What is the Best Way to Calculate DCF length

Hi Taiwo,
From my experience, in general, I would always recommend to check the specifications of all the DCF manufacturers for this dispersion coefficient. In spite of the fact that -80 ps/nm/km is the most standard value for DCF, for standard SMF it may vary due to the requirements for residual dispersion parameter in a particular design. This parameter becomes very important in WDM systems design. The attenuation, which is in dB/km, may slightly vary as well.

Hi Taiwo,Basically it depends upon manufactrur as Ravil said.In most of the papers that i have seen value of dispersion taken is -85ps/nm/km and attenuation 0.5 db/km for dcf.Roughly ,dcf dispersion is negtive 5 times the dispersion of your SMF.If it is 16 ps/nm/km then dcf of -80ps/nm/km would be best and if you are using SMF of dispersion 17 then -85 would be best choice.Rest attenuation may vary 0.5-0.6 dB/km

I agree with Ravil and Samsung’s suggestions. I also add that DCF usually has a lower core diameter than SSMF, which means that you need to be careful with nonlinear effects (for example if you put DCF in the mid-stage of an EDFA, do not go into DCF with too high power!).

Welcome Taiwo Ambali,,as a member its our pleasure to share our knowledge with other participents.Thank you alessandro for adding the important point regarding core diameter linked to non linearities in dcf.

Hello i think i posted it on previous forum too. length of DCF is governed by L1D1+L2D2=0 where L1 is length of transmitting fiber and D1 is its dispersion whereas L2 is DCF length with dispersion D2.
find refrence: IEEE j. of Lightwave Technology 1999 paper by Marhic

I do agree with Ravil and Sam Sung. can any one please explain how nonlinearity arises in DCF

Hello esakkimuthu
The main reason of the more non linearities impairments in DCF is the small effective area of DCF as compared to SMF.Generaly the Aeff area of DCF is around 22um^2 and around 80um^2 in case of SMF.The value non linear phase shift given as
φ=2π/Λ n2 P/Aeff L
So less the value of Aeff,more the phase shift and more the non linearities.However this also have some benefits and drawbacks in signal amplification.
Please visit the link i have given below to read very good discussion on this particular topic

Effective area in optical fiber

Hello!!
I agree with explainations given above.
Dispersion and FWM are inversely related. value od dispersion in DCF is usually taken -85ps/nm/km which adds to non linear impairments.
Check the following links for specific content and research:

http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCAQFjAAahUKEwjZ8IXE8tzGAhViHKYKHVypBn8&url=http%3A%2F%2Fwww.sciencedirect.com%2Fscience%2Farticle%2Fpii%2FS0030402609003295&ei=ejGmVdnLNuK4mAXc0pr4Bw&usg=AFQjCNHCQ8DM6BrbJF9J9vOZN8LHjE4awg&sig2=RYR-2BUeXyun2IUuakNJQg&bvm=bv.97653015,d.dGY

Also check these links:
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Welcome Taiwo,its always pleasurable to participate in discussion and share knowlegde with all the forum participants .your topic are always intersting and good for discussion as we can learn many things from other forum members.Also thanks to Ravil and Alessandro for making such a good points.

Hi Taiwo Ambali Abiola,
I will suggest you to please refer to optisystem library component pdf file where you will various standard values of different parameters in the heading WDM design.
AS DCFs are highly nonlinear heavily-doped fibers with small effective areas.
The condition for perfect dispersion compensation is D1
D1L1+D2L2 = 0
i.e., its length should be chosen to satisfy
L2 = – (D1/D2) L1
Where D1 and D2 are the fiber dispersions of SMF and
DCF respectively. L1 and L2 are lengths. Thus the DCF has a large negative value of D2.

Hi Ranjeet Kumar,

This query seems to be raised almost a year and i dont believe that it would be yet to addressed but anyways thanks for the information..

Regards
Sahil Singh

hi all
the total diispersion along the length should be equla to the zero for the complete dispersion…
Dsmf*Lsmf+Ddcf*Lcf = 0
i.e., DCF length should be chosen so as to to satisfy zero tola dispersion..
Ldcf = – (Dsmf/Ddcf) Lsmf
Where Dsmf and Ddcf represents the fiber dispersion coefficients of SMF and
DCF respectively.

how there is again such condition for the dispersion slope….the total diispersion slope along the length should be equla to the zero for the complete dispersion
with regards

FOR WDM one have to analyze dispersion wrt center frequency

Hi,
I agree to the points of Ranjeet that “length of DCF is governed by L1D1+L2D2= 0 where L1 is length of transmitting fiber and D1 is its dispersion whereas L2 is DCF length with dispersion D2”.
This is actual formula for calculating length of DCF, from this formula you will find dispersion parameters of DCF as negative.
Thanks