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Waveoptics Module, Transmission Numerical Ports

Posted Jun 4, 2019, 6:51 a.m. EDT Wave Optics Version 5.4 1 Reply

Shqiprim Adrian Abazi
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Hello,

I am simulating photonic structures in a multi-mode waveguide operation. For this, I am using numerical ports for exciting specifc modes in the waveguides and using numerical ports as well for measuring transmission values of specific modes. Comsol offers some predefined expressions for the transmittance by port name: ewfd.TportX .

My question is, how specifically these values are calculated and how they compara to the S-Parameters feature in the RF-module. My guess is, that they are equivalent to each other and are calculated in the same manner.

I am using the Wave Optics module and Comsol Version 5.4.

Thank you very much

1 Reply Last Post Jun 4, 2019, 11:01 a.m. EDT
Ulf Olin COMSOL Employee

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Posted: 6 years ago Jun 4, 2019, 11:01 a.m. EDT
Updated: 6 years ago Jun 4, 2019, 11:02 a.m. EDT

Dear Shqiprim Adrian,

You are right that the transmittance variable is defined from the S-parameter variable for the port. If the port name is for instance 2, and the port is not located on the same boundary as your excitation port, you get a transmittance variable defined as

ewfd.Tport_2 = abs(ewfd.S21)^2,

assuming that it is the port named "1" that is the exciting port.

Similarly, if the port is defined on the same boundary as the exciting port, you get a reflectance variable. For instance,

ewfd.Rport_3 = abs(ewfd.S31)^2,

assuming that this port is named "3".

When you use Ports of the Periodic type and when you add Diffraction order ports, you also get reflectance and transmittance variables with names based on the mode number, instead of the port name. For instance, if you add a Diffraction order port to the same boundary as your exciting port, in 2D geometry, with mode number m = 1 and in-plane polarization, you get a variable called

ewfd.Rorder_p1_ip = abs(ewfd.SN1)^2,

where "p1" represents the mode numer m = +1 and "ip" represents the in-plane polarization. Here, "N" in the S-parameter variable ewfd.SN1 is the port name for this port. However, using the "mode" variables you don't need to keep track of the port names.

Best regards,

Ulf Olin

Dear Shqiprim Adrian, You are right that the transmittance variable is defined from the S-parameter variable for the port. If the port name is for instance 2, and the port is not located on the same boundary as your excitation port, you get a transmittance variable defined as ewfd.Tport_2 = abs(ewfd.S21)^2, assuming that it is the port named "1" that is the exciting port. Similarly, if the port is defined on the same boundary as the exciting port, you get a reflectance variable. For instance, ewfd.Rport_3 = abs(ewfd.S31)^2, assuming that this port is named "3". When you use Ports of the Periodic type and when you add Diffraction order ports, you also get reflectance and transmittance variables with names based on the mode number, instead of the port name. For instance, if you add a Diffraction order port to the same boundary as your exciting port, in 2D geometry, with mode number m = 1 and in-plane polarization, you get a variable called ewfd.Rorder_p1_ip = abs(ewfd.SN1)^2, where "p1" represents the mode numer m = +1 and "ip" represents the in-plane polarization. Here, "N" in the S-parameter variable ewfd.SN1 is the port name for this port. However, using the "mode" variables you don't need to keep track of the port names. Best regards, Ulf Olin

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