Ultra-compact plexcitonic electro-absorption modulator

TL;DR

This paper proposes an ultra-compact plexcitonic electro-absorption modulator using 2D WS2 monolayer and plasmonic waveguides, achieving high extinction ratio and low energy consumption for integrated photonics.

Contribution

It introduces a novel design of a sub-micron electro-absorption modulator based on strong exciton-plasmon coupling in 2D materials, with simulated high performance metrics.

Findings

9.1 dB extinction ratio achieved

400 nm footprint with <3 fJ/bit energy

Operates at 15 GHz with 3-dB bandwidth

Abstract

Compact electro-optic (EO) modulators with large extinction ratios, low-switching energies, and high operation speeds are desirable for integrated photonic and linear optical computing. Traditional 3D semiconductors and dielectrics are unsuitable for achieving such modulators due to the small magnitude of EO effects in them. Excitonic 2D semiconductors present a unique opportunity in this regard given their large and tunable optical constants near the excitonic resonances. However, strategies for confining and electrically tuning the excitons into compact EO modulators have not been realized thus far. Here, we design and simulate an ultra-compact, plexcitonic (strongly-coupled exciton-plasmon) electro-absorption modulator (EAM) with a sub-micron linear footprint operating close to the excitonic peak of the WS2 monolayer (641 nm) hybridized with the plasmon mode of a silver slot waveguide. Electrostatically injected free carriers in WS2 modulate the light-matter interaction via Coulomb screening of the excitons as well as promoting the formation of charged excitons (trions). For our optimized designs, the EAM is expected to achieve a 9.1 dB extinction ratio, concurrently with a 7.6 dB insertion loss in a 400 nm lateral footprint operating with a predicted < 3 fJ/bit switching energy at 15 GHz for 3-dB bandwidth modulation. Our work shows the potential of plexcitonic quasi-particles for integrated optical modulators.