Subwavelength Resonant Gratings for Micrometric Strain Sensors

Abstract

A sub-wavelength resonant grating based on plasmonic silver nanowires is proposed and theoretically analyzed. The structure is composed of several Ag nanowires distributed in a parallel configuration with sub-wavelength grating constant. Despite the use of TM mode, we have discovered that for certain subwavelength distances, the combination with the plasmonic resonances of the nanowires produces a strong reflection at the resonant peaks. This structure could be used to measure deformation variation down to the nanometer range and use it as a micrometric all optical gauge. The effects of the size of the cylindrical metal nanowires on the performance of the sensing have been studied in detail. Two operation modes are observed depending on the structural parameters. Either a phase or amplitude modulation in the visible range could be obtained. In the first case, a sensitivity of 7.5 pm/µε has been obtained. In the second case, an amplitude modulation of -256•10 -6 dB/µε has been obtained. This kind of sensor would be cheap and easy to measure by means of a fiber optic link. The structure is simple and easily scalable.