Graphene-based D-shaped fiber multicore mode interferometer for chemical gas sensing.

In this Letter, a graphene-coated D-shaped fiber (GDF) chemical gas sensor is proposed and demonstrated. Taking advantage of both the graphene-induced evanescent field enhancement and the in-fiber multimode interferometer, the GDF shows very high sensitivity for polar gas molecule adsorptions. An extinction ratio of up to 28 dB within the free spectrum range of ~30  nm in the transmission spectrum is achieved. The maximum sensitivities for NH₃ and H₂O gas detections are ~0.04 and ~0.1  ppm, respectively. A hybrid sensing scheme with such compactness, high sensitivity, and online monitoring capabilities may pave the way for others to explore a series of graphene-based lab-on-fiber devices for biochemical sensing.