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Modeling a 3D Waveguide that Support Multiple Modes

Posted Feb 23, 2024, 1:27 p.m. EST RF & Microwave Engineering, Wave Optics Version 6.1 4 Replies

Manal Shlebik
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Dear All

I am simulating a 3D waveguide that supports multiple modes at higher frequencies. I am following the instruction written in this blog: https://www.comsol.com/blogs/modeling-waveguides-that-support-multiple-modes/

Injecting the TE10 and TE20 modes in my model produce the following error message:

  • Feature: Stationary Solver 1 (sol1/s1) Failed to find a solution. Singular matrix.

For mesh case 0 there are 1 void equations (empty rows in matrix) for the variable comp1.emw.S3x. at coordinates: (0,0,0), ... For mesh case 0 there are 1 void equations (empty rows in matrix) for the variable comp1.emw.S4x. at coordinates: (0,0,0), ... and similarly for the degrees of freedom (empty columns in matrix). Returned solution is not converged. Not all parameter steps returned.

Would you please help me with this? Could you please show me, if there is any other method, how to inject multiple modes into a silicon waveguide? I am using RF and waveOptics modules.

Thanks in advance, Manal

4 Replies Last Post Feb 26, 2024, 7:38 p.m. EST
Dave Greve
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Posted: 8 months ago Feb 23, 2024, 2:49 p.m. EST
Updated: 8 months ago Feb 23, 2024, 2:49 p.m. EST
  1. Post your model.
  2. Which is it, RF or Wave optics??
1. Post your model. 2. Which is it, RF or Wave optics??
Manal Shlebik
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Posted: 8 months ago Feb 23, 2024, 3:04 p.m. EST
Updated: 8 months ago Feb 24, 2024, 10:35 a.m. EST

Dear Dave

Thanks for your quick responce,

It is RF like an example on the blog: https://www.comsol.com/blogs/modeling-waveguides-that-support-multiple-modes/

I have attached my model and had to clear the result and Mesh to reduce the size file.

Thanks,

Dear Dave Thanks for your quick responce, It is RF like an example on the blog: https://www.comsol.com/blogs/modeling-waveguides-that-support-multiple-modes/ I have attached my model and had to clear the result and Mesh to reduce the size file. Thanks,
Dave Greve
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Posted: 8 months ago Feb 23, 2024, 3:55 p.m. EST
Updated: 8 months ago Feb 23, 2024, 3:55 p.m. EST

Since this is a clad waveguide, the mode launched at the input port is not a TE01 waveguide mode. When you select a rectangular port the TE01 mode Comsol tries to use satisfies the boundary conditions of a metal-clad waveguide. Clearly that isn't the right mode shape whether you select the entire face or just the silicon face.

To solve this problem you need to do a boundary mode analysis for the ports first and then select "numeric" for the port type. I think you can find examples of this on the Comsol website.

I strongly recommend that you set up and solve a uniform waveguide problem with a single input and output first.

Since this is a clad waveguide, the mode launched at the input port is not a TE01 waveguide mode. When you select a rectangular port the TE01 mode Comsol tries to use satisfies the boundary conditions of a metal-clad waveguide. Clearly that isn't the right mode shape whether you select the entire face or just the silicon face. To solve this problem you need to do a boundary mode analysis for the ports first and then select "numeric" for the port type. I think you can find examples of this on the Comsol website. I strongly recommend that you set up and solve a uniform waveguide problem with a single input and output first.
Manal Shlebik
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Posted: 8 months ago Feb 26, 2024, 7:38 p.m. EST
Updated: 8 months ago Mar 1, 2024, 6:29 p.m. EST

Dear Dave

Many thanks for your reply,

Your help is much appreciated, Manal

Dear Dave Many thanks for your reply, Your help is much appreciated, Manal

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