Coherent optical signal processing systems typically require dynamic, low-loss phase changes of an optical signal. Waveform generation employing phase modulation is an important application area. In particular, laser radar systems have been shown to perform better with non-linear frequency chirps. This work shows how dynamically tunable integrated optical ring resonators are able to produce such phase changes to a signal in an effective manner and offer new possibilities for the detection of phase-modulated optical signals. When designing and fabricating dynamically tunable integrated optical ring resonators for any application, system level requirements must be taken into account. For frequency chirped laser radar systems, the primary system level requirements are good long range performance and fine range resolution. These mainly depend on the first sidelobe level and mainlobe width of the autocorrelation of the chirp. Through simulation, the sidelobe level and mainlobe width of the autocorrelation of the non-linear frequency modulated chirp generated by a series of integrated optical ring resonators is shown to be significantly lower than the well-known tangent-FM chirp. Proof-of-concept experimentation is also important to verify simulation assumptions. A proof-of-concept experiment employing thermally tunable Silicon-Nitride integrated optical ring resonators is shown to generate non-linear frequency modulated chirp waveforms with peak instantaneous frequencies of 28 kHz. Besides laser radar waveform generation, three other system level applications of dynamically tunable integrated optical ring resonators are explored in this work. A series of dynamically tunable integrated optical ring resonators is shown to produce constant dispersion which can then help extract complex spectral information. Broadband photonic RF phase shifting for beam steering of a phased array antenna is also shown using dynamically tunable integrated optical ring resonators. Finally all-optical pulse compression for laser radar using dynamically tunable integrated optical ring resonators is shown through simulation and proof-of-concept experimentation.

Integrated microwave photonics changes the scaling laws of information and communication systems offering architectural choices that combine photonics with electronics to optimize performance, power, footprint and cost. Application Specific Photonic Integrated Circuits, where particular circuits/chips are designed to optimally perform particular functionalities, require a considerable number of design and fabrication iterations leading to long-development times and costly implementations. A different approach inspired by electronic Field Programmable Gate Arrays is the programmable Microwave Photonic processor, where a common hardware implemented by the combination of microwave, photonic and electronic subsystems, realizes different functionalities through programming. Here, we propose the first-ever generic-purpose Microwave Photonic processor concept and architecture. This versatile processor requires a powerful end-to-end field-based analytical model to optimally configure all their subsystems as well as to evaluate their performance in terms of the radiofrequency gain, noise and dynamic range. Therefore, we develop a generic model for integrated Microwave Photonics systems. The key element of the processor is the reconfigurable optical core. It requires high flexibility and versatility to enable reconfigurable interconnections between subsystems as well as the synthesis of photonic integrated circuits. For this element, we focus on a 2-dimensional photonic waveguide mesh based on the interconnection of tunable couplers. Within the framework of this Thesis, we have proposed two novel interconnection schemes, aiming for a mesh design with a high level of versatility. Focusing on the hexagonal waveguide mesh, we explore the synthesis of a high variety of photonic integrated circuits and particular Microwave Photonics applications that can potentially be performed on a single hardware. In addition, we report the first-ever demonstration of such reconfigurable waveguide mesh in silicon. We demonstrate a world-record number of functionalities on a single photonic integrated circuit enabling over 30 different functionalities from the 100 that could be potentially obtained with a simple seven hexagonal cell structure. The resulting device can be applied to different fields including communications, chemical and biomedical sensing, signal processing, multiprocessor networks as well as quantum information systems. Our work is an important step towards this paradigm and sets the base for a new era of generic-purpose photonic integrated systems. / Los dispositivos integrados de fotónica de microondas ofrecen soluciones optimizadas para los sistemas de información y comunicación. Generalmente, están compuestos por diferentes arquitecturas en las que subsistemas ópticos y electrónicos se integran para optimizar las prestaciones, el consumo, el tamaño y el coste del dispositivo final. Hasta ahora, los circuitos/chips de propósito específico se han diseñado para proporcionar una funcionalidad concreta, requiriendo así un número considerable de iteraciones entre las etapas de diseño, fabricación y medida, que origina tiempos de desarrollo largos y costes demasiado elevados. Una alternativa, inspirada por las FPGA (del inglés Field Programmable Gate Array), es el procesador fotónico programable. Este dispositivo combina la integración de subsistemas de microondas, ópticos y electrónicos para realizar, mediante la programación de los mismos y sus interconexiones, diferentes funcionalidades. En este trabajo, proponemos por primera vez el concepto del procesador de propósito general, así como su arquitectura. Además, con el fin de diseñar, optimizar y evaluar las prestaciones básicas del dispositivo, hemos desarrollado un modelo analítico extremo a extremo basado en las componentes del campo electromagnético. El modelo desarrollado proporciona como resultado la ganancia, el ruido y el rango dinámico global para distintas configuraciones de modulación y detección, en función de los subsistemas y su configuración. El elemento principal del procesador es su núcleo óptico reconfigurable. Éste requiere un alto grado de flexibilidad y versatilidad para reconfigurar las interconexiones entre los distintos subsistemas y para sintetizar los circuitos para el procesado óptico. Para este subsistema, proponemos el diseño de guías de onda reconfigurables para la creación de mallados bidimensionales. En el marco de esta tesis, hemos propuesto dos nuevos nodos de interconexión óptica para mallas reconfigurables, con el objetivo de obtener un mayor grado de versatilidad. Una vez escogida la malla hexagonal para el núcleo del procesador, hemos analizado la configuración de un gran número de circuitos fotónicos integrados y de funcionalidades de fotónica de microondas. El trabajo se ha completado con la demonstración de la primera malla reconfigurable integrada en un chip de silicio, demostrando además la síntesis de 30 de las 100 funcionalidades que potencialmente se pueden obtener con la malla diseñada compuesta de 7 celdas hexagonales. Este hecho supone un record frente a los sistemas de propósito específico. El sistema puede aplicarse en diferentes campos como las comunicaciones, los sensores químicos y biomédicos, el procesado de señales, la gestión y procesamiento de redes y los sistemas de información cuánticos. El conjunto del trabajo realizado representa un paso importante en la evolución de este paradigma, y sienta las bases para una nueva era de dispositivos fotónicos de propósito general. / Els dispositius integrats de Fotònica de Microones oferixen solucions optimitzades per als sistemes d'informació i comunicació. Generalment, estan compostos per diferents arquitectures en què subsistemes òptics i electrònics s'integren per a optimitzar les prestacions, el consum, la grandària i el cost del dispositiu final. Fins ara, els circuits/xips de propòsit específic s'han dissenyat per a proporcionar una funcionalitat concreta, requerint així un nombre considerable d'iteracions entre les etapes de disseny, fabricació i mesura, que origina temps de desenrotllament llargs i costos massa elevats. Una alternativa, inspirada per les FPGA (de l'anglés Field Programmable Gate Array), és el processador fotònic programable. Este dispositiu combina la integració de subsistemes de microones, òptics i electrònics per a realitzar, per mitjà de la programació dels mateixos i les seues interconnexions, diferents funcionalitats. En este treball proposem per primera vegada el concepte del processador de propòsit general, així com la seua arquitectura. A més, a fi de dissenyar, optimitzar i avaluar les prestacions bàsiques del dispositiu, hem desenrotllat un model analític extrem a extrem basat en els components del camp electromagnètic. El model desenrotllat proporciona com resultat el guany, el soroll i el rang dinàmic global per a distintes configuracions de modulació i detecció, en funció dels subsistemes i la seua configuració. L'element principal del processador és el seu nucli òptic reconfigurable. Este requerix un alt grau de flexibilitat i versatilitat per a reconfigurar les interconnexions entre els distints subsistemes i per a sintetitzar els circuits per al processat òptic. Per a este subsistema, proposem el disseny de guies d'onda reconfigurables per a la creació de mallats bidimensionals. En el marc d'esta tesi, hem proposat dos nous nodes d'interconnexió òptica per a malles reconfigurables, amb l'objectiu d'obtindre un major grau de versatilitat. Una vegada triada la malla hexagonal per al nucli del processador, hem analitzat la configuració d'un gran nombre de circuits fotónicos integrats i de funcionalitats de fotónica de microones. El treball s'ha completat amb la demostració de la primera malla reconfigurable integrada en un xip de silici, demostrant a més la síntesi de 30 de les 100 funcionalitats que potencialment es poden obtindre amb la malla dissenyada composta de 7 cèl·lules hexagonals. Este fet suposa un rècord enfront dels sistemes de propòsit específic. El sistema pot aplicarse en diferents camps com les comunicacions, els sensors químics i biomèdics, el processat de senyals, la gestió i processament de xarxes i els sistemes d'informació quàntics. El conjunt del treball realitzat representa un pas important en l'evolució d'este paradigma, i assenta les bases per a una nova era de dispositius fotónicos de propòsit general. / Pérez López, D. (2017). Integrated Microwave Photonic Processors using Waveguide Mesh Cores [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/91232 / TESIS

La technologie photonique-RF offre une alternative intéressante à l'approche purement électronique dans différents systèmes micro-ondes pour des applications militaires, spatiales et civiles. Un composant original, l'oscillateur optoélectronique (OEO), permet la génération de signaux RF stables et à haute pureté spectrale. Il est basé sur une liaison photonique micro-onde utilisée comme boucle de rétroaction et comportant soit une fibre longue, soit un résonateur à fort coefficient de qualité. Différentes études ont été menées au cours de cette thèse afin d'optimiser et d'améliorer la performance en termes de stabilité et de bruit de phase pour le cas de l'OEO à résonateur. La caractérisation fine et la modélisation des résonateurs est une première étape de la conception globale du système. La métrologie du résonateur optique est réalisée par une technique originale, dite de spectroscopie RF. Les résultats expérimentaux ont révélé que cette technique permet d'une part d'identifier le régime de couplage du résonateur et d'autre part de déterminer avec une grande précision tous les paramètres d'un dispositif résonant, comme les facteurs de qualité interne et externe ou les facteurs de couplage. Une deuxième étude a été orientée vers l'implémentation d'un modèle non-linéaire fiable du dispositif. Dans un tel modèle, la photodiode rapide nécessitait une description plus précise, dans le but de contrôler la conversion du bruit d'amplitude optique en bruit de phase de l'OEO. Un nouveau modèle non-linéaire d'une photodiode hyperfréquence a été développé sous un logiciel commercial: Agilent ADS. Ce nouveau modèle rend effectivement compte de cette conversion de bruit. Une puissance optique optimale à l'entrée de la photodiode a été déterminée, pour laquelle la contribution de RIN du laser au bruit de phase RF pourrait être négligeable. La performance de l'OEO est affectée par diverses perturbations entrainant un décalage en fréquence entre la fréquence du laser et la fréquence de résonance du résonateur. Il est donc important d'utiliser un système de stabilisation pour contrôler cette différence de fréquence. Des séries d'expériences et de tests ont été menées pour étudier la possibilité, d'une part, de remplacer l'électronique commerciale utilisée auparavant pour le système de verrouillage en fréquence (boucle de Pound-Drever-Hall) par une électronique faible bruit et, d'autre part, d'utiliser un laser à semi-conducteur. Un bilan de ces approches est présenté. / RF photonics technology offers an attractive alternative to classical electronic approaches in several microwave systems for military, space and civil applications. One specific original architecture dubbed as optoelectronic oscillator (OEO) allows the generation of spectrally pure microwave reference frequencies, when the microwave photonic link is used as a feedback loop. Various studies have been conducted during this thesis on the OEO, especially the one that is based on fiber ring resonators, in order to optimize and improve its phase noise performance and its long-term stability. Precise characterization and modeling of the optical resonator are the first step towards overall system design. The resonator metrology is performed using an original approach, known as RF spectral characterization. The experimental results have demonstrated that this technique is helpful for the identification of the resonator's coupling regime and the accurate determination of the main resonator parameters such as the intrinsic and extrinsic quality factors or the coupling coefficients. A second study was directed toward implementing a reliable nonlinear model of the system. In such a model, the fast photodiode require an accurate description, in order to reduce the conversion of the optical amplitude noise into RF noise. A new nonlinear equivalent circuit model of a fast photodiode has been implemented in a microwave circuit simulator: Agilent ADS. This new model is able to describe the conversion of the laser relative intensity noise (RIN) into microwave phase noise at the photodiode output. An optimal optical power at the photodiode's input has been identified, at which the contribution of the laser RIN in RF phase noise is negligible. When it comes to practical applications, the desired performance of an OEO is threatened by various disturbances that may result in a frequency shift of both the laser frequency and the transmission peak of the resonator, which causes a malfunction of the OEO. Therefore it is desirable to use a stabilization system to control the difference between the laser frequency and the resonator frequency. A series of tests and experiments have been carried out to investigate the possibility, on one hand, to replace the commercial servo controller that was used up until now in the Pound-Drever-Hall loop, with a low noise homemade one and, on the other hand, to use a semiconductor laser to reduce the system size. A detailed review of these approaches is presented.

A novel photonic frequency discriminator has been developed. The discriminator utilizes a Mach Zehnder interferometer-assisted ring resonator to achieve enhanced linearity. A numerical frequency-domain two-tone test is performed to evaluate the unique design of the discriminator, particularly for suppression of the third order intermodulation distortion. The discriminator is switchable between linear-intensity and linear-field regimes by adjusting a phase delay on one arm of the Mach Zehnder interferometer. Through the simulation, the linear<intensity discriminator is shown to be advantageous. The discriminator is an optical ring resonator-Mach Zehnder interferometer synthesized passive filter. The ring resonator is made of Arsenic trisulfide (As2S3) and the bus waveguide is a Titanium<diffused Lithium niobate (LiNbO3) waveguide. This As2S3 ring-on-Ti:LiNbO3 hybrid structure offers electro-optic tunability of the device owing to a strong electro-optic effect of the substrate material. A large optical confinement factor achieved by vertical integration of the As2S3 strip waveguide on a LiNbO3 substrate enables a low loss ring resonator. The Mach Zehnder interferometer is formed by the optical path length difference of the birefringent LiNbO3 substrate instead of a physical Y-branch structure, which makes the fabrication tolerances relaxed. In order for this highly birefringent device to be characterized, each polarization mode must be measured separately. A novel algorithm which can measure the wavelength-swept Jones matrix including its phase response is devised. The efficacy of the algorithm is demonstrated by characterizing a ring resonator. Finally, the fabricated discriminator is fully characterized using the algorithm.

<p dir="ltr">Optical frequency combs have revolutionized metrology and advanced other fields such as RF photonics and astronomy. While powerful, they can be bulky, expensive, and difficult to manufacture. This tends to limit uses in real-world scenarios. Within the last decade or so, coherent frequency combs have begun to be generated in millimeter-scale, CMOS fabrication-compatible nonlinear crystals. These so-called “microcombs” have led to hopes of overcoming deployability constraints of more traditional bulk combs.</p><p dir="ltr">One of the first applications for \textit{bulk} frequency combs after their explosion in 2000 was the optical atomic clock. It promised extreme long-term time stability better than that of the Cesium clock that currently defines the SI second. More recently, interest in a fully portable optical atomic clock has grown. Such a device could reliably keep time even without the aid of GPS references, and potentially with greater accuracy than current GPS synchronization can provide.</p><p dir="ltr">Frequency combs have also been used to sample electrical signals more rapidly than traditional electronics can accomplish. This has been used to achieve dramatically increased effective frequency bandwidths for signal detection architectures. One can imagine how this capability would be beneficial in a portable (microcomb-driven) form: a lightweight, comb-enhanced receiver able to capture a broadband snapshot of its surrounding electromagnetic environment could be a powerful tool.</p><p dir="ltr">Timekeeping and RF photonics are the primary applications of microcombs focused upon here. I will attempt to roughly summarize important concepts and highlight relevant work in both subjects in the Introduction. Then I will move a step closer to the hands-on lab work that has largely kept me preoccupied over the last several years and describe important or commonly-employed Methods for experiments. A collection of three journal manuscripts (two published, and the third recently submitted) will follow in the Publications chapter, highlighting some experimental results. Finally, I will conclude with a brief Outlook.</p>