Optical fibers are increasingly being used to create sensing devices. The D-fiber has an elliptical core and exhibits birefringence. This birefringence can be used to create a polarimetric sensor. The elliptical core supports two orthogonal modes that have separate effective indices of refraction. The indices of refraction change with a change in temperature. Since the effective indices of refraction change differently for the two modes, the birefringence also changes. This change in birefringence can be seen as a change in detected power through the fiber through the use of polarizers. The fiber then becomes a temperature sensor. The sensitivity of the fiber can be enhanced by replacing a section of the core of the fiber with a sensing material. With the sensing material in the core of the fiber, it has direct interaction with the light and strongly affects it. A polarimetric temperature sensor is created by replacing a section of the core with a polymer, which is sensitive to temperature. The core-replaced fiber in a polarimetric sensing configuration is compared to a a unetched fiber set up in the same way. The core-replaced fiber sensor is five times as sensitive to temperature as an unetched fiber.

This thesis presents the fabrication of a low loss hybrid waveguide electric field(E-field) sensor based on optical D-fiber. This novel E-field sensor is formed as part of a contiguous fiber resulting in a flexible and small cross-section device that can be embedded into electronic circuitry. The in-fiber nature of this sensor also eliminates the need for alignment and packaging that conventional sensors need. An optical fiber can detect electric fields when the core of the fiber is partially removed and replaced with an electro-optic polymer. This polymer causes a change in the index of refraction in the waveguide of the device when in the presence of an electric field. The change in the effective index of refraction changes the speed of the light in the vertical axis relative to the light in the horizontal axis creating a phase change between the two axes. This phase change can be detected as a change in the polarity of the light coming out of the fiber. The sensor is formed by partially etching out the core of a D-shaped optical fiber and depositing a polymer to form a hybrid waveguide. The polymer becomes sensitive to electric fields through corona poling. The typical corona poling process is not amenable to poling a polymer located in the fiber core. A method of poling conducive to an in-fiber device was developed and demonstrated. Using PMMA and DR1 for proof of concept, the operation of the first in-fiber hybrid waveguide electric field sensor is demonstrated. Etch depth, polymer composition, and polymer spin rate are optimized to provide strong interaction between the light and the sensing portion of the hybrid waveguide while maintaining low optical loss. High frequency testing was demonstrated to show that the effect is electro-optic. AC testing also allows the Epi of the sensors to be determined at lower electric fields than are required for DC testing, eliminating charge build up and electric field break down issues.

This dissertation presents the creation of slab coupled optical sensors (SCOS) for electric field sensing applications. SCOS devices utilize the benefits of an optical fiber system for high bandwidth and low electromagnetic interference. These sensors are fabricated by means of mode coupling between a small section of D-shaped optical fiber (D-fiber) with a multi-mode electro-optic slab waveguide. Electric field detection is accomplished by monitoring the behavior of the resonances, seen as transmission dips in the D-fiber transmission, as they shift with electric fields. The novelties of SCOS devices include their small compact nature, potential for sensor multiplexing and a dielectric structure allowing low electromagnetic interference. The SCOS developed in this work been used to measure fields as low as 30 V/m with 1 kHz resolution bandwidth and a high degree of linearity. Due to their compact size they are capable of placement within devices to measure interior electric fields immeasurable by other sensors that are either too large for internal placement or disruptive of the internal fields due to metallic structure. Wavelength multiplexing allows multiple sensors to be placed on a single fiber for mapping electric fields at multiple instances. As an extension, SCOS multiplexing allows the potential for 3-d field sensing by use of multiple electro-optic crystals having orthogonal orientations of the electro-optic axis. This work performs a thorough analysis of SCOS design in order to optimize sensor efficiency for its various applications. Furthermore, the straightforward fabrication process for these sensors is outlined for the development of future uses of these sensors.

This thesis provides the details of a multi-axis electric field sensor. The sensing element consists of three slab coupled optical fiber sensors that are combined to allow directional electric field sensing. The packaged three-axis sensor has a small cross-sectional area of 0.5 cm x 0.5 cm achieved by using an x-cut crystal. The method is described that uses a sensitivity-matrix approach to map the measurements to field components. The calibration and testing are described resulting in an average error of 1.5º.This work also includes a description of the packaging method used as well as a thorough analysis of the directional sensitivity of potassium titanyl phosphate (KTP) and electro-optic polymer: the two materials used as sensing elements. Each of the two materials is highly direction sensitive creating minimal crosstalk between the sensors.

This dissertation explores techniques for improving slab-coupled optical fiber sensor (SCOS) technology for use in specific applications and sensing configurations. SCOS are advantageous for their small size and all-dielectric composition which permit non-intrusive measurement of electric fields within compact environments; however, their small size also limits their sensitivity. This work performs a thorough analysis of the factors contributing to the performance of SCOS and demonstrates methods which improve SCOS, while maintaining its small dimensions and high level of directional sensitivity. These improvements include increasing the sensitivity by 9x, improving the frequency response to include sub 300 kHz frequencies, and developing a method to tune the resonances. The analysis shows that the best material for the slab waveguide is an electro-optic polymer because of its low RF permittivity combined with high electro-optic coefficient. Additional improvements are based on changing the crystal orientation to a transverse configuration, which enhances the sensitivity due to a combined increase in the effective electro-optic coefficient and electric field penetration into the slab. The transverse SCOS configuration not only improves the overall sensitivity but increases the directional sensitivity of the SCOS. Lithium niobate and electro-optic polymer are both experimentally shown to exhibit minimal frequency dependent sensitivity making them suitable for broad frequency applications. Simultaneous interrogation of multiple SCOS with a single tunable laser is achieved by tuning the resonant wavelengths of KTP SCOS so their resonances overlap.

A sociedade atual está vivendo uma revolução baseada na informação. A recente explosão da popularidade da internet e desregulamentação dos setores públicos de telefonia em muitos países foram os principais responsáveis pelo aumento da demanda por largura de banda. Adicionalmente, houve um aumento no volume de tráfego em função do oferecimento de serviços multimídia de banda larga. Este cresimento rápido e global por demanda de largura de banda está acelerando o desenvolvimento e a implantação de redes de comunicações ópticas empregnando sistemas multiplexados em comprimento de onda (WDM). O emprego de fibras na transmissão de informações em alta velocidade a grandes distâncias já está consolidado, e sua utilização em redes metropolitanas MAN (Metropolitan Area Network) e redes de acesso está aumentando. Verifica-se que a tendência de evolução das redes ópticas é a aproximação das fibras até o usuário final. A forma mais viável economicamente de aproximar o usuário dos benefícios das redes ópticas com grande capacidade é o emprego de redes ópticas passivas PON (Passive Optical Network) empregando o sistema WDM. Este tipo de rede apresenta a flexibilidade de suportar tanto broadcast, onde o mesmo sinal é distribuído a todos os usuários, como serviços ponto-a-ponto. Um dos requisitos mais importantes para o aumento da capacidade destes sistemas ópticos é o aumento do número de canais (comprimentos de onda). Para viabilizar este aumento do número de canais é necessária a utilização de dispositivos com alta seletividade em comprimento de onda proposto neste trabalho. Este filtro é composto pela combinação de três estruturas distintas formando um único dispositivo: fibra tipo D, duplo refletor de Bragg (DBR), e guia multicamada em configuração ARROW ( Antiresonant Reflecting Optical Waveguide). O DBR é previamente definido na fibra tipo D e esta é então colada sobre a estrutura multicamada. ) A estrutura multicamada, por sua vez, possui a configuração ARROW em virtude de suas características de seletividade em comprimento de onda. A utilização de um fibra tipo D no dispositivo proposto permite que as perdas de inserção deste dispositivo no enlace óptico sejam drasticamente reduzidas. Este trabalho realiza um projeto criterioso de um filtro em questão, buscando valores ótimos para cada um dos parâmetros que compõem este dispositivo, tais como: espessuras de camadas, índices de refração, perda de inserção, isolação entre canais, etc. Os resultados obtidos com as simulações são discutidos e uma configuração ótima para o dispositivo é proposta. / The progress in lightwave propagation based on optical fibers has provided our society with an unprecedented communication capability. The deregulation of public telephone companies together with the increasingly popularity of the internet can be pointed out as the major contributors for this huge bandwidth demand we experience today. Additionally, there was a corresponding growth in traffic volume due to wideband multimedia services. As a consequence of this fast growing demand for bandwidth in a global scale, telecom companies have accelerated the development and implementation of optical communication networks based on wavelength division multiplexing (WDM) technology. The tendency in terms of network evolution is to approximate the optical fibers as close as possible to the end user. The most economically viable way of doing so is by way of the so called Passive Optical Networks (PON) based on WDM systems. This type of network is flexible enough to support broadcast, where the same signal is distributed to all users, and point-to-point services. If more capacity is required for these systems, this can be achieved just by adding new channels (wavelengths) to it. Another important issue regarding WDM systems consists in the extraction of channels from the optical network, which can be achieved by using highly selective dropping filters such as the one proposed in this work. This filter is defined by the combination of three distinct structures defining one single device: a d-type fiber, a double Bragg reflector (DBR), and a multilayer ARROW type waveguide (Antiresonant Reflecting Optical Waveguide). The DBR is defined beforehand on the d-fiber, and then the d-fiber is literally glued on top of the multilayer waveguide. This multilayer waveguide is fabricated directly atop of a p-i-n photodetector in such a way that the three structures (d-fiber, multilayer waveguide and photodetector) now form a rigid structure. The ARROW type configuration for the multilayer waveguide and the DBR structure are chosen by virtue of their wavelength selectivity characteristics, helping to improve the device performance. The d-fiber structure, by its tum, has the great advantage of reducing drastically the insertion loss when compared to rectangular waveguide filters. In the analysis provided in this work parameters such as layer thicknesses, refractive indices, insertion loss, channel isolation, etc, and their influence on the device performance, are extensively investigated for optimization purposes. The simulated results are discussed thoroughly and an optimal structure configuration is proposed.

A sociedade atual está vivendo uma revolução baseada na informação. A recente explosão da popularidade da internet e desregulamentação dos setores públicos de telefonia em muitos países foram os principais responsáveis pelo aumento da demanda por largura de banda. Adicionalmente, houve um aumento no volume de tráfego em função do oferecimento de serviços multimídia de banda larga. Este cresimento rápido e global por demanda de largura de banda está acelerando o desenvolvimento e a implantação de redes de comunicações ópticas empregnando sistemas multiplexados em comprimento de onda (WDM). O emprego de fibras na transmissão de informações em alta velocidade a grandes distâncias já está consolidado, e sua utilização em redes metropolitanas MAN (Metropolitan Area Network) e redes de acesso está aumentando. Verifica-se que a tendência de evolução das redes ópticas é a aproximação das fibras até o usuário final. A forma mais viável economicamente de aproximar o usuário dos benefícios das redes ópticas com grande capacidade é o emprego de redes ópticas passivas PON (Passive Optical Network) empregando o sistema WDM. Este tipo de rede apresenta a flexibilidade de suportar tanto broadcast, onde o mesmo sinal é distribuído a todos os usuários, como serviços ponto-a-ponto. Um dos requisitos mais importantes para o aumento da capacidade destes sistemas ópticos é o aumento do número de canais (comprimentos de onda). Para viabilizar este aumento do número de canais é necessária a utilização de dispositivos com alta seletividade em comprimento de onda proposto neste trabalho. Este filtro é composto pela combinação de três estruturas distintas formando um único dispositivo: fibra tipo D, duplo refletor de Bragg (DBR), e guia multicamada em configuração ARROW ( Antiresonant Reflecting Optical Waveguide). O DBR é previamente definido na fibra tipo D e esta é então colada sobre a estrutura multicamada. ) A estrutura multicamada, por sua vez, possui a configuração ARROW em virtude de suas características de seletividade em comprimento de onda. A utilização de um fibra tipo D no dispositivo proposto permite que as perdas de inserção deste dispositivo no enlace óptico sejam drasticamente reduzidas. Este trabalho realiza um projeto criterioso de um filtro em questão, buscando valores ótimos para cada um dos parâmetros que compõem este dispositivo, tais como: espessuras de camadas, índices de refração, perda de inserção, isolação entre canais, etc. Os resultados obtidos com as simulações são discutidos e uma configuração ótima para o dispositivo é proposta. / The progress in lightwave propagation based on optical fibers has provided our society with an unprecedented communication capability. The deregulation of public telephone companies together with the increasingly popularity of the internet can be pointed out as the major contributors for this huge bandwidth demand we experience today. Additionally, there was a corresponding growth in traffic volume due to wideband multimedia services. As a consequence of this fast growing demand for bandwidth in a global scale, telecom companies have accelerated the development and implementation of optical communication networks based on wavelength division multiplexing (WDM) technology. The tendency in terms of network evolution is to approximate the optical fibers as close as possible to the end user. The most economically viable way of doing so is by way of the so called Passive Optical Networks (PON) based on WDM systems. This type of network is flexible enough to support broadcast, where the same signal is distributed to all users, and point-to-point services. If more capacity is required for these systems, this can be achieved just by adding new channels (wavelengths) to it. Another important issue regarding WDM systems consists in the extraction of channels from the optical network, which can be achieved by using highly selective dropping filters such as the one proposed in this work. This filter is defined by the combination of three distinct structures defining one single device: a d-type fiber, a double Bragg reflector (DBR), and a multilayer ARROW type waveguide (Antiresonant Reflecting Optical Waveguide). The DBR is defined beforehand on the d-fiber, and then the d-fiber is literally glued on top of the multilayer waveguide. This multilayer waveguide is fabricated directly atop of a p-i-n photodetector in such a way that the three structures (d-fiber, multilayer waveguide and photodetector) now form a rigid structure. The ARROW type configuration for the multilayer waveguide and the DBR structure are chosen by virtue of their wavelength selectivity characteristics, helping to improve the device performance. The d-fiber structure, by its tum, has the great advantage of reducing drastically the insertion loss when compared to rectangular waveguide filters. In the analysis provided in this work parameters such as layer thicknesses, refractive indices, insertion loss, channel isolation, etc, and their influence on the device performance, are extensively investigated for optimization purposes. The simulated results are discussed thoroughly and an optimal structure configuration is proposed.

This thesis reports an in-fiber magnetic field sensor that is able to detect magnetic fields as low as 2 A/m at a spatial resolution of 1 mm. The small sensor consists of a magneto-optic slab waveguide, bismuth-doped rare earth iron garnet (Bi-RIG) that is coupled to an optical fiber. By coupling light from the fiber to the slab waveguide, it becomes an in-fiber magnetic field sensor. This is due to the Magneto-Optic Kerr effect; a change in refractive index is proportional to the applied magnetic field. When an AC field is applied, an AC component in the output power can be detected by a spectrum analyzer. The novelties of Magneto-Optic Slab Coupled Optical Sensor (MO-SCOS) devices include their small compact nature and a dielectric structure allowing low electromagnetic interference. Due to their compact size they are capable of placement within devices to measure interior electromagnetic fields immeasurable by other sensors that are either too large for internal placement or disruptive of the internal fields due to metallic structure. This work also reports progress on EO SCOS development. The EO sensor has found application in new environments including the electromagnetic rail gun, and a dual-axis sensor.

This dissertation presents the fabrication and analysis of in-fiber devices based on elliptical core D-shaped optical fiber. Devices created inside optical fibers are attractive for a variety of reasons including low loss, high efficiency, self-alignment, light weight, multiplexibility, and resistance to electromagnetic interference. This work details how D-fiber can be used as a platform for a variety of devices and describes the creation and performance of two of these devices: an in-fiber polymer waveguide and a surface relief fiber Bragg grating. In D-fiber the core is very close to the flat side of the ‘D’ shape. This proximity allows access to the fields in the fiber core by removal of the cladding above the core. The D-fiber we use also has an elliptical core, allowing for the creation of polarimetric devices. This work describes two different etch processes using hydrofluoric acid (HF) to remove the fiber cladding and core. For the creation of devices in the fiber core, the core is partially removed and replaced with another material possessing the required optical properties. For devices which interact with the evanescent field, cladding removal is terminated before acid breaches the core. Etching fibers prepares them for use in the creation of in-fiber devices. Materials are placed into the groove left when the core of a fiber is partially removed to form a hybrid waveguide in which light is guided by both the leftover core and the inserted material. These in-fiber polymer waveguides have insertion loss less than 2 dB and can potentially be the basis for a number of electro-optic devices or sensors. A polarimetric temperature sensor demonstrates the feasibility of the core replacement method. This work also describes the creation of a surface relief fiber Bragg gratings (SR-FBGs) in the cladding above the core of the fiber. Because it is etched into the surface topography of the fiber, a SR-FBG can operate at much higher temperatures than a standard FBG, up to at least 1100 degrees Celsius. The performance of a SR-FBG is demonstrated in temperature sensing at high temperatures, and as a strain sensor.

This dissertation presents the novel creation of a surface relief fiber Bragg grating on the flat surface of a D-shaped optical fiber. In order to produce an efficient surface relief grating the grating must be etched into the surface of the glass fiber close to the core. A short etch that removes the cladding above the core is performed in order to decrease the core-to-flat distance and allow the light to interact with the grating on the flat surface. Due to the unique D-shape of the optical fiber the mechanical integrity of the fiber remains high even after the fabrication process. For traditional fiber Bragg gratings the index modulation occurs in the core of the optical fiber. While this method can produce highly reflective gratings they are not well suited for many sensing applications. For example, the operating temperature range is limited to a few hundred degrees Celsius before the index modulation returns to a more uniform index profile. Also because the gratings are created in the core of the fiber, interaction with the surrounding environment is limited. The surface relief fiber Bragg grating created for this work overcomes some of the sensing challenges of traditional gratings. The major accomplishments of this dissertation show a dramatic increase in operating temperature to over 1000 degrees Celsius, the ability to measure multi-dimensional bend, the ability to measure material changes around the fiber such as chemical concentration, and the ability to use a Vernier effect to dramatically increase the sensors sensitivity. In addition to the sensing applications of this work a more thorough understanding of the reflection and transmission properties of the surface relief grating is also presented. Implementation of the transfer matrix method for simulation of the gratings is also shown to be a fast and accurate modeling tool for predicting the grating response.