Compact resonant plasmonic hybrid waveguide refractive index sensors for aqueous medium

Abstract

Ultra-compact and high sensitivity resonant plasmonic refractive index sensors for aqueous medium are proposed. The sensors are based on the resonant coupling between the waveguide mode and the surface plasmon mode supported by a thin metal layer. For optimized layer thicknesses, the periodic coupling between the two hybrid modes guided by the structure takes place and a resonant absorption peak appears for a particular sensor length. The sensors are designed to operate in the spectral mode at visible wavelengths centred about 0.6328 μm. The sensors have been designed for the long range surface plasmon polaritons (LRSPP) as well as the short range surface plasmon polaritons (SRSPP). This study provides a detailed understanding of designing an ultra-short and efficient sensor for the aqueous medium with high spectral sensitivity (S), ultrahigh resolution (R) and figure of merit (FOM). The attained numerical values show that for optimized layer thicknesses, a sensitivity of 9200 nm/RIU for LRSPP mode and 1800 nm/RIU for SRSPP mode can be achieved for the aqueous medium with the sensor lengths of 83.5 μm and 15 μm (shortest to the best of our knowledge) respectively. Also, the values of R and FOM are 1.52 × 10−7 RIU and 7.7 × 103 RIU−1 for the LRSPP based sensor and 6.7 × 10−7 RIU and 4.5 × 103 RIU−1 for the SRSPP mode based sensor.