Digital Resolution Enhancer Employing Clipping for High-Speed Optical Transmission

Driven by the exponentially increasing demand for Internet traffic, single channel capacity in optical transmission systems continues to grow. Therefore, optical transmitter impairments such as low analog bandwidth, nonlinearities and digital-to-analog conversion with low resolution place a considerable burden on the system design. Methods aimed at compensating for the low transmitter bandwidth and transmitter nonlinearities have been introduced and recently, a digital resolution enhancer (DRE) which reduces the quantization noise added by a digital-to-analog converter (DAC) has been proposed. In this work, the interplay between DRE and clipping is introduced and studied. Experimental validation is performed by transmitting single channel 600 Gb/s 64-quadrature amplitude modulation (QAM) and wavelength-division multiplexing 460 Gb/s 128-QAM over 75 km of standard single-mode fiber. The combination of DRE and clipping allows the reduction of the DAC's physical number of bits to 3, while still maintaining performance above the forward error correction (FEC) limit. Low resolution DACs will play an important role in the implementation of low-power transmitters generating high-cardinality modulation formats.