Deep and fast free-space electro-absorption modulation in a mobility-independent graphene-loaded Bragg resonator

TL;DR

This paper demonstrates a high-speed, deep electro-absorption modulation in a graphene-loaded Bragg resonator at 1550 nm, achieving >50 dB extinction ratio at >1 GHz independent of graphene mobility.

Contribution

It introduces a reflection-mode device leveraging critical coupling to achieve high extinction ratios regardless of graphene quality, with potential for sensing applications.

Findings

Achieves >50 dB extinction ratio at >1 GHz speed

Critical coupling enhances extinction for lower graphene mobility

Device can be adapted for sensing and acousto-absorption modulation

Abstract

Deep and fast electro-optic modulation is critical for high-speed near infrared signal processing. We combine the electro-absorption tunability of graphene with the high-Q resonance of a Bragg-based Fabry-Perot resonator at {\lambda}=1550 nm and show that ~100% free-space signal modulation (>50 dB extinction ratio, <1 dB insertion loss) at high speed (>1 GHz) can always be achieved independently of graphene quality (mobility), provided the device is operating in reflection mode and tuned in critical coupling with graphene. Remarkably, the critical coupling mechanism produces a higher extinction ratio for lower graphene mobility. We use practical considerations to optimize the device architecture and operation as a function of graphene mobility. With a small modification this scheme can be turned into a very sensitive acousto-absorption modulator with a ~30 dB/{\AA} extinction ratio, or an index sensor with 10^7 %/RIU sensitivity. These designs can be easily extended throughout the midIR spectrum by appropriate scaling of layer thicknesses.