Graphene/PVA coated D-shaped fiber for sodium nitrate sensing

•D-shaped fiber structure coated with graphene/ PVA.•Sensing of sodium nitrate within 1–7% concentration.•The sensor had sensitivity and linearity of 0.390 dBm/% and 99%.•It shows an improved performance over the uncoated structure. [Display omitted] A graphene/Polyvinyl alcohol (PVA) coated D-shaped fiber structure for sensing sodium nitrate solutions is proposed in this paper. D-shaped single mode fiber (SMF) coated with graphene/PVA was used as a sensor for sodium nitrate liquid solutions with the concentration range of 1–7%. After monitoring the output power and spectral transmission characteristics of the sensor, the graphene/PVA coated sensor showed an improved performance over the uncoated structure. The evanescent mode of the side-polished fiber and the interaction between the nitrate ions and the coating graphene improved the sensor’s performance. The graphene/PVA coated sensor had sensitivity and linearity of 0.390 dBm/% and 99% compared to the uncoated sensor sensitivity and linearity of 0.117 dBm/% and 98% respectively. This shows the advantage of using D-shaped fiber coated with graphene and PVA to detect sodium nitrate concentrations.