just note that the latency of a DCF is 25% of SMF-28+ and 5% of NZ-DSF based on ITU-T. i want to know if we connect a DCF to a SMF-28 and LEAF transmission line, how these amounts will be changed?
Marzieh
How do you specify latency? I assume by "25% of SMF-28+" you mean latency for a length of DCF which exactly compensates a particular length of SMF, but I don't recognize the percentages you quote. Do you have a link to the ITU-T information you quote?
Is the latency calculated for a particular length of fibre, or for a length of transmission fibre + DCF. It the latter case, is the DCF in-line, or inserted as discrete modules which do not contribute to the total transmission length?
In general I would calculate the latency of each individual fibre sections from the physical length of fibre and its group refractive index, then use a simple linear addition.
Corning quote group refractive indices of 1.468 and 1.469 at 1550 nm and 1625 nm respectively for NZ DSF LEAF in PI1107 (February 2008).
Group refractive index for SMF28+ is 1.4676 at 1310 nm and 1.4682 at 1550 nm (Corning PI1463 July 2011).
ITU-T manual "Optical fibres cables and systems" 2008 does not have much to say about latency.
Grüner-Nielsen et. al "Dispersion compensating fibres", J. Lightwave Tech, vol 23 no 11, p 3566 (2005) https://www.osapublishing.org/jlt/abstract.cfm?URI=jlt-23-11-3566 report a range of dispersion values for slope-matching DCF between -120 and -250 ps/nm/km for relative dispersion slope 0.0036 nm-1, and -95 to -160 ps/nm for higher RDS 0.0065 to 0.017 nm-1.
If you have an OTDR and samples of DCF or DCF modules, you can measure latency more or less directly (measured length will be scaled by the group velocity you specify via the group index).
If you don't have precise dispersion and group index values for your particular DCF, then use Grüner-Nielsen's values for dispersion to estimate the length of fibre in each compensating section, and assume a group index of around 1.47.
Latency with be dominated by the total physical length of fibre, whether SMF, LEAF or DCF. Propagation delay is determined by the group velocity vg. For each fibre section of length L
T = L / vg = L ng / c
where ng is the group index, and c is the velocity of light in vacuum. The group index depends on fibre design and wavelength, but the variation is weak compared with the linear increase of delay with fibre length.
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