High-Order Multi-Level Optical Transmission for beyond 100 Gb/s Using High-Speed DACs

Abstract

This paper describes high-speed and high-spectral efficiency optical transmission technologies that focus on channel rates beyond 100 Gb/s. Quadrature amplitude modulation (QAM) is adopted to achieve high spectral efficiency. First, we review recent progress in optical QAM transmission technologies. High-speed digital-to-analog converters (DACs) are key components for generating optical QAM signals. We recently developed a high-speed DAC fabricated by indium phosphide (InP) heterojunction bipolar transistors (HBTs) technology. It has a resolution of 6 bits and operates at up to 28 Gs/s. We performed a 25 GHz-spaced eleven-channel 171 Gb/s 16-QAM transmission experiment using our DAC. We achieved the record spectral efficiency-distance product of 9216 b/s/Hz-km (6.4 b/s/Hz x 1440 km) using the optical 16-QAM format.