Suspended-core fibers for sensing applications

A brief review on suspended-core fibers for sensing applications is presented. A historical overview over the previous ten years about this special designed microstructure optical fiber is described. This fiber presents attractive optical properties for chemical/biological or gas measurement, but it can be further explored for alternative sensing solutions, namely, in-fiber interferometers based on the suspended-core or suspended-multi-core fiber, for physical parameter monitoring.info:eu-repo/semantics/publishedVersio

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)

Three-Dimensional Integrated Photonics in Transparent Substrates Enabled by Femtosecond Laser Fabrication

Unlike integrated electronic circuits that are built mostly on silicon wafers, integrated photonic devices involve a great variety of materials and platforms. The development of integrated photonic devices in both 2-D and 3-D architectures in each material and platform presents distinct fabrication challenges. The research in this dissertation explores the femtosecond laser as a versatile cross-platform manufacturing tool to fabricate 3-D photonic structures in transparent optical substrates. This dissertation first presents the fabrication of multiplexable and distributed optical sensors in silica and sapphire optical fiber with high radius of curvature surfaces. Using a diffraction-limited oil-immersion fabrication setup, a reel-to-reel laser direct writing system was established to deposit laser energy inside optical fibers with micrometer precision. Through careful tuning of laser-matter interaction to form nanograting in fiber core, Intrinsic Fabry-Perot Interferometer arrays were fabricated with a high fringe visibility of 0.49 and low insertion loss of 0.002 dB per sensor. The temperature sensitivity, cross-talk, and spatial multiplexability of sensor arrays were investigated in detail. By continuously introducing nanograting as artificial Rayleigh scattering centers, femtosecond laser-fabricated Rayleigh scattering enhanced section could achieve an optimized propagation loss of 0.01 dB/cm with drastic improvement of the signal-to-noise ratio of over 35 dB for Optical Frequency-Domain Reflectometry-based distributed sensing. Long-term high-temperature performance was successfully demonstrated with improved thermal stability. This dissertation also explores the fabrication of high-density 3-D topological photonic circuits in glass substrates with flat surfaces. Inspired from solid-state physics, topological photonics has found potential applications such as quantum information processing and defect-resistant lasing devices. Through careful control of the multiphoton laser-matter interaction in the femtosecond time scale and nanometer spatial scale, we demonstrate the fabrication of high-density coupled and low-loss 3-D waveguide arrays with varying index profiles. This dissertation presents the experimental verification of lattice braiding, Thouless pumping under the presence of disorder, and the topological pumping in a higher-order system. In sum, the dissertation studies the optics science of femtosecond laser-matter interaction and unveil the potentials of femtosecond laser as a powerful fabrication tool for 3-D photonic device fabrication for studies in optics science and for photonics applications in communication and sensing

Advances in Fiber-Optic Extrinsic Fabry-Perot Interferometric Physical and Mechanical Sensors: A Review

Fabry-Perot Interferometers Have Found a Multitude of Scientific and Industrial Applications Ranging from Gravitational Wave Detection, High-Resolution Spectroscopy, and Optical Filters to Quantum Optomechanics. Integrated with Optical Fiber Waveguide Technology, the Fiber-Optic Fabry-Perot Interferometers Have Emerged as a Unique Candidate for High-Sensitivity Sensing and Have Undergone Tremendous Growth and Advancement in the Past Two Decades with their Successful Applications in an Expansive Range of Fields. the Extrinsic Cavity-Based Devices, I.e., the Fiber-Optic Extrinsic Fabry-Perot Interferometers (EFPIs), Enable Great Flexibility in the Design of the Sensitive Fabry-Perot Cavity Combined with State-Of-The-Art Micromachining and Conventional Mechanical Fabrication, Leading to the Development of a Diverse Array of EFPI Sensors Targeting at Different Physical Quantities. Here, We Summarize the Recent Progress of Fiber-Optic EFPI Sensors, Providing an overview of Different Physical and Mechanical Sensors based on the Fabry-Perot Interferometer Principle, with a Special Focus on Displacement-Related Quantities, Such as Strain, Force, Tilt, Vibration and Acceleration, Pressure, and Acoustic. the Working Principle and Signal Demodulation Methods Are Shown in Brief. Perspectives on Further Advancement of EFPI Sensing Technologies Are Also Discussed

High Sensitivity Optical Fiber Interferometric Sensors

Optical fiber interferometers have been widely employed and investigated for monitoring the changes in both physical and chemical parameters, with the advantages of compact size, light weight, immunity to electromagnetic interference, high sensitivity, capability to work in harsh environments and remote operation capabilities. Among the different kinds of fiber sensors based on interferometry, singlemode-multimode-singlemode (SMS) structures has attracted considerable interest due to their inherent advantages of high sensitivity, ease of fabrication and interconnection to other fiber systems and low cost. However, the challenge is that the sensitivity of the traditional SMS based fiber structure is not sufficient in some cases, for example in bio-chemical applications, where detection of a very small variation in a bio-chemicals’ concentration is required. There is thus a need to investigate how to modify or enhance an SMS structure to achieve ultrahigh sensitivity. This thesis presents research and its applications concerning approaches to improve the sensitivity and detection accuracy of a traditional SMS fiber structure based sensor. The key achievements of this thesis include: Traditional SMS fiber structure for breathing state monitoring A bend SMS structure is investigated as a breathing sensor by attaching it to a thin plastic film in an oxygen mask. Breath rate can be monitored using this sensor by detecting power variations due to the macro bending applied to the SMS section during each inhalation and exhalation cycles. Different types of breathing conditions including regular and irregular breath patterns can be distinguished. The proposed sensor is capable of working in a strong electromagnetic field and radioactive environment. Tapered small core singlemode fiber (SCSMF) for the detection of refractive index (RI), ammonia, and volatile organic compounds (VOCs) A modified SMS structure based on a tapered SCSMF is proposed and investigated with significantly improved RI sensitivity. It is found that the sample with a smaller waist diameter gives higher sensitivity. In the experiment, a maximum sensitivity of 19212.5 nm/RIU (RI unit) in the RI range from 1.4304 to 1.4320 has been demonstrated when the waist diameter of the SCSMF is tapered down to 12.5 μm. The best corresponding theoretical resolution of the proposed sensor is 5.025 × 10-7 RIU which is over 10 times higher than that of many previous reported optical fiber based RI sensors. The proposed structure is capable of monitoring relative humidity level change even without coating of the fiber sensor’s surface with a layer of hygroscopic material. A silica sol-gel based coating has been used as a sensitive material to ammonia for the first time, by applying it to the surface of the tapered SCSMF for the detection of ammonia in water. The proposed sensor shows an ultra-high sensitivity of 2.47 nm/ppm with short response and recovery time of less than 2 and 5 minutes respectively. The corresponding theoretical detection limit of ammonia in water is calculated to be 4 ppb, which is 3 orders of magnitude improvement compared to the previous reported interferometry based ammonia sensor. In addition, the sensor has good performance in terms of repeatability of measurement and selectivity for sensing ammonia compared to that of other common ions and organic molecules in water. VOCs sensors are also demonstrated by coating a mixture of sol-gel silica and Nile red on the surface of two different types of tapered fiber sensors (tapered SCSMF) and a microfiber coupler (MFC)). The MFC based sensor shows better sensitivities to ethanol and methanol than that based on a tapered SCSMF due to its smaller waist diameter. The detectable gas concentration changes of the MFC based sensor are calculated to be ~77 ppb and ~281 ppb for ethanol and methanol respectively which are over one order of magnitude improvement than many other reports. The sensors also show fast response times of less than 5 minutes and recovery times varied from 7 to 12 minutes. Simultaneous measurement of ethanol and methanol is achieved by utilizing two different coating recipes. Hollow core fiber (HCF) structure for high temperature and twist sensing. A modified SMS structure with much improved spectral quality factor (Q) is investigated both theoretically and experimentally. The modified structure is based on a HCF. It is found that periodic transmission dips with high spectral extinction ratio and high Q factor are excited because of the multiple beam interferences introduced by the cladding of the HCF. The HCF structure can be used as a high sensitivity (up to 33.4 pm/°C) temperature sensor in a wide working temperature range (from room temperature to 1000 °C). By coating a thin layer of silver (~ 6.7 nm) on one side of the HCF surface, a twist sensor with a maximum sensitivity of 0.717 dB/°has been achieved, which is the highest twist sensitivity reported for intensity modulation based fiber sensors, with excellent measurement repeatability. Further theoretical and experimental investigation attributes this high twist sensitivity to the polarization dependent reflection coefficient at the outer HCF surface associated with the partial silver coating

Integrated Optical Fiber Sensor for Simultaneous Monitoring of Temperature, Vibration, and Strain in High Temperature Environment

Important high-temperature parts of an aero-engine, especially the power-related fuel system and rotor system, are directly related to the reliability and service life of the engine. The working environment of these parts is extremely harsh, usually overloaded with high temperature, vibration and strain which are the main factors leading to their failure. Therefore, the simultaneous measurement of high temperature, vibration, and strain is essential to monitor and ensure the safe operation of an aero-engine. In my thesis work, I have focused on the research and development of two new sensors for fuel and rotor systems of an aero-engine that need to withstand the same high temperature condition, typically at 900 °C or above, but with different requirements for vibration and strain measurement. Firstly, to meet the demand for high temperature operation, high vibration sensitivity, and high strain resolution in fuel systems, an integrated sensor based on two fiber Bragg gratings in series (Bi-FBG sensor) to simultaneously measure temperature, strain, and vibration is proposed and demonstrated. In this sensor, an L-shaped cantilever is introduced to improve the vibration sensitivity. By converting its free end displacement into a stress effect on the FBG, the sensitivity of the L-shaped cantilever is improved by about 400% compared with that of straight cantilevers. To compensate for the strain sensitivity of FBGs, a spring-beam strain sensitization structure is designed and the sensitivity is increased to 5.44 pm/με by concentrating strain deformation. A novel decoupling method ‘Steps Decoupling and Temperature Compensation (SDTC)’ is proposed to address the interference between temperature, vibration, and strain. A model of sensing characteristics and interference of different parameters is established to achieve accurate signal decoupling. Experimental tests have been performed and demonstrated the good performance of the sensor. Secondly, a sensor based on cascaded three fiber Fabry-Pérot interferometers in series (Tri-FFPI sensor) for multiparameter measurement is designed and demonstrated for engine rotor systems that require higher vibration frequencies and greater strain measurement requirements. In this sensor, the cascaded-FFPI structure is introduced to ensure high temperature and large strain simultaneous measurement. An FFPI with a cantilever for high vibration frequency measurement is designed with a miniaturized size and its geometric parameters optimization model is established to investigate the influencing factors of sensing characteristics. A cascaded-FFPI preparation method with chemical etching and offset fusion is proposed to maintain the flatness and high reflectivity of FFPIs’ surface, which contributes to the improvement of measurement accuracy. A new high-precision cavity length demodulation method is developed based on vector matching and clustering-competition particle swarm optimization (CCPSO) to improve the demodulation accuracy of cascaded-FFPI cavity lengths. By investigating the correlation relationship between the cascaded-FFPI spectral and multidimensional space, the cavity length demodulation is transformed into a search for the highest correlation value in space, solving the problem that the cavity length demodulation accuracy is limited by the resolution of spectral wavelengths. Different clustering and competition characteristics are designed in CCPSO to reduce the demodulation error by 87.2% compared with the commonly used particle swarm optimization method. Good performance and multiparameter decoupling have been successfully demonstrated in experimental tests

Recent advances in biomedical photonic sensors: a focus on optical-fibre-based sensing

In this invited review, we provide an overview of the recent advances in biomedical pho tonic sensors within the last five years. This review is focused on works using optical-fibre technology, employing diverse optical fibres, sensing techniques, and configurations applied in several medical fields. We identified technical innovations and advancements with increased implementations of optical-fibre sensors, multiparameter sensors, and control systems in real applications. Examples of outstanding optical-fibre sensor performances for physical and biochemical parameters are covered, including diverse sensing strategies and fibre-optical probes for integration into medical instruments such as catheters, needles, or endoscopes.This work was supported by Ministerio de Ciencia e Innovación and Agencia Estatal de Investigación (PID2019-107270RB-C21/AEI/10.13039/501100011033), and TeDFeS Project (RTC-2017- 6321-1) co-funded by European FEDER funds. M.O. and J.F.A. received funding from Ministerio de Ciencia, Innovación y Universidades of Spain under Juan de la Cierva-Formación and Juan de la Cierva-Incorporación grants, respectively. P.R-V. received funding from Ministerio de Educación, Cultura y Deporte of Spain under PhD grant FPU2018/02797

Dynamic Micromechanical Fabry-Perot Cavity Sensors Fabricated by Multiphoton Absorption Onto Optical Fiber Tips

This research leveraged two-photon polymerization microfabrication to integrate dynamic mechanical components with Fabry-Perot resonators onto the ends of low-loss optical fibers to prototype 3 micro-optic devices. The first device featured a multi-positional mirror that enabled thin-film deposition onto cavities of any length with mirrors of significant curvature, for refractive index sensing. The second device combined an FP cavity with a spring body featuring easily scalable stiffness for pressure sensing. The third device presented a high-speed rotating micro-anemometer for measuring a wide range of gas flows. All devices represent a significant reduction in size and weight over commercially available devices

Sensores de fibra ótica para meios desafiantes

With the present work, the development of fiber optic sensor solutions for the application in challenging media was intended. New sensor structures based on the post-processing of optical fibers were addressed, taking into account their sensitivity to variations in the external environment. In a first stage, fiber Bragg gratings were embedded in lithium batteries, to monitor temperature in situ and operando. Due to the harsh chemical environment of the battery, fiber optic sensors revealed to be the most advantageous alternative, when comparing to the electronic sensors. Fiber sensors exhibited good sensitivities and fast responses, besides being less invasive, thus they did not compromise the battery response. Furthermore, they were chemically stable. Still in the framework of this theme, and with the objective of monitoring possible strain and pressure variations inside the batteries, new sensors based on in-line Fabry-Perot cavities have been proposed. These sensors were characterized in lateral load, strain, and temperature. In a later stage, the study focused on the development of configurations that allowed to obtain high-resolution and/or sensitivity sensors. One of such configurations was obtained by creating a hollow microsphere at the fiber tip. The sensor was used to detected concentration variations and refractive index of glycerin and water mixtures. The influence of the diaphragm size in the sensor response was also studied, as well as the temperature response. New sensors based on multimode interference have also been characterized, using a coreless silica fiber tip. First, the influence of different parameters, such as length and diameters were analyzed. The sensors were tested in different solutions of glucose and water. It was observed that the sensor diameter is a decisive factor in obtaining devices that are more sensitive to refractive index and, consequently, to concentration. The determination of the thermo-optic coefficient of water/ethanol mixtures was also addressed using a multimode fiber interferometer sensor. Finally, a multimode interferometer sensor was functionalized by depositing agarose throughout the structure, allowing to optimize the response of the sensors to the external environment.Com o presente trabalho pretendeu-se explorar soluções de sensores em fibra ótica para a aplicação em meios desafiantes. Novas estruturas sensoras baseadas em pós-processamento de fibra ótica foram abordadas, tendo em consideração a sua sensibilidade a variações do meio externo. Numa primeira etapa, foram embebidas redes de Bragg no interior de baterias de lítio, para monitorizar variações de temperatura in situ e operando. Devido ao complexo meio químico da bateria, os sensores em fibra ótica revelaram ser uma alternativa mais vantajosa em relação aos sensores elétricos, não só pela sensibilidade e rápida resposta, mas também pelo fato de não afetarem o desempenho da bateria. Além disso, os sensores usados revelaram ser pouco invasivos e quimicamente estáveis. Ainda no âmbito deste tema, e com o objetivo de monitorizar possíveis deformações e variações de pressão no interior da bateria de lítio, foram desenvolvidos novos sensores baseados em cavidades de Fabry-Perot do tipo in-line. Esses sensores foram caraterizados em pressão lateral, deformação e temperatura. Numa fase posterior, o estudo centrou-se no desenvolvimento de configurações que permitissem a obtenção de sensores com elevada resolução e/ou sensibilidade. Uma das configurações consistiu na formação de uma microesfera oca na ponta de uma fibra ótica. Esse sensor foi utilizado para detetar variações de concentração e índice de refração de misturas de glicerina e água. A influência do tamanho do diafragma na resposta do sensor também foi estudada, assim como a resposta em temperatura. Em seguida, desenvolveram-se novos sensores baseados em interferência multimodo, utilizando para tal uma ponta de fibra de sílica sem núcleo. Numa primeira abordagem analisou-se a influência de diferentes parâmetros, como o comprimento e o diâmetro dos sensores. Os sensores foram expostos a diferentes soluções de glucose e água. Verificou-se que o diâmetro do sensor é um fator decisivo para a obtenção de dispositivos mais sensíveis ao índice de refração e, consequentemente, à concentração. Foi também desenvolvido um sensor baseado em interferência multimodo que permitiu determinar o coeficiente termo-ótico de misturas de etanol e água. Por fim, procedeu-se à funcionalização de um sensor baseado em interferência multimodo através da deposição de agarose ao longo da estrutura, permitindo assim otimizar a sua resposta a variações do meio externo.Programa Doutoral em Engenharia Físic