All-inorganic cesium lead halide perovskites (CsPbX3, with X = I, Br, Cl) are of great interest for light-emitting diodes and lasers, as they promise improved thermal stability compared to their organic-inorganic analogues. However, among this family of materials, CsPbI3 shows a detrimental phase instability that causes the perovskite to convert to a thermodynamically preferred non-perovskite phase (yellow phase) at room temperature. In fact, reports on lasers using thin films of CsPbI3 as gain medium are missing, as of yet. Here, the first distributed feedback (DFB) lasers based on CsPbI3 thin films are presented with a resonator directly patterned into the perovskite by thermal nanoimprint. This breakthrough is unlocked by the additive polyvinyl pyrrolidone (PVP), that affords the formation of perovskite layers consisting of phase stable gamma-CsPbI3 nanocrystals, that are even preserved during thermal imprint at 170 degrees C. The DFB lasers show a low lasing threshold of 45 mu J cm(-2) at room temperature under optical pumping and a tunable emission in the deep red spectral region between 714.1 to 723.4 nm. It is anticipated that the findings of this work will have a broad relevance for future electrically driven perovskite lasers and for light-emitting diodes based on CsPbI3 as active medium.

A symmetric laser beam pair can provide unique control over light–matter interactions. When propagating within a symmetric slab waveguide, its non-conical diffraction at a specially designed symmetric leaky waveguide grating can be completely suppressed, a phenomenon we term zero diffraction. This allows for infinite contrast control of light detrapping from the slab waveguide. In this paper, we demonstrate the electric control of the local deflection of a beam pair while preserving its properties. This introduces a novel method for routing optical signals across a planar waveguide. We utilize a waveguide structure that enables zero diffraction under non-conical incidence on a 1D grating and design a grating geometry capable of deflecting the beam pair by approximately 90 degrees. This design is experimentally realized using three different diffractive elements for trapping, deflection, and detrapping. The deflection is controlled by an electric field, allowing the deflected intensity to be tuned by a factor of 21.

Abstract Thermal effects are inevitable when an absorptive nonlinear optical material interacts with long pulse duration or high repetition rate laser pulses. It results in inaccurate characterization and reduction in efficiency of the nonlinear materials for device applications. In this article, the study investigates the influence of an external electric field on the thermal contribution to the nonlinear optical response of nitrobenzene (NB). Z‐scan measurements are performed on NB using 330 ps laser pulses at a wavelength of 532 nm with variable (10 Hz to 1 kHz) repetition rates. At low repetition rates, NB shows a positive nonlinear refractive index (+ n2), which leads to self‐focusing of the laser beam due to the optical Kerr effect. Cumulative thermal effects occur above a repetition rate of 200 Hz. At high repetition rates (>750 Hz), the sign of n2 becomes negative, implying a self‐defocusing behavior of the sample arising from the thermal‐induced nonlinear refractive index. By applying an external DC field to the NB, a reduction of the thermal contribution can be observed. At a sufficiently high electric field strength, the thermal contribution is suppressed and the inherent Kerr nonlinearity can be observed despite the high repetition rate of the pump laser.

The feasibility of introducing optical nonlinearity in poly-dimethyl siloxane (PDMS) using organic solvent swelling was investigated. The third-order nonlinear refraction and absorption properties of the individual materials, as well as the PDMS/solvent compounds after swelling were characterized. The well-established Z-scan technique served as characterization method for the nonlinear properties under picosecond pulsed laser excitation at a 532 nm wavelength. These experiments included investigations on the organic solvents nitrobenzene, 2,6-lutidine, and toluene, which showed inherent optical nonlinearity. We showed that nitrobenzene, one of the most well-known nonlinear optical materials, has proven suboptimal in this context due to its limited swelling effect in PDMS and comparatively high (non)linear absorption, resulting in undesirable thermal effects and potential photo-induced damage in the composite material. Toluene and 2,6-lutidine not only exhibited lower absorption compared to nitrobenzene but also show a more pronounced swelling effect in PDMS. The incorporation of toluene caused a weight change of up to 116% of PDMS, resulting in substantial nonlinear optical effects, reflected in the nonlinear refractive index of the PDMS/toluene composite n2=3.1×10−15 cm2/W.

Short-range surface plasmon polaritons (SR-SPPs) can arise due to the hybridization of surface plasmon polaritons propagating along the two interfaces of a thin metal slab. In optics, they have gained particular interest for imaging and sensing applications because of their short wavelengths at optical frequencies along with strong field enhancement. However, mediating the interaction of SR-SPPs with photons in planar films is difficult because of the large momentum mismatch. For efficient coupling, nanostructuring such thin films (∼20 nm thickness), or placing metallic nanostructures in close proximity to the planar film, is technologically challenging and can strongly influence the SR-SPP properties. In this article, harnessing SR-SPPs in planar silver films is demonstrated using disorder-engineered metasurfaces. Disorder-engineering is realized by the light-controlled growth of silver nanoparticles. The dispersion of the hybrid modes with the silver thickness is measured and compared with simulations. We anticipate these results to introduce a facile method for harnessing SR-SPPs in planar optical systems and make use of their promising properties for imaging, sensing, and nonlinear optics.

Earlier research demonstrated the dependence of 3-aminopropyltriethoxysilane (APTES) wetting properties on cleaning, functionalization, and post-treatment processes on oxide surfaces, e.g., glass surfaces or Si wafer surfaces, but not on float glass surfaces. Also, oxide glass surfaces were functionalized by different silanes and were applied with ultraviolet (UV) radiation-curable inks or adhesives. The resulting adhesion forces differed depending on the silane and the UV-curable ink or adhesive used. The chemical diversity of silanes leads to different surface energy on glass surfaces and was used to gain further insights into a correlation between wetting properties and the resulting adhesion forces. This work investigates the suitability of dynamic contact angle measurement (DCA) for indicating adhesion forces via contact angle hysteresis and the resulting drop age. Two types of test fluids (diiodomethane and water) are applied on hydrophilic float glass surfaces (air side and tin side) and on a hydrophobic PE foil surface. The functionalization of glass substrates is realised by reproducible vapour and solution deposition of APTES, which results in different wetting properties of float glass surfaces. The investigations are complemented by static contact angle measurements of different test fluids, and the appropriate surface energies are evaluated via the Owens, Wendt, Rabel, and Kaelble method. The polar and non-polar surfaces are clearly differentiable by contact angle hysteresis and drop age. The DCA results of the hydrophilic float glass surfaces and the hydrophobic PE foil surface confirm the suitability of using the DCA parameters hysteresis and drop age for indicating adhesion forces on functionalized float glass surfaces. The hysteresis and drop age of assumed completely APTES-functionalized float glass surfaces confirm the suitability of the DCA measurement for indicating adhesion forces, too. The test fluid diiodomethane is suitable for indicating adhesion forces on the air side of the float glass, and the test fluid water is suitable for indicating adhesion forces on the tin side of the float glass. With the increased water contact angle, the hysteresis and drop age increased using the polar test fluid water. This does not support the polarity theory of de Bruyne. By using the non-polar test fluid diiodomethane, the hysteresis and drop age decrease with increasing contact angle and also do not support the adhesion theory of de Bryne. The research results show a way of indicating the adhesion forces of different functionalized float glass surfaces, by using only one silane, and serves as a pre-step for better understanding of e.g. UV- ink adhesion forces dependent on glass surface wetting properties.

Stretchable electronics rely on sophisticated structural designs to allow brittle metallic conductors to adapt to curved or moving substrates. Patterns of soft islands and stable cracks in layered silver-PDMS composites provide exceptional stretchability by means of strain localization as the cracks open and the islands strain. To investigate the reliability and potential failure modes, we study the initiation and propagation of delamination in dependence of structure geometry and quality of the metal-polymer bonding. Our numerical experiments show a well-bonded metal film to be under no risk of delamination. Even weakly bonded metal films sustain moderate strains well above the limits of classical electronic materials before the onset of delamination in the soft islands structures. If delamination occurs, it does so in predictable patterns that retain functionality over a remarkable strain range in the double-digit percent range before failure, thus, providing safety margins in applications.

Diffraction allows to change the direction of light. Therefore, controlling the diffraction efficiency with high contrast enables controlling the pathway of light within optical systems. However, a high contrast requires that the diffraction efficiency is tunable close to zero. Probably the most prominent example for zero diffraction in a waveguide grating is a bound state in the continuum (BIC). Herein, zero diffraction of two plane waves under symmetric incidence to a leaky symmetric waveguide grating is found. The phenomenon not only occurs at singular spectral positions but on continuous curves in the energy–momentum space. The relative phase of the two waves enables large contrast control over diffraction in a wide spectral range. The practical meaning of this finding for local switching is demonstrated. Light is trapped into a nonlinear optical waveguide and detrapped at a desired position with electric control. A switching contrast exceeding 1000 is experimentally shown.

Promising new materials like solution-processable perovskites may provide devices with superior properties, e.g. for opto-electronics. For some applications patterning is required and nanoimprint as a solvent-free, mechanical shaping process has been identified to be particularly favorable for this purpose. The current investigation refers to the organic–inorganic perovskite methylammonium lead bromide (MAPbBr 3 ) and is related to direct imprint under pressure and temperature. Experiments with a single crystal and polycrystalline layers of differing grain size indicate that a large-grained starting layer offers optimum pre-conditions for the replication of micro/nano-structures. The aim of the present study is to develop a physical understanding of the shaping process with this polycrystalline material. To develop such a conception, analogies between the imprint of polycrystalline perovskites and the imprint of thermoplastic polymers are sought, and the consequences resulting from the differences in the microscopic material response are worked out. The main aspect with perovskites is that plastic deformation occurs due to gliding on crystallographic glide planes, similar to the case of metals. With a < 100 > -oriented perovskite layer the imprint pressure activates a (110) < 110 > -type glide system, providing material transport at 45° with respect to the surface normal. The consequences of this preferential direction are investigated by analyzing experiments with partial and complete filling of the cavities of the stamp used for imprint. By considering the geometric correlations during the initial imprint phase the experimental results can be understood. Beyond that, it turns out that under specific conditions the size and the shape of the grains can be controlled by the imprinted pattern. This ‘grain shaping by patterning’ provides unexpected, innovative prospects for the nanoimprint of perovskite layers.

Optical metasurfaces address a plethora of applications in planar optics, as they enable precise control of the phase, amplitude, and polarization of light at nanoscale interaction lengths. However, their implementation requires surface nanostructuring, based on complex design and fabrication methods. In addition, exploiting narrow spectral features, e.g., for sensing, is accompanied by high demands in terms of precise post-process alignments of probing light-impractical for compact optical systems. Here, the realization of plasmonic metasurfaces, based on silver nanoparticles (AgNPs) and using a solution-based growth method, is demonstrated. The particle growth is mediated by localized surface plasmon resonances. The resulting nanostructures are directly applicable as self-optimized metasurfaces in optical systems, as their fabrication and probing procedures allow the use of common-photonic and plasmonic-platforms. Information regarding the electromagnetic (EM) environment is stored during the fabrication via distinct particle positions and dimensions. The resulting optical response is inherently sensitive to deviations from this EM environment-enabling high-performance nanoplasmonic sensing with a maximum discrete Figure of Merit* (FoMmax* of 968 without the need for post-process alignments.

Disordered hyperuniformity (DHU) is one of the most prominent manifestations of the engineered disorder, which aims to circumvent limitations commonly related to order. Considering the k ‐space, isotropic DHU is characterized by an isotropic suppression of scattering for wavenumbers k approaching zero. Thereby, stealthy DHU is a particularly strong form of DHU, where scattering is even suppressed for wavenumbers 0 < k ≤ K within a circular window of radius K . Although experimental demonstrations of DHU in optical structures exist, scalable and low‐cost fabrication methods are still rare and often lack the opportunity for in‐situ control of the k ‐space. Here, a novel and facile bottom‐up approach for the fabrication of DHU metasurfaces is presented. Starting with a solution‐based deposition procedure of silver nanoparticles (AgNPs) in darkness (resulting in DHU), a more extensive way of in‐situ k ‐space engineering is introduced by illuminating the growing metasurface with light (resulting in stealthy DHU). While it is shown that the wavelength of incident light allows for the in‐situ control of K , its lateral momentum k ∥ defines an additional design parameter. The light‐controlled growth under maximum k ∥ via surface plasmon polaritons enables the experimental confirmation of the theoretically predicted phenomenon of anisotropic stealthy DHU.

Waveguide gratings are used for applications such as guided-mode resonance filters and fiber-to-chip couplers. A waveguide grating typically consists of a stack of a single-mode slab waveguide and a grating. The filling factor of the grating with respect to the mode intensity profile can be altered via changing the waveguide’s refractive index. As a result, the propagation length of the mode is slightly sensitive to refractive index changes. Here, we theoretically investigate whether this sensitivity can be increased by using alternative waveguide grating geometries. Using rigorous coupled-wave analysis (RCWA), the filling factors of the modes of waveguide gratings supporting more than one mode are simulated. It is observed that both long propagation lengths and large sensitivities with respect to refractive index changes can be achieved by using the intensity nodes of higher-order modes.

Stretchable electronics exploit the characteristics of soft biocompatible polymers and utilize microstructural designs to push the boundaries of brittle functional electronic materials. Extreme stretchability is required in novel applications such as in situ health monitors or sensors integrated into, e.g., wound dressing. A novel approach to stretchable electronics aims to increase macroscopic stretchability by introducing controlled cracks in the polymer substrate's surface (Polywka et al., 2016). The cracks are deliberately induced by a micropattern of soft island crack starters in the hardened surface. Here, we introduce the first numerical model of fracture and deformation behavior of soft islands structures. We study crack evolution and material strain in dependence of the microstructure's design. The fracture behavior in the polymer is modeled with a cohesive zone model. We examine the microstructured composite's behavior with regard to its material and geometry properties, e.g. ratio of Young's moduli, hardened layer thickness, or distance between cracks. The results show that cracks and 3D soft islands accommodate the majority of the applied macroscopic strain while the hardened surface remains almost strain-free. The soft islands microstructure design, thus, demonstrates outstanding strain relief capabilities and can accommodate rigid functional parts while remaining highly stretchable. The simulations reveal critical parameters and allow to identify design principles for large usable surfaces on polymer substrates utilizing controlled cracking. (c) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The manufacturing of devices from methylammonium-based perovskites asks for reliable and scalable processing. As solvent engineering is not the option of choice to obtain homogeneous layers on large areas, our idea is to 'upgrade' a non-perfect pristine layer by recrystallization in a thermal imprint step (called 'planar hot pressing') and thus to reduce the demands on the layer formation itself. Recently, imprint has proven both its capability to improve the crystal size of perovskite layers and its usability for large area manufacturing. We start with methylammonium lead bromide layers obtained from a conventional solution-based process. Acetate is used as a competitive lead source; even under perfect conditions the resulting perovskite layer then will contain side-products due to layer formation besides the desired perovskite. Based on the physical properties of the materials involved we discuss the impact of the temperature on the status of the layer both during soft-bake and during thermal imprint. By using a special imprint technique called 'hot loading' we are able to visualize the upgrade of the layer with time, namely a growth of the grains and an accumulation of the side-products at the grain boundaries. By means of a subsequent vacuum exposition we reveal the presence of non-perovskite components with a simple inspection of the morphology of the layer; all experiments are supported by X-ray and electron diffraction measurements. Besides degradation, we discuss recrystallization and propose post-crystallization to explain the experimental results. This physical approach towards perovskite layers with large grains by post-processing is a key step towards large-area preparation of high-quality layers for device manufacturing.

The question of how to continuously manipulate a photonic system between a radiating state and a bound state is an important challenge in photonics, as its solution promises broad technological relevance for optical sensors, modulators, switches and displays. Existing approaches utilise the inherent wave-nature of electromagnetic fields to their advantage, and are commonly identified as bound states in the continuum (BICs), as they resemble singular bound states embedded in a band of radiating states. Although quasi-BICs have been demonstrated for numerous symmetric periodic photonic crystals, their existence so far has been limited to narrow spectral ranges, and their application in switches or modulators needs large changes of the refractive index. Here, we show that the incidence of two guided symmetric substrate waves of opposite phase onto a symmetric periodic film waveguide enables the excitation of self-stabilising BICs which are electrically switchable in a broad optical range, with small changes of the refractive index. An experimental verification of the concept shows a switching contrast C=700 at a wavelength of 532 nm and C=1000 at a wavelength of 632.8 nm.

Light can be influenced by permittivity changes in optical resonators to enable optical sensors, modulators, and switches. The best performance (intensity change per permittivity change) is observed for dielectric bound states in the continuum (BICs). However, the lateral size must be large to explore their full potential. In this work, hybrid photonic-plasmonic BICs (hybrid BICs) fabricated using a cost-efficient scalable fabrication method are experimentally realized. While plasmonics is known to enable strong miniaturization, regarding BICs, the introduction of losses is thought to reduce device performance. Hybrid BICs in two operation modes, specular geometry and diffraction geometry, are also theoretically analyzed. While the reduced device performance is confirmed for hybrid BICs investigated in a specular geometry, a different result is obtained using diffraction geometry: hybrid BICs using diffraction geometry exhibit greatly increased performance compared to purely dielectric ones. Hybrid BICs using diffraction geometry as powerful tool to enhance the capability of light manipulation are thus considered.

Cesium lead halide perovskites are of interest for light-emitting diodes and lasers. So far, thin-films of CsPbX 3 have typically afforded very low photoluminescence quantum yields (PL-QY < 20%) and amplified spontaneous emission (ASE) only at cryogenic temperatures, as defect related nonradiative recombination dominated at room temperature (RT). There is a current belief that, for efficient light emission from lead halide perovskites at RT, the charge carriers/excitons need to be confined on the nanometer scale, like in CsPbX 3 nanoparticles (NPs). Here, thin films of cesium lead bromide, which show a high PL-QY of 68% and low-threshold ASE at RT, are presented. As-deposited layers are recrystallized by thermal imprint, which results in continuous films (100% coverage of the substrate), composed of large crystals with micrometer lateral extension. Using these layers, the first cesium lead bromide thin-film distributed feedback and vertical cavity surface emitting lasers with ultralow threshold at RT that do not rely on the use of NPs are demonstrated. It is foreseen that these results will have a broader impact beyond perovskite lasers and will advise a revision of the paradigm that efficient light emission from CsPbX 3 perovskites can only be achieved with NPs.

Silver nanoparticles (AgNPs) show an extraordinary strong interaction with light, which enables confinement and field enhancement at the nanoscale. However, despite their localized nature, such phenomena are often sought to be exploited on a larger device length scale, for example, in sensors, solar cells, or photocatalytic cells. Unfortunately, this is often limited by strong absorption. One way to reduce these losses is to first focus light with low loss dielectric optics and then to place the AgNPs in that focus. Here, we present a clear experimental proof that growth of AgNPs from the liquid phase at a substrate surface can be controlled by light. Violet light of 405 nm and 1.5 W/cm(2) is coupled into thin film resonators and locally focused at their surface. The AgNPs grow at the focus position with sub-Abbe alignment accuracy. Numerical simulations confirm that this alignment causes an increased field enhancement within the AgNPs and is therefore expected to lead to an improved performance of the resulting hybrid devices.

Light can be influenced by permittivity changes in optical resonators, enabling optical sensors, modulators and optical switches. It is straightforward that a high relative change of intensity per change of permittivity, labelled as figure of merit FOM*, is sought. This FOM* is proportional to the product of quality factor Q and sensitivity S of the resonator. In known resonators, an increase of Q is always accompanied by a decrease of S leaving FOM* constant. Hybridization of resonators has always been reported to lead to an averaging of their performance, only. Here, we theoretically show that light diffracted by bound states in continuum (BICs) breaks that rule. Its FOM* is strongly increased by hybridization, thus outperforming both purely dielectric or plasmonic BICs. We suggest a symmetric waveguide geometry for realising topologically protected hybrid BICs, develop a polymer based fabrication technology and show first experimental evidence of hybrid BICs.

Multijunction solar cells are designed to improve the overlap with the solar spectrum and to minimize losses due to thermalization. Aside from the optimum choice of photoactive materials for the respective sub‐cells, a proper interconnect is essential. This study demonstrates a novel all‐oxide interconnect based on the interface of the high‐work‐function (WF) metal oxide MoOx and low‐WF tin oxide (SnOx). In contrast to typical p‐/n‐type tunnel junctions, both the oxides are n‐type semiconductors with a WF of 5.2 and 4.2 eV, respectively. It is demonstrated that the electronic line‐up at the interface of MoOx and SnOx comprises a large intrinsic interface dipole (≈0.8 eV), which is key to afford ideal alignment of the conduction band of MoOx and SnOx, without the requirement of an additional metal or organic dipole layer. The presented MoOx/SnOx interconnect allows for the ideal (loss‐free) addition of the open circuit voltages of the two sub‐cells.