A fiber optic communication system comprising: an optical signal source adapted to receive a binary base signal having a bit period T, and generate a first signal, wherein the first signal is frequency modulated; and an optical spectrum reshaper (OSR) adapted to reshape the first signal into a second signal, wherein the second signal is amplitude modulated and frequency modulated; characterized in that: the optical signal source is a laser in which frequency modulation is generated by modulating the loss of the laser cavity. A method for transmitting a signal, comprising: receiving a binary base signal having a bit period T, and generating a first signal, wherein the first signal is frequency modulated; and reshaping the first signal into a second signal, wherein the second signal is amplitude modulated and frequency modulated; characterized in that: the first signal is frequency modulated by using a laser in which frequency modulation is generated by modulating the loss of the laser cavity. A fiber optic communication system comprising: an optical signal source adapted to receive a binary base signal having a bit period T, and generate a first signal, wherein the first signal is frequency modulated; and an optical spectrum reshaper (OSR) adapted to reshape the first signal into a second signal, wherein the second signal is amplitude modulated and frequency modulated; characterized in that: the optical signal source is a laser in which frequency modulation is generated by modulating the phase of the laser cavity.