Discussion Forum

Posted: 1 decade ago 1 mars 2012, 15:34 UTC−5

Hi have you checked the Derived Vaues both Global Evaluation and Surface Integrated values, COMSOL has many precooked variables, but I do not know them well enough, so far I have hardly had time to work in optics with V4, so I'm not sure which one should est suit youre need ;) -- Good luck Ivar

Posted: 1 decade ago 1 mars 2012, 17:02 UTC−5

Hi Ivar, Thanks for the reply. What is "Derived Vaues both Global Evaluation and Surface Integrated values". I do not understand these terms. Can you bit explain these. where will I find these in Comsol? Please help. Thanks.

Posted: 1 decade ago 1 mars 2012, 17:42 UTC−5

Hi they are the names of the Results sub-nodes and allow to derive values from the solved Data Sets, check your doc and look into the nodes in your tree -- Good luck Ivar

Posted: 1 decade ago 2 mars 2012, 08:48 UTC−5

Thanks Ivar. In Derived values i got complex propagation constant. But value is very high. What does it indicate. Even in Step index fiber model provided by comsol in model library the values for first mode are 1.444 and 5.85512e6i. Does this high value make any sense. Even in my model I am getting such high value. Please help.

Posted: 1 decade ago 10 mars 2012, 09:25 UTC−5

Dear Jain, I believe that you will need some absorbing boundary conditions like PML in order to calculate losses in a bent waveguide. The losses will depend on the curvature and they can get very high. cheers, -- Felipe

Posted: 1 decade ago 10 mars 2012, 20:07 UTC−5

Deepak, I've seen you've already implemented the PML's in your mph file. That's fine, but I will recommend you to ask somebody who knows better the functioning of the comsol's PML. So far I've heard they are not as accurate as you will expect, and I've found that the documentation is very limited about the inside functioning of this PMLs and the meaning of those variables. My other commentary about your mph file is that I don't understand why you are using a different wave equations for the cladding and the core. I've noticed that the core index depends on the curvature (R) but I believe the cladding does depend on this too. Why not define the core and the cladding refractive index as Parameters that are functions of R? cheers, -- Felipe

Posted: 1 decade ago 11 mars 2012, 07:54 UTC−4

Dear Felipe Yes you are right both core and cladding should be a function of R. I have already done it and got sensible result. If cladding wont be a function of R then definitely there wont be no loss from core. Regarding PML its true that the literature is small about it. But I have following info regarding that might be helpful to you:- PML should be given maping mesh. It should be 5% to 10% of total structure. It should have the same refractive index as the surrounding region. But I am not able to understand one thing in this structure since cladding region has refractive index that is function of radius then what should be the value of refractive index of pml. (1) it can also be function of radius with same function as cladding or it can be constant value that is equal to value of refractive index of cladding at cladding n pml interface. Cheers Deepak

Posted: 1 decade ago 11 mars 2012, 11:08 UTC−4

Dear Deepak, there is a plethora of documentation regarding PMLs in FEM codes, the thing is comsol doesn't share much about their implementation. What makes it harder to understand how it works. About the surrounding region: [QUOTE] It should have the same refractive index as the surrounding region. But I am not able to understand one thing in this structure since cladding region has refractive index that is function of radius then what should be the value of refractive index of pml. (1) it can also be function of radius with same function as cladding or it can be constant value that is equal to value of refractive index of cladding at cladding n pml interface. [/QUOTE] Oskooi & Johnson found out that the surrounding region can have a non constant refractive tensor that varies in the direction perpendicular to the PML interface: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.190.5883&rep=rep1&type=pdf in your case, that will mean that having a refractive index that changes radially should not be a problem for a cylindrical PML. Anyway, I recommend that you do their validation scheme in order to validate your results. And if you do so, please tell us your results. cheers, -- Felipe P.S. may I know where did you take the equation for the refractive index as a function of R? [1.4515*((1+(1.6*x/R))^0.5)]

Posted: 1 decade ago 25 juin 2013, 12:44 UTC−4

I want to calculate the bend loss in PCF. I have a Comsol 3.3. How can I calculate the bend loss?