Patent ID: 7668465

Claim:
An optical transmission system that delivers optical signals in upstream and downstream directions, the optical transmission system comprising: (a) upstream and downstream optical transmission lines that are divided into a plurality of repeater sections each composed of a first fiber and a second fiber, the first fiber having positive dispersion, the second fiber having negative dispersion, the second fiber having a smaller mode field diameter than the first fiber, the optical signals propagating from the first fiber to the second fiber; (b) a plurality of optical repeaters, each comprising: a monitor that monitors power levels of the upstream and downstream optical signals, and a pumping unit that controls pump light power based on monitoring results supplied from said monitor, so as to adjust power balance between the upstream optical signals and the downstream optical signals for each dispersion compensation interval, when the second fibers used in the immediately adjacent repeater sections have different lengths; (c) a variable optical attenuator disposed on said optical transmission line that assists said optical repeaters to adjust the power balance between the upstream optical signals and downstream optical signals; and (d) a variable gain equalizer disposed on said optical transmission line that compensates for deviation of optical amplification gain; wherein: said variable gain equalizer resides in a gain equalizing section that is one of the repeater sections; the first fiber and second fiber in the gain equalizing section have equal lengths, and the dispersion compensation interval accommodating the gain equalizing section has a different pattern of section average dispersions from the other dispersion compensation intervals.