Fiber-optic refractometer based on a phase-shifted fiber Bragg grating on a side-hole fiber

A fiber-optic refractive index (RI) sensor based on a π-phaseshifted fiber-Bragg-grating (πFBG) inscribed on a side-hole fiber is presented. The reflection spectrum of the πFBG features two narrow notches associated with the two polarization modes and the spectral spacing of the notches is used for high-sensitivity RI sensing with little temperature cross-sensitivity. The side-hole fiber maintains its outer diameter and mechanical strength. The side-hole fiber is also naturally integrated into a microfluidic system for convenient sample delivery and reduced sample amount. A novel demodulation method based on laser frequency modulation to enhance the sensor dynamic range is proposed and demonstrated

Inter-Cross De-Modulated Refractive Index And Temperature Sensor By An Etched Multi-Core Fiber Of A MZI Structure

We present a relative sensitivity of in-fiber inter-cross demodulation of a Mach-Zehnder interferometer (MZI) based on an etched multi-core fiber (eMCF). The sensor can measure the external refractive index (RI) and temperature with a large fringe visibility of 15 dB. It is tuned using a simple technique of slow chemical etching. When the outer cores of MCF will be exposed to the surrounding, a large difference of relative effective RI is observed, which enhances the sensitivity of the sensor. The sensor\u27s wavelength and intensity responses have displayed that it can function with three different inter-cross-demodulation phenomena. A superior RI sensitivity of 178.20 dB/RIU in the range of 1.334 to 1.370, and temperature sensitivity of 66.73 pm/°C in the range of 30 to 80 °C are obtained, with an adequate linear response. Besides, it can readily resolve the issues of cross-sensitivity. Moreover, it has many advantages including easy fabrication, compact size, multiplex, repeatable, stable, and can easily differentiate RI and temperature, which lack others

Investigation of refractive index sensing based on Fano resonance in fiber Bragg grating ring resonators.

In this paper we theoretically investigate a ring resonant cavity obtained by closing on itself a pi-shifted fiber Bragg grating, to be used for refractive index sensing applications. Differently from a conventional pi-shifted fiber Bragg grating, the spectral structure of this cavity is characterized by an asymmetric splitting doublet composed by a right side resonance having an asymmetric Fano profile and a left side resonance having a symmetric Lorentzian profile. The right side resonance shows a narrower and sharper peak than all the other kinds of resonance achievable with both conventional ring resonators and pi-shifted fiber Bragg gratings. A reduction of the resonant linewidth with respect to a conventional pi-shifted Fiber Bragg grating and a fiber ring resonator, having the same physical parameters, is theoretically proved, achieving up to five orders of magnitude improvement with respect to the usual ring resonator. Due to these resonance features, the pi-shifted Bragg grating ring resonator results suitable for RI sensing applications requiring extremely narrow resonances for high resolution measurements. In particular, by assuming a refractive index sensing to detect the presence of sugar in water, the sensor can show a theoretical resolution better than 10(-9) RIU. (C)2015 Optical Society of Americ

Nuevos esquemas de sensores puntuales de fibra óptica para la detección simultánea de múltiples parámetros

90 p.Los sensores basados en fibra óptica han alcanzado una madurez en entornos industriales gracias a su mayor versatilidad y rendimiento frente a los sensores tradicionales, por lo que se han convertido en una alternativa viable y prometedora. Estos sensores tienen aplicaciones en sectores tan diversos como la salud, telecomunicaciones, seguridad, espaciales, aeronáuticas, entre otras, por lo tanto, los sensores de fibra óptica se han vuelto prácticamente indispensables para todas las ramas de la industria. De hecho, no hay área industrial que pueda prescindir de la medición, las pruebas, la supervisión o la automatización.En esta tesis se presenta como un compendio de artículos publicados. Su estructura consta de una primera sección de síntesis que incluye una introducción al tema de la investigación, la descripción del marco teórico y las herramientas metodológicas utilizadas para tal fin, la definición de la hipótesis y los objetivos que se persiguen. Así mismo un resumen y discusión de los resultados. En la segunda sección se presentan las conclusiones de la investigación realizada durante la tesis, así como las futuras líneas deinvestigación. Por último, en la tercera sección, se mencionan las contribuciones durante la tesis que incluyen una patente europea, trabajos presentados en congresos internacionales, tres artículos publicadosen revistas especializadas. Esto es lo que ha permitido presentar esta tesis como un compendio de artículos. La investigación descrita en esta tesis se divide en dos líneas, en ambas se explican en detalle el diseño, fabricación y prueba de cada sensor. En la primera, se explica el desarrollo de un sensor de índice de refracción con un gran rango de medición e independencia a la temperatura basado en un interferómetro Fabry Perot. Dicha investigación y sus resultados han dado lugar a una patente europea y a un artículo científico que se incluyen en el Artículo 1. En la segunda parte se describen dos sensores basados en fibras multi-núcleo fuertemente acopladas, MCF por sus siglas en inglés. Esta tecnología consiste en excitar y recombinar solo dos modos de luz en un segmento corto de fibra óptica MCF. El primer sensor es capaz de medir dos variables simultáneamente (temperatura e índice de refracción). El segundo sensor se basa en la inscripción de redes de Bragg en una fibra MCF, el cual tiene la capacidad de medir curvatura con independencia a la temperatura, con una aplicación en la monitorización de vibraciones (curvatura cíclica)

Optical fiber sensors by direct laser processing: a review

The consolidation of laser micro/nano processing technologies has led to a continuous increase in the complexity of optical fiber sensors. This new avenue offers novel possibilities for advanced sensing in a wide set of application sectors and, especially in the industrial and medical fields. In this review, the most important transducing structures carried out by laser processing in optical fiber are shown. The work covers different types of fiber Bragg gratings with an emphasis in the direct-write technique and their most interesting inscription configurations. Along with gratings, cladding waveguide structures in optical fibers have reached notable importance in the development of new optical fiber transducers. That is why a detailed study is made of the different laser inscription configurations that can be adopted, as well as their current applications. Microcavities manufactured in optical fibers can be used as both optical transducer and hybrid structure to reach advanced soft-matter optical sensing approaches based on optofluidic concepts. These in-fiber cavities manufactured by femtosecond laser irradiation followed by chemical etching are promising tools for biophotonic devices. Finally, the enhanced Rayleigh backscattering fibers by femtosecond laser dots inscription are also discussed, as a consequence of the new sensing possibilities they enableThis research was funded by the Ministerio de Economía y Competitividad of Spain (TEC2016-76021-C2-2-R), the FEDER/Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (PID2019- 107270RB-C21), and the Ministerio de Educación, Cultura y Deporte of Spain (PhD grant FPU2018/02797)

Progress on Optical Fiber Biochemical Sensors Based on Graphene

Graphene, a novel form of the hexagonal honeycomb two-dimensional carbon-based structural material with a zero-band gap and ultra-high specific surface area, has unique optoelectronic capabilities, promising a suitable basis for its application in the field of optical fiber sensing. Graphene optical fiber sensing has also been a hotspot in cross-research in biology, materials, medicine, and micro-nano devices in recent years, owing to prospective benefits, such as high sensitivity, small size, and strong anti-electromagnetic interference capability and so on. Here, the progress of optical fiber biochemical sensors based on graphene is reviewed. The fabrication of graphene materials and the sensing mechanism of the graphene-based optical fiber sensor are described. The typical research works of graphene-based optical fiber biochemical sensor, such as long-period fiber grating, Bragg fiber grating, no-core fiber and photonic crystal fiber are introduced, respectively. Finally, prospects for graphene-based optical fiber biochemical sensing technology will also be covered, which will provide an important reference for the development of graphene-based optical fiber biochemical sensors

Droplet-like bent multimode fiber sensor for temperature and refractive index measurement

This work proposes and demonstrates a bent multimode interference (MMI) sensor for refractive index and temperature measurement. The MMI structure was fabricated by successive splicing between single-mode-multimodesingle- mode (SMS) fibers. A droplet-like bent was introduced in the multimode fiber section for excitation of modes into the acrylate coating. The excitation of higher modes into the acrylate coating is particularly interesting due high thermooptic coefficient of acrylate which could improve temperature sensitivity, while evanescent field interaction of modes at the acrylate surface with surrounding material could be used for refractive index sensing. These modes experienced phase changes due to temperature and/or refractive index changes, consequently shift the spectra of the sensor. The sensor structure was simulated using BeamProp software to determine the required bending to excite light into acrylate coating for sensing. In experiment, a 3.5 mm bent sensor demonstrated refractive index sensitivity of 42.41 nm/RIU tested with refractive index between 1.30-1.395. Meanwhile, temperature sensitivity of 1.317nm/°C was attained using 5 mm bent sensor between 25 °C to 35 °C. The low cost and simple sensor structure is desirable in many applications including for detection, diagnosis, and determine of health, safety, environmental, liquid food, and water quality control

Four-point Bending Based Low-Carbon Steel Plate Corrosion Monitoring by Optical Fiber Bragg Grating Strain Sensor

Fiber Bragg Grating (FBG) Sensor is very sensible to strain change, with 1.2 pm shift in Bragg wavelength when suffering 1 μm strain change [1]. Metal corrosion is big problem in our world. In order to monitor this process, many methods are proposed, but seldom focus on the strain change of metal plate during corrosion. One reason for this is that the strain change during corrosion is much smaller than the sensitivities of most sensors. Another problem is the residual strain left in metal products, which will also be released during corrosion without an obvious regularity. Our solution is applying a bending to the metal plate, keeping curvature radius at the medium of the metal plate unchanged during corrosion. As to the residual strain, which has a non-negligible influence in order of magnitudes, we set another metal plate made in same process without bending. By comparing the results of the bent and unbent plates, the strain changes only contributed by the bending during corrosion can be achieved. We calculate a model to analyze the strain changes contributed by bending during corrosion. The expected result is that the rate of strain change during corrosion is always in positive correlation with the corrosion speed. After 500 hours corrosion experiment, the low-carbon steel (0.13-0.20% Carbon) plate with 1.59 mm in thickness at the beginning corroded 0.1202 ±0.0088mm, the total strain change contributed by bending is 91.213 ±3.158με. The rate of strain change during corrosion for the results is positive during corrosion, fitting the expectation very well