Single unified platform of fiber optical measuring systems based on combined resonant structures

The work presents an overview and classification of combined fiber-optic resonant structures, which are essentially a combination of a Fabry-Perot interferometer (FPI) and a fiber Bragg structure. The latter can be represented either as a conventional fiber Bragg grating (FBG), or an addressed fiber Bragg structure (AFBS) of various types. It is shown that such combined resonant structures can serve as sensing elements of various fiber-optic measurement systems, detecting such physical impacts as temperature, pressure, acoustic waves, etc. One of the proposed structures is a fiber optic FabryPerot interferometer based on an open macro cavity at the end face of an optical fiber. Immersing the end face of the optical fiber with macro cavity in liquid leads to the formation of an air bubble where interfacial surfaces act as FabryPerot mirrors, which allows to use the structure for detecting pressure or acoustic waves in liquids. Another considered type of an FPI is composed of layer of borosilicate glass at the end of an optical fiber, acting as a temperature sensor. It is demonstrated that the combination of FPI and fiber Bragg structure can be used as a unified basic element for the various optical fiber sensors, utilizing the Fabry-Perot cavity at the end face of the fiber and the Bragg structure as fundamental sensing elements.