A differential optical sensor for long-term monitoring of chemicals

The paper presents an optical sensor suitable to detect small changes in the concentration of chemicals and specifically designed for long-term monitoring applications. The sensor exploits the surface plasmon resonance as the chemical detection technique and implements a differential configuration to compensate for parasitic effects, such as drifts, mechanical instabilities and temperature fluctuations, which greatly impair the accuracy of this type of sensors. An analysis of the impact of unwanted changes in the measurement setup is provided and an example of a compensation procedure applied to angular misalignments is given.