Attojoule-Efficient Graphene Optical Modulators

TL;DR

This paper analyzes the physics and performance of graphene-based optical modulators, highlighting how device design and material properties can achieve attojoule energy efficiency for integrated photonics.

Contribution

It provides a comprehensive physics-based analysis of graphene modulators and demonstrates a near Boltzmann low-voltage, ultra-compact attojoule modulator design.

Findings

Reducing modal area improves energy-bandwidth performance.

In-plane polarization with plasmonic-slot waveguides is essential.

Bi-layer graphene enhances device performance.

Abstract

Electro-optic modulation is a technology-relevant function for signal keying, beam steering, or neuromorphic computing through providing the nonlinear activation function of a perceptron. With silicon-based modulators being bulky and inefficient, we here discuss graphene-based devices heterogeneously integrated. This study provides a critical and encompassing discussing of the physics and performance of graphene modulators rather than collecting relevant published work. We provide a holistic analysis of the underlying physics of modulators including the graphenes index tunability, the underlying optical mode, and discuss resulting performance vectors of this novel class of hybrid modulators. Our results show that the reducing the modal area, and reducing the effective broadening of the active material are key to improving device performance defined by the ratio of energy-bandwidth and footprint. We further show how the waveguides polarization must be in-plane with graphene such as given by plasmonic-slot structures. A high device performance can be obtained by introducing multi- or bi-layer graphene modulator designs. Lastly, we present recent results of a graphene-based hybrid-photon-plasmon modulator on a silicon platform, requiring near Boltzmann approximation (100mV) low drive voltages. Being physically compact this 100 aJ/bit modulator opens the path towards a new class of attojoule opto-electronics.