Photonic crystal fiber half-taper probe based refractometer

A compact singlemode - photonic crystal fiber - singlemode fiber tip (SPST) refractive index sensor is demonstrated in this paper. A CO2 laser cleaving technique is utilised to provide a clean-cut fiber tip which is then coated by a layer of gold to increase reflection. An average sensitivity of 39.1 nm/RIU and a resolvable index change of 2.56 x 10-4 are obtained experimentally with a ~3.2 µm diameter SPST. The temperature dependence of this fiber optic sensor probe is presented. The proposed SPST refractometer is also significantly less sensitive to temperature and an experimental demonstration of this reduced sensitivity is presented in the paper. Because of its compactness, ease of fabrication, linear response, low temperature dependency, easy connectivity to other fiberized optical components and low cost, this refractometer could find various applications in chemical and biological sensing

Applied Fiber Optic Measurement for Geohydraulic Engineering

Engineers have long sought the possibility of measuring parameters such as temperature and pressure continuously in the underground with high precision, high spatial resolution and high band width of parameters. Distributed fibre optic measurement offers the use of a very fast, robust, precise, light and small gauges with an high spatial resolution. In this paper we would like to compile fibre-optic measure-methods which are available now for projects in geohydraulical engineering. This paper will propose new problems for future research work on parameter identification for such parameters as conductivity and anisotropy

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

Optical fiber sensors based on nanostructured materials for environmental applications

La contaminación ambiental es la presencia de agentes físicos, químicos o biológicos presentes en el agua, suelo y aire; siendo perjudiciales para la salud de las personas, así como para la vida vegetal y animal. Las actividades económicas son esenciales para el desarrollo de la sociedad, sin embargo, muchas de estas actividades son una fuente de contaminación constante. Por ejemplo, la fuga de fluidos y gases en plantas industriales afectan negativamente a la salud e higiene para la elaboración de alimentos, bebidas, aditivos y materias primas causando un impacto ambiental y económico negativo en la industria. La búsqueda continua de métodos para el desarrollo de sistemas de medición es una característica de la evolución tecnológica de la humanidad. Las fibras ópticas presentan varias ventajas para ser empleadas en sistemas sensores; tales ventajas son: inmunidad a la interferencia electromagnética, dimensiones reducidas, ligeras, bajas pérdidas, fácil multiplexación y resistencias a la corrosión, entre otras. En general, podemos encontrar una amplia gama de aplicaciones en la industria para el desarrollo de sensores en fibra óptica. Sin embargo, en esta tesis se han seleccionado tres aplicaciones industriales de interés relevante: detección de gas amoniaco a bajas concentraciones, detección de adulteración en bebidas alcohólicas y detección de adulteración de combustibles. Se caracterizan los parámetros de los sensores desarrollados tales como la sensitividad, reversibilidad, reproducibilidad y precisión para la medición de cada tipo de sensor. Los resultados obtenidos en esta tesis serán útiles en el estudio de nuevos materiales aplicables a sensores ópticos, permitiendo la apertura a nuevas vías de investigación en el campo de los sensores en fibra óptica para aplicaciones industriales.Environmental pollution is the presence of physical, chemical or biological agents in water, soil and air which are harmful to our health, safety and welfare of the people as well as plant and animal life. Economic activities are essential to the development of society; however, many of these activities are a constant source of contamination. For example, leakage of fluids and gases in industrial plants adversely affect the health and hygiene for food processing, beverages, additives and raw materials causing serious environmental and economic impact on the general industry. The continual search for methods for developing measurement systems is a feature in the technological evolution of humankind. Optical fibers exhibit several advantages such as being immune to electromagnetic interferences, reduced dimensions, lightweight, low losses, easy multiplexation and resistant to corrosion for the development of optical fibers sensors. However, we selected three applications were the principle of operation of our sensor provides an advantage over other reported sensors: gaseous ammonia detection for low concentrations, adulteration of alcoholic beverages detection and combustibles quality control. The overall objective of this research is to design, fabricate, deploy and verify the correct operation of optical fiber structures for the identification of interesting liquid and gaseous environmental pollutants. The sensors parameters such as its sensitivity, reversibility, reproducibility and accuracy of measurement for each type of sensor are also characterized. These results obtained from this thesis would be a useful work in the study of new materials applicable to optical sensors, while opening new avenues of research in the field of optical fiber sensors for industrial applications.La realización de esta tesis ha sido posible gracias al apoyo recibido por parte del Consejo Nacional de Ciencia y Tecnología (CONACYT) bajo el contrato CB-2010/157866 y CB-2010/156529, así como de la Comisión Interministerial de Ciencia y Tecnología a través de la financiación de los proyectos CICYT fondos FEDER TEC2010-17805.Programa Oficial de Doctorado en Tecnologías de las Comunicaciones (RD 1393/2007)Komunikazioen Teknologietako Doktoretza Programa Ofiziala (ED 1393/2007

Development of Photonic Crystal Fiber Based Gas/ Chemical Sensors

The development of highly-sensitive and miniaturized sensors that capable of real-time analytes detection is highly desirable. Nowadays, toxic or colorless gas detection, air pollution monitoring, harmful chemical, pressure, strain, humidity, and temperature sensors based on photonic crystal fiber (PCF) are increasing rapidly due to its compact structure, fast response and efficient light controlling capabilities. The propagating light through the PCF can be controlled by varying the structural parameters and core-cladding materials, as a result, evanescent field can be enhanced significantly which is the main component of the PCF based gas/chemical sensors. The aim of this chapter is to (1) describe the principle operation of PCF based gas/ chemical sensors, (2) discuss the important PCF properties for optical sensors, (3) extensively discuss the different types of microstructured optical fiber based gas/ chemical sensors, (4) study the effects of different core-cladding shapes, and fiber background materials on sensing performance, and (5) highlight the main challenges of PCF based gas/ chemical sensors and possible solutions

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

Hybrid sensor based on a hollow square core fiber for temperature independent refractive index detection

In this work, a hybrid sensor based on a section of hollow square core fiber (HSCF) spliced between two single mode fibers is proposed for the measurement of refractive index of liquids. The sensor, with a length of a few millimeters, operates in a transmission configuration. Due to the HSCF inner geometry, two different interferometers are generated. The first, a Mach-Zehnder interferometer, is insensitive to the external refractive index, and presents a sensitivity to temperature of (29.2 ± 1.1) pm/°C. The second one, a cladding modal interferometer, is highly sensitive to the external refractive index. An experimental resolution of 1.0 × 10-4 was achieved for this component. Due to the different responses of each interferometer to the parameters under study, a compensation method was developed to attain refractive index measurements that are temperature independent. The proposed sensor can find applications in areas where refractive index measurements are required and the control of room temperature is a challenge, such as in the food and beverage industry, as well as in biochemical or biomedical industries.publishe

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

High Sensitivity Temperature Sensor Based on Singlemode-no-Core- Singlemode Fibre Structure and Alcohol

A high sensitivity temperature sensor based on a singlemode-no-core-singlemode (SNCS) fibre structure and surrounded with alcohol within a silica capillary is described. In this investigation, no-core fibre (NCF) is used as the multimode waveguide and alcohol is chosen as the temperature sensitive medium. By packaging the alcohol solution with a short length of NCF enclosed within a silica capillary, the surrounding temperature can be detected by monitoring the variations of transmission loss at a specific wavelength. The theoretical analysis predicts this temperature sensor can provide high sensitivity, and the experimental results support this. The maximum temperature sensitivity of the sample is 0.49 dB/oC with a potential temperature resolution of 0.02 oC at the operating wavelength of 1545.9 nm. In addition, the repeatability and response time of the sensor of this investigation are investigated experimentally