Optical communication system and dispersion compensation method

A dispersion compensation method for compensating for wavelength dispersion of a transmission optical fiber disposed between an OLT (Optical Line Terminal) and an ONU (Optical Network Unit), comprising:

• connecting a dispersion compensation module to a side of the OLT or a side of the ONU of the transmission optical fiber, wherein
• the dispersion compensation module includes:
• a dispersion compensation optical fiber, the dispersion compensation optical fiber has a negative dispersion value in an anomalous dispersion region corresponding to a longer wavelength side than a zero-dispersion wavelength of the transmission optical fiber disposed between the OLT and the ONU;
• and
• an asymmetrical optical splitter, the asymmetrical optical splitter includes:
• one merge port to which the dispersion compensation optical fiber is connected;
• N split ports (N is an integer of 2 or more) to which an optical network including one or a plurality of the ONUs is connected;
• and
• N−1 split portions that split light from two first ports on a side of the merge port to two second ports on a side of the split port at a predetermined split ratio,
• wherein the split portions are connected so that one of the second ports is connected to one of the split ports and the other of the second ports is connected to one of the first ports of the split portion of a next stage, and
• the split portion of a first stage of the split portions has one of the first ports connected to the merge port, and the split portion of a final stage has the second ports connected to the split port,
• wherein the dispersion compensation optical fiber has a first wavelength dependence property in which a first dispersion value with respect to a peak wavelength at the other of the first ports of the split portion of the first stage is negative, and
• the transmission optical fiber has a second wavelength dependence property in which a second dispersion value at the peak wavelength at the other of the first ports of the split portion of the first stage is positive.