A highly sensitive surface plasmon resonance biosensor using photonic crystal fiber filled with gold nanowire encircled by silicon lining

The proposed photonic crystal fiber structure senses small deviations in the refractive index of liquids by surface plasmon resonance phenomenon. The coupling of core guided mode to surface plasmon polariton modes is modulated by the analyte placed between the central core and gold nanowire. Numerical study on the sensor performance is executed using finite element method. A sensitivity of 2000 nm/RIU is achievable for detection of liquids with refractive index greater than 1.37 and the sensor covers a wide sensing range from 1.37 to 1.45. Loss factors as high as 187.76 dB/cm is achievable. The analysis on the influence of structural modifications such as increase and decrease of gold nanowire diameter on the sensing action is also carried out. Numerical results depict an increase in confinement loss factor as the gold diameter gets reduced and a shift towards longer wavelength. The analysis of the sensor performance is performed when the gold nanowire is coated with silicon and it reveals that the loss factor gets enhanced by three fold, from 115.88 to 360.81 dB/cm for analyte refractive index of 1.4, as compared to without silicon coating due to the enhanced energy coupling between plasmon and core modes. The increased silicon thickness improves the sensitivity factor to 4000 nm/RIU.