The suitability of a terahertz plasmonic sensor for sensing applications is successfully demonstrated using a hybrid planar waveguide composed of a subwavelength plastic ribbon waveguide and a diffraction metal grating. The subwavelength-confined terahertz plasmons on the hybrid waveguide resonantly reflect from the periodic metal structure under phase-matched conditions and perform resonant transmission dips. The resonant plasmonic frequencies are found to be strongly dependent on the refractive indices and thicknesses of analytes laid on the hybrid planar waveguide. Both plastic films with varying thicknesses and granular analytes in different quantities are successfully identified according to the spectral shifts of resonant dips. An optimal refractive index sensitivity of 261 GHz per refractive index unit is achieved. Within localized and enhanced terahertz plasmonic fields, the minimum detectable optical path difference can be reduced to 2.7 μm corresponding to λ/289, and the minimum detectable amount of analytes in powdered form reaches 17.3 nano-mole/mm2. The sensing technique can be used to detect particles in a chemical reaction or monitor pollutants.
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