re-create FBG profile from exported data

[TLW]

In OptiGrating’s ex1a.ifo (chirped apodized FBG example), I have exported profile0,profile1,profile2,profile3.txt and tried to re-create the profile in a plot in Matlab. However exported data doesn’t seem to have enough information to make the plot that OptiGrating has. See my attached picture. I plotted the exported data in green curves. I don’t need to plot the colors like what OptiGrating has, but I do want to make a 1d plot n(z). I don’t understand why profile0 aka f(z) has 256 points but profile1,profile2,profile3 have 200 points. I also don’t understand why f(z) horizontal axis goes from 0 to 0.5317 um even though the entire grating length is 50000 um. Can someone help me with this. Thank you very much.

Attachments:

1. 

   profile.png
   

[Steve Dods]

Profile0 is a plot of the grating shape: the refractive index variation with Z over one grating period. That explains why 0 < z < .5338 for that plot. OptiGrating will display that curve in its own interface if you right click on the Profile tab and select Shape…

Plots 1, 2, and 3 display local period, apodization, and average refractive index. Those are defined over the length of the grating, 0 < z < 50,000. The number of points for display comes from the number of segments specified in the Grating Definition dialog box. The file will show the value at the beginning and the end of each segment: two values per segment. Therefore if there are 100 segments, there will be 200 points.

[TLW]

Thanks. My follow-on question is if the total length is 50000 um and only 100 segments are used for computations, then each segment is 500 um in length. Does that mean that each “segment” contains 500/0.5338=936.65 grating periods?. It looks like 1 segment does not equal 1 grating period.

[Steve Dods]

Yes, that’s right. Segment is not the same as period. Segment means only that within the segment the grating is taken to be uniform – same period, same amplitude. OptiGrating calculates non-uniform gratings by connecting many short uniform ones.

[TLW]

Thanks. Is the profile0 f(z) always 256 points or is there a way to change it to something longer?

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