Four Wave Mixing control in a photonic molecule made by silicon microring resonators

Massimo Borghi,Alessandro Trenti,Lorenzo Pavesi

doi:10.1038/s41598-018-36694-5

Abstract

Four Wave Mixing (FWM) is the main nonlinear interaction in integrated silicon devices, which finds diffuse use in all-optical signal processing and wavelength conversion. Despite the numerous works on coupled resonator devices, which showed record conversion efficiencies and broadband operation, the possibility to coherently control the strength of the stimulated FWM interaction on a chip has received very limited attention. Here, we demonstrate both theoretically and experimentally, the manipulation of FWM in a photonic molecule based on two side coupled silicon microring resonators. The active tuning of the inter-resonator phase and of their eigenfrequencies allows setting the molecule in a sub-radiant state, where FWM is enhanced with respect to the isolated resonators. On the other hand, we can reconfigure the state of the photonic molecule to have energy equipartition among the resonators, and suppress FWM by making the two Signal waves to interfere destructively in the side coupled waveguides. This work constitutes an experimental demonstration of the control of a nonlinear parametric interaction via coherent oscillation phenomena in an integrated optical device.

Highlights

Stimulated Four Wave Mixing (FWM), that is the all-optical, coherent energy transfer of a Signal wave into an Idler wave by means of two auxiliary Pump waves[1], has been extensively studied for all-optical signal processing[2,3], wavelength conversion[4,5], frequency comb generation[6,7], parametric oscillation and amplification[8,9]
In this article we presented, both theoretically and experimentally, a novel method to actively control the FWM interaction in a photonic molecule made by two side coupled silicon microring resonators
We found an enhancement of the Idler conversion efficiency of about a factor of 5 with respect to the maximum attainable level from each single constituent of the molecule, and attributed to the excitation of a sub-radiant mode

Summary

Introduction

Stimulated Four Wave Mixing (FWM), that is the all-optical, coherent energy transfer of a Signal wave into an Idler wave by means of two auxiliary Pump waves[1], has been extensively studied for all-optical signal processing[2,3], wavelength conversion[4,5], frequency comb generation[6,7], parametric oscillation and amplification[8,9]. Photonic molecules[22,23], constituted by two or three coupled resonators, have been analyzed in terms of their inter-cavity distance or their eigenfrequency separation, for the dynamical tuning of the Electromagnetic Induced Transparency (EIT) effect[24,25,26,27,28], as well as for the onset of coherent collective phenomena like super or sub-radiance[29] These studies were principally limited to a linear analysis, since their goal was mainly focused to slow-light or routing applications. We experimentally and theoretically demonstrate that, in the parameter space (φ,δ), the efficiency of FWM can be enhanced, left unchanged or completely suppressed with respect to the one of a single isolated resonator These regimes cannot be resolved and accomplished in large structures, where the structural periodicity makes slow light effects to overwhelm any other side effect. We do experimentally map the energy distribution between the two resonators by monitoring the surface light scattered during the onset of the different FWM regimes, and further validate our comprehension of the phenomenon through an analysis performed in terms of the supermode of the structure

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