A Novel Constellation Phase Rotation Method to Reduce Transmitter Noise in Metro Links

IEEE We present a novel constellation phase rotation method to mitigate the DACs quantization penalty resulting from pre-compensation of chromatic dispersion (CD) in optical metro links where low-resolution digital-to-analog converters (DACs) may be used to be cost- and power-efficient. The CD-induced constellation rotation increases the peak-to-average power-ratio (PAPR) of the emitted signals, hence increasing the DAC quantization penalty. To cancel this rotation, we propose a 2-step method that first determines the suitable rotation angle with an oriented bounding box algorithm, and second applies the rotation just before the DAC input. We experimentally demonstrate a+1 dB of system signal-to-noise ratio improvement for 16-QAM signals with a 4-bit DAC.