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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.

This thesis details work undertaken over the past three and a half years looking at the optical properties of silicon-on-insulator waveguide arrays and 1D photonic crystal microcavities. Chapter 1 contains relevant background information, while chapters 2, 3 and 4 contain results of experimental work. Chapter 5 summarises the results and conclusions of the preceding chapters and also suggests some directions for possible future research. Chapter 1 starts by introducing some of the fundamental aspects of guided wave optics and how these relate to silicon-on-insulator waveguides. The modes of single,uncoupled silicon waveguides are described, along with a brief description of how such waveguides can be fabricated. Following this a short introduction to optical cavities and the relevant parameters that can be used to describe them is provided. In Chapter 2 results are presented that experimentally confirm the presence of couplinginduced dispersion in an array consisting of two strongly-coupled silicon-on-insulator waveguides. This provides an additional mechanism to tailor dispersion and shows that it is possible to achieve anomalous dispersion at wavelengths where the dispersion of a single wire would be normal. In Chapter 3 the focus switches to the linear properties of 1D photonic crystal microcavities in silicon. The optical transmission of a number of different devices are examined allowing the identification of suitable microcavities for use in nonlinear measurements. Microcavities with Q-factors in excess of ∼40,000 were selected for use in the work presented in Chapter 4, whilst the possibility of thermally tuning the microcavity resonances is also investigated. A cavity resonance shift of 0.0770± 0.0004 nm K-1 is measured experimentally. Chapter 4 looks at the nonlinear transmission of those microcavities identified as suitable in Chapter 3. More specifically, the response of the microcavities to thermal and free carrier induced bistability is considered. Thermally induced bistability is observed at a threshold power of 240 μW for the particular cavity chosen, with a thermal time of 0.6 μs also measured. Free carrier induced bistability is then observed for pulses with nanosecond durations and milliwatt peak powers. Following that, the interplay of thermal and free carrier effects is observed using input pulses of a suitable duration.

El silicio es un material de suma importancia en microelectronica y en fotonica. Las propiedades semiconductoras del silicio estan detras de los conceptos que gobiernan el funcionamiento de la mayoría de los dispositivos electronicos como los diodos y los transistores. El concepto de integracion ha permitido procesar dispositivos muy pequeños, llegando a alcanzar un tamaño nanometrico. El alto indice de refraccion del silicio permite confinar la luz en estructuras de tamaño micrometrico. Este es el caso de dispositivos fotonicos tales como las guias de onda y las cavidades. Usualmente, tanto los dispositivos fotonicos como los electronicos estan basados en la tecnologia planar, es decir poseen una topologia plana, siendo esto una fuente de perdidas. Es bien conocido que las cavidades esfericas confinan la luz con mas eficiencia que las cavidades planares. Esta tesis trata sobre el desarrollo de un nuevo tipo de microparticulas esfericas que llamamos Coloides de Silicio. Debido a su forma esferica, su alto indice de refraccion y su suave superficie, estas particulas funcionan como microcavidades opticas con modos resonantes bien definidos en el infrarrojo cercano. La tesis reporta sobre la sintesis, y las propiedades estructurales y opticas de los coloides de silicio con diametro entre 0.5 y 3.5 micrometros. Los coloides de silicio pueden facilitar el desarrollo de microcavidades de alto factor de calidad con alta eficiencia de confinamiento de la luz, y permitir la integracion de dispositivos electronicos y fotonicos tales como una union p-n en una sola particula coloidal. Esta tesis reporta tambien sobre los coloides de silicio como elementos integrantes de las Esponjas Fotonicas, las cuales estan formadas por una red desordenada de microesferas de silicio de diferentes tamaños, e interaccionan con la luz fuertemente en un ancho rango de longitudes de onda. / Tymczenko, MK. (2010). Photonic microcavities and photonic sponges based on silicon colloids [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/8425 / Palancia

Aqui apresentamos um modelo teórico para superfícies super-hidrofóbicas que são formadas por superfícies contendo padrões periódicos na forma de microcavidades. Com este modelo obtivemos a relação ideal entre profundidade e diâmetro das cavidades para que a superfície manifeste seu caráter super-hidrofóbico. Assim, fabricamos superfícies em PDMS (popular silicone) capazes de produzir ângulos de contato elevados. Produzimos amostras contendo microcavidades específicas (paralelepípedas, hexagonais e cilíndricas) as quais foram microfabricadas por litografia de feixes de elétrons e caracterizadas por Microscopia Eletrônica de Varredura (MEV), Microscopia de Força Atômica (AFM), e medidas de ângulo de contato. Os padrões das microcavidades das superfícies produzidas seguiram as considerações da teoria e as medidas dos ângulos de contato de avanço e recesso mostram boa concordância com as previsões do modelo. Portanto, podemos afirmar que a teoria aqui descrita permite projetar superfícies altamente hidrofóbicas. / Here we present a theoretical model for super-hydrophobic surfaces formed by surfaces containing periodic patterns in the form of microcavities. With this model we obtained the ideal relationship between depth and diameter of the cavities so that the surface expresses a super-hydrophobic character. Thus manufacture of PDMS surfaces (with known silicone) is capable of producing high contact angles. We produced samples containing specific microcavities (parallelepipeds, hexagonal and cylindrical) which have been microfabricated by electron beam lithography and characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle measurements. The patterns of the surfaces of the cavities produced following the considerations of theory and measurements of advancing and recending contact angles show good agreement with the model predictions. Therefore, we can attest that the theory described here allows the design of highly hydrophobic surfaces.

<p>This Licentiate presents the main results of theoretical study of light propagation in photonic structures, namely lasing disk microcavities and photonic crystals. In the first two papers (Paper I and Paper II) we present the developed novel scattering matrix technique dedicated to calculation of resonant states in 2D disk microcavities with the imperfect surface or/and inhomogeneous refractive index. The results demonstrate that the imperfect surface of a cavity has the strongest impact on the quality factor of lasing modes.</p><p>The generalization of the scattering-matrix technique to the quantum-mecha- nical case has been made in Paper III. That generalization has allowed us to treat a realistic potential of quantum-corrals (which can be considered as nanoscale analogues of optical cavities) and to obtain a good agreement with experimental observations.</p><p>Papers IV and V address the novel effective Green's function technique for studying propagation of light in photonic crystals. Using this technique we have analyzed characteristics of surface modes and proposed several novel surface-state-based devices for lasing/sensing, waveguiding and light feeding applications.</p> / Report code: LIU-TEK-LIC 2006:5

Semiconducting nanocrystals in open-access microcavities are promising systems in which enhanced light-matter interactions lead to quantum effects such as the modulation of the spontaneous emission process and exciton-polariton formation. In this thesis I present improvements of the open cavity platform which serves to confine the electromagnetic field with mode volumes down to the &lambda;³ regime and demonstrate results in both the weak and strong coupling regimes of cavity quantum electrodynamics with a range of different low-dimensional materials. I report cavity fabrication details allowing a peak finesse of 5 &times; 10⁴ and advanced photonic structures such as coupled cavities in the open cavity geometry. By incorporating two-dimensional materials and nanoplatelets in the cavity I demonstrate the strong coupling regime of light-matter interaction with the formation of exciton-polaritons, quasi-particles composed of both photon and exciton, at room temperature. In the perturbative weak coupling regime I show pronounced modulation of the single-photon emission from CdSe/ZnS quantum dots and the two-dimensional material WSe₂ and demonstrate Purcell enhancement of the spontaneous emission rate by factors of 2 at room temperature and 8 at low temperature. The findings presented in this thesis pave the way to establish open microcavities as a platform for a wide range of applications in nanophotonics and quantum information technologies.

Aqui apresentamos um modelo teórico para superfícies super-hidrofóbicas que são formadas por superfícies contendo padrões periódicos na forma de microcavidades. Com este modelo obtivemos a relação ideal entre profundidade e diâmetro das cavidades para que a superfície manifeste seu caráter super-hidrofóbico. Assim, fabricamos superfícies em PDMS (popular silicone) capazes de produzir ângulos de contato elevados. Produzimos amostras contendo microcavidades específicas (paralelepípedas, hexagonais e cilíndricas) as quais foram microfabricadas por litografia de feixes de elétrons e caracterizadas por Microscopia Eletrônica de Varredura (MEV), Microscopia de Força Atômica (AFM), e medidas de ângulo de contato. Os padrões das microcavidades das superfícies produzidas seguiram as considerações da teoria e as medidas dos ângulos de contato de avanço e recesso mostram boa concordância com as previsões do modelo. Portanto, podemos afirmar que a teoria aqui descrita permite projetar superfícies altamente hidrofóbicas. / Here we present a theoretical model for super-hydrophobic surfaces formed by surfaces containing periodic patterns in the form of microcavities. With this model we obtained the ideal relationship between depth and diameter of the cavities so that the surface expresses a super-hydrophobic character. Thus manufacture of PDMS surfaces (with known silicone) is capable of producing high contact angles. We produced samples containing specific microcavities (parallelepipeds, hexagonal and cylindrical) which have been microfabricated by electron beam lithography and characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle measurements. The patterns of the surfaces of the cavities produced following the considerations of theory and measurements of advancing and recending contact angles show good agreement with the model predictions. Therefore, we can attest that the theory described here allows the design of highly hydrophobic surfaces.

Exciton-polaritons in semiconductor microcavities have been studied intensely, both with respect to their intriguing fundamental physical properties and with respect to their potential in novel device designs. The latter requires ways to control polaritonic systems, and all-optical control mechanisms are considered to be especially useful. In this talk, we discuss and review our efforts to control the polariton density, utilizing optical four-wave mixing instabilites, and the spin or polarization textures resulting from the optical spin Hall effect. Both effects are readily observable in the cavity's far-field emission, and hence potentially useful for optoelectronic and spinoptronic device applications.

Here we present direct investigation of the lasing behaviour by performing gain spectroscopy of solution-based CQDs enabled via in-situ tuning of the feedback wavelength of an open-access hemispherical microcavity. The investigation is performed on two different types of CQDs, namely spherical CdSe/CdS core-shell CQDs and nanopletelets (NPs). The lasing threshold and the differential gain/slope efficiency of the fundamental cavity mode are measured as a function of their spectral position over a spectral range of &Tilde; 32 nm and of &Tilde; 42 nm for the spherical CQDs and NPs, respectively. The results of the gain spectroscopy are described using theoretical models, providing insights into the mechanism governing the observed lasing behaviour. Furthermore, the open-access cavity architecture provides a very convenient way of producing in-situ tunable lasing, and single-mode lasing of the fundamental cavity mode over a spectral range of &Tilde; 25 nm and &Tilde; 37 nm is demonstrated using spherical CQDs and NPs, respectively. In addition, the stability of laser emission is investigated, with the lasing intensity of the fundamental cavity mode remaining constant over a time period of almost 6 mins. It is hoped that the results will provide a detailed understanding of the lasing behaviour of CQDs. This information can be fed back into the design of CQDs in which the lasing threshold can be reduced to the point where useful devices can be constructed, and in the design of resonant optical feedback structures for which the appropriate wavelength must be carefully selected.