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A typical configuration for a SPR sensor is based on Kretschmann configuration

 where a glass prism serves the purpose of coupling the light from an optical source to the SPW excited at the interface between the metal and the bottom dielectric layer. In the experiment the angle, θ, of the incident light is increased while monitoring the intensity of the beam reflected from the interface formed by the base of the prism and the top surface of the metal.

The intensity of the reflected beam, IR, shows a sharp drop at an angle, θe,

Corresponding to the excitation of the SPW, in figure. Since θe depends on the

refractive index of the metal and that of the bottom dielectric, any change in the latter produces a change in θe, hence the operation as a sensor.

                            a) Kretschmann configuration                        b) SPW excitation

An alternative method to angle interrogation is to keep the incident angle fixed and scan the wavelength of operation (spectral interrogation). A drop at the intensity of the reflected signal is observed as a function of the incident wavelength.

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