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effective refractive index RF module

Posted 26.01.2012, 16:37 GMT-5 RF & Microwave Engineering, Geometry, Parameters, Variables, & Functions, Results & Visualization Version 4.2a 4 Replies

Neal Pfeiffenberger
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Hi, quick question that may be easy for some of you. Say I have a fiber with a core of refractive index 1.45 and then I have an array of airholes in a background of refractive index 1.45. So the airholes lower the refractive index of the cladding region. How do I find out what this "average" effective refractive index of the cladding is. I know that I can solve the fiber and get modes with a wide range of effective refractive indices, but I just want to know what the cladding is effectively being "seen as". For example, I could then take this average cladding refractive index value and in a new model, place it as a cladding layer around my my core (think step index fiber, instead of a porous cladding) and compute the number of modes and then check this with the previous porous cladding fiber. Does anyone know how to do this?
4 Replies Last Post 27.01.2012, 14:44 GMT-5
Robert Koslover Certified Consultant
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Posted: 1 decade ago 27.01.2012, 13:04 GMT-5
Yes. I believe that you will find the following paper very helpful:

Knott, E.F., "Dielectric Constant of Plastic Foams," IEEE Trans. Ant. and Propagat., Vol. 41, No. 8, Aug. 1993, pp. 1167-1171.

Knott shows how to determine the contributions of each material to the overall dielectric constant.
And from that, you can get the index of refraction = square root of epsilon_r.
Yes. I believe that you will find the following paper very helpful: Knott, E.F., "Dielectric Constant of Plastic Foams," IEEE Trans. Ant. and Propagat., Vol. 41, No. 8, Aug. 1993, pp. 1167-1171. Knott shows how to determine the contributions of each material to the overall dielectric constant. And from that, you can get the index of refraction = square root of epsilon_r.
Neal Pfeiffenberger
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Posted: 1 decade ago 27.01.2012, 14:14 GMT-5
Thanks Robert, I guess I was just looking at the easiest way to do this using comsol and not by Cuming's approach. I figure I could highlight the area of the cladding (a mixture of air and silica) and get comsol to tell me the volume fraction for each in that region. I could then just plug my silica and air volume fraction into equation 7 in your link and get a good estimate that way. Is there a useful way to do this in comsol or would it just be easier by hand?
Thanks Robert, I guess I was just looking at the easiest way to do this using comsol and not by Cuming's approach. I figure I could highlight the area of the cladding (a mixture of air and silica) and get comsol to tell me the volume fraction for each in that region. I could then just plug my silica and air volume fraction into equation 7 in your link and get a good estimate that way. Is there a useful way to do this in comsol or would it just be easier by hand?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 27.01.2012, 14:40 GMT-5
Hi

to get the volume (or areas in 2D) you need to select the domains, and integrate with an operand of "1"
You can do this in the Results Derived Values section, or define specific variables and an integration operator in the Definition module

--
Good luck
Ivar
Hi to get the volume (or areas in 2D) you need to select the domains, and integrate with an operand of "1" You can do this in the Results Derived Values section, or define specific variables and an integration operator in the Definition module -- Good luck Ivar
Robert Koslover Certified Consultant
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Posted: 1 decade ago 27.01.2012, 14:44 GMT-5
1. You're welcome!
2. Your planned approach sounds good to me. And yes, unless I really needed to automate the process of having various values for some kind of parameter sweep, I would just enter the refractive index value "by hand."
1. You're welcome! 2. Your planned approach sounds good to me. And yes, unless I really needed to automate the process of having various values for some kind of parameter sweep, I would just enter the refractive index value "by hand."

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