Digital Inverse Multiplexing for Transmitters With Symbol Rates Over DAC Bandwidth Limit
Akira Kawai, Masanori Nakamura, Takayuki Kobayashi, Munehiko Nagatani, Hiroshi Yamazaki, Takeo Sasai, Fukutaro Hamaoka, Yutaka Miyamoto
Abstract
Broadband signal generation technology plays a pivotal role in increasing the data rate of optical transceivers. To overcome the bandwidth limitation of digital-to-analog converters (DACs), techniques that generate a single broadband signal by multiplexing the outputs of multiple DACs in the analog domain have emerged as an early solution. Nonetheless, broadband signals experience impairments due to deviations from the ideal DAC multiplexing process. Utilizing a digital-analog symmetric modelling of the DAC multiplexing process, we propose an all-electronic bandwidth doubling scheme that incorporates an analog multiplexing device (bandwidth doubler) and a novel digital pre-processing scheme called digital inverse multiplexing. This can compensate for signal impairments due to the practical DAC multiplexing process. We confirmed that digital inverse multiplexing with a pre-distortion function can improve the signal-to-noise ratio by 3.7-dB in 132 Gbaud coherent signals utilizing an indium phosphide-based integrated bandwidth doubler and complementary metal-oxide semiconductor (CMOS) DACs with only 32 GHz bandwidth. With probabilistically-shaped 64- and 144-ary quadrature amplitude modulation signals, we achieved 1.47 Tb/s (11.1 bits/symbol) back-to-back signal generation and detection and 1.42 Tb/s (10.7 bits/symbol) transmission over a 100 km standard single-mode fiber. These results demonstrate the potential of our digital inverse multiplexing scheme to achieve ultra-broadband transmitters.