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Fiber-optic cable system and method for dispersion compensation at nodes between end points
| Details |
Inventors: Dugan, John M.;
Assignee: Alcatel Network Systems, Inc. (Richardson, TX)
Primary Examiner: Healy; Brian
Assistant Examiner:
Attorney, Agent or Firm: Lutz; Bruce C., Kraft; Dennis O.
The present invention provides a method and system that compensate end-to-end optical dispersion for a fiber-optic cable having a plurality of predetermined compensations sites to within a predetermined dispersion limit using a predetermined dispersion compensation increment. With the method and system, the predetermined dispersion compensation increment may exceed both the predetermined compensation limit as well as the compensation limit divided by the number of sites. The method includes the steps of compensating optical dispersion using the compensation increment for each of the plurality of predetermined compensation sites to yield an end-to-end optical dispersion compensation within the predetermined optical dispersion limit. This may include optical dispersion over-compensation at some sites and optical dispersion under-compensation at other sites. |
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DETAILED DESCRIPTION OF THE INVENTION In FIG.
1, optical path 10 has a length of 322 Km and begins at site 1 12 from transmit station 14.
From transmit station 14, optical fiber amplifier 16 transmits optical energy along segment 18 to dispersion compensating unit (DCU) A 20 of site 2 22.
From DCU A, optical amplifier 24 transmits optical energy along segment 26 to DCU B 28 of site 3 30.
Amplifier 32 amplifies optical energy from DCU B 28 and transmits the optical energy along optical fiber 34 to DCU C 36 of site 4 38.
Optical amplifier 40 amplifies optical energy from DCU C 36 for transmission along segment 42 to DCU D 44 of site 5 46 where receive station 48 receives the optical energy.
In the example, optical path 10 of FIG.
1, the 322 Km path 10 has four segments including 70 Km segment 18, 113 Km segment 26, 93 Km segment 34, and 46 Km segment 42.
FIG.
2 shows the cumulative optical dispersion in ps/nm for the 322 Km path 10 example of FIG.
1.
Along the horizontal axis of the plot of FIG.
2 appears distance measurement in Km beginning at 0 Km and showing a maximum length of 322 Km.
Along the vertical axis appears a scale of cumulative dispersion ranging from -500 to 2000 ps/nm.
sup.
.
km.
Suppose, for example, that the dispersion rate of 18 ps/nm applies to the optical fiber for optical path 10.
Then, for the 70 Km segment 18, the cumulative dispersion is 1260 ps/nm at the point designated as 50, for 113 Km section 26 the cumulative dispersion is 2,034 ps/nm as point 52 indicates, for 93 Km segment 34 it is 1674 ps/nm at point 54, and 828 ps/nm at point 56 for the 43 Km segment 42.
This results in a sum of 5,796 ps/nm as the total dispersion for optical path 10.
Suppose, further, that at the receive end 48 of FIG.
1, a predetermined maximum end-to-end cumulative dispersion must be within .
+-.
100 ps/nm.
This is only 1.
7 percent of the total optical fiber dispersion without compensation.
If dispersion compensation is to be cumulative at the end of each section, then the 1.
7% limit must apply at each section
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