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Tilted FBG – optical Fiber Bragg Gratings (TFBG)

Tilted FBGsThe tilted FBG is a new kind of sensor that includes all the advantages of established usage Bragg grating technology in addition to being able to excite cladding modes resonantly. This device opens possibilities for single-point sensing in hard-to-reach places.

Tilted fiber Bragg gratings are also known as slanted gratings or blazed gratings. This is a special type of short-term optical fiber gratings. TFBGs are fabricated using the same tools and techniques as standard FBGs, i. e. from a permanent refractive index change induced in doped glasses by an interference pattern between two intense ultraviolet laser beams. The boundary surface of the varied index is not vertical with respect to the fiber axis but has a certain angle. One feature of tilted FBG is that they can couple guided modes with copropagating modes or counterpropagating modes in specific wavelengths.

As we have known that tilted FBG can unite light from guided modes into radiation modes or cladding modes. The cladding modes are investigated theoretically by studying a three-layer model of optical fibers, whereas the core mode is investigated by studying a two-layer model of optical fibers. The analysis reveals that to increase the coupling of the energy transferred from the core mode to cladding modes, the cladding radius needs to be decreased. Such behavior is illustrated by studying the change in the electric field distribution and is used to enhance the sensitivity of the sensing refractive index of the surrounding medium.

Connection efficiency with the help of tilted FBGis sensitive to light polarization, various sensors, and devices based on these characteristics have been proposed or developed for a wide range of applications. TFBG sensors are using for mechanical and biochemical applications, including one-dimensional TFBG vibroscopes, accelerometers, and micro-displacement sensors; two-dimensional TFBG vector vibroscopes and vector rotation sensors; reflective TFBG refractometers with in-fiber and fiber-to-fiber configurations; polarimetric and plasmonic tilted FBG biochemical sensors for in-situ detection of a cell, protein, and glucose.