Refractive Index Sensors Based on Long-Period Grating in a Negative Curvature Hollow-Core Fiber

Abstract

Long-period optical fiber gratings (LPGs) are one of the widely used concepts for the sensing of refractive index (RI) changes. Negative curvature hollow-core fibers (NCHCFs), with their relatively large internal diameters that are easy to fill with liquids, appear as a very interesting medium to combine with the idea of LPGs and use for RI sensing. However, to date, there has been no investigation of the RI sensing capabilities of the NCHCF-based LPGs. The results presented in the paper do not only address this matter, but also compare the RI sensitivities of the NCHCFs alone and the gratings. By modeling two revolver-type fibers, with their internal diameters reflecting the results of the possible LPG-inscription process, the authors show that the fibers’ transmission windows shift in response to the RI change, resulting in changes in RI sensitivities as high as −4411 nm/RIU. On the contrary, the shift in the transmission dip of the NCHCF-based LPGs corresponds to a sensitivity of −658 nm/RIU. A general confirmation of these results was ensured by comparing the analytical formulas describing the sensitivities of the NCHCFs and the NCHCF-based LPGs.

An All-Fiber Fabry–Pérot Sensor for Emulsion Concentration Measurements

“…The open path FPI’s sensitivity to residue is, thus, generally decreased by increasing the length of the microcell optical path involved in the sensor design. In contrast, sensors that exploit evanescent field interactions (most FBG RI sensors [ 12 , 13 , 14 ], LPFG sensors [ 15 , 16 , 17 ], modal interference sensors [ 18 , 19 , 20 ], etc.) exhibit substantially higher sensitivity to the formation of deposits and residues, as even a very thin formation of the undesired residue film on the sensor surface results in a substantial change in the average RI of the volume that is involved in the measurement of the RI.…”

High refractive index fiber sensor based on femtosecond laser processing and antiresonant waveguide interference

“…All-fiber refractive index (RI) sensors have gained popularity among researchers due to their compact size, ease of operation, and corrosion resistance. Several fiber-optic sensors have been proposed, capable of detecting RIs based on the Mach-Zehnder interferometer [1], Fabry-Perot interferometer [2], Michelson interferometer [3], fiber Bragg gratings [4], and long-period gratings [5]. However, these devices still face challenges such as poor robustness or difficulties in fabrication.…”

Curcuma longa-Based Optical Sensor for Hydrochloric Acid and Ammonia Vapor Detection

“…The sensor achieved exceptional detection performance, with a lower detection limit of 34 ppb and a response time of 5 s. Due to its complete reversibility, the sensor could be tested up to ten times using the same nanoporous array [ 16 ]. The applications of optical fibers and microfibers for sensing various parameters show different techniques, from very simple to more complex [ 17 , 18 , 19 , 20 , 21 , 22 , 23 ].…”