CFBG with temperature change in the middle

[Quinten Heijn]

Dear sir/madam,

I tried to make a simulation of a cfbg in optigrating. It doesn’t matter much what the specifications of this cfbg are. I want to apply a temperature difference in the middle of the grating length so that the spectrum shifts on the left side and there is a dip at the temperature difference, this all works fine when I apply a temperature difference with the user function at temperature. However, I am now using a temperature difference where the beginning of the fibre has a high temperature and the end has a low temperature (see picture). Actually, it should be a low temperature at the beginning and then to a high temperature. Then I get a peak instead of a dip. It looks like the grating length is the opposite as the length in the temperature function. Is that true?

Yours sincerely,

Quinten

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   hoi.png
   

[Ahmad Atieh]

Hi Quinten,

The x axis is not reversed. I believe the reason for the confusion is that the direction of the applied linear period chirp is the opposite of what you might expect. The equation OptiGrating uses for linear chirp is Lambda(z) = Lamba0 – Delta*(z-L/2)/L, where Delta is the specified chirp rate (Eq. 21 in the OptiGrating User Reference). If you set the chirp parameter to a positive number, the period will decrease along the length of the grating instead of increase. If you set it to a negative number (-10 in your case), the period will increase along the length of the grating, and if you leave everything else the same, the effect will be reversed, as you expected (the dip you saw in reflection becomes a peak, and the peak in transmission becomes a dip, see images below).

Amine

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   Grating-length.png
   

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   Profile-chirp-period.png
   

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