Photonic Time-Stretch Enabled High Throughput Microwave and MM-Wave Interferometry Applied to Fibre Grating Sensors and Non-Contact Measurement

The research presented in this thesis is focused towards developing real-time, high-speed applications, employing ultrafast optical microwave generation and characterisation techniques. This thesis presents a series of experiments wherein mode-locked laser pulses are utilised. Photonics-based microwave and MM-Wave generation and detection are explored and employed for applications pertaining to fibre grating sensors and non-contact measurement. The application concepts leverage techniques from optical coherence tomography and non-destructive evaluation of turbid media. In particular, I use the principle of dispersion-induced photonic Time-Stretch to slow down high-speed waveforms to speeds usable by state-of-the-art photo-detectors and digital signal processors. The concept of photonic time-stretch is applied to map instantaneous microwave frequency to the time instant of the signal, which in turn is related to spatial location as established by the space-wavelength-time conversions. The experimental methods applied throughout this thesis is based upon Michelson interferometer architecture. My original contribution to knowledge is the realisation of Photonics-based, single tone, and chirped microwave and MM-Wave pulse generation applied to deciphering physical strain profile along the length of a chirped fibre Bragg grating employed in a Michelson interferometer configuration. This interrogation scheme allows intra-grating high-resolution, high-speed, and temperature independent strain measurement. This concept is further extended to utilise photonic generation of microwave pulses to characterise surface profile information of thin film and thin plate infrared transparent slides of variable thickness setup in a Michelson interferometer architecture. The method basis for photonically generated high-frequency microwave signals utilises the principle of photonic Time-Stretch. The research was conducted in the Photonics Lab at the University of Kent. In addition, the photonically generated microwave/ MM-Wave pulses is utilised as a potential broadband frequency-swept source for non-contact measurement of turbid media. Investigation of the proof-of-concept based on an MM-Wave coherence tomography set-up is implemented at Vrije Universiteit Brussel (VUB), Department of Electronics and Informatics (ETRO)

Development of advanced structures for optical fiber lasers and sensors

Desde la irrupción de la fibra óptica en las telecomunicaciones, han surgido multitud de desarrollos basados en sus propiedades. Así, en las últimas décadas, la rápida evolución de los sistemas basados en fibra óptica, así como la aparición en el mercado de dispositivos como los amplificadores ópticos, los láseres de semiconductor de alta potencia, y otros elementos, ha hecho avanzar considerablemente la investigación en este campo. Además de la utilización de la fibra óptica en telecomunicaciones, han surgido nuevas aplicaciones, generando nuevas familias de dispositivos. Dos de ellas particularmente interesantes, son los láseres de fibra óptica y los sensores de fibra óptica. Ambas familias pueden combinarse de manera que sensores y redes de sensores de fibra óptica pueden interrogarse por medio de láseres de fibra óptica. En este marco de investigación se centra esta tesis, donde se han desarrollado estructuras avanzadas de fibra óptica para láseres y sensores. El objetivo ha sido mejorar las propiedades de los láseres de fibra, sensores y sus sistemas de monitorización, así como abordar los diferentes problemas que éstos presentan actualmente. Los retos encontrados, así como los objetivos de cada sistema, varían en función del tipo de sistema desarrollado. De esta forma, la primera parte de este trabajo ha sido dedicada al desarrollo de láseres de fibra óptica, buscando mejorar sus propiedades en términos de estabilidad, relación señal ruido, modos longitudinales, múltiples líneas de emisión y anchura de las mismas. Se han abordado diferentes tipos de configuraciones clásicas de láseres en anillo y de cavidad lineal. También se han realizado estudios de láseres de cavidad distribuida mediante dispersión Rayleigh (random). Estos láseres han suscitado gran interés en los últimos años dado que no presentan modos longitudinales. Por otro lado en el ámbito de la monitorización de sensores, se han desarrollado transductores ópticos basados en fibras micro-estructuradas, aprovechando las ventajas que éstas presentan en comparación con las fibras ópticas estándar. Finalmente se han desarrollado diferentes configuraciones de sistemas sensores con el objetivo de contribuir a la mejora de alguno de sus parámetros, como su alcance, capacidad de multiplexación, sensibilidad, rango dinámico y estabilidad de los sistemas sensores.Optical fiber technology as well as its rapidly evolution, has attracted the scientific community attention to develop lasers, fiber optic transducers and sensor networks. In this regard, the appearance in the last decades of commercial devices such as optical amplifiers, semiconductor high power lasers and others, has contributed to the rise of this technology. In this framework, a contribution to the improvement of the performance of fiber lasers and fiber optic sensors is presented in this PhD. work, taking into account their main merits and addressing their principal challenges. The challenges as well as the objectives addressed in each design vary depending on the application. In this way, the first part of the thesis has been dedicated to the development of optical fiber lasers. And it is focused on improving their properties in terms of stability, signal noise ratio, longitudinal modes, multiwavelength emission and bandwidth of the emission lines. Different classical configurations based on ring and linear cavity lasers have been addressed. Also, random cavity lasers, which have attracted great interest in recent years due to their longitudinal modeless behavior, have been studied. On the other hand, in the field of sensor monitoring, optical transducers based on micro-structured fibers have been developed, exploiting their advantages in comparison with standard optical fibers. Finally different optical sensor networks have been developed, whose main goal have been the improvement of features such as monitoring distance, multiplexing skill, sensitivity, dynamic range and stability.Este trabajo se ha llevado a cabo gracias a las aportaciones económicas recibidas de los siguientes organismos y proyectos: - Universidad Pública de Navarra mediante la ayuda de investigación predoctoral, la ayuda para movilidad y las ayudas complementarias a tesis doctorales. - Secretaria de Estado de Investigación, Desarrollo e Innovación, Ministerio de Economía y Competitividad de España a través del programa de Formación del Personal Investigador y asociado al proyecto de investigación TEC2010-20224-C02-01. - Proyecto de investigación TEC2013-47264-C2-2-R a través del Fondo Europeo de Desarrollo Regional (FEDER). - Acción Europea COST- TD1001: Novel and Reliable Optical Fibre Sensor Systems for Future Security and Safety Applications (OFSeSa) - Proyecto INTERREG SUDOE Project “ECOAL-MGT - Ecological Management of Coal Waste Piles, SOE3/P2/P714”. - Ministerio de Economía y Competitividad de España a través del Proyecto campus de excelencia-Iberus (Innocampus). - Grupo de investigación Comunicaciones Ópticas y Aplicaciones Electrónicas de la Universidad Pública de Navarra mediante la financiación de material y participación en congresos.Programa Oficial de Doctorado en Tecnologías de las Comunicaciones (RD 1393/2007)Komunikazioen Teknologietako Doktoretza Programa Ofiziala (ED 1393/2007

A Fast Linearly Wavelength Step-Swept Light Source Based on Recirculating Frequency Shifter and Its Application to FBG Sensor Interrogation

A wavelength step-swept light source (WSSL) using a recirculating frequency shifter loop (RFSL) based on a single-side-band (SSB) modulator is proposed, in order to achieve a linear and fast wavelength-sweeping. The swept step can be tuned from 1.2 pm to 128 pm by adjusting a precise and stable radio frequency (RF) signal that is applied to the SSB modulator. The swept rate can be tuned up to 99 kHz in a range of over 5.12 nm. Wavelength-to-time mapping is used to measure static strain-induced or temperature-induced shifting of the reflected central wavelength of a fiber Bragg grating (FBG). Because of the high linearity of the light source, the interrogation linearity of the strain and the temperature are as high as 0.99944 and 0.99946, respectively. When a dynamic periodic strain applied to FBG sensor, the dynamic performance of the FBG sensor is successfully recorded in the time domain and its power spectral density of a fast Fourier transform (FFT) is calculated. The signal-to-noise ratio (SNR) of the power spectral density is over 40 dB for a 100 Hz dynamic strain and the calculated sensitivity is 0.048 με/Hz1/2. A sharp change in the strain frequency from 100 Hz to 500 Hz is captured in real time