High-sensitivity chirped tapered fiber-Bragg-grating-based Fabry-Perot cavity for strain measurements.

In this Letter, a novel, to the best of our knowledge, Fabry-Perot cavity, based on Bragg grating technology for temperature and strain monitoring, is presented. Such a structure consists of two linearly chirped fiber Bragg gratings of a significant length written in a thermally tapered optical fiber. The technological process for manufacturing such a grating allows for utilization of almost every tapered fiber, by means of its profile and also phase masks with various chirp ratios. For this type of structure, a method for strain discrimination based on monitoring of the cavity length is proposed, enabling potential multiplexation of the sensor of two structures, which have the similar reflection spectra, by means of their spectral position. The utilized sensing mechanism allowed for achieving strain sensitivity by means of the cavity length change as high as 5 µm/µɛ. Also, as it has been experimentally shown a structure can also be employed for measurements of temperature, with the sensitivity equal to 8.96 pm/°C.