Novel Specialty Optical Fibers and Applications

Novel Specialty Optical Fibers and Applications focuses on the latest developments in specialty fiber technology and its applications. The aim of this reprint is to provide an overview of specialty optical fibers in terms of their technological developments and applications. Contributions include:1. Specialty fibers composed of special materials for new functionalities and applications in new spectral windows.2. Hollow-core fiber-based applications.3. Functionalized fibers.4. Structurally engineered fibers.5. Specialty fibers for distributed fiber sensors.6. Specialty fibers for communications

Optical fibre sensors with applications in gas and biological sensing

This thesis describes the study of various grating based optical fibre sensors for applications in refractive index sensing. The sensitivity of these sensors has been studied and in some cases enhanced using novel techniques. The major areas of development are as follows. The sensitivity of long period gratings (LPGs) to surrounding medium refractive index (SRI) for various periods was investigated. The most sensitive period of LPG was found to be around 160 µm and this was due to the core mode coupling to a single cladding mode but phase matching at two wavelength locations, creating two attenuation peaks, close to the waveguide dispersion turning point. Large angle tilted fibre gratings (TFGs) have similar behaviour to LPGs, in that they couple to the co-propagating cladding modes. The tilted structure of the index modulation within the core of the fibre gives rise to a polarisation dependency, differing the large angle TFG from a LPG. Since the large angle TFG couple to the cladding mode they are SRI sensitive, the sensitivity to SRI can be further increased through cladding etching using HF acid. The thinning of the cladding layer caused a reordering of the cladding modes and shifted to more SRI sensitive cladding modes as the investigation discovered. In a SRI range of 1.36 to 1.40 a sensitivity of 506.9 nm/URI was achieved for the etched large angle TFG, which is greater than the dual resonance LPG. UV inscribed LPGs were coated with sol-gel materials with high RIs. The high RI of the coating caused an increase in cladding mode effective index which in turn caused an increase in the LPG sensitivity to SRI. LPGs of various periods of LPG were coated with sol-gel TiO2 and the optimal thickness was found to vary for each period. By coating of the already highly SRI sensitive 160µm period LPG (which is a dual resonance) with a sol-gel TiO2, the SRI sensitivity was further increased with a peak value of 1458 nm/URI, which was an almost 3 fold increase compared to the uncoated LPG. LPGs were also inscribed using a femtosecond laser which produced a highly focused index change which was no uniform throughout the core of the optical fibre. The inscription technique gave rise to a large polarisation sensitivity and the ability to couple to multiple azimuthal cladding mode sets, not seen with uniform UV inscribed gratings. Through coupling of the core mode to multiple sets of cladding modes, attenuation peaks with opposite wavelength shifts for increasing SRI was observed. Through combining this opposite wavelength shifts, a SRI sensitivity was achieved greater than any single observed attenuations peak. The maximum SRI achieved was 1680 nm/URI for a femtosecond inscribed LPG of period 400 µm. Three different types of surface plasmon resonance (SPR) sensors with a multilayer metal top coating were investigated in D shape optical fibre. The sensors could be separated into two types, utilized a pre UV inscribed tilted Bragg grating and the other employed a post UV exposure to generate surface relief grating structure. This surface perturbation aided the out coupling of light from the core but also changed the sensing mechanism from SPR to localised surface plasmon resonance (LSPR). This greatly increased the SRI sensitivity, compared to the SPR sensors; with the gold coated top layer surface relief sensor producing the largest SRI sensitivity of 2111.5nm/URI was achieved. While, the platinum and silver coated top layer surface relief sensors also gave high SRI sensitivities but also the ability to produce resonances in air (not previously seen with the SPR sensors). These properties were employed in two applications. The silver and platinum surface relief devices were used as gas sensors and were shown to be capable of detecting the minute RI change of different gases. The calculated maximum sensitivities produced were 1882.1dB/URI and 1493.5nm/URI for silver and platinum, respectively. Using a DFB laser and power meter a cheap alternative approach was investigated which showed the ability of the sensors to distinguish between different gases and flow rates of those gases. The gold surface relief sensor was coated in a with a bio compound called an aptamer and it was able to detect various concentrations of a biological compound called Thrombin, ranging from 1mM to as low as 10fM. A solution of 2M NaCl was found to give the best stripping results for Thrombin from the aptamer and showed the reusability of the sensor. The association and disassociation constants were calculated to be 1.0638×106Ms-1 and 0.2482s-1, respectively, showing the high affinity of the Aptamer to thrombin. This supports existing working stating that aptamers could be alternative to enzymes for chemical detection and also helps to explain the low detection limit of the gold surface relief sensor

Recent advances in plasmonic sensor-based fiber optic probes for biological applications

Funding: This research was funded by National Natural Science Foundation of China (NSFC), grant number [61675008]. Acknowledgments: KN wishes to thank The Royal Society Kan Tong Po International Fellowship 2018 for the travel fund to visit Hong Kong Polytechnic University and Shenzhen Science and Technology Innovation Commission (Project GJHZ20180411185015272).Peer reviewedPublisher PD

Fibre optic hydrogen sensing for long term use in explosive environments

Hydrogen is an explosive and flammable gas with a lower explosive limit of just 4% volume in air. It is important to monitor the concentration of hydrogen in a potentially hazardous environment where hydrogen may be released as a by-product in a reaction or used as a principal gas/liquid. A fibre optic based hydrogen sensor offers an intrinsically safe method of monitoring hydrogen concentration. Previous research studies have demonstrated a variety of fibre optic based techniques for hydrogen detection. However the long-term stability of the hydrogen sensor and interrogation system has not yet been assessed and is the focus of this study. In the case of sensor heads being permanently installed in-situ, they cannot be removed for regular replacement, making long-term stability and reliability of results an important feature of the hydrogen sensor. This thesis describes the investigation and characterisation of palladium coated fibre optic sensor heads using two designs of self-referenced refractometer systems with the aim of finding a system that is stable in the long term (~6 months). Palladium was the chosen sensing material owing to its selective affinity for absorbing hydrogen. Upon hydrogen absorption, palladium forms a palladium- hydride compound that has a lower refractive index and lower reflectivity than pure palladium. The refractometers measured the changes in the reflectivity to enable calculation of the concentration of hydrogen present. A low detection limit of 10ppm H2 in air was demonstrated, with a response time of 40s for 1000ppm H2 in air. A further aspect to sensor stability was investigated in the form of sensor heads that had a larger area for palladium coverage. Hydrogen induced cracking in palladium is a common failure mechanism. A hypothesis is presented that a larger sensor area can reduce the probability of catastrophic failure resulting from cracks, which may improve the predictability of the sensor’s performance. Two sensor head designs have been proposed – fibre with a ball lens at the tip and fibre with a GRIN lens at the tip, both of which potentially offer a larger area than the core of a singlemode optical fibre. The limit of detection and response times of the sensor heads were characterised in hydrogen. For long term stability assessment of the sensor head and the interrogation unit, the system was left running for a period of 1 to 4 weeks and the noise and drift in the system was quantified using an Allan deviation plot

Enabling Technology in Optical Fiber Communications: From Device, System to Networking

This book explores the enabling technology in optical fiber communications. It focuses on the state-of-the-art advances from fundamental theories, devices, and subsystems to networking applications as well as future perspectives of optical fiber communications. The topics cover include integrated photonics, fiber optics, fiber and free-space optical communications, and optical networking

Optical fibre sensors with applications in gas and biological sensing

This thesis describes the study of various grating based optical fibre sensors for applications in refractive index sensing. The sensitivity of these sensors has been studied and in some cases enhanced using novel techniques. The major areas of development are as follows. The sensitivity of long period gratings (LPGs) to surrounding medium refractive index (SRI) for various periods was investigated. The most sensitive period of LPG was found to be around 160 µm and this was due to the core mode coupling to a single cladding mode but phase matching at two wavelength locations, creating two attenuation peaks, close to the waveguide dispersion turning point. Large angle tilted fibre gratings (TFGs) have similar behaviour to LPGs, in that they couple to the co-propagating cladding modes. The tilted structure of the index modulation within the core of the fibre gives rise to a polarisation dependency, differing the large angle TFG from a LPG. Since the large angle TFG couple to the cladding mode they are SRI sensitive, the sensitivity to SRI can be further increased through cladding etching using HF acid. The thinning of the cladding layer caused a reordering of the cladding modes and shifted to more SRI sensitive cladding modes as the investigation discovered. In a SRI range of 1.36 to 1.40 a sensitivity of 506.9 nm/URI was achieved for the etched large angle TFG, which is greater than the dual resonance LPG. UV inscribed LPGs were coated with sol-gel materials with high RIs. The high RI of the coating caused an increase in cladding mode effective index which in turn caused an increase in the LPG sensitivity to SRI. LPGs of various periods of LPG were coated with sol-gel TiO2 and the optimal thickness was found to vary for each period. By coating of the already highly SRI sensitive 160µm period LPG (which is a dual resonance) with a sol-gel TiO2, the SRI sensitivity was further increased with a peak value of 1458 nm/URI, which was an almost 3 fold increase compared to the uncoated LPG. LPGs were also inscribed using a femtosecond laser which produced a highly focused index change which was no uniform throughout the core of the optical fibre. The inscription technique gave rise to a large polarisation sensitivity and the ability to couple to multiple azimuthal cladding mode sets, not seen with uniform UV inscribed gratings. Through coupling of the core mode to multiple sets of cladding modes, attenuation peaks with opposite wavelength shifts for increasing SRI was observed. Through combining this opposite wavelength shifts, a SRI sensitivity was achieved greater than any single observed attenuations peak. The maximum SRI achieved was 1680 nm/URI for a femtosecond inscribed LPG of period 400 µm. Three different types of surface plasmon resonance (SPR) sensors with a multilayer metal top coating were investigated in D shape optical fibre. The sensors could be separated into two types, utilized a pre UV inscribed tilted Bragg grating and the other employed a post UV exposure to generate surface relief grating structure. This surface perturbation aided the out coupling of light from the core but also changed the sensing mechanism from SPR to localised surface plasmon resonance (LSPR). This greatly increased the SRI sensitivity, compared to the SPR sensors; with the gold coated top layer surface relief sensor producing the largest SRI sensitivity of 2111.5nm/URI was achieved. While, the platinum and silver coated top layer surface relief sensors also gave high SRI sensitivities but also the ability to produce resonances in air (not previously seen with the SPR sensors). These properties were employed in two applications. The silver and platinum surface relief devices were used as gas sensors and were shown to be capable of detecting the minute RI change of different gases. The calculated maximum sensitivities produced were 1882.1dB/URI and 1493.5nm/URI for silver and platinum, respectively. Using a DFB laser and power meter a cheap alternative approach was investigated which showed the ability of the sensors to distinguish between different gases and flow rates of those gases. The gold surface relief sensor was coated in a with a bio compound called an aptamer and it was able to detect various concentrations of a biological compound called Thrombin, ranging from 1mM to as low as 10fM. A solution of 2M NaCl was found to give the best stripping results for Thrombin from the aptamer and showed the reusability of the sensor. The association and disassociation constants were calculated to be 1.0638×106Ms-1 and 0.2482s-1, respectively, showing the high affinity of the Aptamer to thrombin. This supports existing working stating that aptamers could be alternative to enzymes for chemical detection and also helps to explain the low detection limit of the gold surface relief sensor.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Optical Fiber Interferometric Sensors

The contributions presented in this book series portray the advances of the research in the field of interferometric photonic technology and its novel applications. The wide scope explored by the range of different contributions intends to provide a synopsis of the current research trends and the state of the art in this field, covering recent technological improvements, new production methodologies and emerging applications, for researchers coming from different fields of science and industry. The manuscripts published in the Special issue, and re-printed in this book series, report on topics that range from interferometric sensors for thickness and dynamic displacement measurement, up to pulse wave and spirometry applications

Comparison between one layer and bilayer surface plasmon resonance optical fiber chemical sensor

Surface Plasmon Resonance (SPR) - based plastic optical fiber has been provided as a sensor to estimate the refractive index and then the concentration of specific chemical samples. Two configurations were suggested for the design. The first was through using a single layer of gold with a thickness of about 40nm deposited on a 10mm portion in the middle of plastic optical fiber. In the second configuration, a bilayer is deposited on the fiber. This bilayer consisted of a gold layer with a thickness of about 30 nm and an aluminum layer with a thickness of about 30 nm. Both of these configurations are utilized as chemical sensors. The resonance wavelength for the bilayer-based sensor was higher than that of the single-layer sensor for all studied chemical samples. The highest resonance wavelength was for the salt-water solution with a concentration of 30%. For the salt-water solution with a concentration of 30%, the resonance wavelength with the bilayer-based sensor was 568nm while it was 540nm with the single-layer sensor

Refractometric platforms for label-free biochemical sensing

Optical fiber technology, which is well-known for having revolutionized the telecommunications industry, is currently proving to have important roles in applications such as sensing, biomedicine and industry. The sensing technology based on optical fibers has attracted considerable interest due to its unique features. High sensitivity, immunity to electromagnetic interferences, chemically and biologically inert, small size, and capability forin-situ, real-time, remote, anddistributedsensingaresomeofthemost appealing characteristics that motivate a growing scientific community. The principle behind optical fiber sensing is the interaction between radiation traveling into the optical fiber and the parameter of interest. The measurand acts over the material, the waveguide or, depending on the sensing structure, directly in the optical signal and this action will infer variations in one or few parameters of the radiation such as: intensity, wavelength, frequency, phase or polarization. This work fits within this area, specifically on fiber optic refractometric sensors for label-free biochemical sensing. It is presented a review about the most relevant works in this field, results associated with the study, development and characterization of few types of optical fiber sensors based on fiber Bragg gratings, long period gratings, multimode interference and fibertapers. Also, adifferentialinterrogationsystem, basedonwhitelight interferometry is exposed for high resolution refractive index sensing. In all cases, it was also a main objective of the developed work to evaluate the potential application of the new sensing structures and systems researched, particularly in the context of food industry and environmental monitoring.A tecnologia da fibra ótica, bem conhecida por ter revolucionado a indústria das telecomunicações, atualmente está a desempenhar um papel importante em outros campos como o do sensoriamento, a biomedicina e a indústria. A tecnologia de sensores baseados em fibras óticas tem sido alvo de considerável interesse devido às suas características únicas. Elevada sensibilidade, imunidade a interferências eletromagnéticas, química e biologicamente inerte, tamanho e peso reduzido, e capacidade sensoriamento remoto, distribuído, in-situ e em tempo real; são são alguns dos benefícios mais relevantes que motivam a uma crescente comunidade científica. O princípio por trás dos sensores de fibra ótica, é a interação entre a radiação que viaja no interior da fibra óptica e parâmetro de interesse. O mensurandoatuasobreomaterial, guiadeondaou, dependendodaestruturasensoradiretamentenosinalótico,resultandonaalteraçãodeumaou mais propriedades da radiação, tais como a sua intensidade, comprimento de onda, frequência, fase ou polarização. Este trabalho enquadra-se nesta área, especificamente no ramo dos sensores de fibra ótica refratométricos para medição direta (sem utilização de indicadores de cor) de parâmetros bioquímicos. Inicialmente é apresentadaumarevisãodosostrabalhosmaisrelevantesnestedomíniocientífico; seguidamente e exposto o conjunto de sistemas sensores desenvolvidos e caracterizados, baseados em diversas estruturas como redes de difração, tapers e dispositivos de interferência intermodal. Adicionalmente, é tambémdescritoumsistemadeleituradiferencialcombaseeminterferometria de luz branca, desenvolvido para medição de índice de refração com elevada resolução. Em todos os trabalhos, um dos principais objetivos foi avaliar o potencial de aplicação das novas estruturas e sistemas de sensoriamento desenvolvidos, em particular no contexto da indústria alimentar e monitorização ambiental.Fundação para a Ciência e Tecnologia SFRH/BD/63758/200