ABSTRACT
Sensors that use the phenomenon called the surface Plasmon resonance (SPR) have become very popular in recent years. In principle, SPR sensors are thin-film refractometers that measure changes in the refractive index (RI) occurring at the surface of a metal film supporting a surface Plasmon. Surface Plasmons, also known as surface Plasmon polaritons, are the surface electromagnetic waves that propagate parallel along the metal–dielectric interface. The utilization of metal is conditioned by the need of electrons in the conduction band that can resonate with the incoming light at a proper wavelength. The description of these sensors in the present chapter includes the consideration of the following problems: (1) principles of operation, (2) design of SPR-based sensors, including SPR probe design, (3) features of localized surface Plasmon resonance (LSPR), and (4) approaches that can be used for fabrication of SPR-based humidity sensors. It is shown that SPR-based humidity sensors can be realized using planar waveguide, prism couplers, and optical fibers. Comparison of the considered sensors indicates that the simplest variant of SPR-based humidity sensor is sensor, using the LSPR effect. This version is most suitable for practical applications. The use of a prism sometimes prevents the miniaturization of the sample and is not always desirable. Grating coupling does not require any prisms but the preparation of a grating structure on the desired substrate surface is sometimes difficult. The waveguide-based SP excitation is a quite simple and reasonable method. However, the measurements for the waveguide array need a complicated setup. However, it is necessary to take into account that even this approach has limitations.
