Discussion Forum

Hello everyone,

first, I apologize for every mistake regarding grammar and spelling since I am not a native speaker. Hopefully, everything is going to be understandable :).

Right now, I am working on simulating a simple optical fiber, wherein a bragg grating is inscribed. Currently, I am using a piecewise function to modulate the refractive index of the core. Figure 1 shows a plot of the function used: At the beginning the refractive index equals some specified constant. After 5 mm the modulation starts. At 7 mm the refractive index is again constant. Figure 2 shows the definition of the function. The parameter n_core is simply a constant, dn is the "strength" of the modulation and equals , d is actually a "dummy" variable which should represent the space dependence along the z-direction. Unfortunately I was not able to figure out how to use the real global coordinate z as argument (maybe someone can help me with that too). The last parameter is the pitch, which has a value such that the reflected wavelength equals . Using the governing equation for that, the value of the pitch equals approximately . Figure 3 shows how I tried to use that function as a material property for the core of the optical fiber.

Regarding the described situation above, I have following questions:

Why does the defined function looks like as shown in figure 2? It seems like the amplitude is not the same after one period.

Is the way I have defined and used the material property (figure 3) correct?

If I want to have a unitless output from the function, is it enough to just ignore the "Function units", i. e. writing nothing in the corresponding field? Or do I have to type in something?

The questions above came up, because using a parametric sweep for the wavlengths 1500, 1550 and 1600 resulted in same results.

Thanks in advance to everyone trying to help me somehow. I am looking forward for any kind of clue :).

Best regards

Giuseppe