Patent ID: 8503887
Filing Date: 2013-08-06
Classification: H04B

Abstract:
1. A pre-equalized optical transmitter, comprising: 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 being configured to: convert, 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; equalize, by the pre-equalization circuit, degradation in transmission of the digital complex signal, and input the digital complex signal equalized in terms of the degradation in transmission to the at least two D/A converters; convert, by the at least two D/A converters, the equalized digital complex signal into an analog signal; suppress, among the converted analog signals, an analog signal leaking outside a Nyquist bandwidth by at least 23 dB, and input the suppressed analog signal to the optical field modulator; modulate, by the optical field modulator, fight output from the laser source with the analog signal to generate a modulated optical field signal; and transmit the modulated optical field signal, wherein: the digital complex signal includes a space symbol indicating a sampling point with a zero amplitude, and a mark symbol indicating a sampling point with a predetermined amplitude; and the pre-equalized optical transmitter further comprises a waveform compensation circuit for changing a phase of a symbol border of two successive space symbols to a phase shifted by 180 degrees from a phase of the mark symbol in the case where the digital complex signal includes the mark symbol in one of before and after two successive space symbols.