For many years, the use of fiber optic sensors for the measurement of strain, temperature and pressure has been widely investigated. Much less research has been directed towards the use of these sensors for measuring electric and magnetic fields. As existing field meters have conductive parts which inherently cause field distortion, a fiber optic electric field sensor would be preferable due to the immunity of the fibers to electromagnetic interference. A novel electric field sensor is proposed which utilizes the displacement measurement capabilities of the Extrinsic Fabry-Perot Interferometric sensor, and the actuation produced by a piezoelectric material when placed in an electric field. Classical electromagnetic theory is used to mathematically model the performance of the sensor within a given electric field. Experimental and theoretical results are presented which demonstrate the ability of the proposed sensor to detect electric fields. Improvements to the proposed electric field sensor and the transition of this research into magnetic field sensing is suggested for future research. / Master of Science

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.

This thesis discusses the application of Slab Coupled Optical Fiber Sensors (SCOS) in a railgun. The specific goal of these sensors is to create an electric field profile at a specific point in the gun as the armature passes. The thesis explores the theory that powers the railgun as well as the principles of the SCOS sensors. It also elaborates on the various noise sources found throughout the detection system and concludes with a summary of the various field tests that were performed throughout this project. There are many benefits to using a railgun over traditional weapons in the field. These benefits not only include both safety and cost, but also greater overall defense capabilities. Unfortunately, the velocity skin effect (VSE) causes the current railgun designs to have limited life span through wear on the rails. In order to develop superior railguns and railgun armatures, the accurate detection of the VSE through measuring the electric field is of great interest. We used a SCOS, a small directionally precise dielectric sensor, as a small sensing area is required to be able to measure the electric fields inside of the rail gun. The actual usage of the SCOS within the railgun produced an additional set of problems that are not commonly encountered in the lab. The chief amongst these was noise from strain, RF pickup, and phase noise. This thesis also reports various methods used to reduce each of these noise sources.

When underwater sensors are being deployed there is always some uncertainty about the actual position of the sensors. The most common way of determine the sensors position is the use of hydro-acoustic methods. However, for electric field sensors the most favourable would be to use the sensor system itself. The first question being answered in this report is whether it is possible to position electric field sensors with the sensor system itself, and the answer is yes. An algorithm has been developed which calculates the relative position of the sensors based on data measured by the sensors when a dipole passes the sensor group. The algorithm extracts zero crossings of the z-components of the electric field measured by each sensor from the data, which are converted to moments in time, multiplied by the speed and course of the vessel and finally calculated into relative position vectors between the sensors using vector algebra. The result of the predicted relative position is within 0.2 m from the sensors’ actual position, which answers the second question about how accurate the method is. However, the error estimation is within a couple of centimetres indicating that there are other sources of error than speed and course. The third question being answered is whether the method is better than acoustic methods, and the answer is no. Nonetheless, the methods are within the same order of magnitude. In conclusion, the method has acceptable performance, especially considering the fact that it can determine the position of the sensors with the sensor system itself which could be significant.