PERFORMANCE OF SINGLE-ELECTRODE 1.5-MU-M DFB LASERS IN NONCOHERENT FSK TRANSMISSION

We report the results of an investigation of the performance of single-electrode 1.5-mu-m DFB lasers in 1.7 Gb/s noncoherent frequency-shift-keyed (NC-FSK) transmission. Sixteen commercial laser transmitters were characterized in terms of FSK transmission sensitivity, eye-margin, chromatic dispersion penalty, and pattern dependence. Using amplitude-shift-key (ASK) performance as a baseline, FSK out-performs ASK when dispersion is present, while ASK is slightly better with no dispersion. FSK transmitters with commercial single-electrode DFB lasers are shown to provide an attractive alternative to ASK in dispersion limited systems. The FSK degradations mainly result from an inadequate FM modulation index, and a thermal-FM index manifested as a pattern length dependence. We show that NC-FSK performance can be significantly improved with a novel filter bandpass design.