Modal sensitivity enhancement of few-mode fiber Bragg gratings for refractive index measurement

Abstract

Few-mode fibers (FMFs) offer several distinct features from single mode fibers and multimode fibers, in terms of medium core size which is capable of accommodating several transverse modes (2-6 modes). In this work, fiber Bragg grating (FBG) has been inscribed in FMF which exhibits more than one resonant Bragg wavelengths. Few-mode fiber Bragg grating (FM-FBG) can be used as sensing device because of its modal sensitivity to the changes in an ambient environment, such as temperature and refractive index in terms of concentration of the solution. To increase its modal sensitivity for solution concentration, the cladding of FM-FBG is removed, and the Bragg wavelength difference of the modes increases during the etching process. It has been observed that by decreasing the core radius through chemical etching, the Bragg wavelength difference of respective modes increases whereas the power confinement ratio in the core for the respective modes decreases. Therefore we have optimized the core radius as at approximately 7 µm for the enhancement of refractive index modal sensitivities. The fabricated sensor has been characterized with the different concentrations of sodium chloride (NaCl(aq)) solution.

Mixed-Resolution High-Q Sensor Based on Hybridized Spoof Localized Surface Plasmons

“…As compared in Table 1, the mixed-resolution algorithm increases the Q-factor from 96 by 1.93 times to 185.1, and the sensing FoM increases by 2.17 times, from 23.38 to 50.7. The algorithm can almost double the Q-factor and sensing FoM without changing the sensor structure, which is an important breakthrough in the microwave sensor field [34][35][36][37]. With this mixed-resolution algorithm, sensors are expected to achieve multimode enhanced sensing in the future.…”

Spherical Glass Based Fiber Optic Fabry-Perot Interferometric Probe for Refractive Index Sensing

“…Optical fiber sensors have proven to be reliable and robust sensing devices with characteristics such as immunity to electromagnetic interference, compact size, biocompatibility and real time measurement ability, making them suitable for demanding biomedical, chemical and industrial applications [5]. Various RI optical fiber sensors have been proposed in literature such as Fabry Perot interferometer (FPI) sensors [2], evanescent wave sensors [3], etched fiber Bragg grating sensors [6], micro-structured fiber Bragg grating refractive index sensors [7], and whispering gallery mode (WGM) resonators [8], etc. However, the challenge is to improve the simplicity of fabrication process and to introduce the cost effectiveness of the sensor.…”

Digital Matched Filtering (DMF) Technique for the Performance Enhancement of Few-Mode Fiber Bragg Grating Sensor

“…Several theoretical and experimental studies have been performed on the applications and the characteristics of FM-FBG [6][7][8][9][10][11]. Moreover, it has been reported that each mode in few-mode fibre Bragg grating (FM-FBG) shows different sensitivity towards the physical parameter and therefore it can be used as multi-parameter sensor [12][13][14][15].…”

“…The higher is the mode order, the greater is the sensitivity. While the use of HOM can enhance the detection sensitivity of FBG sensor towards RI change, improvement in the capability to detect small resonant wavelength shift can increase the measurement accuracy [13]. In addition, several schemes have been reported for detecting the wavelength shift in FBG sensors by using either a broadband source or various spectral analysis techniques such as edge filters, scanning Fabry-Perot filters, acousto-optic tuneable filters, Mach-Zehnder interferometers, or a tuneable laser source with a broadband detector and Nevertheless, for each of the schemes, the wavelength detection accuracy is limited by various types of noise.…”