High-order coherent communications using mode-locked dark-pulse Kerr combs from microresonators

Attila Fülöp,Peter A Andrekson,Mikael Mazur,Yi Xuan,Abel Lorences-Riesgo,Pei-Hsun Wang,Victor Torres-Company,Óskar B Helgason,Andrew M Weiner,Dan E Leaird,Minghao Qi

doi:10.1038/s41467-018-04046-6

Abstract

Microresonator frequency combs harness the nonlinear Kerr effect in an integrated optical cavity to generate a multitude of phase-locked frequency lines. The line spacing can reach values in the order of 100 GHz, making it an attractive multi-wavelength light source for applications in fiber-optic communications. Depending on the dispersion of the microresonator, different physical dynamics have been observed. A recently discovered comb state corresponds to the formation of mode-locked dark pulses in a normal-dispersion microcavity. Such dark-pulse combs are particularly compelling for advanced coherent communications since they display unusually high power-conversion efficiency. Here, we report the first coherent-transmission experiments using 64-quadrature amplitude modulation encoded onto the frequency lines of a dark-pulse comb. The high conversion efficiency of the comb enables transmitted optical signal-to-noise ratios above 33 dB, while maintaining a laser pump power level compatible with state-of-the-art hybrid silicon lasers.

Highlights

Microresonator frequency combs harness the nonlinear Kerr effect in an integrated optical cavity to generate a multitude of phase-locked frequency lines
It was soon recognized that the performance of microresonator combs is sufficiently high to cope with the requirements in terms of frequency stability, signal-tonoise ratio (SNR), and linewidth of modern coherent communication systems[23,24,25,26]
The high optical signal-to-noise ratio (OSNR) per channel is enabled by the high internal conversion efficiency of the comb, which reaches above 20%–in line with previous observations[38]

Summary

Introduction

Microresonator frequency combs harness the nonlinear Kerr effect in an integrated optical cavity to generate a multitude of phase-locked frequency lines. Recent demonstrations include multichannel nonlinear pre-compensation[8], as well as the possibility to decrease the inter-channel guard bands for an increased total spectral efficiency[9,10] Another exciting prospect for using a frequency comb as a multi-carrier light source in WDM systems is the possibility to relax the resource requirements at the receiver by implementing joint impairment compensation and tracking for multiple data channels[11,12]. Recent experiments have revealed a mode-locked state when the cavity exhibits normal dispersion This comb state corresponds to circulating dark pulses[33,34] in the cavity, and it might be of significant interest for coherent data transmission in WDM systems. This demonstration corresponds to the highest-order modulation format shown with any integrated comb technology to date

Methods

Results

Conclusion