The invention, in one form, is a fiber optic system having an optical signal source adapted to produce a frequency and amplitude modulated optical digital signal and a semiconductor optical amplifier adapted to receive the frequency and amplitude modulated optical digital signal and generate negative transient chirp at the transitions between bits. In another form, the invention is a fiber optic system having an optical source adapted to generate a frequency modulated signal, a semiconductor optical amplifier adapted to receive and amplify the frequency modulated signal, and an optical spectrum reshaper adapted to receive the amplified frequency modulated signal and to utilize the amplified frequency modulated signal to increase the amplitude modulation of the signal.