The development of excessively tilted fiber gratings (Ex-TFGs) provides a new type of sensing device with high refractive index (RI) sensitivity, low thermal crosstalk and vector sensing property. Due to the asymmetric grating structure of Ex-TFG, the light in the core is coupled into high order forward-propagating cladding modes and split into two orthogonal polarization states, resulting in dual-peak resonances in the transmission spectrum. The Ex-TFG also exhibits a non-circularly symmetrical near field distribution, which endows an exceptional orientation sensing capability. Benefitting from the unique mode coupling behavior, Ex-TFGs have been studied and developed for many different sensing applications, such as polarization dependent torsion and loading sensors, vector accelerometer and magnetometer, and a variety of low thermal crosstalk bio/chemical sensors. This paper will review the recent study and development of Ex-TFGs in terms of mode coupling mechanism, fabrication method, transmission and sensor characteristics and the novel applications in sensing areas.
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- Optical fiber grating
- mode coupling in excessively asymmetric structure
- orientation sensing
- refractive index sensing