Wavelength and Phase Detection Based SMS Fiber Sensors Optimized With Etching and Nanodeposition

Abstract

The development of an optical fiber refractometer by 5 hydrogen fluoride etching and sputtering deposition of a thin-film 6 of indium tin oxide on a single-mode-multimode-single-mode fiber 7 structure has been analyzed with the aim of improving the sen-8 sitivity to the changes of the refractive index (RI) of the external 9 medium. The device is sensitive to the RI changes of the surround-10 ing medium, which can be monitored by tracking the spectral 11 changes of an attenuation band or with a fast Fourier transform 12 (FFT) analysis. By using an optical spectrum analyzer combined 13 with a simple FFT measurement technique, the simultaneous real-14 time monitoring is achieved. The results show that the sensitivity 15 depends on the thin-film thickness. A maximum of 1442 nm/RIU 16 (refractive index unit) in the 1.32-1.35 RIU range has been attained. 17 In addition, a theoretical analysis has been performed, where simu-18 lations matched with the experimental results. As a practical appli-19 cation of the developed optical fiber structure, a°Brix (°Bx) sensor 20 has been implemented with a sensitivity of 2.13 nm/°Bx and 0.25 21 rad/°Bx respectively for wavelength and phase shift detection. 22 Index Terms-Etching, optical fiber sensor, refractive index, 23 single-mode-multimode-single-mode (SMS), thin-films. 24 I. INTRODUCTION 25 O PTICAL fiber refractometers have been extensively stud-26 ied for chemical, medicine, and biological applications 27 due their multiple advantages such as compact size and high 28 resolution. They can be used in harsh environments and allow 29 for minimally invasive procedures to be performed [1]. 30 Up until now, several technologies have been used to de-31 velop optical fiber refractometers. Some of these technologies 32

Etched and Nanocoated Single-Mode Multimode Single-Mode (SMS) Fibers for Detection of Wind Turbine Gearbox Oil Degradation

“…Another strategy for increasing the sensitivity is the deposition of a thin film on the coreless region [28]. Moreover, both etching and thin-film deposition can be combined for a highly sensitive SMS structure [29]. The influence of etching will be analyzed by comparing two structures: one without etching and another with a 45-minute immersion in a 40% HF solution.…”

Monitoring the Etching Process in LPFGs towards Development of Highly Sensitive Sensors

“…This effect is attributed to the fiber cross section, which is not completely round in a fiber reduced from 125 to 30 µm, as it has been proved in [8], whereas the etching from 80 to 30 µm is softer and, consequently, the double band in DTP mode (see Figure 4b) is visible without the interference of additional bands.…”

Sensitivity Enhancement in Low Cutoff Wavelength Long-Period Fiber Gratings by Cladding Diameter Reduction

“…Another important question is why the depth of the attenuation bands increases in the output from the simulation ( Figure 3 b), whereas this was not observed in the experimental data ( Figure 3 a). The reason can be found in the shape of the cross section of the etched optical fiber, which was also analyzed in Figure 10a of [ 14 ]. This image is reproduced in Figure 4 b in order to illustrate the non-round shape of the optical fiber after etching.…”