Multi-channel Optical Fiber Surface Plasmon Resonance Sensor with Narrow FWHM, High Figure of Merit, and Wide Detection Range

We propose a multi-channel optical fiber surface plasmon resonance (SPR) sensor with narrow full width at half maximum (FWHM), high figure of merit (FOM), and wide detection range based on side-polished fiber. The sensing surface is modified by a dielectric layer on the top of gold film. By controlling the thickness of the dielectric layer, the resonance wavelength can be adjusted in a large range. Compared to traditional SPR sensors, the SPR dip FWHM of the proposed sensor has been significantly reduced to several nanometers (minimum FWHM reaches 5.2 nm), which results in a significant improvement on the FOM of the SPR sensor (maximum FOM reaches 218 RIU−1), and is great helpful to improve wavelength measurement accuracy. The multi-channel SPR sensor can be easily achieved through above features by cascading multiple sub-channels with different dielectric layer thicknesses, and the SPR spectra can be demodulated by wavelength division multiplexing method. Compared to traditional multi-channel SPR sensors which have usually two sensing channels, in this work, the narrow FWHM makes it easy to produce more SPR dips in the spectrum. In this paper, we demonstrate a three-channel SPR sensor and a four-channel SPR sensor, whose performances exceed most of current multi-channel optical fiber SPR sensors. In addition, the proposed multi-channel SPR sensor has wide refractive index detection range of 1.33–1.43 RIU, which is applicable for detecting most liquid samples. Moreover, the proposed multi-channel SPR sensor is based on single-mode fiber, and the sensor structure is easy to fabricate.