Deliberately introducing disorder in low-dimensional nanostructures like photonic crystal waveguides (PCWs) [1] or photonic crystals (PCs) [2] leads to Anderson localization where light is efficiently trapped by random multiple scattering with the lattice imperfections. These disorder-induced optical modes hace been demonstrated to be very promising for cavity-quantum electrodynamics (QED) experiments where the radiative emission rate of single quantum emitters can be controlled when tuned through resonance with one of these random cavities. Our statistical analysis of the emission dynamics from single quantum dots embeded in disordered PCWs [3] provides detailed insigth about the statistical properties of QED in these complex nanostructures. In addition, using internal light sources reveals new physics in the form of nonuniversal intensity correlations between the different scattered paths within the structure which imprint the local QED properties deep inside the complex structure onto the far-field intensity pattern [2]. Finally, increasing the optical gain in PCWs allows on-chip random nanolasing where the cavity feedback is provided by the intrinsic disorder which enables highly efficient, stable, and broadband tunable lasers with very small mode volumes [4]. The figure of merit of these disorder-induced cavities is their localization length which determines to a large degree the coupling efficiency of a quantum emitter to a disorder-induced cavity as well as the efficiency of random lasing and reveals a strongly dispersive behavior and a non-trivial dependence on disorder in PCWs [5]. [1] L. Sapienza, H. Thyrrestrup, S. Stobbe, P.D. Garcia, S. Smolka, and P. Lodahl, Science 327, 1352 (2010). [2] P. D. García, S. Stobbe, I. Soellner and P. Lodahl, Physical Review Letters 109, 253902 (2012). [3] A. Javadi, S. Maibom, L. Sapienza, H. Thyrrestrup, P.D. Garcia, and P. Lodahl, Opt. Express 22, 30992 (2014). [4] J. Liu, P. D. Garcia, S. Ek, N. Gregersen, T. Suhr, M. Schubert, J. Mørk, S. Stobbe, and P. Lodahl, Nature Nanotechnology, 9, 285 (2014). [5] P.D. Garcia, A. Javadi, and P. Lodahl, In preparation.

My talk will review our recent progress in developing photonic integrated circuits with strong stimulated Brillouin Scattering.

We present a numerical method to characterize the symmetry properties of photonic crystal (PhC) modes based on field distributions, which themselves can be obtained numerically. These properties can be used to forecast specific features of the optical response of such systems, e.g. which modes are allowed to couple to external radiation fields. We use 2D PhCs with a hexagonal lattice of holes in dielectric as an example and apply our technique to reproduce results from analytical considerations. Further, the method is extended to fully vectorial problems in view of 3D PhCs and PhC slabs, its functionality is demonstrated using test cases and, finally, we provide an efficient implementation. The technique can thus readily be applied to output data of all band structure computation methods or even be embedded – gaining additional information about the mode symmetry.

Photonic crystals doped with fluorescent nanoparticles offer a plenty of interesting applications in photonics, laser physics, and biosensing. Understanding of the mechanisms and effects of modulation of the photoluminescent properties of photonic crystals by varying the depth of nanoparticle penetration should promote targeted development of nanocrystal-doped photonic crystals with desired optical and morphological properties. Here, we have investigated the penetration of semiconductor quantum dots (QDs) into porous silicon photonic crystals and performed experimental analysis and theoretical modeling of the effects of the depth of nanoparticle penetration on the photoluminescent properties of this photonic system. For this purpose, we fabricated porous silicon microcavities with an eigenmode width not exceeding 10 nm at a wavelength of 620 nm. CdSe/CdS/ZnS QDs fluorescing at 617 nm with a quantum yield of about 70% and a width at half-height of about 40 nm were used in the study. Confocal microscopy and scanning electron microscopy were used to estimate the depth of penetration of QDs into the porous silicon structure; the photoluminescence spectra, kinetics, and angular fluorescence distribution were also analyzed. Enhancement of QD photoluminescence at the microcavity eigenmode wavelength was observed. Theoretical modeling of porous silicon photonic crystals doped with QDs was performed using the finite-difference time-domain (FDTD) approach. Theoretical modeling has predicted, and the experiments have confirmed, that even a very limited depth of nanoparticle penetration into photonic crystals, not exceeding the first Bragg mirror of the microcavity, leads to significant changes in the QD luminescence spectrum determined by the modulation of the local density of photonic states in the microcavity. At the same time, complete and uniform filling of a photonic crystal with nanoparticles does not enhance this effect, which is as strong as in the case of a very limited depth of nanoparticle penetration. Our results will help to choose the best technology for fabrication of efficient sensor systems based on porous silicon photonic crystals doped with fluorescent nanoparticles.

Porous nanostructured photonic materials in the shape of periodic multilayers have demonstrated their potential in different fields ranging from photovoltaics[1] to sensing,[2] representing an ideal platform for flexible devices. When applications dealing with light absorption or emission are considered, knowledge on how the local density of states (LDOS) is distributed within them is mandatory[3] in order to realize a judicious design which maximizes light matter interaction. Using a combination of spin and dip-casting we report a detail study of how dye doped polystyrene nanospheres constitute an effective LDOS probe to study its distribution within nanostructured photonic media.[4] This full solution process approach allows to cover large areas keeping the photonics properties. Nanospheres with a diameter of 25 nm are incorporated in nanostructured multilayers (Fig. 1a).. This allows to place them at several positions of the structured sample (Fig. 1b). A combined use of photoluminescence spectroscopy and time resolved measurements are used to optically characterize the samples. While the former shows how depending on the probe position its PL intensity can be enhanced or suppressed, the latter allows to probe the LDOS changes within the sample, monitored via changes in its lifetime. We demonstrate how information on the local photonic environment can be retrieved with a spatial resolution of 25 nm (provided by the probe size) and relative changes in the decay rates as small as ca. 1% (Fig. 1c), evidencing the possibility of exerting a fine deterministic control on the photonic surroundings of an emitter. References [1] C. López-López, S. Colodrero, M. E. Calvo and H. Míguez, Energy Environ. Sci., 23, 2805 (2013). [2] A. Jiménez-Solano, C. López-López, O. Sánchez-Sobrado, J. M. Luque, M. E. Calvo, C. Fernández-López, A. Sánchez-Iglesias, L. M. Liz-Marzán and H. Míguez. Langmuir, 28, 9161 (2012). [3] N. Danz, R. Waldhäusl, A. Bräuer and R. Kowarschik, J. Opt. Soc. Am. B, 19, 412 (2010). [4] A. Jiménez-Solano, J. F. Galisteo-López and H. Míguez, Small, 11, 2727 (2015).

Nanostructured dielectric and metallic photonic architectures can concentrate the electric field through resonances, increase the light optical path by strong diffraction and exhibit many other interesting optical phenomena that cannot be achieved with traditional lenses and mirrors. The use of these structures within actual devices will be most beneficial for enhanced light absorption in thin solar cells, photodetectors and to develop new sensors and light emitters. However, emerging optoelectronic devices rely on large area and low cost fabrication routes such as roll to roll or solution processing, to cut manufacturing costs and increase the production throughput. If the exciting properties exhibited photonic structures are to be implemented in these devices then, they too have to be processed in a similar fashion as the devices they intend to improve. In this presentation, I will describe different low cost and large area photonic architectures that coupled to solution processed solar cells, photodetectors and SERS sensors facilitate enhanced light matter interaction within the active layer and are fully compatible with current manufacturing processes.

The extensive benefits of the new generation of nanostructured surfaces is very promising for enhancing light absorption efficiency in photonic devices. However, the low throughput and the high cost of available technologies such as lithography for fabrication of nanostructures has proved to be a difficult technological hurdle for advanced manufacturing. In this research we present a solution based process based on high molecular weight block copolymer (BCP) nanolithography for fabrication of periodic structures on large areas of optical surfaces. Block copolymer self- assembly technique is a solution based process that offers an alternative route to produce highly ordered photonic crystal structures. BCPs forms nanodomains (5-10 nm) due to microphase separation of incompatible constitute blocks. The size and shape of the nanostructure can be customised by the molecular weight and volume fraction of the polymer blocks. However, the major challenge is BCPs do not phase separate into their signature ordered pattern above 100 nm, whereas for nanofeatures to be used as photonic gratings, they must be greater than 100 nm (typically ¼ wavelength). This is due to significant kinetic penalty arising from higher entanglement in high molecular weight polymers. In this work we present the results of exploiting commercially available block copolymers to phase separate into periodic domains greater than 100 nm. The process do not include any blending with homopolymers, or adding colloidal particles, and to our best knowledge, has not been yet achieved or reported in the literatures. We have pattern transferred the BCP mask to silicon substrate by reactive ion etch (ICP-RIE). The final product is black silicon, consists of hexagonally packed conic Si nanofeatures with diameter above 100nm and periodicity of 200 nm. The height of the Si nanopillars varies from 100 nm to 1 micron. We have characterized the angle dependent optical reflectance properties of the black silicon. The antireflective properties of the Si nanofeatures were probed in the 400 nm – 2500 nm wavelength range and compared to an Au reflectance standard. As the subwavelength grating is made from the same material as the substrate (Si), the index matching at the substrate interfaces has lead to highly improved antireflecting performance. The reflectivity of the silicon substrate shows one order of magnitude reduction in a broad range of wavelength from NIR to UV-visible, below 1%. The simplicity of the solution based large block copolymer nanolithography and the capability of integration to existing fabrication process, makes this novel technique a very attractive alternative for manufacturing photonic crystals on large, arbitrary shaped and curved objects such as photovoltaics and IR camera lenses for medical imaging.

Slow light photonic crystal waveguides (PCWs) have been the subject of intensive study due to their potential for on-chip applications such as optical buffers and the enhancement of nonlinear phenomenon. However, due to high group velocity mismatch between the strip waveguide and the slow light waveguide efficient coupling of light is challenging. The coupling efficiency is also very sensitive to the truncation at the interface between the two waveguides. This sensitivity can be removed and light can efficiently be coupled from the strip waveguide to the slow light waveguide by adding an intermediate photonic crystal waveguide (or coupler) that operates at a group index of ∼ 5. Several designs have been proposed for couplers to obtain higher coupling efficiency within the desired group index range. We have studied uniaxial stretched couplers in which the lattice constant is stretched in the direction of propagation by 10-50 nm in the coupler region. Using a Finite Difference Time Domain (FDTD) Simulation Method that allows the extraction of the group index, we have observed 8.5 dB improvement in the coupling efficiency at the group index of 30. Efficient coupling is dominantly determined by the band edge position of the coupler region and maximum transmission efficiency is limited by the maximum transmission of the coupler PCW. If the band edge of coupler PCW is sufficiently red shifted relative to the band edge of the slow light PCW then higher coupling efficiency can be achieved.

We present the design of a photonic crystal-based multilayer structure that allows to experimentally demonstrate, using attenuated total reflectance experiments, the existence of the predicted transverse electric (TE) polarized excitation in graphene. We show that this mode can be excited in a single layer of graphene, even at room temperature. Furthermore, we prove that the observed mode in the reflection spectra corresponds to the TE- polarized graphene excitation and not the Bloch Surface Wave of the photonic crystal experiencing graphene- induced loss. Finally, we point out that adding an extra layer of dielectric material on top of the structure would ensure the unambiguous identification of the TE graphene mode even in the presence of fabrication errors.

Semiconductor optical waveguides have been the subject of intense study as both fundamental objects of study, as well as a path to photonic integration. In this talk I will focus on the nonlinear evolution of optical solitons in photonic crystal waveguides made of semiconductor materials. The ability to independently tune the dispersion and the nonlinearity in photonic crystal waveguides enables the examination of completely different nonlinear regimes in the same platform. I will describe experimental efforts utilizing time-resolved measurements to reveal a number of physical phenomena unique to solitons in a free carrier medium. The experiments are supported by analytic and numerical models providing a deeper insight into the physical scaling of these processes.

We report a numerical and experimental investigation of fabrication tolerances and outcoupling in optically pumped III-nitride nanolasers operating near λ = 460 nm, in which feedback is provided by a one-dimensional photonic crystal nanobeam cavity and gain is supplied by a single InGaN/GaN quantum well. Using this platform, we and others previously demonstrated single-μW lasing thresholds due to the high βQ-product inherent to the nanobeam geometry (β is spontaneous emission coupling fraction into desired mode). In this work, we improved the fraction of emission emitted into our microscope's light cone by combining a redesigned photonic crystal cavity (c.f. [3]) with a cross-grating coupler with period approximately twice the photonic crystal lattice constant. The samples were fabricated in epitaxial III-nitride layers grown on (111) silicon substrates using metal organic vapor phase epitaxy. The photonic crystal and output couplers were patterned using a single electron beam lithography exposure and subsequently transferred to the underlying III-nitride layers using dry etching. The nanobeams were then suspended via vapor phase etching of silicon in XeF2. Scanning electron microscopy cross-sections revealed high-aspect ratio (>5), sub-70 nanometer diameter holes with near-vertical sidewalls. Fabrication-induced geometry errors were characterized by processing scanning electron micrographs with custom critical dimension software. Using UV micro-photoluminescence spectroscopy at room temperature, we measured the nanobeams' emission intensity, far-field profile, and quality factor. By comparing more than ten nominally identical nanobeams for each geometry with finite-difference time-domain simulations taking into account the geometrical deviations measured during fabrication, we characterized the role of fabrication-induced imperfections. Finally, we explored the trade-off between the quality factor and collected signal via lithographic variations of the output coupler grating amplitude. Our results demonstrate the robustness of III-nitrides for short-wavelength photonic crystal applications, such as photonic integrated circuits, optoelectronics, and cavity quantum electrodynamics.

Photonic microcavities (PMC) coupled through their evanescent field are used for a large variety of classical and quantum devices. In such systems, a molecular-like spatial delocalization of the coupled modes is achieved by an evanescent tunnelling. The tunnelling rate depends on the height and depth of the photonic barrier between two adjacent resonators and therefore it is sensitive to the fabrication-induced disorder present in the center of the molecule. In this contribution, we address the problem of developing a post fabrication control of the tunnelling rate in photonic crystal coupled PMCs. The value of the photonic coupling (proportional to the tunnelling rate) is directly measured by the molecular mode splitting at the anticrossing point. By exploiting a combination of tuning techniques such as local infiltration of water, micro-evaporation, and laser induced non thermal micro-oxidation, we are able to either increase or decrease the detuning and the photonic coupling, independently. Near field imaging is also used for mapping the modes and establish delocalization. By water micro-infiltration, we were able to increase the photon coupling by 28%. On the contrary, by laser induced non thermal oxidation, we got a reduction of g by 30%. The combination of the two methods would therefore give a complete control of g with excellent accuracy. This could make possible the realization of array of photonic cavities with on demand tunnelling rate between each pair of coupled resonators. We believe that this peculiar engineering of photonic crystal molecules would open the road to possible progress in the exploitation of coherent interference between coupled optical resonators both for quantum information processing and optical communication.

Photonic crystal slabs have been subject to research for more than a decade, yet the existence of bound states in the radiation continuum (BICs) in photonic crystals has been reported only recently [1]. A BIC is formed when the radiation from all possible channels interferes destructively, causing the overall radiation to vanish. In photonic crystals, BICs are the result of accidental phase matching between incident, reflected and in-plane waves at seemingly random wave vectors [2]. While BICs in photonic crystals have been discussed previously using reflection measurements, we reports for the first time in-situ measurements of the bound states in the continuum in photonic crystal slabs. By embedding a photodetector into a photonic crystal slab we were able to directly observe optical BICs. The photonic crystal slabs are processed from a GaAs/AlGaAs quantum wells heterostructure, providing intersubband absorption in the mid-infrared wavelength range. The generated photocurrent is collected via doped contact layers on top and bottom of the suspended photonic crystal slab. We were mapping out the photonic band structure by rotating the device and by acquiring photocurrent spectra every 5°. Our measured photonic bandstructure revealed several BICs, which was confirmed with a rigorously coupled-wave analysis simulation. Since coupling to external fields is suppressed, the photocurrent measured by the photodetector vanishes at the BIC wave vector. To confirm the relation between the measured photocurrent and the Q-factor we used temporal coupled mode theory, which yielded an inverse proportional relation between the photocurrent and the out-coupling loss from the photonic crystal. Implementing a plane wave expansion simulation allowed us to identify the corresponding photonic crystal modes. The ability to directly measure the field intensity inside the photonic crystal presents an important milestone towards integrated opto-electronic BIC devices. Potential applications range include nonlinear optics, nano-optics, sensing and optical computing. This research was supported by the Austrian Science Fund FWF (Grant No. F2503-N17), the PLATON project 35N, the “Gesellschaft für Mikro- und Nanoelektronik” GMe and the European Research Council (Grant no. 639109). [1] C.W. Hsu et al. “Observation of trapped light within the radiation continuum”, Nature 499, 188 (2013) [2] Y. Yang Y et al., “Analytical Perspective for Bound States in the Continuum in Photonic Crystal Slabs”, Phys Rev Lett 113, 037401 (2014)

Surface addressable Photonic Crystal Membranes (PCM) are 1D or 2D photonic crystals formed in a slab waveguides where Bloch modes located above the light line are exploited. These modes are responsible for resonances in the reflection spectrum whose bandwidth can be adjusted at will. These resonances result from the coupling between a guided mode of the membrane and a free-space mode through the pattern of the photonic crystal. If broadband, these structures represent an ideal mirror to form compact vertical microcavity with 3D confinement of photons and polarization selectivity. Among numerous devices, low threshold VCSELs with remarkable and tunable modal properties have been demonstrated. Narrow band PCMs (or high Q resonators) have also been extensively used for surface addressable optoelectronic devices where an active material is embedded into the membrane, leading to the demonstration of low threshold surface emitting lasers, nonlinear bistables, optical traps... In this presentation, we will describe the main physical rules which govern the lifetime of photons in these resonant modes. More specifically, it will be emphasized that the Q factor of the PCM is determined, to the first order, by the integral overlap between the electromagnetic field distributions of the guided and free space modes and of the dielectric periodic perturbation which is applied to the homogeneous membrane to get the photonic crystal. It turns out that the symmetries of these distributions are of prime importance for the strength of the resonance. It will be shown that, by molding in-plane or vertical symmetries of Bloch modes, spectrally and spatially selective light absorbers or emitters can be designed. First proof of concept devices will be also presented.

We introduce a concept of phase transitions between photonic crystals and all-dielectric metamaterials suggesting a phase diagram that places two classes of such artificial structures on a common parameter plane.1 We consider photonic crystals and all-dielectric metamaterials composed of the similar structural elements and arranged in the similar geometry of a two-dimensional (2D) square lattice of dielectric cylinders of large dielectric permittivity. Such structures can display negative magnetic permeability in the TE-polarization due to the Mie resonance that occurs below the lowest Bragg resonance.2 We define a point of transition from photonic crystals to all-dielectric metamaterials as a point when the lowest Mie resonance splits from the lowest Bragg resonance creating the lowest photonic gap. Based on the numerical results, we construct the phase diagram photonic crystals - all- dielectric metamaterials for the 2D square lattice of circular rods for the TE polarization. We have verified our theoretical concept experimentally by engineering a “metacrystal” composed of glass tubes filled with water forming a 2D square lattice with a variable lattice constant.

Self-assembly of colloidal particles is a promising approach for fabrication of three-dimensional periodic structures which are especially interesting for photonic crystals. This approach is simple and cheap, but it still suffers under the existence of many intrinsic defects. The efforts to improve the self-assembly process have led to many deposition methods with a different degree of controllability. One of the best fabrication techniques is the capillary deposition method leading to non-scattered photon propagation in the order of 80 μm. To improve understanding of the selfassembly process we investigate the stages of the process separately. The most important stage is likely the deposition of suspended particles into a dense arrangement forming a crystal. This is studied spectroscopically. Another crucial stage is the drying of colloidal crystal which is connected with a continuous shrinkage process. Several minutes after starting the drying, a surprise occurs: The system expands shortly before it shrinks monotonously until reaching its final state after about one day. We called this “v“-event because of the characteristic shape of the curve for the Bragg peak. The event is assigned to the start of a nano-dewetting process occurring at the colloidal particles.

The retroreflection spectroscopy have been developed with the aim to investigate the spectra of light scattered at intrinsic defects of photonic crystals. Self-assembled 3-dimensional colloidal crystals, opals, have been investigated. Compared to conventional spectroscopies of reflected and transmitted light, which evaluate the rejected by photonic crystal light, the retroreflectance is designed to visualize the propagating eigenmodes of photonic crystals. The principal advantages of this method are the direct experimental evaluation of the stop-bandwidth and the quantitative estimate of defect concentration by the slope of the angle diagram of the scattered light intensity. The added value of this method is the independent evaluation of the periodicity and the effective refractive index of photonic crystals under interrogation by simultaneous observation of the angle dispersions of volume and surface resonances of the photonic crystal lattice.

We present a concept of a silicon slab based 2D integrating cell where photonic crystal (PhC) reflectors are used in order to confine light in a two-dimensional area to acquire a long propagation length. The evanescent field of the guided wave can be used for sensing applications. We use FDTD simulations to investigate the dependence of the reflectivity of photonic crystal mirrors with a hexagonal lattice. The reflectivity in ΓM direction demonstrates reduced vertical losses compared to the ΓK direction and can be further improved by adiabatically tapering the hole radii of the photonic crystal. A small hexagonal 2D integrating cell was studied with PhC boundaries oriented in ΓM and ΓK direction. It is shown that average reflectivities of 99% can be obtained in a rectangular 2D cell with optimized reflector design, limited only by residual vertical scattering losses at the PhC boundary. This reflectivity is already comparable to the best metallic reflectors.

We report on the humidity-induced swelling behavior of thin film devices composed of 2D phosphatoantimonate nanosheets and study their water uptake mechanism by means of ellipsometric porosimetry. Ambient humidity changes cause significant swelling in thin films composed of turbostratically disordered H₃Sb₃P2O₁₄ nanosheets through water uptake between the nanosheet layers. This phenomenon is exploited to construct humidity responsive colorimetric sensors based on 1D Photonic Crystals. We demonstrate the ultrahigh sensitivity of H₃Sb₃P2O₁₄/SiO₂ Bragg stacks to ambient humidity, as well as reversible transparency switching as a consequence of refractive index matching at high relative humidities. The Photonic Crystals show substantially higher sensitivity to humidity as compared to ethanol vapor, reflecting the less favorable interaction of ethanol with the nanosheet layers as compared to water. Based on their ultrahigh sensitivity to humidity, phosphatoantimonate nanosheet based Bragg stacks can be used to track the motion of a finger by responding to its humidity sheath, without the finger touching the sensor surface. The cycling stability of such optical touchless positioning interfaces as well as the reversibility of the sensing event was demonstrated for more than 100 cycles. While the dew point presents an inherent lower limit to the sensor performance, the sensing ability remains essentially unaffected at elevated temperatures up to 40 °C.

A great interest has been lately initiated in the optoelectronics field for 2D materials with a tunable bandgap. Being able to choose the bandgap of a material is a huge progress in optoelectronics, since it would permit to overcome the limitation imposed by the graphene lack of energy bandgap, but also the restriction imposed by already used semiconductor whose bandgap are fixed and cannot apply for IR-NIR applications. From DFT simulations predictions, Black Phosphorus (bP) becomes a bidimensional semiconducting material with a direct tunable energy bandgap from 0.3 eV to 2 eV by controlling number of layers. This material also has a picosecond carrier response and exceptional mobilities under external excitation. Hence black phosphorus is a promising 2D material candidate for photoconductive switching under a NIR optical excitation as in telecommunication wavelength range of 1.55 μm. In this paper, material electromagnetic properties analysis is described in a large frequency band from optical to microwave measurements executed on different samples allowing energy bandgap and work function dependency to fabrication techniques, anisotropy and multiscale optoelectronic device realization by switch contact engineering and material passivation or encapsulation. Material implementation in microwave devices opens the route to new broadband electronic functionalities triggered by optics, thanks to light/matter extreme confinement degree. In this paper we present fabrication method of bP based microwave photoconductive switch, with a focus on black phosphorus Raman characterization, and obtained performances.

We study the scattering of light from homogeneous cylindrical objects embedded in a transparent and homo- geneous surrounding medium that is know as the Mie problem. We analyze Mie scattering by expansion of the scattering amplitude in the series near resonant frequency and find that Lorenz-Mie coefficient can be de- scribed by Fano formula, while both waves are involved in interaction completely and intensity vanishes at the special point of switching to the invisible regime. We analyze Fano interference between resonant wave and background in general case and discuss scattering-cancellation condition. We study the influence of the aspect ratio on the mode structure and find that Mie modes shift to the long wave lengths when the cylinder aspect ratio r/h decreases. Experimentally measured spectra in microwave range are in agreement with the theoretical predictions.

Here we review and discuss the recent advances of the spatial filtering using the Photonic Crystals (PhCs) in different propagation regimes and for different geometries. We numerically and experimentally explore the spatial filtering in crystals with different symmetries, including axisymmetric crystals; we discuss the role of chirping, i.e., the dependence of the longitudinal period along the structure. Additionally, we present a super-collimation effect, which we observed only in axisymmetric PhCs, which leads to a significant enhancement of axial beam components by depleting the higher angular frequency components. Finally, we discuss several implementations of such filters for intracavity spatial filtering.

We demonstrate a very simple and low-cost method based on one-photon absorption direct laser writing technique to fabricate arbitrary two-dimensional (2D) polymeric submicrometer structures with controllable form. In this technique, a continuous-wave green laser beam (532 nm) with very weak power is tightly focused into a positive photoresist (S1805) by a high numerical aperture (NA) objective lens (OL), depolymerizing the polymer in a local submicrometer region. The focusing spot is then moved in a controllable trajectory by a 3D piezo translation stage, resulting in desired structures. The low absorption effect of the photoresist at the excitation wavelength allows obtaining structures with submicrometer size and great depth. In particular, by controlling the exposure dose, e.g. the scanning speed, and the scanning configuration, the structures have been created in positive (cylindrical material in air) or negative (air holes) form. The 2D square structures with periods in between 0.6 μm and 1 μm and with a feature size of about 150 nm have been demonstrated with an OL of NA = 0.9 (air-immersion). The fabricated results are well consistent with those obtained numerically by using a vectorial diffraction theory for high NA OLs. This investigation should be very useful for fabrication of photonic and plasmonic templates.

Upconversion (UC) presents a possibility to exploit sub-bandgap photons for current generation in solar cells by creating one high-energy photon out of at least two lower-energy photons. Photonic structures can enhance UC by two effects: a locally increased irradiance and a modified local density of photon states (LDOS). Bragg stacks are promising photonic structures for this application, because they are straightforward to optimize and overall absorption can be increased by adding more layers. In this work, we present a comprehensive simulation-based analysis of the photonic effects of a Bragg stack on UC luminescence. The investigated organic-inorganic hybrid Bragg stack consists of alternating layers of Poly(methylmethacrylate) (PMMA), containing purpose-built β-NaYF4:25% Er³⁺ core-shell nanoparticles and titanium dioxide (TiO₂). From optical characterization of single thin layers, input parameters for simulations of the photonic effects are generated. The local irradiance enhancement and modulated LDOS are first simulated separately. Subsequently they are coupled in a rate equation model of the upconversion dynamics. Using the integrated model, UC luminescence is maximized by adapting the Bragg stack design. For a Bragg stack of only 5 bilayers, UC luminescence is enhanced by a factor of 3.8 at an incident irradiance of 2000 W/m2. Our results identify the Bragg stack as promising for enhancing UC, especially in the low-irradiance regime, relevant for the application in photovoltaics. Therefore, we experimentally realized optimized Bragg stack designs. The PMMA layers, containing UC nanoparticles, are produced via spin-coating from a toluene based solution. The TiO₂ layers are produced by atomic layer deposition from molecular precursors. The reflectance measurements show that the realized Bragg stacks are in good agreement with predictions from simulation.

The aim behind this work is to investigate the capabilities of nonlinear photonic crystals to achieve ultra-fast optical limiters based on third order nonlinear effects. The purpose is to combine the actions of nonlinear effects with the properties of photonic crystals in order to activate the photonic band according to the magnitude of the nonlinear effects, themselves a function of incident laser power. We are interested in designing an optical limiter based nonlinear photonic crystal operating around 1064 nm and its second harmonic at 532 nm. Indeed, a very powerful solid-state laser that can blind or destroy optical sensors and is widely available and easy to handle. In this work, we perform design and optimization by numerical simulations to determine the better structure for the nonlinear photonic crystal to achieve compact and efficient integrated optical limiter. The approach consists to analyze the band structures in Kerr-nonlinear two-dimensional photonic crystals as a function of the optical intensity. We confirm that these bands are dynamically red-shifted with regard to the bands observed in linear photonic crystals or in the case of weak nonlinear effects. The implemented approach will help to understand such phenomena as intensitydriven optical limiting with Kerr-nonlinear photonic crystals.

In this contribution we present a versatile sol-gel approach to highly transparent nanocrystalline thin films of (Ho0_,05Y₀,₉₅)2Ti2O₇. We focused on their optical properties and relation between the processing parameters, their structure, and resulting optical properties. Highly transparent and homogenous thin films have been prepared onto planar silica substrates. Coated films were thermally treated to temperatures ranging from 700 to 900 °C. The effect of the structure on the optical properties of prepared films were evaluated. The thickness of prepared layers ranged from 500 to 600 nm and the mean size of nanocrystals ranged around 25 nm in dependence on the processing conditions. Refractive index of prepared films ranged from the value 1.8 up to 2.2. High optical transparency of prepared films along with the ability to tailor the refractive index makes the films to be a suitable material for the construction of planar optical devices.

Eigenmodes and dispersion curves in different configurations of synthetic photonic lattices are studied numerically. Eigenmodes localized on borders between areas with different optical potential are found. Stability of these eigenmodes against potential disturbances of different type is studied.

We have investigated simulation, fabrication, 2D tungsten PhC for selective emitters of TPV system. Using finite difference time domain simulations, we designed and fabricated a 2D W PhC with cylindrical cavities of diameter from 490 nm to 555 nm, depth 1.5 μm. This structure may have a cutoff near the wavelength of 2.0 μm. A marked enhancement is expected in the emissivity of the 2D W PhC at wavelengths below 2.0μm compared to flat W. By using standard silicon processing techniques that are simple, efficient and easily scalable, selective emitting structure can be fabricated at lower cost and reduced complexity of individual components.

We introduced carbon-shell with potassium persulfate structure to modify the repulsive force between particles and minimize scattered light. The reflected structural color varied from blue to red and showed high color purity with high cycle stability.

Photonic amorphous structure (PAS) has attracted increasing research attention due to their interesting characteristics, such as noniridescent structural colors and isotropic photonic band gap. In this work, we present PAS with different characteristic lengths and analyze their structural and topological properties. First, a Fourier spectral method was used to solve Cahn-Hilliard equation and generate a spinodal binary phase structure. By changing the time of the evolution of phase field, mobility, and standard deviation, the characteristic length of amorphous structures can be adjusted. We present the numerical analysis based on finite-difference time-domain (FDTD) method to characterize the density of state (DOS) of PAS based on different time of the evolution of phase field. The corresponding spatial Fourier spectrum of PAS is calculated to examine the characteristic length, and the photonic band gap properties will be discussed in association with the characteristic length. These results are crucial for design of new optical materials display devices base on dielectric amorphous photonic structures.

We present a self-assembled refractory absorber/emitter without the necessity to structure the metallic surface itself, still retaining the feature of tailored optical properties for visible light emission and thermophotovoltaic (TPV) applications. We have demonstrated theoretically and experimentally that monolayers of zirconium dioxide (ZrO₂) microparticles on a tungsten layer can be used as large area, efficient and thermally stable selective absorbers/emitters. The band edge of the absorption is based on critically coupled microsphere resonances. It can be tuned from visible to near-infrared range by varying the diameter of the microparticles. We demonstrated the optical functionality of the structure after annealing up to temperatures of 1000°C under vacuum conditions. In particular it opens up the route towards high efficiency TPV systems with emission matched to the photovoltaic cell.

The optical spectra of the photonic crystal structure is shown to be controlled by changing the structural parameters of plasmonic nanocomposite layer. Variation in particle size and volume fraction has an effect on the number and magnitude of defect modes in the optical spectra. The defect-mode splitting is found to be determined by dispersive properties of nanocomposite layer and PC mirrors.

Optical Tamm surface states are formed in 3-dimensional photonic crystals coated by thin metal films. These states appear in registry with diffraction resonances and localize the electromagnetic energy in resonators formed by diffraction mirrors of lattice planes and metal semishells. Tamm defect states provide the bypass for light in the spectral range of photonic stop-bands and thus reduce the efficiency of the Bragg diffraction resonances. In spite of hidden nature of this effect, its magnitude is comparable to the extraordinary transmission associated with tunneling of surface plasmon polaritons, which are simultaneously excited at surfaces of corrugated metal film coating.

Computer simulation of a few-cycle pulse interaction with a substance covered by disordered structure is performed in order to study the effects imposed on spectra of transmitted and reflected pulses by presence of the cover. The substance is described by semi-classic approach and the cover is described by classic electrodynamics equations for linear isotropic medium. The cover consists of a number of layers with different properties which is considered to be the cause of the distortions. The influence of relation between pulse wavelength and cover layer thickness is illustrated. Computer simulation results are compared with those of physical experiments conducted for paper and other common materials.

Volume holographic gratings, both transmission and reflection-type, may be employed as one-dimensional pho- tonic crystals. More complex two- and three-dimensional holographic photonic-crystalline structures can be recorded using several properly organized beams. As compared to colloidal photonic crystals, their holographic counterparts let minimize distortions caused by multiple inner boundaries of the media. Unfortunately, it’s still hard to analyze spectral response of holographic structures. This work presents the results of thick holographic gratings analysis based on spectral-angular selectivity contours approximation. The gratings were recorded in an additively colored fluorite crystal and a glassy polymer doped with phenanthrenequinone (PQ-PMMA). The two materials known as promising candidates for 3D diffraction optics including photonic crystals, employ diffusion-based mechanisms of grating formation. The surfaces of spectral-angular selectivity were obtained in a single scan using a white-light LED, rotable table and a matrix spectrometer. The data expressed as 3D plots make apparent visual estimation of the grating phase/amplitude nature, noninearity of recording, etc., and provide sufficient information for numerical analysis. The grating recorded in the crystal was found to be a mixed phase-amplitude one, with different contributions of refractive index and absorbance modulation at different wavelengths, and demonstrated three diffraction orders corresponding to its three spatial harmonics originating from intrinsically nonlinear diffusion-drift recording mechanism. Contrastingly, the grating in the polymeric medium appeared purely phase and linearly recorded.