Method to measure the refractive index of a sample using surface plasmon polaritons

A method to measure the refractive index of a sample , includes : providing a plasmonic sensor including a sensing surface in contact with the sample ; providing an optical resonator , the plasmonic sensor being integrated therein as a reflecting surface ; providing a first input field of electro magnetic radiation as a primary carrier ; providing a second input field of electromagnetic radiation as a secondary carrier having a second frequency different from the first and defined as : second frequency = first frequency + Av and having a TE and / or a TM polarized component ; impinging simul taneously with the first and second input field the plasmonic sensor ; tuning the frequency of the first field and / or the value of Av ; detecting a resonator output power corresponding to the first and second intra - cavity fields resonating ; determin ing a difference between the first and the second resonating frequencies ; and calculating the refractive index of the sample from the difference .