An optical transmitter comprising: an optical source modulated with an input digital data signal so as to generate a first, frequency-modulated digital signal; and an amplitude modulator, modulated with the logical inverse of the input digital data signal, for receiving the first, frequency-modulated signal and generating a second, amplitude-modulated and frequency-modulated digital signal; wherein the optical source and the amplitude modulator are each configured so as to produce positive transient chirp. A method for transmitting a signal, the method comprising: generating a first, frequency-modulated digital signal by modulating an optical source with an input digital data signal; and providing a second, amplitude-modulated and frequency-modulated digital signal by passing the first, frequency-modulated digital signal through an amplitude modulator while modulating the amplitude modulator with the logical inverse of the input digital data signal; wherein the optical source and the amplitude modulator are each configured so as to produce positive transient chirp.