High Efficiency Electro-Optic Modulation in a Graphene Silicon Hybrid Tapered Microring Resonator

Yonghua Wang,Ping Xu,Wenchan Dong,Lei Lei,Xinliang Zhang,Junbin Zang

doi:10.1109/access.2021.3089465

Abstract

Graphene silicon devices have attracted significant attention due to their outstanding electronic and optical properties. By electrically tuning the Fermi level of the monolayer graphene sheet, electro-optic (EO) modulators have been widely analyzed. Despite significant progress has been achieved on high-speed modulation with integrated graphene silicon waveguides, it remains challenging to realize a high modulation efficiency since the light absorption in graphene is limited. Here, we propose and experimentally demonstrate a high efficiency EO modulator using a graphene-assisted tapered silicon ring resonator, where the tapered zone is covered by a graphene/graphene capacitor. This graphene-assisted tapered zone strongly enhances the graphene-light interaction that the achieved static and dynamic modulation (1KHz) depths are up to 26 dB and 12 dB, respectively. Physical mechanism of the modulation based on this nanostructure is also discussed in detail. The proposed nanostructure provides a promising alternative method for high-performance EO modulator, which is essential for the on-chip optical communication, optical computing and optical signal processing.

Highlights

Graphene, a two-dimensional version of graphite that consists of a single layer of carbon atoms, has attracted a significant research attention because of its exceptional properties including high carrier mobility [1], large broadband absorption [2], [3], zero-band gap, and tunable Fermi level [4]–[6]
A notable consequence of the low density state is that the charge-carrier density can change, which makes the Fermi level shifting available by applying a gate voltage to the graphene [20]
This electrically tunable Fermi level leads to a synchronous light absorption, enabling the ultra wideband electric-optic modulation in the graphene silicon hybrid nanophotonic integrated circuits. [10]–[13]

Summary

INTRODUCTION

A two-dimensional version of graphite that consists of a single layer of carbon atoms, has attracted a significant research attention because of its exceptional properties including high carrier mobility [1], large broadband absorption [2], [3], zero-band gap, and tunable Fermi level [4]–[6]. The slot dramatically enhances the graphene-light interaction while simultaneously induces high loss, which is of paramount importance for the modulator setup These methods effectively improve the modulation depth, but still suffer from the unexpected nonlinearity and limited carrier mobility associated with the doped silicon back gate. The configuration of the proposed nanostructure consists of a tapered silicon ring resonator, of which the tapered zone is covered by a graphene/graphene capacitor In this structure, the graphenelight interaction is enhanced by the ring resonator that improves the absorption, and by the tapered segment under the graphene, which is mainly in charge of strengthening the graphene-light interaction and correspondingly realizes the high modulation depth. Our structural design and experimental demonstration show that graphene EO modulator has the potential for high speed modulation and for high depth modulation

DEVICE DESIGN

DEVICE PERFORMANCE

CONCLUSION