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Enlarging the evanescent field scope by nanoparticle scattering for nanoparticle sensing of optical fiber sensors

A novel method to improve the sensitivity of evanescent field optical fiber sensors is proposed and confirmed by the numerical simulation. The evanescent field scope can be enlarged by nanoparticle scattering, which is produced by the nanoparticles placed in the evanescent field of the sensing fiber. It is found that the extent of nanoparticle scattering is dominated by the dimensions of the particles. Increasing the radius can enhance the scope of the evanescent filed. As the radius increases, the scattering peak shifts red and the scattering effect becomes obvious. The scattering efficiency accounts for about 74% of the extinction efficiency when the radius is 50 nm with the incident wavelength 420 nm. Moreover, the scope of the evanescent field can be extended to approximately 3 µm by silver nanoparticle scattering, which enhances the evanescent field to a relatively far-field scope.