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Optical active medium

Posted Oct 21, 2010, 5:57 p.m. EDT Wave Optics Version 3.5a, Version 4.0, Version 4.0a 9 Replies

Faraz Monifi
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Hi

Do anybody know how to define an active medium in comsol 4.0a? I thought if I set the Relative permittivity to be complex and set the imaginary part to be negative, my medium will work like a active medium. But it seems that it is not that easy.

Best
9 Replies Last Post Dec 16, 2010, 4:36 a.m. EST
Shakeeb Bin Hasan
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Posted: 1 decade ago Oct 22, 2010, 2:34 a.m. EDT
I think it is that easy - just remember that comsol uses negative sign of imaginary part for absorption and positive for gain :) This is because in Comsol exp(i*w*t) is used as the time harmonic factor.
I think it is that easy - just remember that comsol uses negative sign of imaginary part for absorption and positive for gain :) This is because in Comsol exp(i*w*t) is used as the time harmonic factor.
Faraz Monifi
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Posted: 1 decade ago Oct 22, 2010, 2:15 p.m. EDT
Shakeeb

Thank you for your reply. My results say something else. I want to calculate the quality factor of a ring resonator. When my refractive index is real I get a number and I make my medium active, I expect to get higher Q-factor (The gain compensate the losses ) . When I make my refractive index complex, with either negative or positive imaginary part, I get a very low quality factor. That seems to me comsol get the imaginary part as loss in any case. Do you have any idea?

Best
Faraz
Shakeeb Thank you for your reply. My results say something else. I want to calculate the quality factor of a ring resonator. When my refractive index is real I get a number and I make my medium active, I expect to get higher Q-factor (The gain compensate the losses ) . When I make my refractive index complex, with either negative or positive imaginary part, I get a very low quality factor. That seems to me comsol get the imaginary part as loss in any case. Do you have any idea? Best Faraz
Shakeeb Bin Hasan
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Posted: 1 decade ago Oct 24, 2010, 10:56 a.m. EDT
Well, I am sorry I cannot comment on the peculiarities in your result but I know for sure that in Comsol positive imaginary part means gain and negative loss. This much is settled.

All the best :)
Well, I am sorry I cannot comment on the peculiarities in your result but I know for sure that in Comsol positive imaginary part means gain and negative loss. This much is settled. All the best :)
Mengren Man
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Posted: 1 decade ago Dec 9, 2010, 10:59 p.m. EST
how abt gain saturation?
how abt gain saturation?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Dec 10, 2010, 1:41 a.m. EST
Hi

have you tried to write the imaginary part as a function of the total E intensity ?

--
Good luck
Ivar
Hi have you tried to write the imaginary part as a function of the total E intensity ? -- Good luck Ivar
Shakeeb Bin Hasan
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Posted: 1 decade ago Dec 10, 2010, 10:44 a.m. EST
Hi,

I doubt if it is possible. Harmonic propagation is strictly for linear effects. For nonlinear stuff you have to use transient analysis. But be sure to check if it is fully equipped to handle all requirements of your simulation.
Hi, I doubt if it is possible. Harmonic propagation is strictly for linear effects. For nonlinear stuff you have to use transient analysis. But be sure to check if it is fully equipped to handle all requirements of your simulation.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Dec 10, 2010, 11:31 a.m. EST
Hi
indeed that is a good remark, time transint takes time though

--
Good luck
Ivar
Hi indeed that is a good remark, time transint takes time though -- Good luck Ivar
Zeynab Adelpour
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Posted: 1 decade ago Dec 15, 2010, 2:21 p.m. EST
hi to all

i want to know, do comsol FDTD method for simulation of laser?
hi to all i want to know, do comsol FDTD method for simulation of laser?
Shakeeb Bin Hasan
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Posted: 1 decade ago Dec 16, 2010, 4:36 a.m. EST
Comsol has a transient solver which can basically do the things any FDTD program would.

However, beware that the transient solver until 3.5a is not in the best equipped form. Lack of PMLs and any built-in support for metals make it practically useless for a lot of realistic scenarios. Don't know if in 4.x series this has been upgraded.
Comsol has a transient solver which can basically do the things any FDTD program would. However, beware that the transient solver until 3.5a is not in the best equipped form. Lack of PMLs and any built-in support for metals make it practically useless for a lot of realistic scenarios. Don't know if in 4.x series this has been upgraded.

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