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Abstract-The method and the required installations for fabricating tapered long-period fiber gratings can be simpler than that of standard fiber Bragg gratings, and the fabrication process is faster. To our knowledge, the tapered long-period fiber grating pressure sensor is presented here for the first time. In this paper, the fabrication method for tapered long-period fiber gratings, the sensing principle, the sensor structure, the measurement setup, and the preliminary results are presented and discussed. The pressure sensitivity of the sensor is as high as 5.1 pm/bar. Index Terms-Fiber-optic sensors, long-period fiber gratings, pressure calibration and measurement, step index fiber, tapered long-period gratings (TLPGs), temperature.

This paper presents an investigation of the sensing properties of long-period gratings (LPGs) written with the electric-arc technique in commonly used standard germanium-doped Corning SMF28 and boron co-doped Fibercore PS1250/1500 fibers. In order to increase the sensitivity of the LPGs, we studied and established for each fiber the writing parameters allowing for the coupling of the highest possible order of cladding modes at a resonance wavelength around λ = 1550 nm. The sensitivity of the LPGs to refractive index, to temperature and to hydrostatic pressure was investigated. The experimental results were supported by extensive numerical simulations. Thanks to the well-established and precisely controlled arc-writing process, we were able to reduce the minimum period of the gratings down to 345 and 221 μm, respectively, for LPGs based on the SMF28 and PS1250/1500 fibers. To the best of our knowledge, these are the shortest periods ever achieved for these fibers using the arc-manufacturing technique. The pressure sensitivities of 13 and 220 pm bar −1 are the highest ever measured for LPGs written in the SMF28 and PS1250/1500 fibers, respectively. Moreover, a reduction in the diameters of the SMF28 fiber induced by the arc was found, which significantly affected the distribution of resonances generated by the coupled cladding modes.

The paper presents for the first time a study of long-period gratings (LPGs) applied for label-free detection of specific bacteria using physically adsorbed bacteriophages. For the purposes of the experiment a number of highly sensitive LPGs working at the turning point of phase matching curve was fabricated in SMF28 fiber using UV exposure. We show that the device allows for real-time monitoring of phenomena taking place on the sensor's surface, including phage-bacteria interactions. For the applied conditions a resonance wavelength shift of ~1.3 nm induced by bacteria binding was observed.