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Unknown oscillation in effective index and propagation constant when solving modes in step-index fibers
Posted 25 mars 2013, 06:39 UTC−4 RF & Microwave Engineering Version 4.3a 0 Replies
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I recentely moved over to comsol 4.3a after using comsol 3.5a to do mode calculations in fibers.
I use the step-index model found in the tutorial in Comsol 4.3a and insert the parameters that I am using. Then I make a wavelength sweep where I am running comsol and matlab together through LiveLink. When I compare my results off effective index neff(lambda) and propagation constant beta(lambda) (lambda is wavelength) with my previous results in Comsol 3.5a I see oscillations in both neff and beta in the new results in comsol 4.3a. The funny thing is that the oscillations are minor and oscillate nicely around the values obtained in Comsol 3.5a. The problem is, I cannot do nummerical derivates, which I need to do afterwards, off the obtained neff and beta.
With my inquiry I've attached a png figure of the results of neff, where you can see the blue line (comsol 4.3a result) oscillating nicely around a red line in the middle of the oscillation (comsol 3.5a result).
The other plots are of different precision of the comsol solver. They did not do anything to remove the oscillations.
Furthermore, in comsol 3.5a I use the SPOOLES solver whereas the comsol 4.3a uses MUMS. I do not know much about the difference between the two. The SPOOLES solver in comsol 4.3a cannot solve a single wavelength to solve the modes using the standard settings. This I find peculiar...
The PARDISO solver seems to work, but it works slower than the MUMS solver for my step-index fiber problem. I still need to check the precision of that solver also in terms of my neff and beta calculations .
I hope someone has some other ideas on what to check in terms of precision and other tweaks.
Thank you very much in advance.
Kind regards,
Irnis
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Hello Irnis Kubat
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