Phase interrogation of an integrated optical SPR sensor

A theoretical analysis of the phase behaviour of an integrated optical surface plasmon resonance (SPR) sensor is presented, in which the complex transmittance of a dielectric waveguide coated with a thin film of gold is determined for varying superstrate index. Exploitation of the phase sensitivity is studied theoretically by incorporating gold-coated waveguides on both branches of a Mach–Zehnder interferometer (MZI), one or both of which may be exposed to superstrate index variations or thin adlayers. It is proposed that this device can be used to suppress unwanted refractive index changes common to both branches, for example, due to temperature variations, and may show enhanced sensitivity.