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Refractive Index Fibre and Integrated Optic Sensors

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A special issue of Sensors (ISSN 1424-8220).

Deadline for manuscript submissions: closed (15 March 2020) | Viewed by 13000

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Special Issue Editor

Dr. Tinko Eftimov

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Guest Editor

Photonics Research Center, Département d'Informatique et d'Ingénierie, Université du Québec en Outaouais, P.O.Box 1250, Gatineau, QC J8X 3X7, Canada
Interests: polarization matrix methods; optical fibers; fiber optic sensors and components; sensor interrogation instrumentation and fluorescence studies
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The development of a variety of optical waveguide microstructures that are highly sensitive to surrounding refractive index changes has opened the way for the development of a variety of refractometric sensors for a plethora of applications in biochemical sensing, vapor, humidity, and moisture ingress sensing.

Among the refractive index sensing structures of interest are fiber gratings, more specifically, regular long period gratings (LPGs) and double resonance LPGs (DR-LPGs) around turning point, tilted fiber Bragg gratings (TFBGs), evanescent wave and tapered fiber structures, fiberized plasmonic sensors, fiber microcavity Mach–Zehnder interferometers, integrated optic gratings and interferometers, photonic crystal fibers (PCF), and other specialty microstructures.

The drive to develop practical, lower cost, and higher sensitivity devices poses a number of problems and challenges to be overcome. The reliability and repeatability of a sensor's parameters and performance, temperature compensation or insensitivity, and issues of packaging and manufacturability are all of key importance for a practical product. Also of interest are the performance of interrogation techniques, multiplexing techniques that would allow simultaneous or quasi-simultaneous measurement of a number of parameters, and the construction of sensing networks that will lead to a reduction in the price per sensor.

The objective of this Special Issue is to cover the following topics:

Novel types and developments of sensing structures allowing refractive index measurements in micro-, nano-, and picoliter volumes;
Fabrication technologies for waveguide- and microoptic-based refractometers;
Multiplexing and interrogation techniques for sensing devices and networks;
Multiparameter and multianalyte measurement techniques with applications in biochemical, gas, vapor, and humidity sensing;
Optical waveguide-compatible microfluidic refractometers.

Dr. Tinko Eftimov
Guest Editor

Manuscript Submission Information

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Keywords

refractive index fiber optic sensors
evanescent field and tapered optical fiber refractive index sensors
plasmonic fiber-based sensors
long period grating (LPG) and tilted FBG fiber refractometric sensors
fiber optic microinterferometric sensors
novel fiber/integrated optic refractometric sensors
microfluidic and whispering gallery mode (WGM) sensors
refractive index sensing using fiber microstructured and specialty fiber refractometers
micro-, nano-, and picoliter volume refractometry
fiber refractometry for biochemical and medical applications
moisture ingress, humidity, and vapor sensing
fabrication of fiber refractometric sensors
multiplexing and interrogation of fiber refractometers

Published Papers (4 papers)

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Research

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15 pages, 4874 KiB

Open AccessArticle

Influence of Embedding Fiber Optical Sensors in CFRP Film Adhesive Joints on Bond Strength

by Neele Grundmann, Hauke Brüning, Konstantinos Tserpes, Tim Strohbach and Bernd Mayer

Sensors 2020, 20(6), 1665; https://0-doi-org.brum.beds.ac.uk/10.3390/s20061665 - 17 Mar 2020

Cited by 12 | Viewed by 2810

Abstract

The increasing utilization of carbon fiber reinforced plastic (CFRP) in the aeronautical industry calls for a structural health monitoring (SHM) system for adhesively bonded CFRP joints. Optical glass fiber with inscribed fiber Bragg gratings (FBGs) is a promising technology for a SHM system. This paper investigates the intrusive effect of embedding optical glass fibers carrying FBGs on adhesive bond strength and adhesive layer thickness and quality. Embedding the optical glass fibers directly in the adhesive bond has the advantage of directly monitoring the targeted structure but poses the risk of significantly reducing the bond strength. Optical glass fibers with different cladding diameters (50, 80, 125 µm) and coating types (polyimide, with a thickness of 3−8 µm, and acrylate, with a thickness of ~35 µm) are embedded in structural and repair film adhesives here. Without embedded optical glass fibers, the film adhesives have an adhesive layer thickness of ~90 µm (structural) and ~100 µm (repair) after curing. The intrusive effect of the fiber embedding on the adhesive bond strength is investigated here with quasi static and fatigue single lap joint (SLJ) tensile shear tests. Also, the influence of hydrothermal aging procedures on the quasi static tensile shear strength is investigated. It is found that optical glass fibers with a total diameter (glass fiber cladding + coating) of ~145 µm significantly reduce the quasi static tensile shear strength and increase the adhesive layer thickness and number of air inclusions (or pores) in the structural film adhesive joints. In the repair adhesive joints, no significant reduction of quasi static tensile shear strength is caused by the embedding of any of the tested fiber types and diameters. However, an increase in the adhesive layer thickness is detected. In both adhesive films, no effect on the quasi-static tensile shear strength is detected when embedding optical glass fibers with total diameters <100 µm. The applied aging regime only affects the repair film adhesive joints, and the structural film adhesive joints show no significant reduction. A polyimide-coated 80 µm optical glass fiber is selected for fatigue SLJ tensile shear tests in combination with the more sensitive structural film adhesive. No significant differences between the S-N curves and tensile shear fatigue strength of the reference samples without embedded optical fibers and the samples carrying the polyimide-coated 80 µm optical glass fibers are detected. Thus, it is concluded that the influences of embedding optical glass fibers with total diameters <100 µm on the fatigue limit of the tested film adhesive joints is negligible. Full article

(This article belongs to the Special Issue Refractive Index Fibre and Integrated Optic Sensors)

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12 pages, 3363 KiB

Open AccessArticle

Temperature Self-Compensated Refractive Index Sensor Based on Fiber Bragg Grating and the Ellipsoid Structure

by Binbin Yan, Lei Sun, Yanhua Luo, Liwei Yang, Haifeng Qi, Xiao Chen, Kuiru Wang, Jinhui Yuan, Xinzhu Sang, Chang Wang, Pengfei Lu and Gang-Ding Peng

Sensors 2019, 19(23), 5211; https://0-doi-org.brum.beds.ac.uk/10.3390/s19235211 - 28 Nov 2019

Cited by 9 | Viewed by 2567

Abstract

In this paper, a temperature self-compensated refractive index sensor based on fiber Bragg grating (FBG) and the ellipsoid structure is demonstrated. The ellipsoid can excite the cladding modes and recouple them into the fiber core. Two well-defined wavelength bands are observed in the reflection spectrum of the proposed sensor, i.e., the Bragg resonant peak and the cladding resonant peaks. By measuring the wavelength shift of the cladding resonant peak, the surrounding refractive index (SRI) can be determined, and the wavelength shift of the Bragg resonant peak can be used as a reliable reference to self-compensate the temperature variation (temperature sensitivity of 10.76 pm/°C). When the SRI changes from 1.3352 to 1.3722, the cladding resonant peak redshifts linearly with an average sensitivity of 352.6 pm/RIU (refractive index unit). When the SRI changes from 1.3722 to 1.4426, an exponential redshift is observed with a maximum sensitivity of 4182.2 pm/RIU. Especially, the sensing performance is not very reliant on the distance between the FBG and the ellipsoid, greatly improving the ease of the fabrication. Full article

(This article belongs to the Special Issue Refractive Index Fibre and Integrated Optic Sensors)

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Review

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18 pages, 4771 KiB

Open AccessReview

Long-Period Gratings and Microcavity In-Line Mach Zehnder Interferometers as Highly Sensitive Optical Fiber Platforms for Bacteria Sensing

by Tinko Eftimov, Monika Janik, Marcin Koba, Mateusz Śmietana, Predrag Mikulic and Wojtek Bock

Sensors 2020, 20(13), 3772; https://0-doi-org.brum.beds.ac.uk/10.3390/s20133772 - 05 Jul 2020

Cited by 28 | Viewed by 3354

Abstract

Selected optical fiber sensors offer extraordinary sensitivity to changes in external refractive (RI), which make them promising for label-free biosensing. In this work the most sensitive ones, namely long-period gratings working at (DTP-LPG) and micro-cavity in-line Mach-Zehnder interferometers (µIMZI) are discussed for application in bacteria sensing. We describe their working principles and RI sensitivity when operating in water environments, which is as high as 20,000 nm/RIU (Refractive index unit) for DTP-LPGs and 27,000 nm/RIU for µIMZIs. Special attention is paid to the methods to enhance the sensitivity by etching and nano-coatings. While the DTP-LPGs offer a greater interaction length and sensitivity to changes taking place at their surface, the µIMZIs are best suited for investigations of sub-nanoliter and picoliter volumes. The capabilities of both the platforms for bacteria sensing are presented and compared for strains of Escherichia coli, lipopolysaccharide E. coli, outer membrane proteins of E. coli, and Staphylococcus aureus. While DTP-LPGs have been more explored for bacteria detection in 10²–10⁶ Colony Forming Unit (CFU)/mL for S. aureus and 10³–10⁹ CFU/mL for E. coli, the µIMZIs reached 10²–10⁸ CFU/mL for E. coli and have a potential for becoming picoliter bacteria sensors. Full article

(This article belongs to the Special Issue Refractive Index Fibre and Integrated Optic Sensors)

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23 pages, 5985 KiB

Open AccessReview

A Comprehensive Review: Materials for the Fabrication of Optical Fiber Refractometers Based on Lossy Mode Resonance

by Aritz Ozcariz, Carlos Ruiz-Zamarreño and Francisco J. Arregui

Sensors 2020, 20(7), 1972; https://0-doi-org.brum.beds.ac.uk/10.3390/s20071972 - 01 Apr 2020

Cited by 36 | Viewed by 3845

Abstract

Lossy mode resonance based sensors have been extensively studied in recent years. The versatility of the lossy mode resonance phenomenon has led to the development of sensors based on different configurations that make use of a wide range of materials. The coating material is one of the key elements in the performance of a refractometer. This review paper intends to provide a global view of the wide range of coating materials available for the development of lossy mode resonance based refractometers. Full article

(This article belongs to the Special Issue Refractive Index Fibre and Integrated Optic Sensors)

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