100 km transmission of a 640 Gbit/s OTDM signal using femtosecond pulses

A 640 Gbit/s OTDM (Optical Time Division Multiplexed) signal using femtosecond optical pulses was successfully transmitted over a distance of 101 km. As a signal light source, a regenerative mode-locked fiber laser that generates 10-GHz pulses with a small jitter was used. The transmission path consists of a zero-dispersion dispersion-flattened transmission line 101 km long made of a combination of a 1.3-μm zero-dispersion single-mode fiber, a dispersion-shifted fiber, and a reverse dispersion fiber. The 640 Gbit/s OTDM signal after transmission was demultiplexed by means of an ultra-high-speed nonlinear optical loop mirror with a fiber length of 450 m in which walk-off between the signal light and the control light was reduced. The reverse dispersion fiber in the transmission path had smaller polarization dispersion than both the dispersion slope compensation fiber previously used for compensation of the dispersion slope compensation and the 1.3-μm zero-dispersion single-mode fiber. In addition, the wavelength dependence of its dispersion is small.