Graphene optical modulators using bound states in the continuum

Myunghwan Kim,Sangin Kim,Soeun Kim

doi:10.1038/s41598-022-05253-4

Myunghwan Kim, Sangin Kim + Show 1 more

Open Access

https://doi.org/10.1038/s41598-022-05253-4

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Abstract

Graphene-based optical modulators have been widely investigated due to the high mobility and tunable permittivity of graphene. However, achieving a high modulation depth with a low insertion loss is challenging owing to low graphene-light interaction. To date, only waveguide-type modulators have been extensively studied to improve light-graphene interaction, and few free-space type modulators have been demonstrated in the optical communication wavelength range. In this study, we propose two graphene-based optical free-space type modulators in a simple silicon photonic crystal structure that supports bound states in the continuum. The designed modulator with an ultra-high quality factor from the bound states in the continuum achieves a high modulation depth (MD = 0.9972) and low insertion loss (IL = 0.0034) with a small Fermi level change at the optical communication wavelength. In addition, the proposed modulators support outstanding modulation performance in the normal chemical vapor deposition (CVD) graphene (mobility = 0.5 m2/Vs). We believe the scheme may pave the way for graphene-based optical active devices.

Highlights

Graphene-based optical modulators have been widely investigated due to the high mobility and tunable permittivity of graphene
The outstanding carrier mobility and gate-tunable carrier concentration of graphene enable it to be used as an active medium in optical modulators; the carrier concentrations of graphene can be tuned by applying different gate-voltage (Fermi level variation), which enables gate-tunable absorption of g raphene[16]
Graphene loss is largely determined by the interband transition in the optical communication wavelength region, which is nearly independent of the Fermi level of graphene

Summary

Introduction

Graphene-based optical modulators have been widely investigated due to the high mobility and tunable permittivity of graphene. Only waveguide-type modulators have been extensively studied to improve light-graphene interaction, and few free-space type modulators have been demonstrated in the optical communication wavelength range. To increase absorption in graphene, optical modulators using the epsilon-near-zero effect have been introduced[29,30] These devices achieved a high modulation depth with an extremely enhanced electric field in the graphene layer. Near high Q-factor resonators, such as photonic crystal r esonators[31] and whispering gallery m odes[32,33] These resonators show relatively low Q values (Q = 1 03 ~ 104), which is not enough to achieve highly efficient modulators; Scattering loss by imperfect fabrication and graphene loss deteriorate the Q value

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