Time-expanded phase-sensitive optical time-domain reflectometry

Phase-sensitive optical time-domain reflectometry (ΦOTDR) is a well-established technique that provides spatio-temporal measurements of an environmental variable in real time. This unique capability is being leveraged in an ever-increasing number of applications, from energy transportation or civil security to seismology. To date, a wide number of different approaches have been implemented, providing a plethora of options in terms of performance (resolution, acquisition bandwidth, sensitivity or range). However, to achieve high spatial resolutions, detection bandwidths in the GHz range are typically required, substantially increasing the system cost and complexity. Here, we present a novel ΦOTDR approach that allows a customized time expansion of the received optical traces. Hence, the presented technique reaches cm-scale spatial resolutions over 1 km while requiring a remarkably low detection bandwidth in the MHz regime. This approach relies on the use of dual-comb spectrometry to interrogate the fibre and sample the backscattered light. Random phase-spectral coding is applied to the employed combs to maximize the signal-to-noise ratio of the sensing scheme. A comparison of the proposed method with alternative approaches aimed at similar operation features is provided, along with a thorough analysis of the new trade-offs. Our results demonstrate a radically novel high-resolution ΦOTDR scheme, which could promote new applications in metrology, borehole monitoring or aerospace

A mode-locked fibre laser temperature independent strain sensor based on intracavity pulse interference

High resolution, accurate strain sensors find vital applications in civil, aerospace, and mechanical engineering. Photonic solutions, especially fibre Bragg gratings, despite being promising platforms for strain sensing in harsh environments, and achieving microstrain resolution, suffer from strong sensitivity to temperature fluctuations and require expensive optical detection methods. To tackle these challenges, in this work we present a mode-locked fibre laser strain sensor based on intracavity pulse interference. Our all-fibre sensor, using an intracavity Mach-Zehnder interferometer architecture achieves 20 microstrain resolution with linear response over a 4 millistrain range. Our proposed sensor does not require external locking, and it is environmentally stable, decoupling temperature and strain effects. Furthermore, through a full electronic read-out in radio-frequency domain, our solution can bypass expensive and bulky optical detection. These features pave the way for low-cost and robust photonic strain sensors technology with disruptive real world impact

Polarization dynamics, stability and tunability of a dual-comb polarization-multiplexing ring-cavity fiber laser

In this paper, we present a polarization-multiplexed system capable of generating two stable optical frequency combs with tunable frequency differences in the range from 100 to 250 Hz and an extinction ratio of 16.5 dBm. Also, the polarization dynamics of a dual-frequency comb generated from a single mode-locked Er-doped fiber laser are experimentally studied. The obtained results will extend the application to areas such as polarization spectroscopy and dual-comb-based polarimetry

Multiheterodyne tunable sources for the interrogation of fiber optic sensors applied to acoustic emissions and ultrasound

Mención Internacional en el título de doctorLight is a very useful tool for measuring high frequency and low amplitude mechanical vibrations. Thanks to the interference process and under certain circumstances we can obtain a specific sort of optical sources called multimode multiheterodyne sources, that are very useful to read several optical wavelengths at the same time on a single photodetector and distinguishing them from each other. This characteristic makes them suitable for interrogating fiber optic sensors. In this thesis, I analyze several fiber optic sensor readout methods that mix multiheterodyne techniques, multimode techniques, and interferometry techniques to measure ultrasound and acoustic mechanical waves. These mechanical waves occur when periodic forces are applied to mechanical structures. This disturbs the layout of atoms and may lead to cracks or the complete collapse of the structure. Therefore, the characterization and measurement of such vibrations are of great importance when performing structure health monitoring (SHM) and non-destructive evaluation (NDE). This thesis aims to solve this problem by implementing several systems that employ light-based technology to measure and characterize mechanical vibrations up to 1 MHz of frequency and sub-nano-strain (lower than 10-3 ppm) level of resolution. The proposed systems involve new features and parameters more settable compared to more conventional approaches of optical sensor reading processes and therefore they offer wider possibilities. A total of three systems have been implemented and tested: First, an electro-optic dual optical frequency comb source to read fiber Bragg gratings for dynamic measurements. This set up reaches 120 kHz of mechanical frequency detection. The second system is based on a self-heterodyne acousto-optic comb that reads a random fiber grating sensor. In this case, the system can detect up to 1 MHz of mechanical vibrations. Finally, the third is based on a compact electro-optic dual optical frequency comb that is used to read low reflectivity fiber Bragg gratings with a dispersion interferometer. This system can detect a maximum of 135 kHz of mechanical frequencies. The results of this thesis improve previous systems achievements to satisfy the specifications required to date in this application, both in mechanical bandwidth and in strain amplitude. They also show the potential of these multimode sources for high-precision optical sensing.La luz es una herramienta muy útil para medir vibraciones mecánicas de alta frecuencia y baja amplitud. Gracias al proceso de interferencia y bajo determinadas circunstancias podemos obtener un tipo específico de fuentes ópticas, denominadas fuentes multimodo multiheterodinas, que son muy útiles para leer varias longitudes de onda ópticas al mismo tiempo en un solo fotodetector y distinguirlas entre sí. Esta característica hace que estas fuentes ópticas sean adecuadas para la lectura de sensores de fibra óptica. En esta tesis, analizo varios métodos de lectura de sensores de fibra óptica que mezclan técnicas multiheterodinas, técnicas multimodo y técnicas de interferometría para medir ultrasonidos y ondas mecánicas acústicas. Estas ondas mecánicas se producen cuando se aplican fuerzas periódicas a las estructuras mecánicas. Esto perturba la disposición de los átomos y puede provocar grietas o el colapso completo de la estructura. Por lo tanto, la caracterización y medida de dichas vibraciones son de gran importancia a la hora de monitorizar el estado de las estructuras y de realizar una evaluación no destructiva. Esta tesis tiene como objetivo resolver este problema mediante la implementación de varios sistemas que emplean tecnología basada en la luz para medir y caracterizar vibraciones mecánicas hasta frecuencias de 1 MHz y nivel de resolución sub-nano-deformación (menor que 10-3 ppm). Los sistemas propuestos implican nuevas características y parámetros más configurables en comparación con los enfoques más convencionales de procesos de lectura de sensores ópticos y, por lo tanto, ofrecen posibilidades más amplias. A lo largo de la tesis se presentan tres sistemas de medida: El primero está basado en un doble peine de frecuencias ópticas (dual comb) electroóptico que es capaz de leer sensores de fibra óptica basados en redes de Bragg (FBG) en régimen dinámico. Este sistema ha sido probado con una frecuencia máxima de detección de 120 kHz. En segundo lugar, se presenta un sistema basado en un selfheterodyne comb acustoóptico para leer sensores de fibra con distribución aleatoria de la rejilla en el núcleo (random grating). Este sistema es capaz de detectar señales de vibración de hasta 1 MHz. El tercer sistema presentado se basa en un doble peine de frecuencias ópticas (dual comb) electroóptico compacto que se utiliza para leer sensores FBG de baja reflectividad con un interferómetro de dispersión. Este sistema puede detectar hasta 135 kHz de vibraciones mecánicas. Los resultados de esta tesis mejoran los obtenidos en sistemas anteriores a fin de satisfacer las especificaciones requeridas hasta la fecha en esta aplicación, tanto en el ancho de banda mecánico como en la amplitud de la deformación. También muestran el potencial de estas fuentes multimodo para la detección óptica de alta precisión.Quiero agradecer la financiación de este trabajo dada por el Ministerio de Educación, Cultura y Deporte para la Formación de Profesorado Universitario FPU2016 (Beca FPU16/03695) y a través del proyecto PARAQUA (TEC2017-86271-R), así como por el Ministerio de Ciencia, Innovación y Universidades a través de las ayudas de movilidad EST18/00617.Programa de Doctorado en Ingeniería Eléctrica, Electrónica y Automática por la Universidad Carlos III de MadridPresidente: Óscar Esteban Martínez.- Secretario: Marta Ruiz Llata.- Vocal: Pedro Alberto da Silva Jorg

Definition of a FPGA-based SoC architecture for PRBS transmission in optical spectroscopy

Optical spectroscopy is a well-known tool typically employed for characterizing the properties of materials by analyzing their iteration with light. One of the most spread techniques is the dual comb spectroscopy, since it accomplishes ultra-high resolution, and high sensitivity measurements with a relatively simple platform including a single, relatively narrowband photodetector. The employed optical dual comb can be implemented through electro-optical (EO) modulation driven by pseudo-ransom binary sequences (PRBS) at high data rates, commonly in the range of tens of Gbps. For that purpose, the runtime generation and transmission of adaptive PRBS is still an open challenge, often involving expensive and not flexible high-speed digital systems, with a few commercially available solutions that sometimes do not match the application requirements efficiently. In this context, this work describes the definition and implementation of a System-on-Chip (SoC) architecture, based on a FPGA device, capable of generating and transmitting two PRBS for a dual comb, at a data rate up to 5 Gbps. The architecture can be configured and its operation modified in run time, thanks to the general-purpose processor involved, in charge of managing an Ethernet link to receive new PRBS to be transmitted or set up certain parameters. The proposed design has been validated experimentally on a dual comb spectroscopy measurement, where the absorption of a hydrogen cyanide (HCN) gas cell has been successfully characterized.Agencia Estatal de InvestigaciónMinisterio de Ciencia e Innovació

Micro-combs: a novel generation of optical sources

The quest towards the integration of ultra-fast, high-precision optical clocks is reflected in the large number of high-impact papers on the topic published in the last few years. This interest has been catalysed by the impact that high-precision optical frequency combs (OFCs) have had on metrology and spectroscopy in the last decade [1–5]. OFCs are often referred to as optical rulers: their spectra consist of a precise sequence of discrete and equally-spaced spectral lines that represent precise marks in frequency. Their importance was recognised worldwide with the 2005 Nobel Prize being awarded to T.W. Hänsch and J. Hall for their breakthrough in OFC science [5]. They demonstrated that a coherent OFC source with a large spectrum – covering at least one octave – can be stabilised with a self-referenced approach, where the frequency and the phase do not vary and are completely determined by the source physical parameters. These fully stabilised OFCs solved the challenge of directly measuring optical frequencies and are now exploited as the most accurate time references available, ready to replace the current standard for time. Very recent advancements in the fabrication technology of optical micro-cavities [6] are contributing to the development of OFC sources. These efforts may open up the way to realise ultra-fast and stable optical clocks and pulsed sources with extremely high repetition-rates, in the form of compact and integrated devices. Indeed, the fabrication of high-quality factor (high-Q) micro-resonators, capable of dramatically amplifying the optical field, can be considered a photonics breakthrough that has boosted not only the scientific investigation of OFC sources [7–13] but also of optical sensors and compact light modulators [6,14]

Advanced Photonic Sciences

The new emerging field of photonics has significantly attracted the interest of many societies, professionals and researchers around the world. The great importance of this field is due to its applicability and possible utilization in almost all scientific and industrial areas. This book presents some advanced research topics in photonics. It consists of 16 chapters organized into three sections: Integrated Photonics, Photonic Materials and Photonic Applications. It can be said that this book is a good contribution for paving the way for further innovations in photonic technology. The chapters have been written and reviewed by well-experienced researchers in their fields. In their contributions they demonstrated the most profound knowledge and expertise for interested individuals in this expanding field. The book will be a good reference for experienced professionals, academics and researchers as well as young researchers only starting their carrier in this field

Ultrafast coherent control and multidimensional spectroscopy on the nanoscale

Strüber C. Ultrafast coherent control and multidimensional spectroscopy on the nanoscale. Bielefeld: Universität Bielefeld; 2014.The combination of femtosecond polarization pulse shaping and time-resolved photoemission electron microscopy (TR-PEEM) enables the ultrafast coherent control of optical near-fields at nanostructured surfaces. The optical excitation is confined at locations separated by sub-wavelength spatial distance as well as femtosecond temporal delay providing the possibility of ultrafast spatiotemporal spectroscopy on the nanoscale. 2D nanoscopy is a nonlinear spectroscopy technique based on coherent optical 2D spectroscopy. Collinear sequences of ultrashort laser pulses with variable relative delays and phases transfer the local electron distribution into excited electronic states which is finally leading to localized electron emission. The local photoemission yield is detected via TR-PEEM permitting the retrieval of local spectroscopic information via phase cycling and Fourier transformation of the pulse delays. Ultrafast coherent control and 2D nanoscopy is applied to investigate artificially nanostructured devices as well as corrugated silver surfaces, which are relevant for SERS, and localization of photonic modes in amorphous silicon thin-film solar cells