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No wave propagation
Posted Jun 22, 2017, 5:49 a.m. EDT Modeling Tools & Definitions, Parameters, Variables, & Functions, Results & Visualization, Studies & Solvers Version 5.2a 2 Replies
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Hello,
I am new to COMSOL and am trying to simulate propagation through a waveguide. I found this 2D model of dielectric slab waveguide to get an idea. However, when I just change the dimensions of the waveguide keeping everything else constant, the wave does not propagate and I see an electric field only at the input edge. The same happens when I create a new model.
Can someone please help me?
Cheers,
Shashank
I am new to COMSOL and am trying to simulate propagation through a waveguide. I found this 2D model of dielectric slab waveguide to get an idea. However, when I just change the dimensions of the waveguide keeping everything else constant, the wave does not propagate and I see an electric field only at the input edge. The same happens when I create a new model.
Can someone please help me?
Cheers,
Shashank
2 Replies Last Post Jul 12, 2017, 6:54 a.m. EDT
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Posted:
7 years ago
Updated:
7 years ago
Although you didn't provide the details of your model, one of the most common causes of this type of behavior is that the frequency is below the cutoff frequency for the waveguide mode that you are trying to launch. If your adjustment to the waveguide geometry involved reducing the size of a cross-section dimension, then that raises the cutoff frequency. If the cutoff frequency is above your specified frequency, then the mode will not propagate and you will see a (generally rapid) exponential decay of the field away from the launching port.
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Posted:
7 years ago
Hello Mr. Koslover,
Thank you for your reply. I do see the behavior of rapid decay of the field away from the launching port. However, the interesting thing is that I observe this behavior if I increase the waveguide cross-section (CS). When I decrease the waveguide CS, smaller wavelengths propagate!
My understanding of the cut-off frequency (wavelength) is its inverse sqrt dependence on the waveguide cross section dimensions. So, for a given cross-section of the waveguide, I can theoretically calculate the cut-off frequency (wavelength). However, what I observe in COMSOL is that no field propagates above the cut-off frequency (or below the cut-off wavelength). This is opposite of what must happen. No light should propagate below the cut-off frequency (or above the cut-off wavelength).
I am not sure if I am doing any mistake here. The model is the standard model that can be downloaded from COMSOL website (www.comsol.com/model/dielectric-slab-waveguide-14709).
Thank you for your reply. I do see the behavior of rapid decay of the field away from the launching port. However, the interesting thing is that I observe this behavior if I increase the waveguide cross-section (CS). When I decrease the waveguide CS, smaller wavelengths propagate!
My understanding of the cut-off frequency (wavelength) is its inverse sqrt dependence on the waveguide cross section dimensions. So, for a given cross-section of the waveguide, I can theoretically calculate the cut-off frequency (wavelength). However, what I observe in COMSOL is that no field propagates above the cut-off frequency (or below the cut-off wavelength). This is opposite of what must happen. No light should propagate below the cut-off frequency (or above the cut-off wavelength).
I am not sure if I am doing any mistake here. The model is the standard model that can be downloaded from COMSOL website (www.comsol.com/model/dielectric-slab-waveguide-14709).