Hybrid Integrated Photonic Platforms and Devices

Integrated photonics has the potential to revolutionize optical systems by achieving drastic reductions in their size, weight and power. Remote spectroscopy, free-space communications and high-speed telecommunications are critical applications that would benefit directly from these advancements. However, many such applications require extremely wide spectral bandwidths, leading to significant challenges in their integration. The choice of integrated platform influences the optical transparency and functionality which can be ultimately achieved. In this work, several new platforms and technologies have been developed to meet these needs. First, the silicon-on-lithium-niobate (SiLN) platform is discussed, on which the first compact, integrated electro-optic modulator in the mid-infrared has been demonstrated. Next, results are shown in the development of the all-silicon-optical-platform (ASOP), an ultra-stable suspended membrane approach which offers broad optical transparency from 1.2 to 8.5 um and enables efficient nonlinear frequency conversion in the mid-IR. This fabrication approach is then taken further with anchored-membrane waveguides, (T-Guides) enabling single-mode and single-polarization waveguiding over a span exceeding 1.27 octaves. Afterward, a new photonic technology enabling integrated polarization beam-splitters and polarizers over unprecedented bandwidths is introduced, called topographically anisotropic photonics (TAP). Next, results on high-performance microphotonic chalcogenide glass waveguides are presented. Finally, several integrated photonics concepts suitable for further work will be discussed, such as augmentations to T-Guides and a novel technique for quasi-phase-matching

Fabrication and characterisation of tellurite planar waveguides

Tellurite glasses, which contain Tellurium dioxide as the main component, have some remarkable optical properties which are well recognised and exploited in the bulk optics and fibre fields. They include a high acousto-optic figure of merit, wide mid infrared transparency, the highest optical nonlinearity amongst oxides, and excellent rare earth hosting, etc. Despite these attractive properties, until now, no one has succeeded in fabricating low loss planar waveguides in these materials. This work develops high quality optical planar waveguides in Tellurium dioxide for the first time. The project investigates the materials science for optical Tellurium dioxide films and discovers an appropriate waveguide fabrication method. The thin films have been fabricated by reactive radio frequency magnetron sputtering using a Tellurium target in an oxygen and argon atmosphere. Propagation losses at 1550nm in the planar films are 0.1dB/cm or lower in stoichiometric composition. The properties of films have been also found to be stable with thermal annealing up to 300 degree Celsius. Plasma etching of tellurite glasses has been systematically studied. High quality etching of Tellurium dioxide and chalcogenide glass films has been demonstrated with a Methane/Hydrogen/Argon gas mixture. As a result, a fabrication recipe which produces low loss (0.1dB/cm) planar waveguides has been discovered. The nonlinear coefficient of the sputtered TeO2 has been characterised by self-phase modulation (SPM) experiments and the second order nonlinear coefficient has been measured to be around 25 times that of silica. Significant signal conversion, -4dB, has achieved with large bandwidth of 30nm in the four-wave mixing (FWM) experiment pumped at 1550nm in a slightly normal dispersion waveguide. Erbium doped Tellurium oxide thin films have also been fabricated by co-sputtering of Erbium and Tellurium targets into an Oxygen and Argon atmosphere. The obtained films have been found to have good properties for Erbium doped waveguide amplifiers. The Erbium concentration can be controlled within the range of interest with Erbium/Tellurium ratios ranging from 0.1% to 3% or more. The 1.5 micrometre photoluminescence properties of the films are excellent with effective bandwidth of more that 60nm and intrinsic lifetime of order of 3ms. Despite the fact that there was OH contamination in the films, single mode Erbium doped waveguide amplifiers with high internal gain have been successfully obtained. The 1480nm pumped amplifier achieved internal gain from below 1520nm to beyond 1600nm. The peak gain of 2.8dB/cm and 40nm 3dB gain bandwidth have been accomplished. These results are a major stepping stone towards ""system-on-chip"" optical applications for telecom and mid infrared optics given the multifunctional nature of tellurite materials. -- provided by Candidate

Optimization and design of radio frequency piezoelectric MEMS resonators

Radio frequency (RF) microelectromechanical system (MEMS) resonators employing Lamb waves propagating in piezoelectric thin films have recently attracted much attention since they combine the advantages of the bulk acoustic wave (BAW) and surface acoustic wave (SAW) technologies: high phase velocity and multiple frequencies on a single chip. In particular, aluminum nitride (AlN) resonators based on fundamental symmetric (S0) Lamb mode have shown great promise because they can offer high phase velocities (10,000 m/s), low dispersive phase velocity characteristic, small temperature-induced frequency drift, low motional resistance, and monolithic integration compatibility with complementary metal–oxide–semiconductor (CMOS). However, there are still a few outstanding technical challenges, including spurious modes suppression, quality factor (Q) enhancement, frequency scalability, and electromechanical coupling improvement. These issues obstruct the wide deployment and commercialization of AlN Lamb mode resonators. This dissertation presents comprehensive investigations and solutions to these issues. This thesis is organized as follows: Chapter 1 gives a brief introduction of the basics on piezoelectric MEMS resonators and their promising applications. Chapter 2 first investigates the various available Lamb wave modes in AlN and then identifies the S0 mode as the promising resonator solution to overcome several challenges associated with SOA. Chapter 2 also discusses several outstanding challenges with S0 devices, including spurious mode suppression, Q enhancement, scaling resonant frequency, and enlarging fractional bandwidth. In response, Chapters 3-7 address these outstanding challenges by developing new designs and models, resorting to new acoustic mode, and incorporating new piezoelectric material. More specifically, Chapter 3 proposes two techniques to suppress the spurious modes in the responses of S0 resonators, namely mode conversion and mode shifting. Chapter 4 address the challenge of a conventionally vague question of reflection at the interface between released and unreleased regions in S0 resonators, and then demonstrates Q enhanced resonators with defined released regions achieved by a sandbox process. Chapter 5 first characterizes the S1 Lamb mode and optimizes its resonator configuration. A high-frequency S1 resonator at 3.5 GHz with a coupling of 3.5% is fabricated and demonstrated. Chapter 6 presents a hybrid filtering topology with a mode conversion AlN S0 resonator and lumped elements for widening the bandwidths of resonator-based filters. Chapter 7 proposes lithium niobate (LiNbO3) multilayered resonators with large electromechanical coupling, structure robustness, and good temperature stability. The analysis of Bragg reflectors, resonator simulation, stress control, fabrication, and measurements are covered in this chapter

GaN directional couplers for integrated quantum photonics

Large cross-section GaN waveguides are proposed as a suitable architecture to achieve integrated quantum photonic circuits. Directional couplers with this geometry have been designed with aid of the beam propagation method and fabricated using inductively coupled plasma etching. Scanning electron microscopy inspection shows high quality facets for end coupling and a well defined gap between rib pairs in the coupling region. Optical characterization at 800 nm shows single-mode operation and coupling-length-dependent splitting ratios. Two photon interference of degenerate photon pairs has been observed in the directional coupler by measurement of the Hong-Ou-Mandel dip with 96% visibility.Comment: 4 pages, 5 figure

New Photonic devices based on NLO(non-linear optical) crystalline waveguides

El RbTiOPO4 és un cristall de òptica no lineal amb alts coeficients electró-òptics i un llindar de dany òptic elevat, això el converteix en un material potencial per aplicacions electro-òptiques. Actualment hi ha un interès en el desenvolupament de components òptics basats en materials dielèctrics, identificat com un tema de recerca punter per Europa Horitzó 2020. La finalitat d’aquesta tesis és explorar el RTP com a plataforma dielèctrica per dispositius fotònics, que tenen aplicacions en les telecomunicacions i en el sensat biològic. En aquesta tesis s’han crescut materials monocristal•lins en volum de RTP, K:RTP i Na:KTP pel mètode de Top seeded solution growth. Els cristalls obtinguts són òptims per ser utilitzats com a plataforma per fabricar guies d’ona i com a substrats pel creixement de capes epitaxials. Capes epitaxials de (Yb,Nb):RTP sobre RTP(001), RTP sobre K:RTP(001) i K.:RTP(100), i KTP sobre Na:KTP(001) s’han crescut per la metodologia de liquid phase epitaxy. Aquesta metodologia ha permès obtenir capes monocristal•lines amb una interfase d’alta qualitat cristal•lina La fabricació de guies d’ona ha esta realitzada per RIE i ICP-RIE. Es reporta en aquesta tesis, un avanç en el coneixement del procés de etching del RTP. El mètode d’intercanvi iònic, amb Cs+ com ió, s’ha utilitzat per produir guies rectes, corbes i MZ. Degut a l’alta conductivitat iònica del RTP al llarg de la direcció c cristal•logràfica, l’ intercanvi iònic és altament factible i gairebé unidireccional. S’ha obtingut exitosament el procés de guiat de llum en totes les guies d’ona fabricades. Pels Y-splitters i els MZ fabricats sobre els cristalls RTP/(Yb,Nb):RTP/RTP(001) estructurats amb RIE sobre la capa activa o bé el substrat, la guia obtinguda és monomode amb polarització TM a 1550 nm. Les pèrdues de propagació són de 3.5 dB/cm. Per les guies d’ona rectes fabricades sobre RTP/(Yb,Nb):RTP/RTP(001) per estructuració del recobriment per ICP-RIE, les pèrdues de propagació són 0.376 dB/cm a 1550 nm.El RbTiOPO4 es un cristal de óptica no-lineal con altos coeficientes electro ópticos y un límite de daño óptico elevado, eso lo convierte en una potencial material para aplicaciones electrópticas. Actualmente existe un gran interés en el desarrollo de componentes ópticos basados en materiales dieléctricos, esto ha sido identificado como un tema puntero de investigación por Europa Horizonte 2020. La finalidad de esta tesis es explorar el RTP cómo plataforma dieléctrica para dispositivos fotónicos, que tienen aplicaciones en les telecomunicaciones y en el sensado biológico. En esta tesis, se han crecido materiales monocristalinos en volumen de RTP, K:RTP y Na:KTP por el método de Top seeded solution growth. Los cristales crecidos son óptimos para ser utilizados como plataforma para fabricar guías de onda y como sustratos para el crecimiento de capas epitaxiales. Capas epitaxiales de (Yb,Nb):RTP sobre RTP(001), RTP sobre K:RTP(001) yK.:RTP(100), i KTP sobre Na:KTP(001) se han crecido mediante la metodología de liquid phase epitaxy. Esta metodología ha permitido obtener capes monocristalinas con una interfase de alta calidad cristalina. La fabricación de guías de onda se ha hecho por RIE y ICP-RIE: Se reporta en esta tesis un avance en el conocimiento del proceso de etching en el RTP. El método de intercambio iónico, con Cs+ como ion, se ha utilizado para producir guías de onda rectas, curvas y MZ. Debido a la alta conductividad iónica del RTP a lo largo de la dirección c cristalográfica, el intercambio iónico es altamente factible y casi unidireccional. Se ha obtenido el guiado con éxito en todas las guías de onda fabricadas. En los Y-Splitters y MZ fabricados sobre los cristales RTP/(Yb,Nb):RTP/RTP(001) estructurados con RIE sobre la capa activa o bien el sustrato, la guía obtenida es monomodo con la polarización TM a 1550 nm. Las pérdidas de propagación son de 3.5 dB/cm. Para las guías de onda rectes fabricadas sobre RTP/(Yb,Nb):RTP/RTP(001) por estructuración del recubrimiento por ICP-RIE, las pérdidas por propagación son de 0.376 dB/cm a 1550 nm.RbTiOPO4 is a non-linear optical crystal with high electro-optic coefficients and high optical damage threshold, which makes it suitable for electro-optic applications. There’s a current interest in developing dielectric based photonic components for integrated optics, identified as a topic of research by the Europe Horizon 2020. The aim of this thesis is to explore RTP for dielectric based photonic platforms, which have applications in telecommunications and biosensing. In this thesis is reported the successful grow of bulk single crystals of RTP, K:RTP and Na:RTP by Top Seeded Solution Growth technique. The crystals obtained are suitable to be used as platforms to fabricate optical waveguides and for substrates for growth of epitaxial layers. Epitaxial layers of (Yb,Nb):RTP were grown on RTP(001), RTP was grown on K:RTP(001) and K:RTP(100) and KTP was grown on Na:KTP(001) by Liquid phase epitaxy. This methodology allows obtaining a single crystalline layer, with high quality crystalline interface. Waveguide fabrication was performed by RIE and ICP-RIE. Advancement in this etching process on RTP is reported in this thesis. Cs+ ion exchange method was used to produce straight, bends and MZ waveguides. Due to the RTP high ionic conductivity along the c crystallographic direction, ion exchange is highly feasible and almost unidirectional. Waveguiding of the fabricated channel waveguides has been successful. For the Y-Splitter and MZ waveguides fabricated on the RTP/(Yb,Nb):RTP/RTP(001) crystals, by structuring the active layer or the substrate by RIE, the waveguides obtained were single mode in TM polarization at 1550 nm. The propagation loss was 3.5 dB/cm. For straight waveguides fabricated on the RTP/(Yb,Nb):RTP/RTP(001), by structuring the cladding by ICP-RIE, the propagation losses were 0.376 dB/cm at 1550 nm. The waveguides fabricated by Cs+ ion exchange have larger losses due to inhomogeneity on the Cs exchange among different ferroelectric domains present in the structure