# Long-haul coherent communications using microresonator-based frequency combs

## TL;DR

This paper demonstrates the use of normal dispersion microresonator-based frequency combs for long-distance coherent optical communications, achieving record transmission distances with high data rates.

## Contribution

It is the first to experimentally show coherent communications with normal dispersion microresonator combs, enabling energy-efficient high-capacity fiber links.

## Key findings

- Transmitted data over 6300 km with polarization multiplexed QPSK.
- Achieved over 700 km with PM 16QAM at 900 Gbit/s.
- Set the record for longest fiber transmission with an integrated comb source.

## Abstract

Microresonator-based frequency combs are strong contenders as light sources for wavelength-division multiplexing (WDM). Recent demonstrations have shown the potential of microresonator combs for replacing tens of WDM lasers with a single laser-pumped device. These experiments relied on microresonators displaying anomalous dispersion. Devices operating in the normal dispersion offer the prospect of attaining high power conversion efficiency - an aspect that will be crucial in the future for enabling energy-efficient coherent communications with higher order modulation formats or lighting several spatial channels in space-division multiplexing. Here we report the experimental demonstration of coherent communications using normal dispersion microresonator combs. With polarization multiplexed (PM) quadrature phase-shift keying, we transmitted data over more than 6300 km in single-mode fiber. In a second experiment, we reached beyond 700 km with PM 16 quadrature amplitude modulation format and an aggregate data rate above 900 Gbit/s assuming 6% error correction overhead. These results represent the longest fiber transmission ever achieved using an integrated comb source.

---
Source: https://tomesphere.com/paper/1701.08569