Consideration on influence of directly modulated DFB LD spectralspread and fiber dispersion in multigigabit-per-second long-spanoptical-fiber transmission systems

The relation between optical-fiber dispersion and directly modulated distributed-feedback laser diode (DFB LD) spectral spread in multigigabit-per-second long-span transmission systems is discussed. It is observed that two peak spectra at the leading edge of the pulse induce spectral spread in directly modulated DFB LDs. Specifications for the difference between the DFB LD oscillation wavelength and the optical-fiber zero-dispersion wavelength in a multigigabit-per-second long-span transmission system, considering these two peak spectra, are predicted. Experimental confirmation was provided by 2-Gb/s-140-km and 5-Gb/s-100-km transmission experiments, using 1.5-μm zero-dispersion shifted optical fiber