Ultrafast All-Optical Graphene Modulator

TLDR

Graphene’s linear band structure and strong interband transitions enable broadband, ultrafast light–matter interactions, and recent electrically tuned modulators have been limited to about 1 GHz by the driving circuit response. This work proposes an all‑optical approach to overcome that bandwidth limitation. A graphene‑clad microfiber modulator achieves a 38 % depth and a ∼2.2 ps response limited only by graphene’s intrinsic carrier relaxation, making it compatible with high‑speed fiber networks and promising for future ultrafast optical processing.

Abstract

Graphene is an optical material of unusual characteristics because of its linearly dispersive conduction and valence bands and the strong interband transitions. It allows broadband light-matter interactions with ultrafast responses and can be readily pasted to surfaces of functional structures for photonic and optoelectronic applications. Recently, graphene-based optical modulators have been demonstrated with electrical tuning of the Fermi level of graphene. Their operation bandwidth, however, was limited to about 1 GHz by the response of the driving electrical circuit. Clearly, this can be improved by an all-optical approach. Here, we show that a graphene-clad microfiber all-optical modulator can achieve a modulation depth of 38% and a response time of ∼2.2 ps, limited only by the intrinsic carrier relaxation time of graphene. This modulator is compatible with current high-speed fiber-optic communication networks and may open the door to meet future demand of ultrafast optical signal processing.