There is provided a fiber optic transmission system, comprising: an optical signal source adapted to produce a frequency modulated signal; and a multi-ring resonator optical spectrum reshaper (OSR) adapted to convert the frequency modulated signal into a substantially amplitude modulated signal. And there is provided a method for transmitting an optical signal through a fiber comprising: producing a frequency modulated signal; passing the frequency modulated signal through a multi-ring resonator optical spectrum reshaper (OSR) so as to convert the frequency modulated signal into a substantially amplitude modulated signal; and passing the substantially amplitude modulated signal into the fiber.