Advanced Fabrication Technologies for Micro/Nano Optics and Photonics XVIII

We demonstrate low-cost, scalable manufacturing of optical metasurfaces using three approaches: dielectric particle-embedded resin, low-loss hydrogenated amorphous silicon (a-Si:H), and high-index ALD structural resin. These create effective metasurfaces across infrared, visible, and ultraviolet spectra. High efficiencies are achieved: 90.6% (a-Si, 940 nm), 47% (TiO2, 532 nm), 60% (ZrO2 PER, 325 nm), and 30% (ZrO2 PER, 248 nm). Engineered low-loss a-Si:H enables efficient beam-steering metasurfaces across the visible spectrum. Hybrid ALD structural resin with deep-UV lithography produces highly efficient visible metalenses (up to 77.8% efficiency). This approach extends to UV metalenses using ZrO2 ALD. These methods enable low-cost, large-area manufacturing of efficient optical metasurfaces across various wavelengths, advancing metasurface-based photonic device commercialization.

Solid-state emitters such as defect centers in diamond are promising candidates for quantum information and sensing applications. Despite ongoing efforts to achieve bright and fast sources, low photon extraction efficiencies and slow spontaneous emission rates limit the practicality of devices. Here, we discuss a novel ultrathin diamond membrane fabrication technique to realize sub-diffraction limited plasmonic cavities coupled to silicon vacancy (SiV) centers in diamond [1]. Au nanodisks are prepared by electron beam lithography and arrays are transferred onto diamond membranes using a PDMS stamping procedure. Plasmonic integration of SiV centers results in over 135-fold spontaneous emission rate and 19-fold brightness enhancement. Our investigations into implantation depth, diamond thickness and cavity parameters provide guidelines for creating bright and ultrafast plasmonic photon sources for next-generation quantum applications. Reference 1. Boyce, A. M.; Li, H.; Wilson, N. C.; Acil, D.; Shams-Ansari, A.; Chakravarthi, S.; Pederson, C.; Shen, Q.; Yama, N.; Fu, K. C.; Loncar, M.; Mikkelsen, M. H. Nano Letters 24 (12), 3575-3580 (2024).

In this work, we have employed several novel large-area nanofabrication methods to fabricate different surface-enhanced Raman scattering (SERS) sensor chips. The SERS sensor chips can be uniformly developed over a large-area with high reliability and reproducibility. These SERS sensor chips are employed for the detection of chemical molecules (such as pesticides and dyes) and biological molecules. Furthermore, numerical modeling of the proposed substrates was carried out using Finite Difference Time Domain (FDTD) modeling to study the effect of structural parameters of the plasmonic nanostructures on the resonance wavelengths and the electromagnetic (EM) enhancement factors.

Advances in 3D nanofabrication can enable photonic materials and devices that are currently infeasible, including photonic metamaterials, ultra-compact imaging devices, and biosensors. Here we present the 3D assembly of hundreds of nanoscale building blocks using optical positioning and linking (OPAL), which is based on optical tweezers and biotin-avidin chemical linking. A microfluidic chip is used to deliver different building blocks to different loading zones surrounding an assembly zone. A quadrant photodiode signal processed using principal component analysis provides feedback for automatic loading of the optical trap. A computer-controlled translation stage precisely places each building block according to a predefined set of coordinates. We use a combination of the discrete dipole approximation, finite difference time domain, and finite element methods to design arrangements of particles for different applications, including metasurface design, 3D magnetic metamaterial design, and nanostructured microtoroidal optical resonator sensors for toxic gases.

We present a method for fabricating customized microlenses by deforming and curing liquid polymer droplets in electrical fields. This technique allows control over lens parameters on both fiber and planar substrates. Combining experimental techniques and numerical modeling, we use shadowgraphy imaging and finite element analysis (FEA) to study droplet deformation. An empirical model is derived, to deformation based on voltage and material parameters, enabling fine-tuning of lens shapes. UV-curable polymer can solidify the deformed droplets, and LightTools simulations study the light distribution. This method is relevant for rapid prototyping and has applications in optical communication, illumination, and imaging systems.

The micro lens arrays (MLA) are the important optical component in variety of optics related application. In the present work an efficient, one-step, flexible, scalable and cost-effective method based on the electrochemical discharge (ECD) processing is presented to form the MLAs in glass. The ECD processing involves generation of EC discharges through the arrayed tool electrode in an electrochemical cell where glass workpiece placed underneath of tool electrode. Material patterning by combined action of high temperature melting and evaporation, and localized chemical etching. Here an array of MLAs have been formed average size and depth of sub-100 µm range with the lower fabrication time of 10 to 20 s. Moreover, the optical performance of the formed MLAs has also been evaluated.

Large area micro- and nanoscale patterns are crucial for advancing technologies like displays, light-trapping films, and plasmonic metamaterials. Traditional nanofabrication methods are too slow and costly for industrial-scale applications. This work presents a fabrication technique using nanocoining and roll-to-roll (R2R) embossing to produce truly large area nanopatterned films and metals to enhance flexible solar panels and create a tuned IR plasmonic absorber.

Trapping photons in a dye high-Q microcavity comprising two dielectric mirrors allows for studying Bose-Einstein condensation (BEC) of the two-dimensional photon gas under ambient conditions. Adding polymer nanostructures on the surface of the mirrors by direct laser writing provides additional trapping potentials for the photon gas. As the dimensionality of a system profoundly influences its physical behavior, trapping potentials with different effective dimensionality allow to study the modifications of the behavior for the 2d-1d transition. Here, we experimentally study the properties of a harmonically trapped photon gas undergoing Bose-Einstein condensation along this dimensional crossover. By varying the aspect ratio of the harmonic trap, we tune from an isotropic two-dimensional confinement to an anisotropic, highly elongated one-dimensional trapping potential. We discuss the fabrication of the micro potential on the highly reflective dielectric mirrors and determine the caloric properties of the photon gas and discuss prospects of our polymer-based potential landscapes.

A scalable and single-step method exploiting capillary interactions for creating sub-100nm non-coalescent liquid metal nanodroplets on soft substrate elastomeric substrate, is shown herein. It enables tuneable gap-plasmonic resonances between the nanodroplets, thus allowing mechanochromic sensing and display applications.

Attoseconds: When intense light interacts with a gas of atoms (or a transparent solid), electron wave packets are released. Attosecond pulse formation exploits the correlated electrons and holes, forcing the electron to return. Without the plasma connection, two of the most important strong-field process that accompany attosecond pulse formation—hot electron formation (inverse Bremsstrahlung) and non-sequential double ionization (collisional ionization)—seemed mysterious. These plasma-like processes lead to laser induced electron diffraction and orbital tomography. THz generation: Terahertz pulse formation by ionization has a similar linage. Using PIC codes to describe azimuthally polarized l=4 mm and 2 mm light interacting with a 150 µm thick jet of helium, we calculate THz pulses reaching 8.5 Tesla. But 10 Tesla is not a limit. 30 THz azimuthally polarized beams can be amplified in high-pressure CO2 reaching isolated magnetic fields of 1-gigagauss.

In recent years, topological phenomena in photonic systems have attracted much attention, with their striking features arising from robust states in the energy gaps of spatially periodic media. However, light waves are entities that extend in space as well as time, such that one may ask whether topological effects can also occur in the temporal domain, or even space-time. Intuitively, systems that are periodic in time may be gapped in momentum, leading to topological states localized at time interfaces. However, time - in contrast to space - exhibits a unique unidirectionality often referred to as the “arrow of time”. Inspired by these features, I will present our most recent experiments on topological states residing at temporal interfaces. Moreover, I will discuss the formation of spacetime-topological events and demonstrate unique features such as their limited collapse under disorder and causality-suppressed coupling.

Quantum technologies promise a change of paradigm for many fields of application, for example in communication systems, in high-performance computing and simulation of quantum systems, as well as in sensor technology. However, the experimental realization of suitable system still poses considerable challenges. Current efforts in photonic quantum science target the implementation of practical devices and scalable systems, where the realization of quantum devices and controlled quantum network structures is key for envisioned future technologies. Here we present our progress on the engineering of integrated photonic systems, which can overcome current limitations for the realization of scalable photonic systems. Specifically, our research currently focuses on three different but complementary topics: integrated devices based on lithium niobate circuits, engineering and harnessing the temporal-spectral structure of quantum states of light, and photonic quantum computation.

Redox-tunable conducting polymers offer novel ways for dynamic control of light in different spectral regions. Applications ranges from reflective color displays and dynamic radiative cooling to tunable metasurfaces and adaptive camouflage. This presentation will cover our most recent work on those topics, including how to use strain to induce hyperbolic properties of conducting polymers and their use for dynamic broadband chiroptics.

We showcase two-photon grayscale lithography (2GL) with in-situ alignment as the next step towards scalable fabrication of micro-optics. While the laser-based direct write technology is known to create true 3D structures with sub-micron resolution, the use of Grayscale Lithography (2GL®) enables high-speed of the fabrication with surface roughness below 5nm and shape accuracy down to below 200nm. We demonstrate user friendly 3D detection algorithms in our nanoPrintX software for automatic alignment towards a variety of topographies and material platforms with very high accuracy better than 100 nm. The versatility of our approach is shown via micro-optical elements aligned to fiber tips, photonic edge couplers, and photonic grating couplers for improved coupling losses and beam quality. We demonstrate the automatic fabrication of 480 on-chip optical coupling elements on a photonic integrated circuit with excellent optical surface qualities and highly reproducible placement accuracy.

We present innovative fabrication materials and methods for creating multi-refractive index, multi-transparency, and complex micro-optics. This study utilizes polymetric silsesquioxane (PSQ) processed through direct laser writing (DLW) with two-photon polymerization (TPP). By precisely adjusting laser power, scanning speed, structure thickness, and heating rates during the 3D printing process, we achieve controlled and accurate final properties of the glass after thermal treatment. This method allows for the production of multifunctional structures without requiring additional external processes. Furthermore, we demonstrate new applications by directly printing stops, apertures, mounts, and clear glass lenses in a single additive manufacturing procedure. These techniques enable the fabrication of high-NA stray light-resistant glass optical objectives, high-NA achromatic glass optical objectives, forward and side-looking glass OCT objectives, and high-NA miniature fiber glass endoscopes, all with superior image quality.

The advancement of photonics and cryptography will be fostered by the development of new materials that can introduce advanced functionalities in integrated photonics and secure information storage. To make them relevant for these applications, they must be integrated at the nano- and micro-scale. This is possible by the lithographic technique of two-photon direct laser writing (2P-DLW), which is capable of 3D printing polymeric materials with nanometric resolution and high speed. By combining 2P-DLW and liquid crystal-based materials, we demonstrate 3D-printed microstructures for reconfigurable linear and non-linear photonics [1] and secure information encoding [2]. References [1] De Bellis, I., Martella, D., Parmeggiani, C., Wiersma, D.S. and Nocentini, S., 2023. Adv Funct Mater, p.2213162. [2] Donato, S., Nocentini, S., Martella, D., Kolagatla, S., Wiersma, D.S., Parmeggiani, C., Delaney, C., Florea, L., 2024, Small, 20, 2306802.

We demonstrate techniques to create dynamic plasmonic metasurfaces. First, we show the assembly and modification of optical metasurfaces using bio-molecular and chemical recognition, achieved by patterning fixed metasurface arrays with molecular recognition sites to capture individual nanoparticles. Next, we present polarization-sensitive nanostructures patterned onto phase change substrates, producing devices with temperature and light-responsive plasmonic resonance modes. Doing so, we construct nanopixels with four distinct color states, creating ultra-high resolution security features with that change color based on environmental conditions and light polarization.

Ultralight plasmonic paints offer a groundbreaking, eco-friendly alternative to traditional pigment-based paints, overcoming issues like toxicity, fading, and instability. Unlike conventional structural colors, which are limited by complex nanofabrication methods, this innovation uses a lithography-free, self-assembled plasmonic cavity system. By employing aluminum nanoislands on a thin aluminum oxide layer with a reflective mirror backing, the structure selectively absorbs and reflects light, producing vibrant, angle-independent colors. Remarkably lightweight at only 0.4 g/m², this plasmonic paint is also easily transferable to various substrates. The fabrication process utilizes scalable, cost-efficient techniques, such as electron-beam evaporation, making high-volume production feasible. The flexibility of this design allows for a broad color spectrum, making it suitable for diverse industries. This breakthrough bridges the gap between lab research and industrial production, offering a scalable, low-cost, and sustainable solution for color applications with minimal environmental impact.

We first discuss all-optical modulation with single photons using electron avalanche, resulting in record-high nonlinearities. Then we show that transparent conducting oxides (TCOs) operating in the near-zero index (NZI) regime can provide strong single-cycle modulation, thus enabling novel photonic time crystals. Finally, we discuss scalable quantum photonics with single-photon emitters in silicon nitride that we recently discovered as well as the intriguing possibility to generate indistinguishable single photons by using plasmonic speedup that could enable important quantum photonics applications, including quantum communication and quantum computing.

Surface engineering, and thus the tuning of surface properties, is closely related to the degree of complexity and anisotropy of superficial features. An interesting micropatterning strategy is the direct surface structuring based on mass migration in azopolymers. These materials can be directly and reversibly structured on a large-scale, in a single step and using spatially structured UV/visible light fields. The final surface geometry depends on the irradiated intensity pattern and polarization state of the light over the sample. By exploiting the polarization-driven transport, large-scale surface anisotropic textures are produced. By including the effect of the different light penetration depths within the material volume at different wavelengths, the control on the final texture shape can be extended to three dimensions. The approach allows the engineering of surfaces able to tailor their functionalities, while preserving the possibility of further modifications to meet possible other application requirements.

Metasurfaces are flat optical platforms capable of unprecedented wavefront control. To push the limits of experimental device performance, scalable design methodologies that balance device performance and manufacturability are required. We introduce a reparametrized topology optimization framework for large-area freeform metasurfaces in which nanoscale elements are explicitly constrained to feature basic shapes. Despite the simplicity of the geometric features, these devices are able to utilize nonlocal near-field coupling to achieve highly efficient and extreme wavefront scattering beyond conventional design methodologies. Utilizing this approach, we design and experimentally demonstrate a series of large-area, multifunctional, high-numerical-aperture metadevices.

In this talk, we discuss our recent progress on the design, modeling, fabrication and characterization of optical metastructures, and their use for emission manipulation, field confinement, wavefront shaping, imaging and sensing. We tailor the nanofabrication scheme to leverage a wide set of materials, heterostructures and broken symmetries in order to tailor the optical response to the wavelength of interest and the desired functionality. In the talk, we discuss various recent approaches that we have developed in the quest of optimizing the overall optical response of the resulting metastructures.

e-skin Displays has developed a graphene-based uncooled infrared sensor operating at the nanophotonic level. This single-atom-thick sensor has a specific detectivity (D*) exceeding 10^9 and a noise equivalent temperature difference (NETD) below 50 mK. Its nanosecond response enables MHz frame rates, capturing dynamic infrared scenes. The key innovation is integrating this graphene sensor onto an existing FLIR readout integrated circuit (ROIC) with a 1/2 million pixel focal plane array (FPA). This creates a highly sensitive, uncooled infrared camera system operating at room temperature. The sensor's nanoscale dimensions and CMOS compatibility ensure seamless ROIC integration. The sensor's broadband absorption allows for multi-spectral and hyperspectral “color” infrared imaging, enabling object detection based on spectral signatures. This opens new possibilities in material identification, gas sensing, and advanced thermal analysis. This technology demonstrates the feasibility of nanophotonic device integration for next-generation infrared imaging systems. It holds potential across defense, security, industrial monitoring, medical diagnostics, and scientific research.

Here, we present Subsurface Controllable Refractive Index via Beam Exposure (SCRIBE), a direct-write lithographic approach that enables fabrication of low-loss volumetric microscale gradient refractive index lenses, waveguides, and metamaterials with a resolution of better than one micron. The basis of SCRIBE is multiphoton polymerization inside monomer-filled nanoporous silicon and silica scaffolds. Adjusting the laser exposure during printing enables 3D submicron control of the polymer infilling and thus the refractive index over a range of greater than 0.3 and chromatic dispersion tuning. A Luneburg lens operating at visible wavelengths, achromatic doublets, multicomponent optics, photonic nanojets and subsurface 3D waveguides were all formed. Various optical elements were combined to create the building blocks for volumetric photonic integrated circuits.

Diffractive optical elements (DOEs) are ubiquitous in optics and photonics thanks to their ability to perform complex wavefront shaping in a compact form. However, their widespread applicability is limited by what often are cumbersome or expensive fabrication methods. Here, we introduce a straightforward and cost-effective fabrication approach for solid, high-performance DOEs. This involves conjugating two nearly refractive index-matched solidifiable transparent materials, which enables extreme scaling up of the elements in the axial dimension. This facilitates simple fabrication of a template using commercially available 3D printing with tens-of-micrometer resolution. We demonstrated this approach by fabricating DOEs that function as microlens arrays, vortex plates, and phase masks for various applications.

The study showcases the evolution and versatility of two-photon absorption (2PA) in 3D printing. Using the in-situ material exchange system MergeOne system, we successfully fabricated diverse structures and analyzed laminar flow dynamics with fluorescence microscopy. Computational flow dynamics simulations confirmed the observed behavior. We demonstrated lateral multi-material micro-lens printing, along with precise control over material exchange and polymerization parameters. This approach enhances design flexibility and functionality, particularly in additive manufacturing, marking significant advancements in commercial 2PA technology.

3D laser-printed microstructures often differ from the intended models due to various mechanisms, such as dose accumulation, shrinkage, or unintended printing below the substrate. So far, the deviations between the intended model and the ex-situ characterization result had to be compensated iteratively, leading to a tedious feedback loop. Here, we present a novel deep learning-driven in-situ tomographic reconstruction technique based on stacks of widefield optical intensity images taken during the printing process. A deep neural network is trained to reconstruct specimens by simulated optical intensity images. The reconstruction before development during the printing process itself can drastically accelerate material design and characterization.

The rapidly developing frontiers of additive manufacturing, especially multi-photon lithography, create a constant need for optimization of new process parameters. The recently developed projection multi-photon lithography process used in this work is one such example. This work presents an active machine learning framework which can serve as a guide for exploration of these uncharted parameter spaces. The framework uses Bayesian optimization to guide experimentation to dynamically collect the most optimal data for training of a Gaussian process regression machine learning model. This model then serves as a surrogate for the manufacturing process by predicting optimal process parameters for printing of a target geometry. The results of the framework for several 2D shapes are shown and the extension of this framework to 3D structures is discussed.

In this work we demonstrate the capabilities of our diode laser based multi-photon polymerization (MPP) system, which aims at significantly reducing the required investment compared to available machines. While currently available systems rely on ultra short optical pulses from fibre lasers or titanium Sapphire lasers, we employ monolithically mode-locked diode lasers at a repetition rate of 6 GHz and emission wavelength around 780 nm to induce the polymerization process. These lasers allow for direct switching of the gain current and do therefore not require additional fast shutters. Overall, this results in a cost effective and compact machine that can work with conventional resins for MPP without any further adaption to our system. We will introduce our system, show the properties of the used diode lasers and demonstrate the manufacturing capabilities.

Micro and nanoscale additive manufacturing using projection multi-photon lithography has the potential to print 3D structures at high speeds. Optimizing parameters for precise 2D layer printing by trial and error requires time-consuming and costly methods. This study introduces a convolutional neural network machine learning scheme to optimize printing using a fast and inexpensive data collection method. By training autoencoders with input patterns and optical microscope images, we can visualize how printed layers would look and explore input layer pattern generation from an inverse model, significantly reducing time and cost in achieving precise micro-nanoscale 3D printed structures.

The ultimate dream of 3D laser nanoprinting is to manufacture arbitrary macroscopic complex 3D structures with nanometer feature sizes by exposing an ink with a single femtosecond laser pulse. We argue that the corresponding light fields can be shaped by optical holography, which literally allows to print at the speed of light. We further argue that currently available single-box regeneratively amplified femtosecond lasers with mJ pulse energy, 100-fs pulse duration, 800-nm wavelength, and 1-10 kHz repetition rate together with multi-photon absorption should allow for exposing 3D objects containing 10^8 to 10^9 voxels within one picosecond, leading to peak print rates of 10^20 to 10^21 voxel/s. Such values would surpass the current best peak print rates of about 10^8 voxel/s by a very large margin. We give an introduction and review steps in this direction by other groups.

Two-photon 3D laser printing has been established as an excellent tool for precise micro- and nanoscale fabrication with applications in a wide range of fields. The properties of 3D printed microstructures strongly depend on material formulation and printing parameters. Comprehensive understanding and systematic characterization methods are crucial for successful integration of the developed materials into real-world applications. The lack of standardized procedures and control of the (macro)molecular architecture of the printing formulations remains a challenge. In recent studies, we demonstrate that the combination of defined (macro)molecular printable materials and systematic characterization methods at the microscale is critical for materials design.

Since the latest ISO 25178 publication, calibration of areal measuring instruments has been fully documented, emphasizing its importance all over. We previously highlighted the advantages of direct laser written calibration structures, such as design freedom, high resolution, and thermal stability, leading to an universal calibration artifact for all ISO-based metrological characteristics. Now, we report on extensive international comparison measurements to apply multiscale analysis (MSA) to direct laser written structures for the first time. Generally, MSA characterizes surface topographies across several scales, crucial when calibration standard and measuring device operate on different size scales. Specifically, areal and volumetric analysis methods were used to investigate the transfer behaviour of areal measuring instruments. We found a clear correlation between MSA results and ISO-conform metrological characteristics, linking scale-dependent transfer behaviour, resolution limits, and the ability to capture large surface angles. These findings suggest that MSA enhances performance verification and uncertainty determination of areal surface topography measuring instruments.

In this work, we propose a new alternative to perform the true 3D alignment of liquid crystal elastomers (LCEs) in a precise manner compatible with 3D direct laser writing (3D DLW). By playing both on the orientation strategy and the fabrication parameters, different deformations can be programmed starting from a single CAD model. A collection of building block is first demonstrated, then assembly of these building block is achieved, leading to 3D micro-objects presenting sophisticated behaviour. Finally, the fine control offered by our approach is illustrated i) by building a micro-actuator and investigating its performance ii) by elaborating miniaturized colorimetric sensors.

The recent implementation of two-step photoinitiators (Nat. Photon. 15, 932-938 (2021)) for three-dimensional nanoscale direct laser writing has enabled printing with low cost, low power laser diodes while preserving the nonlinear relationship between printing and incident light intensity found in two-photon absorption. Thus far, this method has been able to achieve very high printing resolutions at the diffraction-limit. In order to further improve this resolution, we implement a photoinhibition scheme inspired by stimulated emission depletion (STED). Similar schemes have previously been used in two-photon absorption-based printing and have successfully demonstrated printing resolutions beyond the diffraction limit. Thus, in this work we use a novel, depletable, two-step photoinitiator to combine two-step printing with STED-inspired techniques and achieve sub-diffraction limited printing resolution in a compact, stable optical setup.

The formation of three-dimensional objects through the tomographic reconstruction of a patterned light dose, also known as computed axial lithography (CAL), is enabled by careful co-optimization of the reactive material’s composition, the algorithm that computes the delivered light patterns, and the opto-mechanical system that delivers the light. To approach industrially relevant component sizes, spatial resolution, and dimensional accuracy, work is needed on all three of these technological pillars. Firstly, I will describe recent progress in formulating ceramic-photopolymer nanocomposites where careful selection of particle geometry, mixing protocol, and illumination wavelength offer a path towards CAL printing. Secondly, I will describe a first-principles approach to modeling the aggregate scattering behavior of such materials, based on Mie scattering theory, to aid in the computation of projected light patterns. Thirdly, I will explore some physical considerations for scaling up the printing volume of CAL systems. Finally, I will describe some ongoing work to expand the range of CAL-printable materials to those shaped by ring-opening metathesis polymerization.

In tomographic volumetric additive manufacturing (VAM), 3D objects are printed by irradiating a rotating body of photocurable resin with time-varying near-UV light patterns. Operating a VAM printer requires significant user skill and familiarity. In particular, the correct UV exposure time is estimated before or manually during printing. This results in poor repeatability and wasted resin, resulting from variation in printing rates due to resin history, object geometry, and temperature variability. In this talk we will present a robust approach to automatic print exposure setting by quantifying the side-scattered light signal, allowing the user to walk away from the printer during printing. The print is terminated automatically when print completion is detected. To demonstrate the accuracy of this technique, we will present objects built with multiple VAM-printed parts, VAM-printed mechanical metamaterials, and x-ray computed tomography scans of test objects to quantify print fidelity.

This presentation about Tomographic Volumetric Additive Manufacturing (TVAM) shows that advances in the computer graphics literature can be leveraged to build a more general optimization framework for TVAM pattern generation. We show that obtaining suitable projection patterns can be formulated as an inverse light transport problem. We present Dr.TVAM, a new open-source framework that implements a physically-based differentiable renderer suited to TVAM, producing high-quality patterns. This approach can account for various printing process effects like refraction and scattering, and outperforms prior methods.

In this talk we present improvements and novel printing results obtained with our differentiable ray optical framework (called Dr. TVAM) for Tomographic Volumetric Additive Manufacturing (TVAM). In TVAM different 2D patterns are illuminated on a rotating vial containing a photosensitive resin. Dr. TVAM produces patterns which outperform printing results in scattering media by simulating the ray optical propagation physically. Also, for the first time we print in a square vial without index matching bath. And for striation mitigation we print in a tilted TVAM geometry where the light illumination is not perpendicular to the rotation axis.

The use of additive manufacturing to produce Graded Index (GRIN) lenses has taken the forefront in the search for new design techniques. While multiphoton direct laser writing and inkjet technologies are the leading technologies into this venture, digital light processing (DLP) printers have scarcely been investigated. Using the principles of partial polymerization and a conversion prediction model designed to restrict polymerization exposure, DLP printers can be utilized to generate spatial conversion gradients which further enables the tuning of refractive index profiles. Following the production of a GRIN lens, both optical and chemical characterization must be performed to verify proper performance has been achieved. Recent advances in model development and characterization techniques have displayed more accurate results and produced parts on par with equivalent AM techniques. This work aims to utilize the grayscale capabilities of DLP 3D printers alongside an in-house developed model to produce GRIN lenes with performance approaching the diffraction limit.

To meet future demands for microelectronic devices—dimensional, environmental, functional—new fabrication technologies are sought after. Manufacturing technologies that minimize the footprint of such devices while concurrently integrating electronics with other functionalities such as microfluidics. This is made possible by 3D printing electronics at high resolution and incorporating and interconnecting bare die chips. At Holst Centre, we have been developing a multi-material additive manufacturing technology to meet these demands. “3D Additive Lithography for Electronics” combines high-resolution direct imaging lithography with groove filling with conductive metal pastes to build structural electronics with down to 10 µm feature sizes. The structural material, a photopolymerizable resin, is patterned using a DMD-based light engine that scans over the build area. A custom-built foil recoating solution provides fresh resin to the build area as the printing progresses, and industry-standard metal pastes are used to interconnect incorporated functional components in the 100 µm to several mm size range.

Recent developments in Volumetric Additive Manufacturing (VAM) have demonstrated the potential to print intricate objects using a more efficient light engine based on coherent light patterns encoded in Lee holograms displayed on a digital micromirror device (DMD) within a holographic configuration. Here we present an implementation of a Phase-only Spatial Light Modulator (PLM), a piston-mode design of a DMD for Holographic Volumetric Additive Manufacturing (HOLOVAM) based on reverse tomography. In this work, we characterize the PLM at 405nm and measure the diffraction efficiency. By synchronizing the laser, the rotation stage, and the PLM, we experimentally demonstrate the printing of centimeter-scale objects with diffraction-limited resolution in less than one minute. The PLM opens new avenues for Tomographic VAM with low-cost single mode UV laser diodes.

Chirality transfer in chemistry typically refers to the transfer of stereochemical information between chiral and achiral molecules during molecular interactions. In chiral nanophotonics, this phenomenon is observed when a chiral molecule interacts with a non-chiral resonator, resulting in a resonant shift of the chirality towards that of the resonator. Traditionally, this effect has been widely used for chirality sensing; however, the fundamental mechanisms underlying chirality transfer remain elusive. In this presentation, I will discuss how we leverage single-molecule methods and decoupled optical nanoscopy to interrogate chirality transfer between achiral nanoresonators, chiral resonators, and chiral molecules.

3D printed micro-optics has revolutionized medical imaging as well as sensor and AR/VR applications in the last decade. Two-photon polymerization lead to the fabrication of singlet and multiplet optical elements which included aspherical and non-rotational free-form elements, as well as a combination of diffractive and refractive elements. Multiple materials with different dispersion properties allowed for achromatic performance, and 3d printed black polymers enabled aperture stops as well as absorptive hulls. Diffraction limited performance over a large field of view with complete suppression of 1st and 3rd order abberations as well as apochromatic properties for three different colors were made possible by two-photon direct laser written micro-optics, leading to wavefront aberrations as small as lambda/100. In this contribution, we expand the performance parameters to very large optics in the range of up to 5mm as well as to more complex light fields, such as multiple foci. 3D printed elements take therefore a large step towards applications such as high-performance microscopy, trapping of multiple particles or atoms, in a variety of complex fields, on the tip of a single fiber.

Additive manufacturing (AM) of complex multimaterial devices could provide transformative solutions for future electronics. Functional materials, including nanomaterials, are formulated for use in inkjet printing and in two-photon polymerization process. We demonstrate additively manufactured electrically conductive, optically active and dielectric layers, to produce devices, such as photon detectors, field effect transistors and multifunctional sensors. Our work highlights the opportunities for scalable AM of optoelectonic devices and quantum sensors.

This presentation explores gravity's impact on dispensed optical lens production. The experiment utilizes a jet dispenser and UV curing setup within the Einstein-Elevator (3rd generation drop tower) to create sessile droplets during a flight phase with adjustable gravity. Microlenses in three sizes are manufactured under six different gravity conditions ranging from microgravity to Earth’s gravity. Based on the geometric dimensions and shape of the lenses, the results reveal that the production of larger lenses is more affected by the effect of gravity than smaller ones. These findings contribute to the development of additive manufacturing technologies, particularly for in-space applications.

We report on the realization of Q-plate structures using femtosecond 3D laser printing technique in photoresist. The Q-plates are obtained by combining multiple laser-printed anisotropic, form birefringent 3D photonic crystal regions having the same magnitude of phase retardation (half-wavelength) and space-variant orientation of their optical axis. Q-plate structures operating at visible wavelengths and capable of converting spin angular momentum (SAM) of photons to orbital angular momentum (OAM) are demonstrated.

For high-speed Raman spectroscopy low intensity signals are a common problem. This complicates the identification of molecules even though in many applications the number of possible molecule outcomes is very limited. We present an approach to improve the amount of information gained with only a small number of detectors. Following the example of sequencing proteins with only 20 possible amino acids using only four detectors we first find optimized spectral regions that should be covered by one detector each to maximize the gained information. Next, we show a refractive-optical element that is capable of selecting and guiding the light from each of these spectral regions onto one detector each simultaneously. The element is fabricated using the benefits of two-photons grayscale lithography and later characterized in an optical experiment. The results match our simulations, indicating that our optical element indeed improves the performances of a real Raman spectrometer.

Volumetric additive manufacturing technologies have solved translations between 3D object and image spaces for rapid fabrication in homogeneous, high viscosity resin without layering or support structures. Parallax manufacturing (PM) expands these capabilities by introducing a fourth dimension of address. PM rapidly moves an optical toolhead above a flat slab of photosensitive resin that addresses resin voxels with individually controlled beamlets tilted in two angles. This approximately squares the number of beams that intersect at each voxel, dramatically increasing the solution space available to the optimization algorithm. The resin slab used in PM is unlimited in transverse extent, allowing for large area fabrication. In contrast, the transverse size of the computed axial lithography cylinder must be equal to its depth which is limited to several cm by diffraction. This architecture importantly utilizes a translation geometry that matches established manufacturing platforms including assembly lines, CNC machine tool beds and roll-to-roll processing.

Volumetric Additive Manufacturing (VAM) is an optical 3D printing technique in which patterned light is projected into a volume of photoactive resin from multiple angles. As the resin absorbs light and the energy dose accumulates, polymerization occurs, transforming the resin from liquid to solid and forming a volumetrically printed object. By enabling simultaneous printing of an entire object, VAM offers unique capabilities compared to other additive manufacturing techniques, including “overprinting”—the ability to print inside, around, or alongside an object embedded in the resin. In this work, we present a novel approach to detect and correct misalignment in a computed tomography system, enabling high-resolution 3D tomographic reconstructions even in misaligned systems. Using this reconstruction, we accurately determine the seven degrees of freedom (3 spatial, 3 angular, and 1 size) of an object embedded in the resin. Finally, we demonstrate how this information is used to precisely print an object relative to the embedded object, enhancing the accuracy and potential of overprinting in VAM.

One of the distinctive advantages of volumetric additive manufacturing is the ability to overprint freeform structures onto pre-made objects such as electronics components and reinforcing structural elements. However, these objects typically attenuate or completely block the patterning light, causing a shadowing effect that negatively impacts reconstruction accuracy. For this reason, the limit of reconstruction accuracy is highly dependent on the exact distribution of occlusions. So far, the impact of problem setting on reconstruction quality has not been well-studied in this field. In this talk, we first present two quantitative metrics that indicate the local difficulty of reconstruction and then demonstrate their utility under different occlusion arrangements and tomographic configurations. These metrics can be readily evaluated to guide design for manufacturing and system design.

Multimode interference (MMI) couplers have been long considered as key enabling components for splitting optical signals. Building on recent advancements in two-photon polymerization-based direct laser writing (2PP-DLW) and the capability to operate with full 3D freedom, we report on MMI couplers with an unconventional triangular cross-section. We developed first in their kind MMI couplers operating around the 1550 nm telecom wavelength that receive a 2-micrometer diameter waveguide at the input and generate a 3 or 4-node interference pattern in a triangular lattice at the output. As a proof-of-concept application, we developed an interconnection component that splits light from an input single-core fiber into four cores of a triangular core layout multi-core optical fiber. We fabricated the splitter with 2PP-DLW technology to experimentally demonstrate a novel type of single-core to multi-core fiber splitter, measuring losses at -3 dB per channel and achieving a length as short as 180 micrometers.

Photopolymerization-based methods for additive manufacturing like Stereolithography (SLA) and Digital Light Processing (DLP) combine high resolution with decent fabrication speeds. However, these methods use a layer-by-layer approach, resulting in anisotropic properties of printed objects and visible surface steps, making them less suited for 3D printing optical elements. In contrast, Xolography as volumetric 3D printing technology rapidly produces isotropic objects with optical-grade surfaces. Layer-less curing is achieved within the volume of a photopolymer by intersecting a thin UV light sheet with a visible light projection. Printed objects show surface roughness down to Ra = 10 nm without additional polishing or coating, rendering Xolography a game-changing technology for the additive manufacturing of optical elements. The presentation highlights our latest developments in dual-color photoinitiation allowing for 3D printing of optically transparent objects as well as Xolography’s capacity to fabricate smooth optical elements without any additional surface treatment. Volumetrically printing optics around other functional parts paves the way for integrated optical components.

Using visible light volumetric bioprinting technologies and novel, protein-derived photoresponsive hydrogels, fragile complex mini-organ models, also termed organoids, can be safely assembled into centimeter scale living tissues in a matter of few seconds. Herein, the most recent advances in light-driven biofabrication will be presented, together with our efforts to engineer functional blood vessels, breast gland tissue, and pancreatic tissues as advanced biological models, using organoids as living building blocks. Novel volumetric light projection techniques will also be presented, highlighting how single photon projection technologies can enable advanced printing, biomolecules patterning, and imaging across large, anatomically relevant constructs.

Computed axial lithography (CAL) is mathematically founded on the Radon transform which is the 1:1 invertible linear transform between 3D object space (x,y,z) and 3D image space (row,column,theta). However, this cannot be applied in the presence of the nonlinear constraint of non-negative image intensity, motivating the current practice of image-set optimization to meet image intensity and object dose constraints. The optimal solution can be improved by providing more linearly independent degrees of freedom in image space. These additional degrees of freedom include the six rigid body transformations of the projector point-spread function of which axial rotation used in CAL is just one. We demonstrate efficient image generation algorithms able to solve the optimization between 3D object and 4D and 5D image spaces. A specific VAM architecture that enables these high dimensional image projections is shown and its properties are discussed.

By using two-photon lithography to pattern materials within a 3D nanoporous scaffold, we are able to pattern arbitrary 3D gradients of refractive index with index contrast up to 0.6 and features down to <50 nm. This is a general paradigm of 3D nanofabrication that applies to a wide variety of materials. So far we have demonstrated different scaffold materials, including polymers, silica, and silicon, with a variety of different fill materials, including polymers, metals, and chalcogenides. We have used these techniques to fabricate several novel demonstrations of 3D devices that could not otherwise be made, including multi-layered metalenses, nanoscale free space optics, 3D freeform GRIN optics, and more. Furthermore, we show that having an index contrast comparable to glass in air means that the design and techniques of traditional freespace optics can be directly translated into the microscale, leading to what we call Integrated Free-Space Optical Microsystems.

Volumetric additive manufacturing (VAM) is rapidly changing the 3D printing landscape due to its ability to rapidly fabricate complex parts without the need for support materials. The printing process that gives VAM these attractive properties also presents unique challenges, such as layer-like artifacts that prohibit the production of smooth surfaces, as well as the requirement of using highly-viscous photoresins. In this talk, two methods are introduced that overcome these challenges. First, we discuss recent progress using VAM to fabricate micro-optical components in a method we call blurred tomography, and demonstrate imaging performance that is comparable to off-the-shelf commercial lenses. Next, we introduce a new VAM approach that enables high-fidelity printing of low-viscosity photoresins, with viscosities as low as 12 cP or 100X less viscous than previous reports.

Tomographic volumetric bioprinting is a groundbreaking biofabrication technique that rapidly produces complex free-form structures within seconds. It uses a precise 3D light dose to create intricate designs in a range of materials, from soft hydrogels to sturdy ceramics. This method is gentle on living cells, featuring short printing times, low photoinitiator concentrations, and no shear stress, ensuring high cellular viability and function. The technology supports multiple wavelengths, enhancing its versatility and expanding potential applications. Examples include modeling liver functions with hepatic organoids and mimicking cancer-associated fibroblast responses in pancreatic cancer models. At Readily3D, we develop these advanced bioprinters to enable researchers to model biological tissues swiftly and accurately, pushing the boundaries of biomaterials research and applications.

Volumetric additive manufacturing (VAM) and its most popular form, often called computed axial lithography (CAL), has been under active development for most of the last decade. This layer-less and support-free paradigm for 3D printing has drawn significant research attention owing to its speed, structural freedom, and material versatility. Presently, several dozen investigators worldwide are advancing the development of new materials, optical systems, and computational algorithms that underpin the implementation of volumetric 3D printing. This presentation will take stock of the state of technology, highlighting key accomplishments and major areas of progress, while identifying the most important challenges for future development.

Femtosecond laser irradiation followed by chemical etching (FLICE) is a powerful and enabling technology for microstructuring glass substrates in 3D. The irradiated focal volume expresses increased etching selectivity with respect to the pristine material, enabling the fabrication of optical components with micrometric resolution, but with critical residual roughness (about 100 nm rms). Here we compare the surface quality of microlenses processed with different methods as CO2 laser annealing, thermal annealing in oven and polishing by direct dielectric barrier discharge inert gas plasma at atmospheric pressure. The optimized optical elements will be integrated on more complex devices for optical investigations of biological specimens.

This study investigates the improvement of planar waveguide performance for advanced optical sensors by optimized hot embossing on polymethylmethacrylate (PMMA) substrates with Ormocomp photoresist and integration of zeolite imidazole framework-8 (ZIF-8). We have produced planar waveguides with significantly reduced optical transmission losses of 2.32 dB/cm which is suited for the sensing application intended. The integration of ZIF-8-based optical films improves carbon dioxide (CO2) sensing, with adsorption taking 55 seconds and desorption only 10 seconds, achieving a sensitivity of about 7 μW/5 vol% and demonstrating excellent reversibility of gas adsorption/desorption cycles. Future research will investigate different photoresists to further optimize waveguide performance and expand application cases. This study may thus lay the foundation for next optical sensing technologies in the biomedical, environmental, and industrial fields based of functionalized planar-optical waveguide arrays.