Ioannis Tomkos and coworkers at Corning Incorporated's Photonic Research and Test Center (Somerset, NJ) and NTT Electronics Corp. (Ibaraki, Japan) demonstrated transmitting a 10-Gbit/s 1.55-µm signal from a directly modulated distributed-feedback laser over 100 km of fiber without any dispersion compensation.1 They managed the feat—the longest transmission distance for such a system yet reported—using a commercially available nonzero dispersion-shifted fiber that has a negative dispersion over the entire bandwidth from 1280 to 1620 nm.
Commercially available 1.55-µm directly modulated distributed-feedback lasers are attractive for use in metropolitan-area networks because they supply enough power to transmit 80 to 100 km. The frequency chirp of the lasers, however, severely limits the distance over standard single-mode fiber at bit rates of 10 Gbit/s and faster, and it precludes the use of wavelength-division multiplexing.
The group uses negative-dispersion fiber to balance the "positive" dispersion in the frequency chirp. They investigated transmission performance of the 1.55-µm 10-Gbit/s modulated laser at different biases and driving conditions. When the laser bias current was 55 mA and the modulation voltage was 2 V (peak-to-peak), the extinction ratio was 5 dB, and the measured peak-to-peak transient chirp was about 19 GHz. When transmitted over 100 km of the MetroCor negative-dispersion fiber and run through a preamplifier, the resulting signal had a bit-error rate of less than 10-15 (or a Q of 9.4 dB). This corresponds to a dispersion-length product of about 750 ps/nm.
With this remarkably high value for the dispersion-length product, and the group's previous WDM experiments, they believe that similar performance could be achieved for channels across the C- and L-bands amplified by erbium-doped fiber amplifiers.
For more information contact Ioannis Tomkos at email@example.com.
- I. Tomkos et al., IEEE Photon. Tech. Lett. 13, 735 (July 2001).