Silicon photonic Bragg-based devices : hardware and software

L'avènement de la photonique intégrée a attiré beaucoup de recherche et d'attention industrielle au cours des deux dernières décennies, plusieurs croyant qu'il s'agit d'une révolution équivalente à la microélectronique. Tout en tirant parti des procédés de fabrication de masse hérités de la microélectronique, la photonique sur silicium est compacte, éconergitique et permet l'intégration complète de dispositifs et de circuits photoniques à l'échelle nanométrique pour des applications cruciales dans les télécommunications, la détection et le calcul optique. À l'instar des débuts de la microélectronique, les efforts de recherche actuels en photonique sur silicium sont principalement consacrés à la proposition, à la conception et la caractérisation de composants standardisés en vue d'une éventuelle intégration de masse dans des circuits photoniques. Les principaux défis associés à ce développement comprennent la complexité de la théorie électromagnétique dans le fonctionnement des dispositifs, les variations et les non-uniformités du procédé de fabrication limitant les performances, et les ressources informatiques considérables nécessaires pour modéliser avec précision des circuits photoniques complexes. Dans ce mémoire, ces trois limitations sont abordées sous forme de contributions de recherche originales. Basées sur des dispositifs photoniques sur silicium et l'apprentissage machine, les contributions de ce mémoire concernent toutes les réseaux de Bragg intégrés, dont le principe de fonctionnement de base est la réflexion optique sélective en fréquence. Premièrement, un nouveau filtre optique double-bande basé sur les réseaux de Bragg multimodes est introduit pour des applications dans les télécommunications. Deuxièmement, une nouvelle architecture de filtre accordable basée sur un coupleur contra-directionnel à étage unique avec un dispositif de micro-chauffage segmenté permettant des profils de température arbitraires démontre une accordabilité de la bande passante record et des capacités de compensation des erreurs de fabrication lorsqu'opérée par un algorithme de contrôle. Troisièmement, un modèle d'apprentissage machine basé sur un réseau de neurones artificiels est introduit et démontré pour la conception de coupleurs contra-directionnels et le diagnostic de fabrication, ouvrant la voie à la production de masse de systèmes photoniques intégrés basée sur les données.The advent of integrated photonics has attracted a lot of research and industrial attention in the last two decades, as it is believed to be a hardware revolution similar to microelectronics. While leveraging microelectronics-inherited mass-production-grade fabrication processes for full scalability, the silicon photonic paradigm is compact, energy efficient and allows the full integration of nano-scale optical devices and circuits for crutial applications in telecommunications, sensing, and optical computing. Similar to early-day microelectronics, current research efforts in silicon photonics are put toward the proposal, design and characterization of standardized components in sights of eventual black-box building block circuit design. The main challenges associated with this development include the complexity of electromagnetic theory in device operation, the performance-limiting fabrication process variations and non-uniformities, and the considerable computing resources required to accurately model complex photonic circuitry. In this work, these three bottlenecks are addressed in the form of original research contributions. Based on silicon photonic devices and machine learning, the contributions of this thesis pertain to integrated Bragg gratings, whose basic operating principle is frequency-selective optical transmission. First, a novel dual-band optical filter based on multimode Bragg gratings is introduced for applications in telecommunications. Second, a novel tunable filter architecture based on a single-stage contra-directional coupler with a segmented micro-heating device allowing arbitrary temperature profiles demonstrates record-breaking bandwidth tunability and on-chip fabrication error compensation capabilities when operated by a control algorithm. Third, an artificial neural network-based machine learning model is introduced and demonstrated for large-parameter-space contra-directional coupler inverse design and fabrication diagnostics, paving the way for the data-driven mass production of integrated photonic systems

The Photonic Lantern

Photonic lanterns are made by adiabatically merging several single-mode cores into one multimode core. They provide low-loss interfaces between single-mode and multimode systems where the precise optical mapping between cores and individual modes is unimportant.Comment: 45 pages; article unchanged, accepted for publication in Advances in Optics and Photonic

A review of silicon subwavelength gratings: building break-through devices with anisotropic metamaterials

Abstract Silicon photonics is playing a key role in areas as diverse as high-speed optical communications, neural networks, supercomputing, quantum photonics, and sensing, which demand the development of highly efficient and compact light-processing devices. The lithographic segmentation of silicon waveguides at the subwavelength scale enables the synthesis of artificial materials that significantly expand the design space in silicon photonics. The optical properties of these metamaterials can be controlled by a judicious design of the subwavelength grating geometry, enhancing the performance of nanostructured devices without jeopardizing ease of fabrication and dense integration. Recently, the anisotropic nature of subwavelength gratings has begun to be exploited, yielding unprecedented capabilities and performance such as ultrabroadband behavior, engineered modal confinement, and sophisticated polarization management. Here we provide a comprehensive review of the field of subwavelength metamaterials and their applications in silicon photonics. We first provide an in-depth analysis of how the subwavelength geometry synthesizes the metamaterial and give insight into how properties like refractive index or anisotropy can be tailored. The latest applications are then reviewed in detail, with a clear focus on how subwavelength structures improve device performance. Finally, we illustrate the design of two ground-breaking devices in more detail and discuss the prospects of subwavelength gratings as a tool for the advancement of silicon photonics

Gratings photowritten in ion-exchanged glass channel waveguides

Gratings are photowritten in ion-exchanged glass channel waveguides. The transmission of these waveguides shows a rejection dip of almost 20dB. The polarisation dependence of these waveguide gratings is measured and discussed

Inscription of narrow bandwidth bragg gratings in polymer optical fibers

We report on the production and characterization of narrow bandwidth fiber Bragg gratings (FBGs) in two spectral regions using polymer optical fibers (POFs). Narrow bandwidth FBGs are increasingly important for POF transmission systems, WDM technology and sensing applications. Long FBGs with resonance wavelength around 850 nm and 1550 nm were fabricated in several types of polymer optical fibers. The 3 dB FBG bandwidth varies from 0.22 nm down to 0.045 nm considering a Bragg grating length of 10 mm and 25 mm, respectively

Room-Temperature Power-Stabilized Narrow-Linewidth Tunable Erbium-Doped Fiber Ring Laser Based on Cascaded Mach-Zehnder Interferometers with Different Free Spectral Range for Strain Sensing

An automatically power-stabilized (with power fluctuation <0.155 dB), narrow-linewidth (0.0171 nm), wavelength-tunable (10.69 nm) erbium-doped fiber laser has been proposed by cascading two fiber Mach-Zehnder interferometers (MZI) without using any temperature controlling device. One of the MZIs (here called the 1st MZI) is composed of two 3 dB couplers to form interference patterns while the other MZI (here termed the 2nd MZI) is constructed with a tapered seven-core fiber (SCF) and based on the principle of supermode interference. For the two MZIs, the free spectral range (FSR), the passband bandwidth and the extinction ratio (ER) at 1560 nm are 0.37 nm, 0.19 nm, 16.6 dB and 13.93 nm, 7.93 nm, 10.1 dB, respectively. Due to the major difference between the two FSR values, the 1st MZI and the 2nd MZI respectively play a role in controlling the laser linewidth and suppressing the homogeneous broadening effect to reach to a satisfactory level of power stability. The 2nd MZI is also used to fine tune the laser wavelength by applying strain to the tapered SCF (TSCF) over the spectral range of 1570.22-1559.33 nm, with an incremental step of 0.37 nm being used. The side-mode suppression ratio (SMSR) of the tunable fiber laser can be up to 45 dB. By appropriately adjusting the polarization controller, dual wavelength lasing can also be achieved. For single wavelength lasing, the 3 dB laser linewidth is 0.0171 nm. The power fluctuation, without a temperature controlling device being used and operating at room temperature, is found to be less than 0.155 dB over 1 hour while the central wavelength drift is less than 0.19 nm

Photonic RF signal processors

The purpose of this thesis is to explore the emerging possibilities of processing radiofrequency (RF) or microwave signals in optical domain, which will be a key technology to implement next-generation mobile communication systems and future optical networks. Research activities include design and modelling of novel photonic architectures for processing and filtering of RF, microwave and millimeter wave signals of the above mentioned applications. Investigations especially focus on two basic functions and critical requirements in advanced RF systems, namely: • Interference mitigation and high Q tunable filters. • Arbitrary filter transfer function generation. The thesis begins with a review on several state-of-the-art architectures of in-fiber RF signal processing and related key optical technologies. The unique capabilities offered by in-fiber RF signal processors for processing ultra wide-band, high-frequency signals directly in optical domain make them attractive options for applications in optical networks and wide-band microwave signal processing. However, the principal drawbacks which have been demonstrated so far in the in-fiber RF signal processors arc their inflexible or expensive schemes to set tap weights and time delay. Laser coherence effects also limit sampling frequency and introduce additional phase-induced intensity noise

Simultaneous measurement of humidity and temperature based on a partially coated optical fiber long period grating

A humidity and temperature optical fiber sensor based on a long-period grating (LPG), which can provide simultaneous response to both magnitudes, is proposed and demonstrated via experiments. Previously, the LPG was fully coated with humidity sensitive nanostructured polymeric thin films by the Layer-by-Layer (LbL) nano assembly technique. Hence the surrounding refractive index was changed, so provoking wavelength shifts of the attenuation bands of the transmission spectrum. This fully coated LPG was exposed to relative humidity (RH) and temperature tests, varying from 20% to 80% RH and from 25 to 85ºC, respectively. Then, half of the LPG coating was chemically removed and this results in the splitting of the main attenuation band into two different contributions. When this semi-coated LPG was also exposed to RH and temperature tests, the new two attenuation bands presented different behaviors for humidity and temperature. This novel dual-wavelength based sensing method enables the simultaneous measurement of RH and temperature using only one LPG.This work was supported in part by the Spanish Ministry of Economy and Competitiveness - through the projects CICYT-FEDER TEC2013-43679-R and TEC2014-60378-C2-1-R. It was also supported by a UPNA pre-doctoral research grant, by the Program of International Excellence Campus VLC/Campus, by the grant of program SANTIAGO GRISOLIA, and by the Research Excellency Award Program GVA PROMETEO 2013/012.Urrutia, A.; Goicoechea, J.; Ricchiuti, AL.; Barrera Vilar, D.; Sales Maicas, S.; Arregui, FJ. (2016). Simultaneous measurement of humidity and temperature based on a partially coated optical fiber long period grating. Sensors and Actuators B: Chemical. 227(5):135-141. https://doi.org/10.1016/j.snb.2015.12.031S135141227

Subwavelength grating devices in silicon photonics

Subwavelength grating (SWG) waveguides in silicon-on-insulator are emerging as an enabling technology for implementing compact, high-performance photonic integrated devices and circuits for signal processing and sensing applications. We provide an overview of our recent work on developing wavelength selective SWG filters based on Bragg gratings and ring resonators, as well as optical delay lines. These components increase the SWG toolbox and can be used to realize more complex photonic integrated circuits with enhanced or new functionality