Enhancing the Vertical Resolution of Coherent Optical Receivers

The constantly increasing capacity demand in optical fiber transmission systems has driven the development of higher-order modulation to share the cost and power-consumption of optoelectronic components across many bits. However, higher-order modulation imposes challenging requirements on high-speed optoelectronic transceiver components such as on the vertical resolution of analog-to-digital and digital-to-analog converters. State-of-the-art high-speed converters limit the development of next-generation systems above 6 bit/s/Hz/pol at symbol rates beyond 100 Gbaud for Nyquist shaped channels. Ultimately, in the absence of fiber nonlinearity the upper limit on the available signal-to-noise ratio is bounded by the transceiver subsystems. Here we propose a novel optoelectronic technique to enhance the effective vertical resolution of coherent receivers through optical intensity reshaping. Finally, we show that the proposed technique to increase the effective resolution will also boost the performance of digital backpropagation used to mitigate fiber Kerr nonlinear response.