An optical transmission line allows optical signals to be transmitted with
higher stability over longer distances. According to a first aspect, an
optical NRZ signal is split in two, one half is presented to a clock
extraction circuit, and the other half is presented to an EA modulator.
An optical RZ signal is obtained as an output because the EA modulator is
energized by the provided clock component. According to a second aspect,
a nonlinear phase shift based on cross-phase modulation is induced in an
RZ pulse train by an optical NRZ signal, and only the RZ pulses
corresponding to the optical NRZ signal are extracted. According to a
third aspect, first dispersion compensator is provided to a preceding
stage of an optical fiber transmission line for transmitting optical
pulses, and second dispersion compensation compensator is provided to a
subsequent stage. Pulse widening in the optical fiber transmission line
is controlled by a nonlinear chirp induced in the first dispersion
compensator.