problem with single mode

[Dr. MohammadMahdi Ariannejad]

I have single mode when ever I have design of splitter but once I change to the straight line it would be multi mode, would you please help me how to design a straight line to have single mode?

[Damian Marek]

The size of a waveguide impacts the resultant number of modes greatly. In your example it seems to be quite wide! Try making the core and cladding dielectric to be almost equal. That might work. You can also try making it less thick.

Good luck

[Dr. MohammadMahdi Ariannejad]

Yes you are right so for solving this problem that I found after one week is you have to find out till where your design for example will be single mode for my case 600 micron then I duplicate it and one more time, still it is single mode, the question is why when I draw in a single waveguie it was multi-mude but after I cut it in to three straight waveguide it changed to a very nice single mode? because in reality in my fabrication the machine will not understand I cut it to three waveguide, and it will fabricate as a straight waveguide, so how I can be sure my waveguide is single mode? I already simulate both of them, or we can say because of the single mode is 600 micron now I have 3 of them it will obey this rule? otherwise it would be multi mode? I need a strong answer many thanks 🙂

[Damian Marek]

Could you please attach your OptiBPM project file and OptiMode file if you have one. Any diagrams or articles you have that clearly shows the geometry would be very helpful as well. I am having trouble visualized what your structure looks like.

Are the waveguides end to end? Are they parallel to each other?

[Dr. MohammadMahdi Ariannejad]

Dear;
I attach it here by this post, this problem solved, but I do not have any cause to say about it, please describe for me why when i split the wave guide it got single mode otherwise in one wave guide it was multi mode, thanks.

[Dr. MohammadMahdi Ariannejad]

any cause or any tips for this matter? 🙁 I am wishing to have some description about it, many thanks.

[Damian Marek]

I think the main problem with your project is the width of the simulation domain, which is very large compared to the y dimension. Looking at the modal fields you can tell these are not real modes because it looks like they are enclosed in the borders of the simulation domain. The field should be confined to the small waveguide core. Did you use transparent boundary conditions?

I re-sized the domain and placed the waveguide adjacent to the substrate, as in the picture attached. For this geometry and refractive index contrast I found 10+ physical modes. Attached is also the project file I changed.

You might have to reduce the index contrast and make a smaller waveguide core to achieve single mode operation.

[Dr. MohammadMahdi Ariannejad]

would you mind to tell me this things that you wrote in here is from which lesson in tutorial? many thanks, indeed I am using version 11 bpm and i cannot open this file, would you please help me about it? it said it cannot be open! 🙁

[Damian Marek]

I didn’t take this information from any tutorial specifically. Have you looked at this one?:

Create a Chip-to-Fiber Butt Coupler

Unfortunately, our products don’t support forward compatiblity, so you won’t be able to open the project files unless you upgrade. Sorry for the inconvenience.

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