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Light Polarization-Assisted Sensing with Tilted Fiber Bragg Gratings

Tilted fiber Bragg gratings (TFBGs) are short-period gratings for which the refractive index modulation of the fiber core is angled by a few degrees with respect to the perpendicular to the propagation axis. They induce two kinds of light coupling: the self-backward coupling of the core mode at the Bragg wavelength and the backward coupling between the core mode and several tens of cladding modes, each with its own effective refractive index and mode field shape. The information contained in their spectral content is such that they inherently provide novel sensing modalities and improve the sensitivity in comparison to uniform fiber Bragg gratings. In particular, TFBGs are intrinsically temperature- insensitive by referencing spectral measurements to the wavelength and power level of the core mode resonance. As the tilt angle breaks the circular symmetry of the optical fiber cross-section, TFBGs are strongly dependent on light polariza- tion effects, which can be advantageously used when they are coated with nanoscale metal coatings or thin films. In this review, we report the latest achievements obtained with bare and coated TFBGs used for high-resolution refractometry and biochemical sensing through surface Plasmon wave generation.