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The internal quantum efficiency of organic light-emitting diodes (OLEDs) has reached nearly 100%, and thus further improvement in the external quantum efficiency can be achieved only through outcoupling enhancement. However, light propagation in OLEDs for achieving high outcoupling has mainly been controlled not by the internal organic semiconductor layers but by external optical elements, which inevitably increase process cost. Here, a method is proposed for outcoupling enhancement that actively controls the refractive index of a hole transport layer (HTL) in OLEDs using a stably evaporable perfluororesin, which has a low refractive index and high amorphousness. The co-deposition of the perfluororesin with a hole transport material lowers the refractive index of the HTL to 1.56 at 550 nm without deteriorating the electrical properties. Owing to the nano-sized pillar-like phase separation between the perfluororesin and the hole transport material, the path of charge transport is retained. Using the low-index co-deposited HTL, a 1.22-fold enhancement of the outcoupling efficiency of a phosphorescent OLED is demonstrated. The proposed method can be generally applied to OLEDs to significantly enhance their outcoupling efficiency without increasing process cost. The results show the potential of active refractive index control as a major strategy for achieving further high-efficiency OLEDs.

Cholesteric liquid crystals are tunable self-assembled photonic bandgap materials. Because of their unusual properties and potential for applications in photonics, their optical properties have rec...

Controlling the direction of light propagation, or light switching, enables the addressing of individual optical elements in high-density and complex photonic integrated devices. Light switching is...

Development of tomographic reconstruction for three-dimensional optical imaging: From the inversion of light propagation to artificial intelligence

Resonance lineshapes of a side-coupled waveguide-microring resonator (MRR) is crucial for the performances of MRR-based on-chip photonic devices. Much efforts have been made to modify the resonance lineshapes to other types, such as asymmetric Fano profiles. However, complex photonic structures are required to integrate with waveguide-MRR. Here, we model the light propagation in a waveguide-MRR into the interactions of a discrete resonance mode and a continuum waveguiding mode and propose the phase delay between the two states plays great roles in controlling the resonance lineshape into symmetric Lorentzian dips, Lorentzian peaks, and Fano lineshapes with arbitrary asymmetric factors. We experimentally verify this by fabricating silicon waveguide-MRR with an air-hole inserted in the bus-waveguide section coupled with the MRR, where the air-hole with varied dimensions could control the phase delay. The results not only have potentials to strengthen the performances of MRR-based devices, but also provide a simple strategy to control resonance lineshapes in other optical resonators, including photonic crystal cavity, microtoroid, etc.

Interaction between nanoparticles and optical resonators contributes to the conceptual and experimental demonstration of nanoparticle sensors and scattering-induced coupling between two counter-pro...

This paper is about the various limitations of the novel Li-Fi technology and perhaps those which have an adverse impact on its security and efficiency. Line of sight has been one of the major barriers for VLC based technology which causes eminent hindrance in the widen applicability of the technology. Li-Fi is a non-Line of Sight alternative which does not merely confine its limits or depreciates its efficiency; in fact, it makes it an ineffective option for the LoS based scenarios. This paper will discuss the hybrid approach to wireless solutions in an effort to address the said impediments. This paper also discusses the methods to minimize the lope holes which jeopardize the gains associated with the non Line of sight (NLoS) nature of the light propagation and explains ways to control eavesdropping.

Self-healing of an Airy beam during propagation is of fundamental interest and also promises important applications. Despite many studies of Airy beams in the quantum regime, it is unclear whether an Airy beam only including a single photon can heal after passing an obstacle because the photon may be blocked. Here we experimentally observe self-healing of a heralded single-photon Airy beam. Our observation implies that an Airy wave packet is robust against obstacle caused distortion and can restore even at the single-photon level.

Transparent wood (TW), a biocomposite material demonstrating optical transparency in the visible range, has attracted much interest in recent years due to great potential for ecofriendly applications, for instance, in construction industry and functionalized organic materials. Optical properties of TW, including transparency and haze, depend on a particular structure of cellulose-based backbone compound, (mis-)matching of the refractive indices (RIs) between TW compounds, and the polymer matrix. Although there are data of cellulose RIs for various forms of cellulose (fibers, powder, hot-pressed films, etc.), these values might differ from an effective RI of the TW substrate. Herein, a numerical model of light propagation in the TW, based on the real cellular structure in wood, is presented and applied to estimate an effective RI of the delignified wood reinforcement in the experimentally investigated TW material. Ray-tracing and rigorous electromagnetic approaches are compared for modeling light propagation in the TW. Ray tracing demonstrates considerably simplified yet accurate and efficient solutions. The work brings substantial progress toward realistic and practical wood modeling for the purpose of applications, materials design, and fundamental studies. QC 20230511

The goal of this thesis is to steer light deep inside otherwise opaque media. Opaque media are those that strongly interact with light, leading to low transmission and high scattering or reflection. We perform experimental studies on samples that interact with light in different manners. The opaque samples range from randomly distributed nanoparticles that scatter light in all directions to 3D periodically ordered photonic crystals with a forbidden range of light frequencies, a full photonic band gap, and even superperiodic structures, namely 3D arrays of coupled resonating cavities in a 3D band gap. In presence of multiple scattering, the wavefront shaping phase modulation technique is used to focus light behind or inside the medium. We apply this technique to photonic crystals with a forbidden energy gap for light that have intrinsic fabrication disorder that results in multiple scattering. By adding periodically repeated cavities in 3D band gap crystals, we finally present a novel controlled wave transport in superperiodic media, where light hops from cavity to cavity within an otherwise forbidden photonic band gap.

Recently, near-field optical tweezers integrated on a chip based on silicon on insulator (SOI) have attracted more attention and are promising for biological and chemical analyses. Here we propose a low-loss tapered Si waveguide with a high intensity gradient in the electric field to trap microparticles whose diameters vary from 1 μm to 5 μm. The high transmittance allows for cascading the traps along the direction of light propagation. Optical forces in all three dimensions are analyzed around a high-stiffness potential well obtained.

The concept of silicon photonics beyond the singlemode regime is proposed to help solve the issue of propagation losses and random phase errors for light propagation along silicon photonic waveguides. It shows the great potential for enhancing the performance of photonic devices. A review for recent progresses is given in this paper.

We study the propagation of light through a three-dimensional (3D) superlattice of cavities that is embedded in a 3D photonic band gap. In such a superlattice of cavities, light propagation takes place as a result of inter-cavity coupling. Light supported by the cavity modes takes certain preferred high-symmetry paths inside the structure, hence known as ‘Cartesian light’ [1] .

Analysis of morphological changes of the peritoneal membrane is an essential part of animal studies when investigating molecular mechanisms involved in the development of peritoneal fibrosis or testing the effects of potential therapeutic agents. Current methods, such as histology and immunohistochemistry, require time consuming sample processing and analysis and result in limited spatial information. In this paper we present a new method to evaluate structural and chemical changes in an animal model of peritoneal fibrosis that is based on hyperspectral imaging and a model of light transport. The method is able to distinguish between healthy and diseased subjects based on morphological as well as physiological parameters such as blood and scattering parameters. Furthermore, it enables evaluation of changes, such as degree of inflammation and fibrosis, that are closely related to histological findings.

We investigate rigorously the behaviour of light propagation in the closed contour of the linear Sagnac effect. Assuming that the local light speed is c in a section of the contour, our approach ma...

Unique properties can be achieved in engineered nanoparticle films, including those related to quantum confinement, surface chemistry, and light propagation, which can be exploited for energy appli...

An analytical model for light propagation in abrupt tapered single mode fiber Mach-Zehnder interferometer based on coupled mode theory is proposed. The mode propagation process is calculated with this model and compared with previous numerical simulation results. To experimentally verify the model, an in-line Mach-Zehnder interferometer based on abrupt tapered fiber is fabricated and tested in lab. The spectrum calculated by the model matches well with the measured spectrum.

The asymmetric or unidirectional light propagation has attracted enormous research interest in optical communication system. Most of these waveguides are static and cannot be modulated. In order to achieve a dynamic and tunable asymmetric waveguide, we propose a two-dimensional photonic crystal waveguide with a localized PT-symmetry. With the band coalesce, the structure achieves a unique waveguide mode band. With an excitation of line source the light in the waveguide undergoes an asymmetric or symmetric propagation in the two opposite directions of the waveguide, dependent on the source position and frequency. For a frequency in the waveguide mode band, the contrast of the field amplitudes in the two directions change periodically with the displacement of the source; whereas for the fixed source, the contrast can be modulated by the source frequency.

The paper presents theoretical study of an electromagnetic wave propagation in a planar total internal reflection waveguide with a centrally located quantum well. The calculation is based on transfer matrix method application that gives the possibility to describe the propagation of light in layered structures and calculate the reflection spectrum having related it with the eigenmodes of the system. The prediction is made that the interaction appears between the excitons of the quantum well and the electromagnetic wave in the form of the anticrossing in the reflection spectrum. This behavior is a characteristic feature of such quasiparticles as exciton-polaritons. It is predicted that the value of the Rabi splitting is about several millielectronvolts for exciton-polaritons in the total internal reflection waveguide with a GaAs quantum well. It is also shown that the interaction between the excitons of the quantum well and TE and TM polarized electromagnetic waves is different that can be seen in the reflection spectrum of the structure and agrees with the optical selection rules. As a result, the alternative exciton-polariton system is proposed, which in return can be used in the modern semiconductor industry as a system for information transfer.

A refractive index (RI) sensor based on a tapered no cladding fiber (NCF) is proposed theoretically and experimentally. The RI sensor is fabricated by splicing a NCF in the middle of two single mode fibers (SMF), and then the NCF is tapered to get lower waist diameter. Due to the lack of cladding, surrounding refractive index (SRI) can directly affect the light propagation of NCF, and the decrease of diameter can further improve the RI sensitivity by strengthening the evanescent field. The sensitivity with different lengths and waist diameters of NCF is investigated. It is observed that there are different linear relationships in different refractive interval and the RI sensitivity increases obviously with the waist diameter decreasing, especially when it is below 30 μm. RI sensitivity of the sensor reaches 686 nm/RIU when the waist diameter is 13 μm and SRI is at the range of 1.333–1.350. The sensor can be widely used in biosensing for its simple operation and high sensitivity at low SRI.

In this paper, a generalized numerical model describing the pump light propagating in the distributed side-coupled cladding-pumped (DSCCP) fibers with identical pump cores is present, with which the pump light propagation in the DSCCP fiber is analytically investigated. It is found that the local pump absorption should be smaller than the inner-cladding pump absorption of signal fiber. It is also revealed that the DSCCP fiber length for a given total pump absorption should be inversely proportional to the up-limitation of local pump absorption which decreases monotonously with the pump cores number. Furthermore, it is found that the peak pump power coupled into the signal fiber increases monotonously, while its ratio to the total pump power (i.e., normalized peak pump power) decrease monotonously with the increment of pump cores number. The dependences of pump light propagation on the coupling coefficients and the inner-cladding pump absorption of signal fiber are also discussed. We believe that these results can provide significant guidance on understanding and designing of DSCCP fiber and its lasers and amplifiers.

This PhD thesis describes the design, modelling, fabrication, and characterization of metasurfaces capable of controlling the propagation of light beams with low insertion losses. Metasurfaces are planar subwavelength structures that allow local control of phase, amplitude and/or polarization of light. These structures have proven to be extremely versatile, finding applications in imaging, holography, polarization optics and sensing, to mention only a few. One key aspect in the design of a metasurface is the material choice of its constituents, as it plays a significant role in defining the physical mechanism underlining its operation. In this sense, we can divide metasurfaces into two groups: plasmonic and dielectric. Plasmonic metasurfaces, which use metallic structures, were the first metasurfaces demonstrated in the literature. Nevertheless, the efficiencies of these metasurfaces are severely impacted by Ohmic losses and are theoretically limited in 25% when operating in transmission mode. For example, it is shown in this thesis that the transmission efficiencies of plasmonic metasurfaces based on aluminium are of the order of ~13%, which is typically too low for holography, for instance. Recently, all-dielectric metasurfaces based on high refractive index materials have been proposed as an alternative to circumvent the low transmission problem of plasmonic metasurfaces. In this thesis, it is shown how the transmission efficiencies of metasurfaces are dramatically improved by dielectric materials. The dielectric of choice in this thesis is crystalline silicon (c-Si), which has a combination of advantageous properties, such as: high refractive index, ease of patterning, and low absorption in the visible (as compared to amorphous silicon). Two metasurface designs are then proposed for holography applications. The first design uses cylindrical nanoposts to impose a phase modulation in the transmitted light. The hologram shows high fidelity and high efficiency, with measured transmission and diffraction efficiencies of ~65% and ~40%, respectively. Although originally designed to achieve full phase control in the range [0-2π] at 532 nm, these holograms have also performed well at 444.9 nm and 635 nm. The high tolerance to both fabrication and wavelength variations demonstrate that holograms based on cSi metasurfaces are quite attractive for diffractive optics applications, and particularly for fullcolour holograms. The second design uses elliptical cross-section nanoposts that are form-birefringent, that is, they provide independent control of phase for two orthogonal polarizations in the visible spectrum. Relying on these properties, a holographic stereogram was encoded in the metasurface. Briefly, a stereoscopic image (stereogram) is composed of a pair of orthogonally polarized images taken from the same scene but recorded in slightly shifted positions to replicate the natural parallax of the human eye. For the stereoscopic effect (depth perception) to occur, each of these two images has to be directed to each of the user\'s eyes separately with the help of cross-polarized glasses. The stereoscopic effect is obtained by combining two holograms on the same metasurface (one for each polarization). The hologram was encoded with four phase levels. Two additional non-stereoscopic holograms using two uncorrelated images were also fabricated to help assessing polarization cross-talk. The reconstruction plane consists of a fine-sanded aluminium surface to preserve the polarization of the scattered light. The stereoscopic view is obtained with a pair of cross-polarized filters (or glasses) placed in front of the observers\' eyes. The theoretical bandwidth is 110 nm with a signal to noise ratio (SNR) >15 dB. The measured transmission and diffraction efficiencies are about 70% and 15%, respectively, at 532 nm. Such high efficiency is due to a combination of low absorption and high index of c-Si at visible: the index is sufficiently high to enable sufficiently small posts to alleviate the material losses. We also investigated the metasurfaces at 444.9 nm and 635 nm to experimentally assess their bandwidth performance. The quality of the stereoscopic effect is surprisingly high at 444.9 nm (but not so much at 635 nm) with transmission and diffraction efficiencies around 70% and 18%, respectively. The proposed structure was able to successfully capture the depth effect on the reconstructed images, with potential applications in diverse areas such as visual arts, entertainment, and security. The latter, in particular, will certainly benefit from the increased degree-of-freedom conveyed by stereoscopic information. Leveraging on the experience obtained with the research on holograms, we focused on the problem of monochromatic aberrations on metalenses. Metalenses are nanostructured surfaces that mimic the functionality of optical elements. Many exciting demonstrations had already been made, for example, focusing into diffraction-limited spots or achromatic operation over a wide wavelength range. The key functionality that was yet missing, however, and that is most important for applications such as smartphones or virtual reality, is the ability to perform the imaging function with a single element over a wide field of view. Thus, relaxing the constraint on diffraction-limited resolution, we demonstrated the ability of single-layer metalenses to perform wide field of view (WFOV) imaging while maintaining high resolution suitable for most applications. We also discussed the WFOV physical properties and, in particular, we showed that such a WFOV metalens mimics a spherical lens in the limit of infinite radius of curvature and infinite refractive index. Finally, we explored the expertise acquired with the design of nanostructures to address an important problem in the renewable energy community: how to improve the performance of solar cells using nanostructures. In particular, we analysed the impact of these structures on the performance of a new class of solar cells: the tandem solar cell employing perovskites and silicon. Such tandem solar cells require careful photon management for optimum performance, which can be achieved with intermediate photonic structures. We first identified that a photonic intermediate structure in a perovskite/c-Si tandem solar cell should act as an optical impedance matching layer at the perovskite-silicon interface. This conclusion did not tally with the perception in the tandem community at the time, which tented to ascribe the role of a tailored reflector to intermediate structures. Relying on the new insights gained, we analysed two simple designs and compared their performances with intermediate reflectors based on Distributed Bragg Reflectors (DBR). Our conclusion was that the intermediate structures acting only as an optical impedance matching layer show similar performance as the DBR reflectors but are much simpler. We completed the analysis by simulating a realistic device configuration and showed that optical impedance matching alone can increase the short circuit current of the silicon solar cell by 18.5% (corresponding to a boost of 2.8 mA/cm2), thus resulting in an expected tandem efficiency in excess of 30%. Esta tese de doutorado descreve o projeto, a modelagem, a fabricação e a caracterização de metassuperfícies para o controle da propagação de feixes de luz com baixas perdas. Metassuperfícies são estruturas planas compostas de estruturas menores que o comprimento de onda operante que permitem o controle local da fase, amplitude e/ou polarização da luz. Tais estruturas se provaram extremamente versáteis com aplicações demonstradas em imageamento, holografia, polarização da luz e sensoriamento, por exemplo. Uma característica fundamental no projeto de uma metassuperfície é a escolha material de seus elementos, pois ele dita o mecanismo físico no qual ela se baseia. Dessa forma, podemos agrupar as metassuperfícies em duas categorias: as plasmônicas e as dielétricas. As metassuperfícies plasmônicas, que são compostas de estruturas metálicas, foram as primeiras metassuperfícies demonstradas na literatura. Porém, suas eficiências são afetadas por perdas ôhmicas e teoreticamente limitadas em 25% quando operando em transmissão. Por exemplo, nesta tese é mostrado que a eficiência de transmissão de metassuperfícies plasmônicas feitas em alumínio é da ordem de 13%, o que é muito baixo para muitas aplicações como holografia. Recentemente, metassuperfícies baseadas em materiais dielétricos de alto índice de refração foram propostas como uma alternativa para solucionar o problema da baixa transmissão das metassuperfícies plasmônicas. Nesta tese, nós demonstramos que as metassuperfícies dielétricas apresentam, de fato, uma melhora significativa na eficiência de transmissão quando comparadas com as plasmônicas. Para tanto, utilizamos como material dielétrico o silício cristalino (c-Si), que possui uma combinação de propriedades favoráveis, tais como: alto índice de refração, facilidade de corrugação e baixas perdas no visível quando comparadas com outros tipos de silício como o amorfo e o policristalino. Assim, foram propostas e projetadas duas metassuperfícies para aplicações em holografia. A primeira é baseada em nanopostes cilíndricos capazes de modular a fase de feixes não polarizados transmitidos através da metassuperfície. Os hologramas apresentam alta fidelidade e alta eficiência, com eficiências de transmissão e difração aproximadamente de 65% e 40%, respectivamente, medidas experimentalmente. Apesar de terem sido projetadas para operar em 532 nm, os hologramas também apresentaram bons resultados em comprimentos de onda de 444.9 nm e 635 nm. Portanto, as altas tolerâncias a variações na fabricação e comprimento de onda evidenciam que hologramas baseados em metassuperfícies de silício cristalino são ótimos candidatos para aplicações em ótica difrativa e, particularmente, para hologramas coloridos. O segundo projeto utiliza nanopostes com seção transversal elíptica que apresentam birrefringência de forma no visível. Ou seja, tais nanopostes modulam diferentemente a fase da luz transmitida de acordo com o estado de polarização da luz incidente. Dessa forma, um estereograma holográfico foi gerado com tal metassuperfície. Resumidamente, uma imagem esterocópica (estereograma) é composto de duas imagens tomadas de uma mesma cena mas fotografadas em posições diferentes para replicar a paralaxe natural da visão humana. Para o efeito estereoscópico (percepção de profundidade) ocorrer, cada uma dessas imagens deve ser vista independentemente por cada um dos olhos do observador. Para tanto, decidimos realizar dois hologramas com quatro níveis de fase cada, um para cada imagem do estereograma e numa mesma metassuperfície birrefringente em cada um dos dois estados de polarização ortogonal. Assim, o efeito estereoscópico pode ser visto na reconstrução birrefringente com o uso de óculos cujas lentes apresentam polarizadores ortogonais. Além disso, projetamos os hologramas de duas imagens diferentes para facilitar a análise de efeitos de cross-talk na polarização. O plano de reconstrução, para os hologramas estereoscópicos, consiste de uma superfície de alumínio lixada levemente para preservar o estado de polarização da luz espalhada. A largura de banda estimada teoreticamente é de 110 nm com uma relação de sinal ruído maior que 15 dB. As medidas de eficiências de transmissão e difração são da ordem de 70% e 15%, respectivamente, no comprimento de onda de 532 nm. Tais valores são consequências das baixas perdas e alto índice de refração do silício cristalino no visível. Ou seja, o índice de refração é alto o suficiente para minimizar as perdas materiais. As metassuperfícies foram investigadas experimentalmente quando iluminadas com lasers em 444.9 nm e 635 nm para avaliar experimentalmente sua largura de banda. A qualidade do efeito estereoscópico é surpreendentemente alta em 444.9 nm com eficiências de transmissão e difração de 70% e 18%. Já em 635 nm, as reconstruções não foram tão boas. Dessa forma, verificamos que a estrutura proposta foi capaz de demonstrar o efeito estereoscópico nas reconstruções com potencial para aplicações em diversas áreas como artes visuais, entretenimento e segurança. A última, em particular, certamente irá beneficiar do grau de liberdade adicional fornecido pela informação birrefringente. Com base na experiência obtida na pesquisa de metassuperfícies holográficas, decidimos focar no problema de aberrações monocromáticas em metalentes. Metalentes são metassuperfícies que reproduzem as funcionalidades de elementos óticos. Muitas demonstrações surpreendentes já foram demonstradas tais como foco em pontos no limite de difração e operação acromática em uma larga banda de comprimentos de onda. Uma característica importante que ainda não havia sido propriamente solucionada e que é fundamental em aplicações como smartphones e realidade virtual é a capacidade de formar imagens com alto campo de visão e apenas uma metalente. Para tanto, abdicando a operação no limite de difração, nós demonstramos a habilidade de apenas metalente obter imagens com alto campo de visão (WFOV) com resoluções altas o suficiente para grande parte das aplicações em imageamento. Também são discutidas as propriedades físicas de tais metalentes e, em particular, é mostrado que elas simulam uma lente esférica no limite de raio de curvatura e índice de refração interno infinitos. Por fim, a experiência no projeto de nanoestruturas para o controle da luz foi utilizado para resolver um problema importante no contexto de energia renovável: como aprimorar o desempenho de células solares com nanoestruturas. Em particular, foram analisados os impactos de tais estruturas na performance de uma nova classe de células solares tandem que utilizam peroviskitas e silício. Esse tipo de célula solar tandem requer um cuidados controle fotônico para obter o melhor desempenho e isso pode ser realizado com estruturas fotônicas intermediárias, ou seja, postas entre as camadas de silício e peroviskita. Primeiramente, nós identificamos que, para essa classe de célula solar tandem, a estrutura fotônica intermediária deve casar a impedância entre a peroviskita e o silício. Tal conclusão não concorda com a percepção da comunidade científica, que era a de que deveria utilizado refletor otimizado como estrutura intermediária. Com base na conclusão que obtivemos, nós decidimos avaliar duas estruturas simples, que agem como casadoras de impedância, e comparar seu desempenho com refletores intermediárioas baseados em refletores Bragg distribuídos. Assim, concluímos que, de fato, estruturas intermediárias baseadas em casadores de impedância ótica mostram desempenhos muito semelhantes aos dos refletores intermediários mas com a vantagem de serem muito mais simples.

Light propagation in a 4 layer slab waveguide is considered. The supported modes are of higher orders than zero, with a larger node concentration toward the layers with larger refractive index. Additionally, we consider the geometric optics approximation to describe very thick waveguides. Light can be coupled from LED by direct focusing with a lens, and coupling can be optimized by introducing a transverse displacement in order to focus it on the layers with larger refractive index. Further optimization can be done by tilting the lens and bringing in some degree of coma aberrations.

Non-invasive determination of the optical properties is essential for understanding the light propagation in biological tissues and developing optical techniques for quality detection. Simulation-based models provide flexibility in designing the search space, while measurement-based models can incorporate the unknown system responses. However, the interoperability between these two types of models is typically poor. In this research, the mismatches between measurements and simulations were explored by studying the influences from light source and the incident and detection angle on the diffuse reflectance profiles. After reducing the mismatches caused by the factors mentioned above, the simulated diffuse reflectance profiles matched well with the measurements, with R2 values above 0.99. Successively, metamodels linking the optical properties with the diffuse reflectance profiles were respectively built based on the measured and simulated profiles. The prediction performance of these metamodels was comparable, both obtaining R2 values above 0.96. Proper correction for these sources of mismatches between measurements and simulations thus allows to build a simulation-based metamodel with a wide range of desired optical properties that is applicable to different measurement configurations.

An active ultra-compact plasmonic waveguide composed of a subwavelength slit and perforated in vanadium dioxide (VO 2 ) followed by a metallic layer is proposed and numerically analyzed. Refractive index variation of VO 2 by external stimuli provides a feasible way for tuning the optical properties of the waveguide. Varying the refractive index of VO 2 corresponds with changing the phase of VO 2 to the metallic state (“on” state). Consequently, the entire structure becomes a typical metal–insulator–metal (MIM) waveguide that routes the incident light through the slit. In addition, during the “off” state, the incident light thereby propagates in the slit and VO 2 medium and mitigates rapidly. By adding a MIM waveguide attached to the Fabry–Perot (FP) cavity, spectrally wide stopband and passband filtering features in telecommunication frequency regime are demonstrated. Tailoring the resonance wavelength can be performed through the geometrical parameters. Such active plasmonic waveguides with high transmission, coupling, and compact size can be utilized in future fully integrated all plasmonic chip technology.

Understanding light transportation in skin tissues can help improve clinical efficacy in the laser treatment of dermatosis, such as port-wine stains (PWS). Patient-specific cross-bridge PWS vessels are structurally complicated and considerably influence laser energy deposition due to shading effects. The shading effect of PWS vessels is investigated using a tetrahedron-based Monte Carlo (MC) method with extended boundary condition (TMCE). In TMCE, body-fitted tetrahedra are generated in different tissues, and the precision of photon–surface interaction can be considerably improved via mesh refinement. Such improvement is difficult to achieve with the widely used voxel-based MC method. To fit the real physical boundary, the extended boundary condition is adapted by extending photon propagation to the semi-infinite tissue layers while restricting the statistics of photon propagation in the computational domain. Results indicate that the shading parameters, such as the cross angle, vessel distance, and geometric shadow (GS), of cross-bridge blood vessel pairs determine the peak characteristics of photon deposition in deep vessels by affecting the relative deposition of collimated and diffused light. Collimated light is shaded, attenuated, and partially transformed into diffused light due to the increase in vessel distance and GS of vessel pairs, resulting in difficulty in treating deep and shallow vessels with one laser pulse. The TMCE method can be used for the individualized and precise forecasting of laser energy deposition based on the morphology and embedding characteristics of vascular lesions.

Reinforcing light harvesting is an effective means to improve photocatalytic efficiency of semiconductors. In this study, carbon-quantum-dot-modified BiOBr mixed with SiO2 nanospheres (BiOBr/CQDs + SiO2) were prepared via stepwise chemical precipitation route. The characterizations of X-ray diffraction, field-emission scanning electron microscopy and energy-dispersive X-ray apparatus demonstrated that the as-prepared BiOBr/CQDs + SiO2 displayed nanosheets-building spherelike hierarchical nanostructures mixing with dispersive SiO2 nanospheres. Control photocatalytic degradation of orange II under natural sunlight illumination indicated that the presence of SiO2 nanospheres could further promote the photocatalytic behaviors of BiOBr/CQDs apart from CQDs. Diffuse reflection spectrum demonstrated that SiO2 nanospheres were capable of reflecting UV − Vis light near to 100%. The possible mechanism for the enhanced light-absorption surface of suspending hierarchical photocatalyst in presence of SiO2 nanospheres was proposed via light propagation over suspending SiO2 nanospheres under vertical light illumination. Our method for enhancing photocatalytic efficiency provided a general method to enhance light harvesting of every suspending two- or three-dimensional photocatalysts.

Computed axial lithography (CAL) is a volumetric additive manufacturing method in which a three-dimensional light dose distribution is constructed in a photopolymer from the superposition of illumination patterns from many different angles. The technique’s advantages over layer-by-layer light printing methods stem from the fact that in CAL hydrodynamic stresses are effectively eliminated from the resin precursor material during printing. This key difference allows a wider range of materials to be processed, including high-viscosity or thermally gelled precursors, and allows polymeric objects to be printed around pre-existing solid objects (‘overprinting’). In this talk we describe some of the current limitations on spatial resolution, printing speed, and mechanical properties in CAL. We also describe a computationally efficient approach to modeling the occlusion of light by objects suspended in the printing volume, which supports the optimization of overprinting processes.

We have developed CUP to record 70 trillion fps. CUP can record the fastest phenomenon, namely, light propagation, and can be slowed down for slower phenomena. CUP can image in 2D non-repetitive events. CUP has a prominent advantage of measuring an x, y, t scene with a single exposure, thereby allowing observation of transient events occurring on a time scale down to 10s of fs. Further, CUP is receive-only—avoiding specialized active illumination required by other single-shot ultrafast imagers. CUP can be coupled with front optics ranging from microscopes to telescopes for widespread applications in both fundamental and applied sciences.

We demonstrate the usefulness of differentiable optimization approaches, as implemented in machine learning frameworks, for adaptive optics in microscopy. We show that aberrations can be corrected in an epidetection configuration only using reflected light. The method is also extended to two-photon scanning fluorescence microscopy.

We introduce ultrafast optical rotation: a highly efficient method for chiral discrimination using few-cycle pulses. Sub-cycle optical control enables full control over the enantio-sensitive response of matter in a molecule-specific manner and on ultrafast timescales.

Currently, in CD6, a new line of research devoted to polarimetric imaging is being developed. The use of polarization adds new information that is not reachable using other conventional imaging modes. In addition, recent literature explores the capability of using polarized illumination and detection to extend the range and enhance image contrast in turbid media such as fog, dust or smoke. Different computational and experimental tools are presented, in order to study polarized light behavior when propagating through foggy media. This work was supported by the Secretary of Universities and Research from the Generalitat of Catalunya and the European Social Fund under the grant 2019FI-B-00543 and partially supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under the project FIS2017-89850R.

We report on the first observation of a gain-induced topological response in a photonic lattice exhibiting asymmetric long-range interactions enabled by unidirectional microrings under pumping. This new platform is used to implement the Haldane lattice.

We show that anisotropic planar anti-guiding waveguide structures with two radiation channels toward the surrounding cladding materials can support unidirectional guided resonances (UGRs), where radiation is canceled in one of the radiation channels and redirected into the other. Their formation is subtle as it requires breaking the so-called polar anisotropy-symmetry of the structures. Then, UGRs appear at specific wavelengths and light propagation directions, are robust, and are characterized by phase singularities in the channel in which radiation is canceled. The mechanism we describe allows for ready selection of the radiation direction, as well as tuning of the wavelength and the propagation angle at which UGRs occur. H2020 Marie Sklodowska-Curie Action GA665884; Government of Spain (grants PGC2018-097035-B-I00; Severo Ochoa CEX2019-000910-S); Fundació Cellex; Fundació Mir-Puig; Generalitat de Catalunya (CERCA and AGAUR 2017-SGR-1400).

We demonstrate an integrated electro-optic frequency circulator on thin-film lithium niobate. Our device operates at telecommunications wavelengths, exhibiting fre-quency conversion and isolation of 37.3 dB, with insertion loss of 3.8 dB.

We study the resonant frequency gap in the short-range order photonic system. The decay rate measurements are performed for an emitter embedded in these structures to validate the changes in the local density of states.

Multimode silicon photonics is promising to further increase the link capacity of optical interconnects thus attract more and more attention. Moreover, the introduction of higher-order modes also greatly enhances the flexibility for the design of on-chip photonic devices, showing great potential in some emerging applications. Currently multimode silicon photonic devices have been tremendously investigated. This paper gives a tutorial review for the recent progresses in this field.

We present an automated data analysis procedure for clinical spectral-domain OCT, capable of correcting instrument-related hyperreflective artifacts, and its application to normal corneas. Quantitative parameters related to corneal transparency are extracted from 85 eyes.

Teaching About Geometric Optics: Teacher’s Notes guides physics teachers to help students develop a foundational understanding of geometric optics. The cornerstone of photonics systems, geometric optics, have applications in a wide range of industries including technology, medical, and military sectors. This book covers the basics of light propagation, reflection and refraction and the use of simple optical elements such as mirrors, prisms, lenses, and optical fibers. Key elements include:46 activities on geometric optics, covering a wide range of topicsEasy implementation, with a copy-ready student sheet and teacher notes includedReferences to appropriate Next Generation Science Standards Physics educators and teachers in other science disciplines will fi nd this book to be an invaluable resource to teach the fundamentals. This volume contains only the notes for Teaching About Geometric Optics: Student Edition.

There are many factors of methodological origin that influence the measurement of optical properties of the entire circulatory system which consists of blood as the basic component. The basic idea of this review article is to provide the optical properties of the circulatory system with all those factors of influence that have been employed in biomedical optics for different applications. We begin with the available optical properties, i.e., absorption, scattering and, reduced scattering coefficient, in general for any tissue inside the human body and prominent scattering theories (e.g., light, X-rays, neutrons) that are helpful in this regard. We have reviewed and compiled already available formulas and their respective available data for different human tissues for these optical properties. Then we have descended to the blood composition and to different scattering techniques available in the literature to study scattering and light propagation inside blood. We have reviewed both computational and theoretical scattering techniques.

The fast quasi-adiabatic dynamics (FAQUAD) protocol has proven to be an effective approach to provide shortcuts to adiabatic light evolution in optical waveguides, resulting in short and robust devices. However, the FAQUAD approach of homogeneously distributing device adiabaticity only works for a single mode (polarization, wavelength, or spatial mode group) system. We propose an adiabaticity engineering approach to redistribute the adiabaticity of optical waveguides in multi-mode systems. By engineering the adiabaticity distribution using a single control parameter, we obtain shortcuts to adiabaticity in optical waveguides for multi-mode systems. The concept is applied to the design of a compact polarization-independent adiabatic 3-dB coupler on silicon.