ABSTRACT
Digital signal processing (DSP) is the principal functionality of modern optical communications systems at both the coherent optical receivers and the transmitter. At the transmitter,the DSP is employed for shaping the pulse at the output of optical modulators and for compensation of the limited bandwidth of the digital to analog converter (DAC) as well as that of the transfer characteristics of the electro-optic external modulators and de-skewing of the electrical path differences between the in-phase and quadrature-phase signals, which occur often in ultra-high-speed systems. It is noted that the mixing of the received signals and the local oscillator (LO) laser happens in the photo-detection stage.
