property of Optical Fiber

[Ajay Vyas]

Hi
I want to analysis the nonlinear distortion due to the optical fiber. I enable all the type of nonlinear & linear distortion present in the property of fiber component. In the non linear tab there is the nonlinear index parameter n2. There is two type is given one is from file or constant. As we know the NLD is depend on the fiber length then how we can justify it. How the n2 vary with length of fiber. Only the varies shows with respect to wavelength. Can we calculate the order ( 2nd or 3rd order) or types like even or odd for nonlinearity.

[Alessandro Festa]

Hi Ajay, non-linear effects do depend on fiber length only below the so called “Effective length Leff”, which means that if the length of the link is higher that Leff, the effect does no longer depend on L.
For example: for Raman effect, the Raman gain depends on the fiber length if L<about 30km, otherwise you have the same gain no matter the length.

[Ajay Vyas]

Thanks for your information. What about the order of nonlinearity?
It mean the length of fiber is long then which parameter those affect the nonlinear distortion.
How we can analyze it?

[Ravil]

Hi Ajay,

I agree with the point made by Alessandro about the effective length of an optical fiber. According to your question about the order of non-linearity, most of times we consider only the second order of non-linearity in optical fiber, i.e. we are limiting the Taylor expansion of polarization density by its second coefficient only. We do all our analysis with this approximation. However, we can go for 3rd, 4th, etc. order extension as well.

[Ajay Vyas]

thanks to both of you. I agree the on the point of second order. But actually we are working on nonlinear compensation for Radio over Fiber link. It is a close loop system in which we have to go for high order of nonlinearity. Then what will the pattern of nonlinearity for higher order. thus we can design the predistorter for it ( ie memory polynomial based predistorter)

[Alessandro Festa]

That’s an interesting area of research! I know Optisystem has an integrated nonlinear compensation in the DSP, have you ever tried it?

[Ajay Vyas]

Yes i already try with DSP component. but We want to develop the predistorter special memory polynomial based it is a close loop system.

[alistu]

Hi all,

I would also like to ask a question regarding “Optical Fiber Properties”. Are the characteristics of the optical fiber at Optisystem’s Optical Fiber Library the same as those of a standard single mode fiber(SSMF)? If not, could anyone upload an osd file containing a fiber with the same characteristics as SSMF? Thanks in advance.

[Alessandro Festa]

I think that if you put a fiber without touching any parameter, the characteristics are xactly for G652 standard singlemode fiber (like corning SMF-28). Then you can change parameters also using libraries integrated in Optisystem itself.

[alistu]

Thanks Alessandro.
However since some part of my works depends on the knowledge of the fiber used, I need a more definite answer. Attenuation and some other characteristics of SMF-28 are variable with wavelength, while they’re constant in the Optisystem model. So I would like to know if there is a way to use a SSMF in Optisystem.

[alistu]

Thanks Alessandro.
However since some part of my works depends on the knowledge of the fiber used, I need a more certain answer. Attenuation and some other characteristics of SMF-28 are variable with wavelength, while they’re constant in the Optisystem model. So I would like to know if there is a way to use a SSMF in Optisystem.

[Alessandro Festa]

Ok I understand your question.
If you want to use SSMF dispersion: go under Components/Data/Fiber Dispersion/corningsmf 28 1550.dat

[alistu]

Thanks Alessandro.
But what about attenuation variations? Does “corningsmf 28 1550.dat” which is in “Fiber Dispersion” folder also consider attenuation changes with wavelength?

[Ajay Vyas]

what will be possible maximum value of n2 that can put in optisystem & simulate the project file .
or can we differentiate the nature odd & even nonlinearity.

[Alessandro Festa]

What do you mean by maximum value of n2? That depends on the fiber…

[Ajay Vyas]

I mean that if we accounting the higher order of nonlinearity then which value of n2 we chose. We are working on memory based predistorter.
because n2= 26e-21 for second order nonlinearity.

We can plot or observe the response of that order

[Alessandro Festa]

n2 correlates the change in fiber refractive index respect to optical intensity, so it does depends on on fiber properties. I don’t know if it makes sense to change that value to take into account higher order nonlinearities…

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