Дисертації з теми "Photonic crystal cavity (PhC cavity)"

In recent years, Silicon Photonics has emerged as a promising technology for cost-effective fabrication of photonic components and integrated circuits, the application of which is recently expanding in technological fields beyond tele- and data-communications, such as sensing and biophotonics. Compact, energy-efficient laser sources with precise wavelength control are crucial for the aforementioned applications. However, practical, efficient, electrically-pumped lasers on Silicon or other group IV elements are still absent, owing to the indirect bandgap of those materials. Consequently, the integration of III-V compounds on Silicon currently appears to be the most viable route to the realization of such lasers. In this thesis, I present and explore the potential of an External Cavity (EC) hybrid III-V/Silicon laser design, comprising a III-V-based Reflective Semiconductor Optical Amplifier (RSOA) and a Silicon reflector chip, based on a two-dimensional Photonic Crystal (PhC) cavity vertically coupled to a low-refractive-index dielectric waveguide. The vertically coupled system functions as a wavelength-selective reflector, determining the lasing wavelength. Based on this architecture mW-level continuous-wave (CW) lasing at room temperature was shown both in a fiber-based long cavity scheme and die-based short cavity scheme, with SMSR of > 25 dB and > 40 dB, respectively. Furthermore, by electrically modulating the refractive index of the PhC cavity in the reflector chip, tuning of the emitted wavelength was achieved in the die-based short cavity EC laser configuration. In this way, I demonstrated the suitability of the examined EC configuration for direct frequency modulation. The proposed scheme eliminates the need for wavelength matching between the laser source and a resonant modulator, and reveals the potential of employing low-power-consumption resonant modulation in practical Silicon Photonics applications.

Today's information and communication industry is confronted with a serious bottleneck due to the prohibitive energy consumption and limited transmission bandwidth of electrical interconnects. Silicon photonics offers an alternative by transferring data optically and thereby eliminating the restriction of electrical interconnects over distance and bandwidth. Due to the inherent advantage of using the same material as that used for the electronic circuitry, silicon photonics also promises high volume and low cost production plus the possibility of integration with electronics. In this thesis, I introduce an all-silicon optical interconnect architecture that promises very high integration density along with very low energy consumption. The basic building block of this architecture is a vertically coupled photonic crystal cavity-waveguide system. This vertically coupled system acts as a highly wavelength selective filter. By suitably designing the waveguide and the cavity, at resonance wavelength of the cavity, large drop in transmission can be achieved. By locally modulating the material index of the cavity electrically, the resonance wavelength of the cavity can be tuned to achieve modulation in the transmission of the waveguide. The detection scheme also utilizes the same vertically coupled system. By creating crystal defects in silicon in the cavity region, wavelength selective photodetection can be achieved. This unique vertical coupling scheme also allows us to cascade multiple modulators and detectors coupled to a single waveguide, thus offering huge channel scalability and design and fabrication simplicity. During this project, I have implemented this vertical coupling scheme to demonstrate modulation with extremely low operating energy (0.6 fJ/bit). Furthermore, I have demonstrated cascadeability and multichannel operation by using a comb laser as the source that simultaneously drives five channels. For photodetection, I have realized one of the smallest wavelength selective detector with responsivity of 0.108 A/W at 10 V reverse bias with a dark current of 9.4 nA. By cascading such detectors I have also demonstrated a two-channel demultiplexer.

Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2019
Cataloged from PDF of thesis. "The Table of Contents does not accurately represent the page numbering"--Disclaimer page.
Includes bibliographical references (pages 45-47).
The growing demand for efficient infrared sensors for light ranging, thermal-cameras, and soon, free-space optical communications has yet to be answered. In this study, we use polycrystalline silicon in conjunction with a photonic crystal cavity (PhCC) to enhance light absorption for efficient sensing. We present a cost-effective alternative to the current III-V detectors. By adding a 2D-PhC resonator layer, surface-illuminated light can be confined within a 10 micron region with great intensity, leading to a higher effective path-length and improved detector responsivity. More than 1000 variants of this detector are designed and implemented in a 65nm CMOS process. Using a nearest neighbor method, we find the optimized designs. We validate experimental findings by simulating mode behavior of the PhCC structures using FDTD models. In addition, a numerical study on cavity parameter optimization for achieving high Q-factors and extinction ratios specifically for surface-illumination is presented. We report polysilicon PhCC-enhanced sensors with Q-factors of 6500 resulting in responsivities at 1300nm up to 0.13mA/W -a 25x improvement over non-resonant surface-illuminated Silicon detectors.
by Ebrahim Dakhil Al Johani.
S.B.
S.B. Massachusetts Institute of Technology, Department of Physics

High quality factor, small mode volume photonic crystal cavities and single emitter quantum dots are the topic of this dissertation. They are studied as both a combined system with InAs quantum dots grown in the center of a 2D GaAs photonic crystal slab nanocavity as well as individually. The individual studies are concerned with passive 1D silicon photonic crystal nanobeam cavities and deterministic, site-selectively grown arrays of InAs quantum dots.For the combined system, strong light matter coupling in a quantum dot photonic crystal slab nanocavity is discussed. Vacuum Rabi splitting is seen when the interaction strength exceeds the dissipative processes of the coupled system. In order to increase the probability of a spectral matching between cavity modes and quantum dot transitions, a technique for condensing an inert gas onto a sample is used. This can lead to a spectral tuning of up to 4 nm of the cavity mode with minimal change in the cavity quality factor while maintaining cryogenic temperatures down to 4 K. The effect of a large density of quantum dots within a quantum dot photonic crystal slab nanocavity is also addressed. Gain and absorption effects are found to occur, changing the cavity emission linewidth from that of its intrinsic value, as well as lasing with a low number of quantum dots and with high spontaneous emission coupling factors. Additionally, methods for improving the quality factor of GaAs photonic crystal cavities and better understanding different loss mechanisms are discussed.In the individual studies, the site-selective growth of InAs quantum dots on pre-structured GaAs wafers is shown as a promising method for the eventual deterministic fabrication of photonic crystal cavities to single quantum dots. An in-situ annealing step is used to reduce quantum dot density, helping ensure that dots are not grown in unwanted locations.Given silicon's potential for achieving higher quality factors than its GaAs counterpart, a study of 1D passive silicon photonic crystal nanobeam cavities is carried out. Transmission through a coupled microfiber is used to measure quality factors of the cavities and compared with that of a crossed polarized resonant scattering measurement.

The topic of this dissertation is photonic crystal nanocavities for semiconductor cavity quantum electrodynamics. For the purposes of this study, these nanocavities may be one dimensional (1D) or two dimensional (2D) in design. The 2D devices are active and contain embedded InAs quantum dots (QDs), whereas the 1D devices are passive and contain no active emitters. The 2D photonic crystal nanocavities are fabricated in a slab of GaAs with a single layer of InAs QDs embedded in the slab. When a cavity mode substantially overlaps the QD ensemble, the dots affect the linewidths of the observed modes, leading to broadening of the linewidth at low excitation powers due to absorption and narrowing of the linewidths at high excitation powers due to gain when the QD ensemble absorption is saturated. We observe lasing from a few QDs in such a nanocavity. A technique is discussed with allows us to tune the resonance wavelength of a nanocavity by condensation of an inert gas onto the sample, which is held at cryogenic temperatures. The structural quality at the interfaces of epitaxially grown semiconductor heterostructures is investigated, and a growth instability is discovered which leads to roughness on the bottom of the GaAs slabs. Adjustment of MBE growth parameters leads to the elimination of this roughness, and the result is higher nanocavity quality factors. A number of methods for optimizing the fabrication of nanocavities is presented, which lead to higher quality factors. It is shown that some fundamental limiting factor, not yet fully understood, is preventing high quality factors at wavelengths shorter than 950 nm. Silicon 1D devices without active emitters are investigated by means of a tapered microfiber loop, and high quality factors are observed. This measurement technique is compared to a cross-polarized resonant scattering method. The quality factors observed in the silicon nanocavities are higher than those observed in GaAs, consistent with our observation that quality factors are in general higher at longer wavelengths.

A photonic crystal (PC) structure for trapping a 50nm radius dielectric particle at a precise location on a silicon surface in an organic solvent environment has been designed and all of its key components have been fabricated. The high gradient of electric field intensity in a PC cavity mode, with wavelength ~ 1.5 microns, exerts a radiation force toward the center of the cavity. The Finite Difference Time Domain (FDTD) modeling method was used to design a symmetric (input/output) structure that consists of two grating couplers, two parabolic tapered waveguides, two single mode ridge waveguides, two photonic crystal waveguides and a single three-missing-hole (L3) PC cavity. The radiation force on the dielectric sphere was exactly calculated using FDTD simulations to evaluate the Maxwell Stress Tensor (MST) in the presence of the particle to be trapped. This result was compared to that obtained using the simpler dipole approximation, and good agreement between them was found. The fabrication of the structure was done by electron beam lithography and chlorine plasma etching. The Q factors for some of the fabricated samples were measured from the cavity enhanced photoluminescence emission of PbSe quantum dots deposited on the sample surface. A vertical Q factor of 3600 (in vacuum environment) was measured for an isolated cavity, which corresponds to a Qv of 3800 ( in solvent environment) in the FDTD simulations. Also, the Q, of the overall structure (cavity and the waveguides) was measure to be 1050 in vacuum, which from simulations is equivalent to a Q of 1800 in a solvent. These Q values and the resonant frequencies of the modes are in close, but not perfect agreement with the simulation results.

Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 31-34).
We propose a design of photonic crystal cavity with self-similar electromagnetic boundary conditions, that achieve ultrasmall mode volume (Vff). The electric energy density of a cavity mode can be maximized in the air or dielectric region, depending on the choice of boundary conditions. We illustrate the design concept with a silicon-air ID photon crystal cavity that reaches an ultrasmall mode volume of Vff ~ 7.01 x 10- 5 [lambda]3 at [lambda] ~ 1550 nm. We show that the extreme light concentration in our design can enable ultra-strong Kerr nonlinearities, even at the single photon level. These features open new directions in cavity quantum electrodynamics, spectroscopy, and quantum nonlinear optics.
by Hyeongrak Choi.
S.M.

Dans le premier chapitre de la thèse, nous étudions la possibilité d’améliorer le couplage opto- mechanique photon-phonon entre le mode de résonance d’une cavité Fabry-Pérot de haute finesse et les vibrations mécaniques des éléments diélectriques (membranes) à l’intérieur de la cavité. En introduisant un défaut quadratique dans la disposition des membranes, nous montrons que le deux couplages (linéaire et quadratique) augmentent. Enfin, nous proposons un modèle très simple avec lequel on cherche à simuler un cristal photonique quasipériodique. Dans le deuxième chapitre de cette thèse, nous présentons nos résultats de recherche sur le transport d’excitons à travers une cavité visant à augmenter l’efficacité du transport. Le modèle que l’on étudie est une chaîne unidimensionnelle d’atomes froids comprenant chacun deux niveaux énergétiques. Grâce au couplage entre exciton et photon, ces deux quanta s’hybrident et forment deux branches de polariton à l’intérieur de la cavité. Nous avons observé qu’à résonance avec un des deux modes de polariton, on peut transmettre l’exciton via le mode polaritonique dans un temps très court. En outre, le désordre n’affecte la propagation excitonique que de façon algébrique. Dans le troisième chapitre de cette thèse, nous présentons nos résultats de recherche sur la réalisa- tion d’interactions entre photons grâce à la médiation d’atomes ultrafroids piégés dans un réseaux optique unidimensionnelle et placés à l’intérieur d’une fibre à cristaux photoniques. Nous avons détecté un régime dans lequel on peut réaliser le “bunching” photon-photon.Dans le quatrième et dernière chapitre de cette thèse, nous étendons les résultats du chapitre précédent aux atomes de Rydberg
In the first chapter of this thesis, we study a quasiperiodic array of dielectric membranes inside a high-finesse Fabry-Pérot cavity. We work within the framework of the transfer matrix formal- ism. We show that, in a transmissive regime, the introduction of a quadratic spatial defect in the membrane positions enhances both the linear and quadratic optomechanical couplings between optical and mechanical degrees of freedom. Finally, we propose a theoretical model to simulate a one-dimensional quasiperiodic photonic crystal. In the second chapter of this thesis, we consider the problem of the transport of an exciton through a one-dimensional chain of two-level systems. We embed the chain of emitters in a transverse optical cavity and we show that, in the strong coupling regime, a ultrafast ballistic transport of the exciton is possible via the polaritonic modes rather than ordinary hopping. Due to the hybrid nature of polaritons, the transport efficiency is particularly robust against disorder and imperfections in the system. In the third chapter of this thesis, we consider an ordered array of cold atoms trapped in an optical lattice inside a hollow-core photonic crystal fiber. We study photon-photon interactions mediated by hard-core repulsion between excitons. We show that, in spite of underlying repulsive interac- tion, photons in the scattering states demonstrate bunching, which can be controlled by tuning the interatomic separation. We interpret this bunching as the result of scattering due to the mismatch of the quantization volumes for excitons and photons, and discuss the dependence of the effect on experimentally relevant parameters. In the fourth chapter of the thesis, we extend the results of the previous chapter to Rydberg atoms

Optical microcavities can find broad application areas, like tunable and compact sources, dynamic filters for optical communications, biological and chemical sensors, etc. Optical microcavities are key component allowing one to obtain compact laser devices exhibiting small cavity volume and low threshold. Among the different resonators architectures for microcavities laser, photonic crystal (PC) structures are one of the most promising. These structures feature the periodicity in one or more dimensions, and are resonant for light waves of a specific wavelength. Two-dimensional PCs are planar dielectric waveguide where photons are vertically confined by the vertical profile of the optical index, while the crystal periodicity acts only in the slab plane. In photonic crystals the refractive index contrast of the periodic structure is high enough to open a full band gap, and thus to fully confine light at very small scale. Strong coupling is theoretically feasible, and quality factor of more than 106 have been experimentally achieved for small modal volumes. Substantial additional gains are possible with confinement improvement in microfabrication techniques and with implementation of low loss design. Photonic crystal whose index contrast is lower can be used as DFB gratings. In a DFB device, the laser modes receive feedback at one specific wavelength, determined by the grating period of the structure. The feedback strength is related to the coupling constant, ?, which in turn depends on the grating index contrast, and to the grating length, L. The ?L product must be high enough to ensure the feedback required for lasing. In an optically pumped laser, an external source supplies the excitation energy necessary to get the population inversion. To do that, it must be on resonance with one of the absorption transitions of the active medium. When the external source provides enough energy, the active material exhibits gain: more photons are generated than lost. For intense incoming beams, i.e. intense laser sources, multiple-photon absorption processes become appreciable. It is thus possible to have absorption also by pumping with sources having photon energies lower than the resonance energy of the active medium. The two-photon absorption (TPA), described from the 3rd order susceptibility, involves the simultaneous absorption of two photons with energy: E_exc-E_ground=2?? The absorption of the first photon causes the promotion of the electron to the virtual level. Here the simultaneous absorption of the second photon promotes the electron to the real excited state. The system can then decay to the ground state emitting an up-converted photon, i.e., a photon having energy higher than that of the exciting ones. A large part of this work is devoted to the realization and characterization of active microresonators behaving as laser sources. Two main research subjects will be pursued: An integrated InP semiconductors photonic crystal microcavity laser, operating in the telecommunication wavelength. A distributed feedback laser for two-photon induced IR-to-visible up-conversion lasing. Within the second subject, particular attention will be devoted to the characterization of the two-photon induced emission properties of organic push-pull dyes and II-VI semiconductors quantum dots (QDs) to evaluate their potentiality as candidates for all-solid-state up-converted laser devices. The third reported research subject is the exploitation of hybrid silica-titania sol-gel films for UV lithography application, finalized to the production of surface relief gratings. MICROLASER BASED ON EFFECTIVE INDEX CONFINED, SLOW-LIGHT MODES IN PC WAVEGUIDES This research regards the study of photonic crystal microcavity having small mode volume V and high quality factor Q, for the production of low threshold integrated laser devices. The light propagation inside the PC is modified because of its periodicity. In this study we exploit the low-light guided modes at the high symmetry point of the dispersion curve of a PC-W1 waveguide. The PC-W1 waveguide is a PC having triangular symmetry with a missing row of hole along the ?K direction. The linear defect entails the appearance of defect modes with frequencies localized inside the unperturbed PC band gap, and thus modes that exponentially decay inside the PC. The band associated with the defect mode becomes flat at the K point of the band diagram, leading to slow-modes whose group velocity goes to zero. The lateral confinement of low-group velocity modes is controlled by locally changing the refractive index of the two dimensional photonic crystal waveguides. The index modulation is induced by post-processing a dielectric strip on top of the two-dimensional PC waveguide. This results in a photonic heterostructure whose confinement properties are the result of the effective index shift and the local curvature of the band associated with the waveguide mode. In this thesis the results of the device simulation, experimental realization and characterization will be reported. Computational tools, such as MPB and 3D-FDTD software have been used for the device design and for the study the electromagnetic field behavior inside the cavity. The realization of the PC structure has been accomplished through lithography techniques like e-beam lithography and reactive ion etching. Intense clean-room activities have been necessary to reach optimized structure quality. The characterization of the microcavity laser has been pursued with a proper optical set-up, in such a way to determine its performance. UP-CONVERTED LASING The up-converted lasing is an alternative method to convert the emission of a cheap, easily available IR laser into that of a more technological valuable visible laser. It involves the two photon pumping (TPP) mechanism, i.e., the NLO system is excited through the simultaneously absorption of two photons in the near-IR range. In this work we report our effort towards the realization of a solid-state visible laser device based on a TPP induced emission. The starting point of this technology is to find a system able to efficiently convert the IR incoming radiation to a visible one. We have studied the up-conversion process both in push-pull organic dyes embedded in sol-gel hybrid films and in semiconductor core-shell CdSe-CdS-ZnS quantum dots embedded in zirconia films. The excitation source is an amplified Ti:Sapphire laser at 800 nm. Concerning the organic compounds, it has been possible to characterize the emission properties only in solution, because of their poor photostability when they are embedded in sol-gel matrices. On the opposite, quantum dots embedded in zirconia films show promising amplified emission properties, with interesting gain value and extremely long time stability. We have investigated the possibility to implement this material with a distributed feedback optical resonator for obtaining compact and integrated laser devices. The grating parameters have been determined with MPB software, and first attempts of e-beam lithography of the pattern have been done. We have also prepared a devoted optical set-up for the optical characterization of the laser devices. SILICA-TITANIA SOL-GEL FILM FOR DIRECT PHOTOPATTERNIG APLICATIONS The possibility to exploit the photocatalytic action of hybrid silica-titania sol-gel film towards the decomposition of their organic component, for the direct patterning of surface structure has been investigated. These films have been characterized to study their microstructural properties, and to confirm the presence of crystalline titanium oxo-clusters. Their photocatalytic efficiency has been measured using stearic acid as reference material. To test the potentiality of this system for UV-lithography, it has been exposed to a UV-lamp. The organic component decomposition leads to a film shrinkage of about 60%, accompanied by a refractive index increases of about 0.1 By irradiating the spin-coated films through an UV-mask, structures of different shapes and micrometer dimension have been achieved.
Lo studio delle microcavità ottiche riveste un grande interesse per applicazioni in svariati campi, quali la ricerca di sorgenti laser tunabili e compatte, filtri per le telecomunicazioni, sensori chimici e biologici, etc. Le microcavità ottiche sono fondamentali per l’ottenimento di dispositivi laser compatti, aventi bassa soglia di emissione laser, ove il campo elettromagnetico è confinato in volumi estremamente ridotti, con conseguente aumento dell’interazione radiazione-materia,. Tra le possibili architetture della cavità risonante, per dispositivi pompati otticamente, i cristalli fotonici rappresentano una delle soluzioni più promettenti. Questi ultimi sfruttano la periodicità in una o più direzioni e sono risonanti con determinate lunghezze d’oda della radiazione elettromagnetica. In un cristallo fotonico bidimensionale il confinamento verticale è garantito dal profilo verticale dell’indice di rifrazione, mentre il confinamento nel piano del cristallo è opera della strutture periodica. Nei cristalli fotonici il contrasto di indice di rifrazione della struttura periodica è tale da aprire un intervallo completo di energie proibite per la propagazione della radiazione nel mezzo. Essa può quindi essere confinata in volumi molto piccoli, dell’ordine del cubo della lunghezza d’onda, con fattori di qualità sperimentali superiori a 106. Inoltre i valori ottenuti sperimentalmente sono inferiori a quelli previsti teoricamente, e ulteriori passi in avanti saranno possibili con lo sviluppo delle tecniche litografiche e di produzione del materiale attivo. I cristalli fotonici nei quali il contrasto di indice di rifrazione è insufficiente per aprire un band-gap completo si comportano come reticoli distributed feedback, DFB. In un dispositivo DFB, i modi risonanti ricevono il feedback a lunghezze d’onda specifiche, determinate dal periodo del reticolo. La forza dell’accoppiamento è legata alla costante di accoppiamento ?, la quale, a sua volta, dipende dal contrasto di indice nel reticolo e all’estensione totale del reticolo. Il prodotto ?L deve essere sufficiente per garantire il feedback richiesto per l’emissione laser. In un laser a pompaggio ottico, una sorgente esterna fornisce al mezzo attivo l’energia di eccitazione richiesta per raggiungere l’inversione di popolazione, requisito necessario per ottenere il guadagno all’interno del mezzo e quindi l’amplificazione. Affinché si verifichi assorbimento, l’energia del fascio di pompa deve essere in risonanza con una delle transizioni del mezzo attivo. Per campi incidenti molto intensi, come possono essere quelli legati a fasci laser focalizzati, diventano tuttavia apprezzabili anche fenomeni di assorbimento multi fotonici. Si può quindi avere assorbimento anche utilizzando sorgenti di pompa aventi energie inferiori all’energia di risonanza del mezzo attivo. L’assorbimento a due fotoni (TPA), legato alla suscettibilità non lineare al terzo ordine, comporta l’assorbimento simultaneo di due fotoni, con energia: E_exc-E_ground=2?? L’assorbimento del primo fotone promuove l’elettrone dallo stato fondamentale a uno stato virtuale, dal quale esso passa immediatamente allo stato eccitato attraverso l’assorbimento simultaneo di un secondo fotone incidente. Infine il sistema può tornare allo stato fondamentale, attraverso l’emissione di un fotone a energia superiore rispetto ala pompa. Gran parte del lavoro di dottorato è incentrato sulla realizzazione e caratterizzazione di microcavità attive per l’ottenimento di sorgenti laser. All’interno di tale attività sono stati studiati due sistemi differenti: Una microcavità laser a semiconduttore, realizzata sfruttando le proprietà dei cristalli fotonici bi-dimensionali, che emette alla lunghezza d’onda delle telecomunicazioni. Un dispositivo laser DFB, pompato oticamente a due fotoni, per la conversione di emissione laser dall’infrarosso al visibile. All’interno della seconda tematica, particolare attenzione è stata rivolta alla caratterizzazione delle proprietà di emissione indotta a due fotoni di un cromoforo organico e di quantum dots di un semiconduttore II-VI, il CdSe, entrambi inglobati in matrice sol-gel. Un terzo soggetto è costituito dallo studio delle proprietà foto catalitiche di film sol-gel ibridi a base di silica e titania, in vista di possibili applicazioni per il patterning diretto tramite radiazione UV. CONFINAMENTO DI MODI LENTI IN GUIDA D’ONDA A CRISTALLO FOTONICO PER L’OTTENIMENTO DI MICROCAVITA’ LASER Questa ricerca riguarda lo studio di cavità, ottenute sfruttando cristalli fotonici bidimensionali, a basso volume modale e alto fattore di qualità Q, finalizzate all’ottenimento di dispositivi laser integrati a bassa soglia. Questo lavoro si basa sull’utilizzo dei modi guidati lenti corrispondenti al punto ad elevata simmetria K della curva di dispersione di una guida d’onda W1-PC. Una guida d’onda W1-PC si ottiene da un cristallo fotonico a simmetria triangolare, attraverso la rimozione di una fila di buche lungo la direzione ?K. In questo modo si introduce un difetto lineare, il quale si riflette nella comparse di modi del difetto, aventi frequenze localizzate all’interno del band-gap del cristallo fotonico, che pertanto decadono esponenzialmente all’interno del cristallo. Le bande associate ai modi del difetto hanno curvatura nulla in corrispondenza dei punti a elevata simmetria, e ciò implica una velocità di gruppo del modo nulla in corrispondenza di tali punti. L’estensione laterale dei modi lenti viene controllata agendo sull’indice di rifrazione del cristallo fotonico, in modo da creare una etero struttura in grado di confinarli efficacemente. L’indice effettivo della guida viene modificato localmente depositando un film di polimero all’interfaccia superiore della guida. La forza del confinamento dipende dall’entità della variazione dell’indice e dalla curvatura della banda associata al modo lento. L’attività svolta all’interno di questo progetto consiste nel design della struttura, nella sua realizzazione sperimentale e infine nella caratterizzazione ottica del dispositivo. Per ottimizzare i parametri del dispositivo e comprendere il comportamento della radiazione elettromagnetica all’interno della cavità, sono stati impiegati strumenti di calcolo computazionale, quali i software MPB e TESSA 3D-FDTD. I parametri delle simulazioni sono stati poi utilizzati per la realizzazione del cristallo fotonico, effettuata tramite tecniche litografiche, quali la litografia con fascio elettronico e l’etching ionico. La caratterizzazione ottica del dispositivo è stata effettuata con un apposito set-up, al fine di determinarne le prestazioni. EMISSIONE LASER CON CONVERSIONE DI FREQUENZA La conversione di frequenza laser fornisce l’interessante possibilità di convertire una sorgente laser economica e di facile reperibilità nell’infrarosso, in una sorgente laser nel visibile di enorme interesse tecnologico. Essa si basa sull’emissione indotta a seguito di processi di assorbimento a due fotoni nel vicino IR. In questo lavoro verranno presentati gli sforzi profusi e i risultati preliminari ottenuti nella ricerca di un dispositivo laser allo stato solido per la conversione di frequenza. A tal fine sono state investigate le proprietà di conversione di un cromoforo push-pull organico disperso in matrici sol-gel ibride, e di quantum dots di semiconduttore II-VI, CdSe-CdS-ZnS, dispersi in una matrice inorganica a base di zirconia. Il composto organico presenta interessanti proprietà di emissione indotta a due fotoni in soluzione. Tuttavia la sua scarsa resistenza al pompaggio ottico in matrice solida preclude un suo possibile impiego e rende estremamente problematica la stessa caratterizzazione ottica. Al contrario i film di QDs-ZrO2 mostrano una buona efficienza di conversione di frequenza, con valori di guadagno per l’emissione spontanea amplificata interessanti, e elevata stabilità del segnale emesso nel tempo. E’ stata pertanto studiata la possibilità di implementare i film di QDs-ZrO2 all’interno di una cavità risonante di tipo distributed feedback per ottenere un dispositivo laser compatto e integrabile. I parametri del reticolo sono stati determinati con il software MPB e sono stati fissati in modo da avere amplificazione in corrispondenza del massimo di emissione dei QDs. Sono tutt’ora in corso delle prove di realizzazione del reticolo DFB tramite litografia elettronica su film sol-gel appositamente sviluppati per il patterning diretto. Infine è stato messo appunto un set-up dedicato per la caratterizzazione ottica dei dispositivi prodotti. FILM SOL-GEL IBRIDI A BASE DI SILICA-TITANIA PER IL PATTERNING DIRETTO CON LUCE UV E’ stata studiata l’attività fotocatalitica di film sol-gel ibridi a base di silica-titania, promossa dalla radiazione UV. I film sono stati caratterizzati a livello micro strutturale tramite spettroscopia infrarossa, e sono stati osservati al microscopio elettronico per confermare la presenza di cluster di titanio cristallino al loro interno. L’efficienza del processo di fotocatalisi è stata determinata mediante test standard che si avvalgono dell’acido stearico come materiale di riferimento. Quest’ultimo infatti è in grado di simulare efficacemente i comuni inquinanti organici, è può essere depositato facilmente per spin-coating. Successivamente è stata valutata la possibilità di sfruttare l’attività foto catalitica per il patterning diretto dei film. Tale studio parte dall’osservazione che la fotocatalisi si manifesta anche nei confronti della componente organica dei film sol gel ibridi.. Questo fenomeno è accompagnato da una diminuzione dello spessore del film, fino al 60% sullo spessore iniziale, e può pertanto essere sfruttato per la realizzazione di strutture a rilievo. Test di patterning diretto sono stati effettuati irradiando il film con una lampada UV attraverso una maschera in quarzo, ottenendo strutture di dimensione micrometrica ben definite.

Orientador: Thiago Pedro Mayer Alegre
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: A área de optomecânica de cavidades passou por um grande desenvolvimento na última década. O crescente interesse nesta área foi impulsionado principalmente pela interessante conexão entre movimentos mecânicos e campos ópticos. Tal acoplamento é amplamente explorado em diversos experimentos, com escalas variando de interferômetros quilométricos a cavidades ópticas microestruturadas. O principal desafio em todos estes experimentos é criar um dispositivo optomecânico com um longo tempo de vida óptico e mecânico, ao mesmo tempo em que mantém um grande acoplamento. Neste contexto, as cavidades de cristal fotônico surgiram como fortes candidatas já que elas são capazes de confinar campo óptico em um volume modal muito reduzido e por um longo tempo de vida. No regime clássico, estes pequenos dispositivos, que podem oscilar mecanicamente com frequências de alguns poucos MHz até dezenas de GHz, permitem detectar forças, massas e deslocamentos muito pequenos. Elas também são usadas para produzir osciladores mecânicos de alta qualidade, que podem ser sincronizados por intermédio do campo óptico. No regime quântico, a optomecânica quântica de cavidades tem sido usada para ajudar na compreensão do fenômeno de decoerência em uma escala mesoscópica, criando estados não-clássicos fortemente acoplados entre campo óptico e movimento mecânico, intermediado pela interação optomecânica. Entretanto, até agora, foram realizados poucos estudos sobre a possibilidade de produção destes dispositivos em larga escala, um passo necessário para massivas aplicações tecnológicas e científicas destes dispositivos. Neste trabalho, descrevemos um estudo detalhado de cavidades optomecânicas baseadas em cristais fotônicos produzidos numa fábrica de dispositivos compatíveis com indústria CMOS. Nós demonstramos a viabilidade desta plataforma explorando três geometrias distintas de cristais fotônicos. Primeiramente, nós mostramos como atingir fatores de qualidade muito elevados usando uma geometria consistente com as limitações de fabricação. Nossos fatores de qualidade são os maiores já reportados usando cavidades de cristal fotônico fabricadas com litografia óptica. Em seguida, investigamos uma cavidade do tipo fenda, possibilitando a produção de alto acoplamento optomecânico usando um movimento mecânico planar. Por fim, desenhamos um escudo acústico, com dimensões variadas, para restringir o modo mecânico para dentro da região óptica. Essa estratégia foi usada de forma bem sucedida para produzir altos fatores de qualidade mecânicos e acoplamentos optomecânicos, permitindo a observação de resfriamento e amplificação de modos mecânicos à baixa temperatura
Abstract: The field of cavity optomechanics has experienced a rapid growth in last decade. The increasing interest in this area was mostly driven by the intricate interface between mechanical motion and the optical field. Such coupling is widely explored in a variety of experiments scaling from kilometer long interferometers to micrometer optical cavities. The challenge on all these experiments is to create an optomechanical device with long-living optical and mechanical resonances while keeping a large coupling rate. In this context photonic crystal cavities have emerged as a strong candidate since they are able to produce very small optical mode volume and long optical lifetime. In the classical regime, these tiny devices, which can mechanically oscillate from frequencies ranging from couple MHz up to tens of GHz, allows for highly sensitive small forces, masses, displacements and acceleration detectors. They are also used to produce high quality optically driven mechanical oscillators which can be synchronized via an optical field. In the quantum regime, cavity quantum optomechanics is being used to understand decoherence phenomena in a mesoscopic scale by creating nonclassical states between light and mechanical modes intermediated by optomechanical interaction. However up to now, few studies have been done concerning the possibility of large scale production of these devices, a necessary step towards massive technological and scientific application of these devices. In this work, we describe a detailed study of optomechanical cavities based upon photonic crystal cavities fabricated in a CMOS-compatible commercial foundry. We prove the feasibility of this platform exploring three photonic crystal designs. First, we show how to achieve ultra-high optical quality factors using a design resilient to the fabrication constrains. Our demonstrated quality factors are the largest ever reported using photonic crystal cavities manufactured by optical lithography. Secondly, we investigate a slot type optical cavity, able to produce very large optomechanical coupling using a simple in-plane motion. Finally, we design a trimmable acoustic shield to restrict the mechanical motion inside the optical region. Such strategy was successfully used to produce high mechanical quality factor and optomechanical coupling which enabled the observation of cooling and amplification of mechanical modes at low temperature
Mestrado
Física
Mestre em Física
2014/12875-4
132737/2014-0
FAPESP
CNPQ

A 2-D photonic crystal cavity device is investigated in this thesis. A simplified flexible local approximation method (FLAME) is used to analyze the electromagnetic characteristics of the cavity.
FLAME is a computational technique that is well suited to problems involving a large number of repeated structures. It has been used before to analyze photonic crystal cavities. In this thesis, an improved FLAME is developed, leading to a standard eigenproblem, which allows the use of sparse-matrix solution methods. Consequently, much larger problems can be solved. In addition, a graded perfectly matched layer (PML) is applied to absorb more effectively the out-going waves.
The new method is applied to cavities based on NxN arrays of rods, from N=3 to 9. Good accuracy is achieved compared with the finite-element method (FEM), with an error of less than 0.001% in the resonant frequency for a density of 42.6 nodes per wavelength (when N=5), which shows better consistency than the previous FLAME. Further, the new method converges more quickly than the FEM with linear elements, as the node density is increased, though it is less accurate than the FEM with quadratic elements.

Nano-emitters are the new generation of laser devices. A photonic-crystal cavity, which highly confines light in small volumes, in combination with quantum-dots can enhance the efficiency and lower the threshold of this device. The practical realisation of a reliable, electrically pumped photonic-crystal laser at room-temperature is, however, challenging. In this project, a design for such a laser was established. Its properties are split up into electrical, optical and thermal tasks that are individually investigated via various device simulations. The resulting device performance showed that with our design the quantum-dots can be pumped in order to provide gain and to overcome the loss of the system. Threshold currents can be as low as 10’s of μA and Q-factors in the range of 1000’s. Gallium arsenide wafers were grown according to our specifications and their diode behaviour confirmed. Photonic-crystal cavities were fabricated through a newly developed process based on a TiOₓ hard-mask. Beside membraned cavities, also cavities on oxidised AlGaAs were fabricated with help to a unique hard-mask removal method. The cavities were measured with a self-made micro-photoluminescence setup with the highest Q-factor of 4000 for the membrane cavity and a remarkable 2200 for the oxide cavity. The fabrication steps, regarding the electrically pumped photonic-crystal laser, were developed and it was shown that this device can be fabricated. During this project, a novel type of gentle confinement cavity was developed, based on the adaption of the dispersion curve (DA cavity) of a photonic-crystal waveguide. Q-factors of as high as 600.000 were measured for these cavities made in Silicon.

In this thesis, Fabry-Perot (FP) cavity structures aimed at a 850nm wavelength are modeled and analyzed by Finite-Difference Time-Domain (FDTD) simulations, for the purpose of fabricating resonant cavity detectors and Vertical-Cavity Surface-Emitting Lasers (VCSELs). The structures are based on square-lattice photonic crystals. In designing a VCSEL, different types of highly reflective mirrors such as GaAs/AlGaAs Distributed Bragg Reflectors (DBRs), and a GaAs-based Sub-Wavelength Grating (SWG) or a Photonic Crystal (Phc) Slab are used to form a FP cavity. FDTD phase analysis is implemented to estimate resonant conditions in a simple but very effective technique. For the fabrication of a resonant cavity detector, square-lattice photonic crystal arrays are written by (1) Focused Ion Beam (FIB) and (2) e-beam lithography, followed by dry-etching. The quality of air holes, etching depths, and sidewalls are scrutinized by Scanning Electron Microscopy (SEM) imaging and Atomic Force Microscopy (AFM). Post-patterning, a sacrificial layer is etched away by Buffered Oxide Etch (BOE) and a suspended photonic crystal membrane is released by Critical Point Drier (CPD). The SWG and Phc slab used as one of the mirrors in the FP cavity structures are beneficial for achieving a compact-sized resonator, as well as forming multi-wavelength arrays, in which the resonance can be widely tuned by lithographically defined parameters (i.e., for the SWG: period and duty factor and for the Phc slab: lattice constant and radius of the air hole).
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

[ES] La optomecánica de cavidades se ocupa de la interacción entre la luz y la materia a través del efecto de presión de radiación cuando las ondas ópticas y mecánicas implicadas están confinadas en una cavidad. En estos sistemas optomecánicos, la interacción entre fotones y fonones da lugar a multitud de fenómenos en función de las condiciones en las que se excita el sistema. En particular, se pueden obtener dos regímenes distintos en los que se puede, o bien absorber fonones (denominado como enfriamiento de la cavidad), o bien éstos se pueden amplificar (régimen conocido como calentamiento de la cavidad). El primer régimen puede usarse, por ejemplo, para reducir la ocupación térmica del sistema y se usa comúnmente para aplicaciones relativas al procesado de información cuántica. Sin embargo, la amplificación de fonones, que puede ser desarrollada a temperatura ambiente, ha permitido conseguir alcanzar incluso las condiciones necesarias para obtener láseres de fonones, lo cual permite poder usar esta característica como elemento de referencia en aplicaciones relativas al procesado de señales de radiofrecuencia (RF). En esta tesis se aborda el confinamiento simultáneo y la interacción de fotones y fonones en estructuras periódicas y en guías no suspendidas desarrolladas en sistemas CMOS compatibles basados en tecnología de silicio. A través del estudio experimental de estas estructuras periódicas, hemos demostrado que las cavidades optomecánicas pueden actuar como elementos clave en el dominio de la fotónica de microondas, donde todo el procesado de la información puede ser realizado en el dominio óptico a través de la manipulación de fonones en este sistema. En particular, mostramos que un solo oscilador optomecánico puede actuar tanto como un oscilador local y un mezclador de RF, y éste puede operar como un conversor de frecuencias de señales de cadenas de datos reales. Para mejorar esta funcionalidad, también se demuestra que es posible obtener tanto peines de frecuencias ópticos así como múltiples modos mecánicos confinados, aumentando así su rendimiento. Por otro lado, con el objetivo de poder solventar las posibles limitaciones de estos sistemas, en esta tesis también se exploran diferentes configuraciones que permiten la interacción acusto-óptica simultánea en la misma estructura. Específicamente, se analiza la interacción optomecánica en discos de alto índice que soportan estados cuasi-ligados en el continuo así como una propuesta de guías no suspendidas que soportan altas ganancias de Brillouin. Este último estudio debería permitir el desarrollo de sistemas optomecánicos no suspendidos donde el problema de la pérdida de fonones hacia el sustrato se resuelva, hecho que permitiría enormemente simplificar la fabricación de estos sistemas optomecánicos en chips de silicio así como su uso en múltiples aplicaciones.
[CA] L'optomecànica de cavitats s'ocupa de la interacció entre la llum i la matèria a través de l'efecte de pressió de radiació quan les ones òptiques i mecàniques implicades estan confinades en una cavitat. En aquests sistemes optomecànics, la interacció entre fotons i fonons dona lloc a multitud de fenòmens en funció de les condicions de les condicions en les quals s'excita el sistema. En particular, es poden obtindre dos règims diferents en els quals es pot, o bé, absorbir fonons (denominat com a refredament de la cavitat), o bé, es poden amplificar (règim conegut com a calfament de la cavitat). El primer règim pot usar-se, per exemple, per a reduir l'ocupació tèrmica del sistema i s'usa comunament per a aplicacions relatives al processament d'informació quàntica. No obstant això, l'amplificació de fonons, que pot ser desenvolupada a temperatura ambient, ha permés aconseguir fins i tot les condicions necessàries per a obtindre làsers de fonons, la qual cosa permet poder usar aquesta característica com a element de referència en aplicacions relatives al processament de senyals de radiofreqüència (RF). En aquesta tesi s'aborda el confinament simultani i la interacció de fotons i fonons en estructures periòdiques i en guies no suspeses en sistemes CMOS compatibles basats en tecnologia de silici. A través de l'estudi experimental d'aquestes estructures periòdiques, hem demostrat que les cavitats optomecàniques poden actuar com a elements clau en el domini de la fotònica de microones, on tot el processament de la informació pot ser realitzat en el domini òptic a través de la manipulació de fonons en aquest sistema. En particular, vam mostrar que només un oscil·lador optomecànic pot actuar tant com un oscil·lador local i un mesclador de RF, i aquest pot operar com un convertidor de freqüències de senyals de cadenes de dades reals. Per a millorar aquesta funcionalitat, també es demostra que és possible obtindre tant tren de freqüències òptics així com múltiples modes mecànics confinats, augmentant així el seu rendiment. D'altra banda, amb l'objectiu de poder solucionar les possibles limitacions d'aquests sistemes, en aquesta tesi també s'exploren diferents configuracions que permeten la interacció acusto-òptica simultània en la mateixa estructura. Específicament, s'analitza la interacció optomecànica en discos d'alt índex que suporten estats quasi-lligats en el continu així com una proposta de guies no suspeses que suporten altes ganancies de Brillouin. Aquest últim estudi hauria de permetre el desenvolupament de sistemes optomecànics no suspesos on el problema de la pèrdua de fonons cap al substrat es resolga, fet que permetria enormement simplificar la fabricació d'aquests sistema optomecànics en xips de silici així com el seu ús en diverses aplicacions.
[EN] Cavity optomechanics deals with the interaction of light and matter through the radiation pressure effect, when the involved optical and mechanical waves are confined in a cavity. In optomechanical systems, photon and phonon interaction give rise to a plethora of phenomena as a function of the driving conditions of the system. Relative to that, two distinctive regimes can be obtained which enable either the absorption of phonons (cavity cooling) or their amplification (cavity heating). The first regime can be used to reduce the thermal occupancy of the system and it is commonly used for quantum processing information applications. However, the amplification of phonons, which can be performed at room temperature, has enabled to even reach phonon lasing conditions, a feature that could be used as a reference element for RF processing applications. In this thesis, we address the simultaneous confinement and interaction of photons and phonons in periodic structures and unreleased waveguides on CMOS-compatible silicon-based technology. Throughout the experimental study of those periodic structures, we demonstrate that optomechanical cavities can perform as key blocks in the microwave photonics domain where all the information processing can be performed in the optical domain through phonon manipulation. In particular, we show that a single optomechanical oscillator can perform as both a local oscillator and an RF mixer, and it can operate as a frequency-converted of real data stream signals. To improve its performance, it is also demonstrated that optical frequency combs can be obtained by means of this system and multiple mechanical mode confinement can also be achieved, thus improving the functionality of the system. On the other hand, in order to fulfill the possible limitations of those systems, we explore different configurations enabling the simultaneous acousto-optic interaction together into the same structure. Especially, optomechanical interaction in high-index disks supporting quasi-bound states in the continuum is addressed, as well as a proposal of unreleased waveguides supporting strong Brillouin gains is also reported. The last one should lead to unreleased optomechanical interacting systems where the issue of phonon leakage into the substrate is solved, which could enormously simplify the fabrication of optomechanical systems in silicon chips as well as their practical use in multiple applications.
This work has been carried out under the framework of the H2020 FET-Open EU project PHENOMEN. This Thesis was also supported by the Programa de Ayudas de Investigación y Desarrollo (PAID-01-16) de la Universitat Politècnica de València
Mercadé Morales, L. (2021). Phonons Manipulation in Silicon Chips Using Cavity Optomechanics [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/171461
TESIS

The real-time detection of trace species is key to a wide range of applications such as on-line chemical process analysis, medical diagnostics, identification of environmentally toxic species and atmospheric pollutant sensing. There is a growing demand for suitable techniques that are not only sensitive, but also simple to operate, fast and versatile. Most currently available techniques, such as spectrophotometry, are neither sensitive enough nor fast enough for kinetic studies, whilst other techniques are too complex to be operated by the non-specialist. This thesis presents two techniques that have been developed for and applied to liquid-phase analysis, with supercontinuum (SC) radiation used for liquid-phase absorption for the first time. Firstly, supercontinuum cavity enhanced absorption spectroscopy (SC-CEAS) was used for the kinetic measurement of chemical species in the liquid phase using a linear optical cavity. This technique is simple to implement, robust and achieves a sensitivity of 9.1 × 10−7 cm−1 Hz−1/2 at a wavelength of 550nm for dye species dissolved in water. SC-CEAS is not calibration-free and for this purpose a second technique, a time-resolved variant called broadband cavity ring-down spectroscopy (BB-CRDS), was successfully developed. Use of a novel single-photon avalanche diode (SPAD) array enabled the simultaneous detection of ring-down events at multiple spectral positions for BB-CRDS measurements. The performance of both techniques is demonstrated through a number of applications that included the monitoring of an oscillating (Belousov-Zhabotinsky) reaction, detection of commercially important photoluminescent metal complexes (europium(III)) at trace level concentration, and the analysis of biomedical species (whole and lysed blood) and proteins (amyloids). Absorption spectra covering the entire visible wavelength range can be acquired in fractions of a second using sample volumes measuring only 1.0mL. Most alternative devices capable of achieving similar sensitivity have, up until now, been restricted to single wavelength measurements. This has limited speed and number of species that can be measured at once. The work presented here exemplifies the potential of these techniques as analytical tools for research scientists, healthcare practitioners and process engineers alike.

Die vorliegende Forschungsarbeit widmet sich der Entwicklung und Untersuchung neuartiger photonischer Kristallstrukuren für Anwendungen in den Gebieten der Nanophotonik und Optofluidik. Dabei konzentriert sich eine erste Serie von Experimenten auf die Charakterisierung und Optimierung photonischer Kristallresonatoren im sichtbaren Spektralbereich, wobei bisher unerreichte Resonatorgüten von bis zu 3400 gezeigt werden können. Diese Strukturen werden anschließend als Plattformen zur Herstellung von hybriden nanophotonischen Bauelementen verwendet, indem externe Partikel (wie z.B. Diamant-Nanokristalle und Metall-Nanopartikel) in kontrollierter Art und Weise an die Resonatoren gekoppelt werden. Zu diesem Zweck wird eine Nanomanipulationsmethode entwickelt, welche Rastersonden zur gezielten Positionierung und Anordnung von Partikeln auf den photonischen Kristallstrukturen benutzt. Verschiedene Arten solcher Hybridelemente werden realisiert und untersucht, einschließlich diamant-gekoppelter Resonatoren, plasmon-gekoppelter Resonatoren und Metall-Diamant Hybridstrukturen. Außer für Anwendungen auf dem Gebiet der Nanophotonik werden verschiedene photonische Kristallstrukturen auch hinsichtlich ihres Leistungsvermögens als biochemische Sensorelemente erforscht. Zum ersten Mal wird eine umfassende numerische Analyse der optischen Kräfte auf Objekte im Nahfeld photonischer Kristallresonatoren durchgeführt, welche neue Möglichkeiten zum Einfang sowie zur Detektion und Untersuchung biologischer Partikel in integrierten optofluidischen Bauteilen bieten. Weiterhin werden unterschiedliche photonische Kristallfasern bezüglich ihrer Detektionssensitivität in Absorptions- und Fluoreszenzmessungen untersucht, wobei sich eine klare Überlegenheit von selektiv befüllten Hohlkern-Designs im Vergleich zu Festkern-Fasern offenbart.
This thesis deals with the development and investigation of novel photonic crystal structures for applications in nanophotonics and optofluidics. Thereby, a first series of experiments focuses on the characterization and optimization of photonic crystal cavities in the visible wavelength range, demonstrating unprecedented cavity quality factors of up to 3400. These structures are subsequently employed as platforms for the creation of advanced hybrid nanophotonic elements by coupling external particles (such as diamond nanocrystals and metal nanoparticles) to the cavities in a well-controlled manner. For this purpose, a nanomanipulation method is developed, utilizing scanning probes for the deterministic positioning and assembly of particles on the photonic crystal structures. Various types of such hybrid elements are realized and investigated, including diamond-coupled cavities, plasmon-coupled cavities, and metal-diamond hybrid structures. Apart from applications in nanophotonics, different types of photonic crystal structures are also studied with regard to their performance as biochemical sensing elements. For the first time a thorough numerical analysis of the optical forces exerted on objects in the near-field of photonic crystal cavities is conducted, providing novel means to trap, detect, and investigate biological particles in integrated optofluidic devices. Furthermore, various types of photonic crystal fibers are studied with regard to their detection sensitivity in absorption and fluorescence measurements, revealing a clear superiority of selectively infiltrated hollow-core designs in comparison to solid-core fibers.

La croissance continue et rapide du trafic de données dans les infrastructures de télécommunications, impose des niveaux de débit de transmission ainsi que de puissance de traitement de l'information, que les capacités intrinsèques des systèmes et microcircuits électroniques ne seront plus en mesure d'assurer à brève échéance : le développement de nouveaux scenarii technologiques s'avère indispensable pour répondre à la demande de bande passante imposée notamment par la révolution de l'internet, tout en préservant une consommation énergétique raisonnable. Dans ce contexte, l'intégration hétérogène fonctionnelle sur silicium de dispositifs photoniques à émission par la surface de type VCSEL utilisant des miroirs large-bandes ultra-compacts à cristaux photoniques constitue une stratégie prometteuse pour surmonter l'impasse technologique actuelle, tout en ouvrant la voie à un développement rapide d'architectures et de systèmes de communications innovants dans le cadre du mariage entre photonique et micro-nano-électronique.

Silicon Photonics has been a major success story in the last decade, with many photonic devices having been successfully demonstrated. The only missing component is the light source, however, as making an efficient light source in silicon is challenging due to the material's indirect bandgap. The development of a silicon light source would enable us to make an all-silicon chip, which would find many practical applications. The most notable among these applications are on-chip communications and sensing applications. In this PhD project, I have worked on enhancing silicon light emission by combining material processing and device engineering methods. Regarding materials processing, the emission level was increased by taking three routes. In all the three cases the emission was further enhanced by coupling it with a photonic crystal (PhC) cavity via Purcell effect. The three different approaches taken in this PhD project are listed below. 1. The first approach involves incorporation of optically active defects into the silicon lattice by hydrogen plasma treatment or ion implantation. This process results in broad luminescence bands centered at 1300 and 1500 nm. By coupling these emission bands with the photonic crystal cavity, I was able to demonstrate a narrowband silicon light emitting diode at room temperature. This silicon nano light emitting diode has a tunable emission line in the 1300-1600 nm range. 2. In the second approach, a narrow emission line at 1.28µm was created by carbon ion implantation, termed “G-line” emission. The possibility of enhancing the emission intensity of this line via the Purcell effect was investigated, but only with limited success. Different proposals for future work are presented in this regard. 3. The third approach is deposition of a thin film of an erbium disilicate on top of a PhC cavity. The erbium emission is enhanced by the PhC cavity. Using this method, an optically pumped light source emitting at 1.54 µm and operating at room temperature is demonstrated. A practical application of silicon light source developed in this project in gas sensing is also demonstrated. As a first step, I show refractive index sensing, which is a simple application for our source and demonstrates its capabilities, especially relating to the lack of fiber coupling schemes. I also discuss several proposals for extending applications into on-chip biological sensing.

En esta tesis se realiza un estudio teórico de la interacción luz-sonido en estructuras foxonicas, con las cuales es posible el control de la luz y el sonido a la misma vez. Esta interacción en dichas estructuras se estudia, tanto desde un punto de vista macroscópico (diseño de estructuras para el confinamiento y guiado de ondas electromagnéticas y elásticas) como microscópico (estudio de la interacción fotón-fonón en microcavidades y desarrollo teórico de modelos cuánticos para la comprensión de dicha interacción).
Escalante Fernández, JM. (2013). Theoretical study of light and sound interaction in phoxonic crystal structures [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/33754
TESIS

El objetivo de esta tesis es la investigación de estructuras y técnicas de acoplo para minimizar las pérdidas de acoplo entre guías dieléctricas y cristales fotónicos planares. En primer lugar se ha estudiado el modelado del acoplo entre guías dieléctricas y guías en cristal fotónico así como la influencia de los principales parámetros del cristal en la eficiencia de acoplo. Se han obtenido expresiones cerradas para las matrices de reflexión y transmisión que caracterizan totalmente el scattering que ocurre en el interfaz formado entre una guía dieléctrica y una guía en cristal fotónico. A continuación y con el fin de mejorar la eficiencia de acoplo desde guías dieléctrica de anchura arbitraria, se ha propuesto como contribución original una técnica de acoplo basada en la introducción de defectos puntuales en el interior de una estructura de acoplo tipo cuña realizada en el cristal fotónico. Diferentes soluciones, incluida los algoritmos genéticos, han sido propuestas con el objetivo de conseguir el diseño óptimo de la configuración de defectos. Una vez conseguido un acoplo eficiente desde guías dieléctricas a guías en cristal fotónico, se ha investigado el acoplo en guías de cavidades acopladas. Como contribución original se ha propuesto una técnica de acoplo basada en la variación gradual del radio de los defectos situados entre cavidades adyacentes. Además, se ha realizado un riguroso análisis en el dominio del tiempo y la frecuencia de la propagación de pulsos en guías acopladas de longitud finita. Dicho estudio ha tenido como objetivo la caracterización de la influencia de la eficiencia del acoplo en los parámetros del pulso. Finalmente, se han presentado los procesos de fabricación y resultados experimentales de las estructuras de acoplo propuestas.
Sanchis Kilders, P. (2005). Coupling techniques between dielectric waveguides and planar photonic crystals [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/1854
Palancia

This Ph.D. thesis contains experimental and theoretical analysis of nonlinear optical pattern formation in monolithic mini-cavity optical parametrical oscillators and spatial properties of linear photonic crystal resonators. The thesis consists of introduction, literature review and two chapters. In the first chapter experimental investigation of optical parametrical oscillation (OPO) in broad aperture monolithic (5x5x1.5 mm) BBO type I crystal mini-cavity is described. OPO was pumped by second harmonic (532 nm) 13 ns duration, 7 15 mJ energy pulses, of Nd:YAG laser. Optical patterns were registered in a near and far field of OPO emission. Experiments and theoretical interpretation revealed that emission of such resonator can be conical and multiconical and direction of signal and idler waves can be controlled by changing the mini-cavity orientation with respect to pump beam. It was also showed, that the stabilization of stripes (or roll) pattern can be achieved by a weak seed injection at subharmonic frequency and temporal spectrum of the stripe pattern degenerate OPO emission is 1/f – like noise spectrum . In the second chapter plane-mirror Fabry-Pérot resonators filled with a single period of photonic crystal (PhC) are introduced and analyzed. PhC resonators are realized by adding periodical 2 µm, 4 µm and 15 µm refraction index modulation on a resonator mirror surfaces (i.e. fabricating 1D or 2D phase diffraction grating). PhC resonator angular transmission measured by... [to full text]
Šioje disertacijoje teoriškai ir eksperimentiškai tiriamas erdvinių šviesos darinių formavimasis didelės apertūros monolitiniuose parametriniuose šviesos generatoriuose (PŠG), nagrinėjamos fotoninių kristalų (FK) rezonatorių erdvinės dispersijos savybės. Darbas susideda iš įvado, literatūros apžvalgos ir dviejų pagrindinių dalių. Pirmoje dalyje aprašomas PŠG tyrimas didelės apertūros (5x5x1,5 mm) BBO I fazinio sinchronizmo tipo kristalo monolitiniame mini rezonatoriuje. Generatoriui kaupinti naudojami antros Nd:IAG lazerio harmonikos (532 nm) 13 ns trukmės ir 7-15 mJ energijos impulsai. Erdviniai šviesos dariniai registruojami artimajame ir tolimajame laukuose. Eksperimentiškai parodoma ir teoriškai interpretuojama, kad tokio rezonatoriaus emisija gali būti kūginė ir daugiakūgė, o signalinės ir skirtuminės bangų kryptys gali būti valdomos keičiant kampą tarp rezonatoriaus optinės ašies ir kaupinimo pluošto. Taip pat parodoma, kad dryžių erdvinio šviesos darinio formavimasis gali būti pasiekiamas injektuojant pagrindinio dažnio užkrato signalą. Antrojoje disertacijos dalyje pristatomi ir tiriami plokščiųjų veidrodžių Fabri ir Pero tipo rezonatoriai su vidine lūžio rodiklio moduliacija, atitinkančia vieną fotoninio kristalo (FK) išilginį periodą. FK rezonatoriai sukurti veidrodžių paviršiuje suformuojant 2 µm, 4 µm ir 15 µm periodinę lūžio rodiklio moduliaciją (t.y. suformuojant vienmatę arba dvimatę fazinę difrakcinę gardelę). FK rezonatorių kampinis pralaidumas matuotas... [toliau žr. visą tekstą]

Ce travail de thèse est essentiellement consacré à l'étude et à la réalisation d'un laser Raman basé sur les structures à cristaux photoniques (CP) en filière silicium. Nous avons montré que des guides d'onde ridges d'accès combinés avec des tapers inversés permettent d'améliorer efficacement le couplage expérimental de la lumière externe dans des CP. Nous avons réalisé des cavités à CP en approche membrane qui ont permis d'atteindre des facteurs de qualité supérieurs à 2 millions avec un volume modal de l'ordre de la longueur d'onde au cube. Nous avons montré également que le facteur de qualité des cavités à CP dépend de la position des guides d'onde à CP utilisé pour le couplage. Parallèlement, les modélisations numériques sur un nouveau design des cavités en approche SOI nous ont donné un facteur de qualité élevé jusqu'à 8 millions. Nous avons observé une mise en forme du spectre Raman et un renforcement de l'efficacité de la diffusiion Raman d'un factuer supérieur à 10 dans un guide d'onde à CP W1 par rapport à un guide d'onde ridge mono-mode. En particulier, nous avons analysé cette exaltation à travers l'effet Purcell. Nous avons montré qu'une valeur déterministe et une mesure du facteur de Purcell dans une micro-cavité en semi-conducteur peuvent être obtenues en utilisant la diffusion Raman spontanée comme source interne. Un nouveau design de cavité supportant une double résonnance nous a permis d'observer une diffusion Raman stimulée à température ambiante sous une excitation continue. Ces résultats nous permettent de prévoir un seul laser inférieur à 100 mW si l'absorption par porteurs libres peut être rendue négligeable
This work of this thesis has been primarily devoted in the studies and the realization of a Raman laser based on silicon photonic crytal structures. We have shown that access ridge waveguides combined with the inverted tapers allow in optimise efficiently the experimental coupling of the light from an optical fibes into the photonic crystal. We have fabricated the photonic crystal cavities in membrane approach which have allowed to reach quality factor above 2 million with a modal volume of the order of cube wavelenght. The quality factor of photonic crystal cavities has been found dependent on the position of the photonic crystal waveguide used for the coupling. In parallel, the numerical modelings on a new design of the photonic crystal cavities in SOI approach have demonstrated an ultra-high quality factor above 8 000 000. We have observed a reshaping of the Raman spectrum and a more than tenfold enhancement of the Raman scattering efficiency in a W1 photonic crystal waveguide as compared to a single mode ridge waveguide. In particular, we have analysed this enhancement through the Purcell effect. We have shown that a deterministic value and measurement of the Purcell factor in a semiconductor microcavity can be obtained by using spontaneous Raman scattering as an internal source. A new design of a microcavity supporting a double resonance has allowed us to observe stimulated Raman scattering at room temperature under continuous excitation. The model, which accounts for stimulated scattering, two-photon absorption and free-carrier absorption, allows us to predict the onset of Raman lasing in silicon photonic crystals

Depuis les premiers travaux d’Ashkin sur les pinces optiques classiques, beaucoup d’efforts ont été fait pour piéger des nano particules. Néanmoins, elles peuvent difficilement piéger des particules inférieures à 200 nm à cause des limites imposées par la diffraction. Cette limite peut être dépassée grâce aux forces optiques de gradient provenant du champ évanescent généré et amplifié par des nano cavités photoniques. Cependant, cette approche est confrontée à deux verrous importants pour les applications : La surface de piégeage est très faible ce qui rend peu probable la capture d’une nanoparticule animée d’un mouvement brownien et pour les pinces « ultimes » de type nanoantenne où le mode est confiné dans des régions nanométriques, leur excitation en espace libre n’est pas très efficace. L’objectif de ce travail vise à lever ces deux verrous. Pour augmenter la surface de piégeage, nous présenterons d’abord une approche utilisant le mode de Bloch d’une cavité étendue à double période dans un cristal photonique fabriqué sur SOI. Nous montrerons que cette approche permet le piégeage de particules de 200, 100 et 75 nm sur une surface étendue de 5x5 µm² en utilisant un faisceau laser d’excitation en espace libre. Dans un deuxième temps, nous nous intéresserons à l’excitation optique en espace libre de structures nanométriques. Nous présenterons une structure hybride nano antenne – cristal photonique, où le cristal photonique joue le rôle de réservoir à photons pour la nano antenne. Cela permet ainsi un effet « entonnoir à photon» où la lumière issu d’un faisceau large (5µm) est concentrée dans la nanoantenne. Nous démontrerons la pertinence de cette approche par le piégeage particules de 100 nm
Since the first work on optical tweezers by Ashkin, a lot of efforts have been made to trap nanoparticles. However, optical tweezers are diffraction limited and can hardly trap particles below 200 nm. This limit can be overstepped using the optical gradient forces of an evanescent field generated and amplified by a photonic nano cavity. Nonetheless, this approach faces two major issues for applications: the trapping section is very small, making the capture of a Brownian motion animated particle very unlikely, and for the “ultimate” nano antennas with nanometric optical modes, their excitation from free space is not effective. The goal of this work is to overcome these two difficulties. To increase the trapping surface, we will first present a device using slow Bloch modes within a double period extended cavity designed in a photonic crystal made out of SOI. We will show that this approach allow for the trapping of 200, 100 and 75 nm particles on an extended surface of 5x5 µm² using a free space laser beam excitation. Secondly, we will investigate the free space excitation of nanometric structures. A photonic crystal – nano antenna mixed structure will be presented, where the photonic crystal is used as a photon pool for the nano antenna. This lead to a funnel effect where the light coming from a large free space laser beam (5µm wide) is focused into the nano antenna. The trapping of 100 nm particles will demonstrate the relevance of this approach

Nanophotonic circuits for single photon emitters. The work demonstrated in this thesis is dedicated to the engineering, simulation, fabrica-tion and investigation of the essential element base to develop hybrid fully integrated nanopho-tonic circuit with coupled single photon emitter on chip. Combining several individually opti-mized stages of photonic devices, interconnected by nanoscale waveguides on chip with eva-nescently coupled single photon emitter, is a key step to the realization of such a scheme. The main requirements which should be satisfied for building such a hybrid system on-chip, and are thus the subject of this Thesis, are, namely: integration of single photon photostable source with high Quantum Yield (QY) on chip, efficient coupling of the emitted light to nanophotonic cir-cuits, and efficient filtering of the excitation light. Silicon nitride-on-insulator was used in all the projects described in this Thesis as the platform for the realization of photonic circuits. It provides low-loss broadband optical transparency covering the entire visible range up to the near infrared spectrum. Furthermore, sufficiently high refractive index contrast of Si3N4 on SiO2 enables tight confinement of the mode in the waveguide structure and the realization of photonic circuits with small footprint. A drastic increase of the coupling efficiency of the emitted light into the waveguide mode can be achieved by placing single-photon emitter on photonic crystal cavity because of its high Quality factor and small mode volume enabling a high Purcell enhancement. To this end, a novel cross-bar 1D freestanding photonic crystal (PhC) cavity was developed for evanescent integration of single photon emitter, in particular Nanodiamonds (NDs), onto the region of the cavity. The novelty of this photonic structure is that collection of emitted light is provided via waveguide, which consists of PhC, whereas direct optical excitation is obtained through a crossed waveguide in the orthogonal direction of the in-plane cavity. Optimization of the PhC cavity architecture was performed via rounds of simulations and ver-ified by experimental measurements of fabricated devices on chip, which were found in excel-lent agreement. The next round of simulations was performed to define an optimal position of the source in the cavity region to achieve maximum Purcell enhancement, which was realized via Local Density of States (LDOS) computation. Thus, placing a single photon emitter into a determined position on the cavity region of the developed cross-bar 1D freestanding PhC enables an increase in the transmission coupling efficiency into cavity up to =71% in comparison with computed 41% in the case of coupling into waveguide mode of cross-bar structure without PhC. To block the pump light and at the same time transmit the fluorescent emitted light, compact and low-loss cascaded Mach–Zehnder interferometers (MZIs) tunable filters in the visible region embedded within nanophotonic circuit, were realized. Tunability was provided via thermo-optic effect. The design of this device, namely geometry and shape of the microheater, was optimized via thermo-optic measurements, to achieve low electrical power consumption (switching power of 12.2 mW for the case of a spiral-shape microheater), high filtration depth and low optical insertion loss. The novel design with double microheaters on top of both arms of single and cascaded MZIs allows doubling the range of the shifting amplitude of the interference fringes. The demonstrated architecture of tunable filter is multifunctional, namely allowing transmission and filtering of the desired wavelengths in a wide wavelength range. In particular, filtration depth beyond 36.5 dB of light with 532 nm wavelength and simultaneous transmission of light with 738 nm wavelength, which correspond respectively to excitation and emission wavelength of the silicon-vacancy color center in diamond, was demonstrated. The results were published in Ovvyan, A. P.; Gruhler, N.; Ferrari, S.; Pernice, W. H. P. Cascaded Mach-Zehnder interferometer tunable filters. Journal of Optics 2016, 18, 064011 https://doi.org/10.1088/2040-8978/18/6/064011 Another filter with non-repetitive stopband with bandwidth of several nanometers was developed in this thesis. A non-uniform Bragg grating filter with novel double Gaussian apodization was proposed, whose fabrication required a single lithography step. This optimized Bragg filter provides a 21 dB filtration depth with a 3-dB bandwidth of 5.6 nm, insuring negligible insertion loss in the best case, while averaged insertion loss in reflected signal is 4.1dB (including loss in splitter). One of the first Hybrid organic molecule Dibenzoterrylene (DBT) coupled on chip to a nanophotonic circuit was demonstrated in this thesis. DBT is a photostable single photon source in the near infrared spectrum at room and at cryogenic temperature, with almost unitary quan-tum yield. In order to protect the molecule against oxidization DBT was embedded in a host matrix – thin Anthracene crystal (DBT:Ac), which increases photostability. Mirror enhanced grating couplers were employed as convenient output ports for ridge Si3N4 waveguide to detect single photons emitted from integrated Dibenzoterrylene (DBT) molecules at room temperature. The coupling ports were designed for waveguide structures on transparent silica substrates for light extraction from the chip backside. These grating ports were employed to read out optical signal from waveguides designed for single-mode operation at λ=785 nm. DBT molecule was coupled evanescently to the waveguide, and upon excitation of isolated single molecule, emitted single photon signal was carried inside the waveguide to the outcou-pling regions. Using a Hanbury Brown and Twiss setup pronounced antibunching dip was read out from a single molecule via the grating couplers, which confirms the quantum nature of the outcoupled fluorescent light. Simulated and measured transmission coupling efficiency of sin-gle photon emission into the waveguide mode equals =42%. The results were published in P. Lombardi*, A. P. Ovvyan*, S. Pazzagli, G. Mazzamuto, G. Kewes, O. Neitzke, N. Gruhler, O. Benson, W. H. P. Pernice, F. S. Cataliotti, and C. Toninelli. Photostable Molecules on Chip: Integrated Sources of Nonclassical Light. ACS Photonics 2018, 5, 126−132, DOI: 10.1021/acsphotonics.7b00521. * P. Lombardi and A. P. Ovvyan contributed equally to this work. Engineered nanophotonic elements integrated in optical circuits with coupled single photon emitter on chip allow simultaneously to enhance the emitted light by coupling it into resonant PhC cavity modes, to spatially separate the excitation light from the enhanced single photon emission and to filter out pump light. Enhancement of the emission rate leads to a sig-nificant increase of the coupling efficiency into cavity. Beforehand performed simulations were an essential step in order to design, build and optimize the architecture of the nanophotonic devices. Local Density of States enhancement computation was especially necessary to pre-cisely determine optimized position of the source on PhC cavity region to obtain maximum enhancement of the emission rate. To evaluate transmission coupling efficiency of emitted light into the cavity (β-factor), an extra round of simulations was performed. The integrated photonic elements investigated and optimized in this Thesis, will be further employed for the realization of hybrid photonic circuits with integrated single photon sources: silicon-vacancy, nitrogen-vacancy centers in diamond as well as single organic molecule and semiconducting single-walled carbon nanotubes.

Photonic crystal (PtC) cavities are an increasingly important way to create all optical methods to control optical data. Not only must the data be controlled, but interfacing it with high frequency electrical signals is particularly interesting especially if this occurs in the 1.55µm telecom band. We present an experiment that uses Rayleigh surface acoustic waves (SAWs) to modulate the frequency of the guided mode of an L3-cavity PtC created on a silicon slab. This work has the potential to interface optical and electrical signals via a mechanical strain wave operating at gigahertz frequencies. Defects are carefully designed into a triangular lattice PtC to realize a waveguide coupled optical cavity. The cavity can be experimentally accessed through grating couplers excited by polarized light at 10 degrees incidence from normal. The optical components are fabricated on a silicon-on-insulator platform, with light confined to the silicon slab region. Through transmission experiments, the L3 cavity was found to have a narrow resonance characterized by a Lorentzian distribution. A quality factor of 165 centered at 6255 1/cm (1.599µm) was measured. Aluminum interdigitated transducers (IDTs) were fabricated through a lithography liftoff process. Their ability to create SAWs requires a piezoelectric medium. As silicon does not have this property, growth of a thin ZnO film was required. The transducers were measured using a network analyzer and were found to produce Rayleigh SAWs at a frequency of 179MHz and a wavelength of 24µm. The acoustic energy traveled 70µm to the target optical device. The L3 cavity has dimensions of around 4µm a side - less than 1/2 a SAW wavelength. Modulation of the L3 PtC resonant frequency was monitored through a repeat of the transmission experiment but with RF excitation of the IDTs at the SAW frequency. A broadening of the transmission spectrum was expected. Unfortunately no change in the fitting parameters could be measured. An HF etch was used to undercut the L3 PtC such that a silicon slab suspended in air could be realized. Simulations had been conducted showing an order of magnitude increase in the quality factor was possible. Broken wirebonds on the transducers created unintended etch channels rendering the SAW non-operational.
Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2013-04-29 12:33:49.254

碩士
國立中央大學
物理研究所
97
Owing to the spontaneous emission coupling factor (β) in photonic crystal cavity, it can efficiently reduce the lasing threshold in quantum dots laser. In this paper, we will investigate qL2 cavity. By the measurement of micro-photoluminescence (μ-PL) in room temperature, the β of qL2 cavity are around 0.5~0.75, and the lasing threshold are around 6~12μW. Owing to the high β of photonic crystal quantum dots laser, the light-in light-out curve show the soft turn-on behavior around the threshold, and narrowing degree of the line-width is not obvious around the threshold. We study coherence property of light source by measuring coherence length in using Michelson interferometer. In addition to the μ-PL system, adding another way to study Laser property photonic crystal laser.

碩士
國立中正大學
光機電整合工程所
95
In this thesis, we utilized the finite different time domain (FDTD) and planer wave expansion (PWE) methods to simulate the band gap properties and structures of photonic crystals. By this two simulation methods, we can obtain the resonance defect modes in optical communication wavelength. In the fabrication process, we use e-beam lithography technique to do the triangle air-hole 2D photonic crystals with defects on electro-resist that agreed with the simulation results. And then use reactive ion etching (RIE) to transfer the patterns into SOI wafer. Finally, remove silica between the silicon of SOI wafer by 3 wt-% HF. This method can suspend the silicon photonic crystal, and the refractive index contrast is become larger in the vertical direction. This 2D slab photonic crystal can be expected to match the photonic band gap properties with 3D photonic crystals.

碩士
國立中央大學
物理研究所
96
Photonic crystal is an artificial device which arranges its dielectric material periodically. We can fabricate it as a wave guide or cavity via different design ideas. Two- dimension photonic crystals had significant development in recently decade. Numerous researchers were interested in H1 cavities and L3 cavities which were demonstrated possessing high quality factor as 45000. My thesis investigates resonance modes of H1 cavities and L3 cavities. Via adjusting the geometry structures of these cavities, we can understand the correlation of cavity modes between H1 and L3 cavities. Comparing theory analysis and measurement experiment, we can know well about behaviors of these cavity modes. Furthermore, we realize the variation of quality factor more deeply.

碩士
健行科技大學
電子工程系碩士班
103
Photonic crystals are composed of periodic dielectric that has photonic band gap. It can effectively control the light of propagation. In this thesis, we analysis the band gaps of the square lattice photonic by plane wave expansion method, and design of optical power divider by using finite element time domain method. We simulated the light wave propagation in power divider by using finite-difference time-domain method. We also discussed the relationship of the cylindrical size and the transmission coefficient in the divider. Besides, we have simulated the structure of coupled-resonator optical waveguides. From the results that the two-dimensional square lattice arrangement in the center wavelengths characteristic of broadbandandhigh transmission. Further, we proposed the power beam splitter of multimode interference in photonic crystal waveguides. It is a nanometer scale of optical component and it has the ability to guide, split and filter. The results of this study should be applied for photonic integrated circuit in the future.

碩士
國立中央大學
物理研究所
99
In this thesis, we investigate the coupling behavior of photonic crystal coupled L3 cavities through micro-photoluminescence (μ-PL) spectroscopy. By spatial separation tuning, we found that the mode splitting is proportional to the cavity coupling strength, and both of them decrease with the increasing distance between the two cavities. By air-holes-shift tuning, the movement of air holes results in size detune of the two cavities and decreases the coupling strength. By substrate heating tuning, the rising temperature causes the resonant wavelength red shift, but the change of refractive index of substrate does not influence the coupling strength significantly. By laser local heating tuning, the refractive index detune of the two cavities increases the mode splitting and decreases the cavity coupling strength. While the laser power exceeds 11mW, we observe spectral bifurcation phenomenon which results from the thermal vibration on photonic crystal membrane.

碩士
國立交通大學
顯示科技研究所
95
We investigate and discuss the strong whispering gallery mode (WGM) mode dependence on inner-most air-holes of Dodecagonal quasi-periodic photonic crystal (DQPC) D2 (formed by 7 missing air-holes) micro-cavity and its fabrication tolerance by randomly varying the lattice of two separate regions. Hence, we design and fabricate DQPC micro-cavity lasers sustaining WGM. And we measure the basic lasing characteristic of two separate regions to verify WGM mode dependence. For comparison, we also fabricate traditional triangular PC D2 micro-cavity with the same lattice variation regions. From the results between DQPC D2 micro-cavity and PC D2 micro-cavity, we can verify the WGM mode dependence on the inner-most air-holes of DQPC D2 micro-cavity again. Next, we extend the WGM mode in DQPC twin-cavity and triple-cavity. And we investigate the coupling behavior in these structures. We calculated resonance spectrum and resonance mode profiles of the DQPC twin and triple-cavity by 3D finite-difference time-domain (FDTD) method. And we fabricate the real device of DQPC twin and triple-cavity. The basic characteristics of DQPC twin and triple-cavity are measured by a micro-photoluminescence system. The measurement results are compared with the 3D FDTD simulation results.

碩士
國立雲林科技大學
光學電子工程研究所
95
In this thesis, we report experimental demonstration of transverse optical pattern distribution and its evolution in photonic-crystal-structured VCSELs by using near-field scanning optical microscope and optical microscope imaging technologies. In our study, Laguerre-Gaussian mode in conventional 850 nm VCSEL and fundamental mode are observed in single defect photonic crystal VCSEL, spectively. Besides, linear and nonlinear localized patterns are observed in photonic crystal VCSELs, including Whispering-Gallery modes and soliton-like patterns.

碩士
國立交通大學
電子物理系所
99
Photonic crystal D0 cavity InGaAsP quantum well laser have been studied by photoluminescence (PL). The monopole, WG, and dipole mode have been clarified by the μPL, SNOM, and FDTD simulation. By power-dependent PL, we study the spectral change of lasing process in the D0 photonic crystal structure. By the calculating the rate equation of lasing, we can acquire the spontaneous coupling factor β and the lasing threshold power. Then we study the photon correlation of the multi-excitonic states in quantum dots (QDs) embedded in photonic crystal L3 structure by HB-T interferometer. We can clarify the QD emission and the cavity mode by power- and temperature-dependent PL measurement. And we use time-resolved PL and HB-T experiment to study the photon correlation between multi-excitonic states in QD. The six-level rate equation has been set to simulate the photon correlation behaviors.

碩士
國立交通大學
光電工程系所
93
This thesis presents our study on GaAs based vertical-cavity surface-emitting laser (VCSEL) and is divided into two parts. The first part discuss the improvement of high speed performance of oxide VCSEL by utilizing tapered oxide layer. We setup wafer-level high speed measurement system which allows us to test device immediately and avoids parasitic effect from package. The damping rate from the modulation response was found to reduce two times in the tapered oxide VCSEL and therefore enhanced the maximal modulation bandwidth. With same oxide aperture size 5.5 μm, tapered oxide VCSEL shows better modulation bandwidth of 13.2 GHz while blunt oxide VCSEL has 9.5 GHz. A very clean eye was demonstrated from improved VCSEL with rising time of 26 ps, falling time of 40 ps and jitter of less than 20 ps, operating at 10Gb/s with 6mA bias and 6dB extinction ratio. We also build an equivalent circuit model to analyze the bandwidth limitation affected by VCSEL intrinsic impedance. The simulation results could make the modulation limitation clearly and help us to modify the VCSEL process for high speed operation. In the second part of the thesis, we report a high power (>1 mW) singlemode proton-implanted photonic crystal vertical-cavity surface-emitting laser (PC-VCSEL) with high SMSR (> 40 dB) throughout the whole operation current range. This PC-VCSEL, with an aperture of about 10 μm, has ultra-low threshold current of about 1.25 mA. We analyze the L-I curve, emission spectra, near field pattern, divergence angles of photonic crystal VCSELs fabricated with oxide-confined and implant structure. The present results indicate that a VCSEL using proton implantation for current confinement and photonic crystal for optical confinement is a reliable approach to achieve high-power singlemode operation of a VCSEL. This concept will be applied to a 1.3μm VCSEL and other commercial applications in the future.

碩士
龍華科技大學
電機工程系碩士班
101
In high-density optical integrated circuits, waveguide crossings are two straight waveguides crossing each other. In this thesis, the dielectric rod structure of two-dimensional photonic crystals with cubic lattice is used for design and analysis. Dielectric rods used for filters are introduced to form cavities within the waveguide crossing devices. The proposed cavity-type waveguide crossing devices are simulated and analyzed by numerical methods. By the results of simulations, we find that by changing the radii and distances of the filtering dielectric rods, the characteristics of the transmission spectrum of the filter is under controlled. In this thesis, we proposed a novel cavity-type waveguide crossing device for two-dimensional photonic crystal by introducing dielectric-rod filters. By the simulation and analysis, the central frequency of transmission mode is controlled by the distance of the dielectric-rod filters. The full width at half maximum of the transmission mode is also controlled by the radii of the dielectric-rod filters. Therefore, the proposed cavity-type waveguide crossing has the advantages of easily controlling the central frequency and the full width at half maximum of the transmission mode. The results of this research show practical values for the optical integrated circuits in the future.

碩士
逢甲大學
光電研究所
99
A hollow core photonic crystal fiber (HC-PCF) can be used to enhance the light intensity and the interaction length with gas sample. These features are important for nonlinear spectroscopy. However, in case of saturation absorption spectroscopy, the interference fringes originated from the counter propagation of beams inside the HC-PCF usually destroy the nonlinear signal. In this paper, we show that the splicing end of a 35-cm HC-PCF can be served as one end mirror of a fiber cavity with the help of a piezo-electrically actuated mirror serving as the other end mirror. The incident laser frequency was locked to one cavity modes to eliminate the interference effect, and the stability of the laser relative to the cavity was 8.1× 10-8. As a first demonstration of this scheme, we observed the Doppler absorption spectrum of ν1+ν3 P(9) line of acetylene molecule, we also observed a weak saturated absorption, but still have to improved the signal to noise ratio of spectroscopy.

碩士
國立中央大學
電機工程研究所
97
Abstract In recent years, photonic crystal defect cavity is widely used to achieve high Purcell factor for high efficiency single photon sources. As the defect cavity is operated at single mode condition, all the photons generated inside the cavity are forced to funnel through this single mode and lead to enhanced coupling efficiency. Previous study shows that a quasi-L2 defect cavity offers not only three clearly resonant modes but also a very small mode-volume, which is essential for high Purcell effect. In this study, we adjust the geometric parameters of quasi-L2 photonic crystal defect cavity, and successfully realize a 1.3??m single mode photonic crystal cavity. For a cavity with quality factor of 1100, the quantum dot luminescence intensity is enhanced over 70 fold, demonstrating its potential of q-L2 photonic crystal cavity for high efficiency single photon sources and lasers.

碩士
國立中山大學
光電工程學系研究所
106
Fiber-optic Mach-Zehnder interferometers (MZIs) have been widely proposed due to their advantages such as compact size, high resolution, and high sensing sensitivity. Especially, MZIs with open cavities exhibit ultrahigh refractive index (RI) sensitivities, which can be applied in detecting slight RI variation. Previous studies have proposed several open-cavity MZIs by splicing fibres with a large lateral offset, which are difficult to be fabricated due to the required precise alignment. Some research groups utilize femtosecond (fs) lasers to fabricate open-cavity MZIs, which results in high cost. In this thesis we propose a method to fabricate an open-cavity MZI by splicing an etched photonic crystal fiber (PCF) with a beveled fiber formed by fiber polishing technology. Our manufacturing process is simple, and no high-cost fs lasers are required. The interference properties of our MZI are experimentally demonstrated and discussed with different core sizes and cavity lengthes. It is proved by the increase of the free spectrum range that the liquid indeed can be filled into the open cavity successfully. In sensing properties, our MZI exhibits an ultrahigh RI sensitivity of 10462.7 nm/RIU in the RI range of 1.3330 to 1.3418 and pressure sensitivity of -63.71 pm/psi in the pressure range of 0 to 20 psi. Besides, the corresponding detection limits are -6 4.78 10  RIU and 0.159 psi, respectively, which indicates that our MZI can detect slight RI variation. Moreover, the temperature sensitivity of our MZI is 31.23 pm/℃, and the strain sensitivity of the MZI is 1.06 pm/με and -4 1.04 10  dB/με. As a result, our fabricated MZI sensor possess good potential in environmental parameter sensing.

博士
國立交通大學
電子工程學系 電子研究所
102
This dissertation mainly researches the photoluminescence characteristics of single quantum dot. We report on the magnetic responses of neutral exciton (X), biexcitons (XX) and positive/negative trions (X+/X-) in single self-assembled InAs/GaAs quantum dots. Unlike the conventional quadratic diamagnetic shift for neutral excitons, the observed X- diamagnetic shifts are small and nonquadratic. In particular, we also observed a reversal in sign of the conventional diamagnetic shift. A theoretical analysis indicates that such anomalous behaviors for X- arise from an apparent change in the electron wave function extent after photon emission due to the strong Coulomb attraction induced by the hole in its initial state. This effect can be very pronounced in small quantum dots, where the electron wave function becomes weakly confined and extended much into the barrier region. When the electrons gradually lose confinement, the magnetic response of X- will transit gradually from the usual quadratic diamagnetic shift to a quartic dependence, and finally into a special paramagnetic regime with an overall negative energy shift. On the other hand, we purpose to study the coupling effect between single quantum dot and photonic crystal cavity, a method for designing H1 photonic crystal cavity is introduced to enhance its quality factor (Q factor). The highest theoretical Q factor of 120,000 is obtained. The Fourier transformation of field distribution shows that the enhancement arises from the component reduction of leaky mode. The Q-factor improvement has also been demonstrated experimentally with the highest value of 11700. Our design could be useful for studying light-matter interaction in H1 cavity as the mode volume only increases slightly. Finally, we successfully demonstrated the strong coupling effect in the H1 photonic crystal cavity embedded single InAs/GaAs quantum dot. Two polariton states arise from the hybridization of the cavity mode and quantum dot, which reflect in the alterations of observed emission characteristics, such as emission wavelength, full width half maximum and intensity. Via analysis, the strongest coupling effect occurs at about 37.75 K, while Rabi splitting is equal to 156.7 μeV.