The coupling characteristics of a hybrid coupler comprised of a long-range surface-plasmon-polariton (LRSPP) waveguide and a dielectric waveguide is analyzed with different detecting layers. Calculation results show that the coupling strength between the LRSPP mode and the dielectric-waveguide mode is rather sensitive to the refractive index of the detecting layer. This is promising to realize an integrated refractive index sensor with high resolution better than 4 x 10(-7) refractive index units or a modulator with rather low driving power and insert loss.