Optical planar waveguide sensors, able to detect and process information from the environment in a fast, cost-effective, and remote fashion, are of great interest currently in different application areas including security, metrology, automotive, aerospace, consumer. Optical planar waveguide sensors, able to detect and process information from the environment in a fast, cost-effective, and remote fashion, are of great interest currently in different application areas including security, metrology, automotive, aerospace, consumer. Optical planar waveguide sensors, able to detect and process information from the environment in a fast, cost-effective, and remote fashion, are of great interest currently in different application areas including security, metrology, automotive, aerospace, consumer electronics, energy. Planar waveguides, also called slab waveguides, are waveguides with a planar geometry, which guide light only in one dimension. They are often fabricated in the form of a thin transparent film with increased refractive index on some substrate, or possibly embedded between two substrate layers. For. Optical sensors can be classified into two main types: fiber optic sensors and planar waveguide sensors. Planar waveguides are optical structures that confine the optical radiation in the direction of propagation. There are two independent electromagnetic modes in planar waveguides: transverse. Al-though waveguides can be created in numerous geometries, this article focuses on waveguides with a planar geometry that are used to study thin films and interfaces.