example W0.8.
>
> To simulate the W0.8 waveguide, two methods are used:
> 1, use the triangular lattice, and shift the lateral holes (three  
> holes on each side) along the two in-plane axes.
> 2, use the rectangular lattice (three lines on each side). It is  
> easier to set the position of the lateral holes this way.
> By using mpb-data and h5topng, it is checked that the waveguides  
> constructed under both lattices are the same.
>
> However, after run-even, only half the guided modes are founded by  
> using the rectangular lattice (kx=0.5, kx along the waveguide  
> direction), these modes share the same line at x=a/2 (a is the  
> period) with Hz=0 and some images of Hz for other modes show some  
> lines along the x direction which make them not as smooth as other  
> images. For the W0.8 waveguide, it seems that the first method works  
> by comparing the field images with those of W1 waveguide.

I'm not sure what you mean about getting only half the guided modes.   
If you have the right structure, you should get all the guided modes.

If what you want is a line defect in a triangular lattice with varying  
width, you're right that the best way is to use a rectangular  
supercell.  It should look something like the one I described in this  
message:

http://thread.gmane.org/gmane.comp.science.photonic-bands/1262/focus=1376

Steven