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

We present a novel constellation phase rotation method to mitigate the digital-to-analog converters (DACs) quantization penalty resulting from pre-compensation of chromatic dispersion (CD) in optical metro links, where low-resolution DACs may be used to be cost- and power-efficient. The CD-induced constellation rotation increases the peak-to-average power ratio of the emitted signals, hence increasing the DAC quantization penalty. To cancel this rotation, we propose a two-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.