The latest progresses in polaritonic solar devices, in which molecular absorbers and photon modes of a resonator are hybridized as a result of strong coupling regime, have revealed that light-matter interaction can be an interesting tool to control and enhance devices performances. In this talk, light harvesting properties of broadband absorbers operating under weak, strong and ultra-strong coupling regimes are discussed. The spectral and directional response, together with the effect of polaritons on unproductive absorption due to the presence of metallic films in the structure are discussed in detail. These results allow to establish the optimum configuration to exploit the potential of solar cells devised as optical resonators.

Materials with a high index of refraction can find a broad range of applications, including light-emitting diodes (LEDs), CMOS sensors, large-area displays, eyeglasses, and optical elements for virtual and augmented reality. We demonstrate the development of two classes of materials: purely organic polymers and nanocomposites with a high refractive index (n up to 2.00) for thin-film applications. The synthesized polymers show high transparency in the visible wavelength. They are among the materials with the highest refractive index ever reported. The developed polymers can be nanopatterned via nanoimprint lithography following a scalable and straightforward process.

We present a tomographic reconstruction algorithm that is able to reconstruct waveguide profiles from a set of intensity images taken at different illumination angles. Very recently, such algorithms have become the state of the art in the community of bio imaging, but have never been applied to direct laser written structures such as waveguides. We adapt the algorithm to our application of characterizing translation-invariant structures and extend it to jointly estimate optical aberrations introduced by the imaging system. We show that a correct estimation of these aberrations is necessary for making effective use of high-angle tomographic data. Furthermore, we present a novel method for cross-validating our RI reconstructions by comparing en-face widefield images of thin waveguide sections with matching simulations based on the retrieved RI profile.

Metasurface technology has allowed the use of ultrathin optical materials to realize complete control of the amplitude, phase, and polarization of light, leading to a versatile platform for optical wavefront manipulation with nanoscale resolution. However, conventional metasurface fabrication relies on planar lithography methods that lead to metasurfaces with limited design freedom in a 2D plane. Here we present the design and 3D laser nanoprinting of 3D meta-optics in a polymer matrix with unlocked height degree of freedom. We show that these 3D-nanoprinted metasurfaces can be used for high-bandwidth holography and on-fiber wavefront engineering.

We demonstrate that nonlocal metasurfaces based on quasi-bound states in the continuum (q-BICs) are a key enabling technology for highly efficient and highly selective flat optics. We show that spatially varying a small geometric perturbation across an otherwise regular array confers control over the leakage to free-space of otherwise bound states. The result is an ultrasharp Fano resonant response that engages light exclusively within the bandwidth of the resonance; nonresonant light is unaffected. This capability enables customized narrowband transformations of electromagnetic waves for use in highly multifunctional flat optics, including thermal metasurfaces capable of generating quasi-monochromatic designer wavefronts.

The ability to precisely manipulate nanoscale objects and form defined assemblies with extraordinary optical properties has been attracting researchers’ interest for decades. Top-down lithography approaches were the first choice to define sub-wavelength patterns of metasurfaces. Recently, template-based self-assembly methods emerged allowing to deposit chemically synthesized nanoparticle (NP) colloids into tailored traps. Clean-room lithography techniques are required only once—to produce the template master, which can be replicated in an elastomer and used as the NP deposition template. The capillary force deposition ensured nearly 100% yield of tailored single or multi-particle assemblies over cm scales. When the pitch between scattering NPs overlaps the localized surface plasmon band, a high-quality surface lattice resonance (SLR) emerges. We have demonstrated that the SLR can couple to the NP optomechanical oscillations or can be exploited for sensing and nanolasing applications.

Several nanoengineered materials have been proposed as potential alternatives to chemical colorants. Although they are non-toxic and stable, they suffer from severe angle and polarization sensitivity, lack of saturation, limited color-palette, and are impractical to integrate with industrial standards. Here, we present an approach to structural coloration that avoids these limitations by exploiting the strong hybridization of localized and cavity modes of a layer of self-assembled plasmonic nanoparticles in the proximity of a mirror. Our approach offers a versatile platform for environmental-friendly, large-scale, and low-cost paint solution that bridges the gap from proof-of-concept science to real-world industrial applications.

We present a study on coherent light scattering effects in the white scales of the beetle Cyphochilus as well as in a simple model of the scales based on disordered Bragg stacks. For both structures the occurrence of random resonances is experimentally shown via ultrafast time-resolved scattered light spectroscopy. These resonances contribute about 20% to the total reflected light, revealing that resonant effects cannot be neglected in the explanation of brilliant whiteness. Accompanying numerical simulations further confirm that the so far presumed purely diffusive light transport is insufficient to fully describe the light scattering in ultrathin, white structures.

The novelty in structural colors arise from recent discovery that individual elements are capable of generating a wide range of colors, instead of the use of repeated units. Here, we discuss basic structures 3D printed using two-photon polymerization lithography (TPL) to investigate new mechanisms for generating colors. Such structures enable new approaches to fully 3D print optical devices that previously rely on precise mechanical assembly, e.g. high-resolution lightfield prints. Structures printed using in-house shape memory polymer resin or elastomers allow for reconfigurable micro-prints that exhibit unique behavior under compressive and tensile stress.

Femtosecond lasers are a powerful tool for high-precision material processing. Femtosecond laser induced micro- and nano-scale surface patterning can also lead to surface functionalization. In my lab, the laser processing led to a range of technological developments, including the so-called black and colored metals. In this talk, I will discuss our recent developments in laser-induced structural coloring and its various applications. I will also discuss some of our recent work on non-laser-induced structural coloring and applications. Other associated surface functionalization induced by laser irradiation, such as superhydrophillic and superhydrophobic surfaces, will also be discussed.

We proposed a new optoelectronic solid-sate thin-film architecture for active structural color and experimentally demonstrated this proof-of-concept recipe composed of amorphous iron oxides and high-mobility silver layers. Scanning transmission electron microscope (STEM) reveals that multiple iron oxide-silver laminates with various thicknesses have been driven by the bias electrical field to float at various heights with tunable layer sequences, which is responsible for the multiple robust, non-volatile, and reversible high-resolution structural color. Our work breaks the limitations of the current approaches relying on static structures of solid-sate devices and opens an unexplored way for constructing active modern devices for optics, optoelectronics, and semiconductors, etc.

Light-based 3D printing techniques use patterned light, triggering polymerizations within a volume of a photoresin and yielding 3D objects. The process of printing in a vat of resin using light that varies temporally and spatially creates dynamics within the resin that ultimately influences properties of the printed part. This presentation will cover how concentration gradients and changes in miscibilities during printing causes phase separation and diffusion of species that effect the printing process. By tuning the formulations, changes in diffusitivity, viscosity and gelation rates can be control and therefore allow control over phase separation or deviations from nominal print dimensions.

Two-photon absorption (TPA) 3D laser nanoprinting typically requires femtosecond lasers, which are expensive and bulky. Here, we introduce two-step absorption (TSA) replacing TPA as the nonlinear excitation mechanism. In TSA, the virtual intermediate state in TPA is replaced by a real electronic intermediate state, allowing to use inexpensive continuous-wave lasers. Concerning degenerate TSA, we demonstrate scanning single-focus nanoprinting of state-of-the-art 3D woodpiles with rod spacings down to 300 nm and below, using about 45 µW power from a compact 405 nm semiconductor laser diode. Concerning non-degenerate TSA, we present the status of our work on light-sheet 3D laser projection printing.

Modern Two-Photon Lithography (TPL) is a golden standard among various 3D micro- and nano-fabrication techniques. The two-photon absorption phenomenon allows to selectively initiate the polymerization reaction in different points in 3D space, enabling accurate point-by-point 3D. TPL has a well-known constraint, the limited speed of printing related to the time it takes to scan a volume by a focused femtosecond laser beam. The inherent need for extremely high illumination intensity required for initiation of the polymerization reaction poses a fundamental problem. We are developing an alternative 3D printing technique based on a multi-wavelength polymerization process that requires orders of magnitude lower illumination intensities while still allowing localization of the polymerization reaction in 3D space. Multi-wavelength polymerization was previously used to break the diffraction limit in 2D and semi-3D lithography. We are exploiting this phenomenon to implement a highly parallelized fully-three-dimensional method. Since the multi-wavelength polymerization requires relatively low illumination intensities, a low cost full-field illumination system can be implemented increasing the printing speed by several orders of magnitude. The existing nano- and micro-3D printing methods demonstrated an outstanding potential in rapid prototyping of a wide range of applications ranging from micro-optics to micro-fluidics and bio-scaffolds. We believe that our approach will shift the paradigm of micro-3D printing from prototyping and R&D applications to serial production of final products.

Point-by-point femtosecond laser writing of filaments was used to open high aspect ratio nano-holes transversely through the core of a single-mode telecommunication fiber (SMF-28). On infiltration with nematic liquid crystal, the small 200 nm diameter holes induced strong capillary alignment to facilitate strong birefringence responses when the filament was aligned into second-order (~1 micrometer period) Bragg arrays. Geometric arrangement of the nano-hole arrays provided the unique opportunity of designing customized all-fiber polarization filter inside of traditional single-mode fiber, with properties tunable by device length, azimuthal and chiral orientation of the filament array, and thermo-optic responses.

To further improve the technology of 3D µ-printing, we show a promising deep learning approach for correcting aberrations of the most prominent point spread functions in (STED-inspired) multi-photon lithography. Moreover, detailed forecasts of 3D printed structures are of high interest. Therefore, an analytical method predicting deformations due to, e.g. proximity or shrinkage effects is presented. These predictions can be used as pre-compensations to achieve a maximum match between target and actual structures from the beginning. As third topic, we discuss the recently presented continuous frequency band chirp material measure for calibration utilization with regard to its different evaluation routines.

In this invited presentation we introduce aligned multiphoton lithography (AML®). In contrast to traditional mask(less) aligners based on one-photon lithography, in AML®, 3-dimensional shapes can be generated and aligned to 3-dimensional topographies. The unique resolution and design freedom of AML® opens new horizons for optical applications, hybrid photonic integration, MEMS, medicine, or life science applications. In this session we present the design and fabrication of micro-optical elements aligned to fiber tips, chip edge couplers, and laser output facets. The characterization of these elements is in very good agreement with simulations allowing us to also present experiments demonstrating low-loss coupling between the elements.

We present novel fabrication methods for complex microoptics. Gray scale lithography enables the writing of complex microoptical doublet structures with unprecedented surface smoothness and without slicing steps. We demonstrate diffraction limited imaging performance. Interferometric wavefront measurement confirm wavefront aberrations below lambda/10. Furthermore, we present new applications using black photoresists for direct printing of hulls and aperture stops.These techniques enable printing of high-NA achromatic optical trapping objectives directly on fibers, forward and side-looking OCT objectives, highly efficient couplers from quantum dots into fibers, couplers for single photon quantum detectors, and high-NA miniature fiber endoscopes with unprecedented image quality.

On-chip hollow-core waveguides represent a promising platform for microfluidic analysis, nonlinear optics and quantum information processing, due to light guidance directly inside the medium of interest. Recently, we have reported a 3D printed hollow-core waveguide ⎯ light cage ⎯ which consists of a ring of high-aspect-ratio cylinders and combines a high fraction of field in the core (>99%) with transverse access. Here we will discuss our results on interfacing light cages with optical fibers, the measurement of electromagnetically induced transparency within light cages filled with alkali vapour, the potential of the light cage concept for spectroscopy and nanoparticle tracking analysis.

Lensless photography is a recently-developed computational imaging technique that uses light-modulating phase masks instead of lenses to build ultra-compact and low-cost cameras. Here, we propose a method to design and fabricate custom phase-masks to create deterministic point spread functions for lensless imaging. Phase-masks are designed using our wave-optics-based algorithm and are fabricated in single-shot via grayscale maskless lithography technique. Using this method, we can design and fabricate phase-masks with various surface profiles and have validated that the fabricated masks match the designed profiles. Our technique allows for a fast and efficient process that can be applied to the fab-level fabrication of lensless cameras for commercialization. We also show that lensless cameras using our custom phase-masks can effectively obtain images in a compact form factor.

Here, we describe progress made in the field of additive manufacturing “unchained” via post processing of composites. Hybrid prepolymers are known for their usefulness in forming complex micro-/nano- devices using various forms of laser lithography. They contain metal-oxide constituents and are special for their sol-gel form, relatively low shrinkage and high laser damage threshold (LIDT) properties during/after exposure. Yet, there is one more new property that can be induced due to their special composition: present metal and oxide elements can form into a purely inorganic glass or ceramic lattices in a heat-treatment process without the loss of the previous geometry. This area of research recently gained rapid traction and is coming into fruition as an enabler of full 3D nanophotonics, micro-optics, medical devices and more. This is due to fact that new materials can be produced with a simple process, resulting in increased refractive index and LIDT, together with inertness.

A pilot study on laser 3D printing of inorganic free-form micro-optics is experimentally validated. Ultrafast laser nanolithography is employed for structuring hybrid organic-inorganic material SZ2080^TM followed by high-temperature calcination post-processing. The combination allows production of 3D architectures and the heat-treatment results in converting the material to inorganic substance. The produced miniature optical elements are characterized and their optical performance is demonstrated, focusing and imaging properties are evaluated. Finally, the concept is validated for manufacturing compound optical components such as stacked lenses. This is opening for new directions and applications of laser made microoptics under harsh conditions such as radiation, temperature, acidic environment, pressure variations, which include open space, astrophotonics, and remote sensing.

Laser 3D nanolithography as an additive manufacturing technology allows the fabrication of various objects at a micro-scale, with possible nano-scale single features. An absorption mechanism plays the key role, thus polymerization reaction starts only at a certain value of light intensity I, which also alters because of possible different non-linearities of light-matter interaction when different wavelengths are used. Both polymerization and optical damage thresholds and the feature size depend on the applied I and energy dose E. In this work, the experiment was performed within the 700-1250 nm wavelength range while varying pulse duration (~ 100-300 fs). We present how the polymerization process (thresholds and feature sizes) depends on both wavelength and pulse duration in the SZ2080TM prepolymer.