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Surface plasmon resonance based fiber optic refractive index sensor utilizing cobalt metal

In this work, we have experimentally studied the surface plasmon resonance (SPR)-based fiber-optic refractive index sensor introducing a layer of cobalt in addition to gold layer. The sensor is based on wavelength interrogation method. The advantage of cobalt is that it possesses both SPR and magnetic properties and hence can also be used for magnetic field sensing. Addition of a thin layer of cobalt to the SPR probe enhances the sensitivity of the sensor. Further, the operating wavelength can be tuned by varying the thickness of the cobalt layer. Experimental results show a red shift in the resonance wavelength with the increase in the refractive index of the sensing layer for a given thickness of the cobalt layer. Further, as the thickness of the cobalt layer increases, the sensitivity of the sensor increases. Use of cobalt in place of gold reduces the cost of the probe. In the bilayer metallic structure that has been studied, the ferromagnetic material (cobalt) induces the magneto-optic activity and the noble metal allows the excitation of non damped plasmons, which increases the electromagnetic field intensity inside the cobalt layer and enhances the sensitivity of the sensor.