Provided is a pre-equalized
optical transmitter, comprises: a
laser source; a duo-binary pre-coder circuit; a pre-
equalization circuit for applying an inverse function of chromatic dispersion; at least two D / A
converters; and an
optical field modulator comprising at least two input terminals for an
electric signal. The pre-equalized
optical transmitter: converts, by the duo-binary pre-coder circuit, a digital information
signal of a predetermined symbol time to be transmitted into a digital complex
signal including one sampling point per symbol; equalizes, by the pre-
equalization circuit, degradation in transmission of the digital complex
signal; converts, by the D / A
converters, the equalized digital complex signal into an analogue signal; suppresses an analogue signal leaking outside a Nyquist bandwidth by at least 23 dB; modulates, by the
optical field modulator, light output from the
laser source with the analogue signal to generate a modulated
optical field signal; and transmits the modulated optical field signal.