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Simultaneous measurement of strain and temperature using a long period fiber grating based on waist-enlarged fusion bitapers

A new long period fiber grating (LPFG) fabrication method based on periodically arranging a series of waist-enlarged fusion bitapers (WFBs) along the axis of a standard single mode fiber has been proposed and experimentally demonstrated. A strong grating modulation induced by the WFBs excites the mode coupling between the core and cladding modes, resulting in the formation of a grating resonance band. The mode coupling strength is directly proportional to the number of WFBs. A compact WFB-LPFG with a length of 3.28 mm has been achieved by five periods and displays a contrast of over 30 dB. By measuring the transmission intensity and resonant wavelength shift of the transmission spectrum, strain and temperature can be simultaneously determined.