Optical Metasurfaces – planarized patterned devices with thickness smaller than or comparable to the operational wavelength – can engineer the light wavefront beyond the limitations of natural materials, and they offer novel opportunities for optical technologies. I will discuss our recent efforts in the design, optimization, fabrication and characterization of all-dielectric high-index-contrast metasurfaces enabling different linear and nonlinear functionalities, such as analog image processing, efficient displays for augmented reality and nonreciprocal wave propagation. I will discuss the main potentials and challenges of current approaches and provide an outlook on possible future directions.

There is an intrinsic link between a lens' physical geometry and its optical properties. By tailoring the geometric shape of a homogeneous optical medium, accumulation of phase across different optical path can mold the flow of light: a cylinder creates a focal line along the optical axis, whereas a sphere creates a focal point. Decoupling geometrical and optical contributions is a requirement to impart arbitrary phase profiles over a wide variety of surfaces and enable seamless integration between advanced photonic components such as metalenses and our daily world. In this work we describe several perspectives to meet this technological challenge.

We report on the latest advances in printing 3D complex optical systems. We report inclusion of the color black into printing materials, as well as printing without additional alignment onto both sides of a substrate. We examine the influences of strain and stess onto the polarization state of light after propagation. We also present our ansatz to include shrinkage into the systems design. We report on applications in quantum technology, in particular on coupling quantum emission into single mode fibers, on optical trapping, and on multimode imaging in micro endoscopy. We also report on the smallest wide-angle endoscope in the world, which gives aberration corrected images for a viewing angle of 120°.

We report on the 3D printing of high transparency and resiliency free-form micro-optics. The fabrication is realized employing combining femtosecond laser direct write 3D nanolithography (fs-LDW or a.k.a. two-photon polymerization) with high temperature calcination (sintering) and atomic layer deposition (ALD) techniques. The developed approach allows production of diverse single optical elements and stacked components ranging in dimensions from 10 to 100 µm. Produced micro-optic objects are characterized of their optical performance (focusing, imaging, transparency) and determining their laser induced damage threshold (LIDT). This opens novel applications of laser 3D printed microoptics under harsh conditions: radiation, temperature, acidic environment, pressure variations.

3D nanoprinting of free-form structures enables provides exciting perspectives for hybrid integration of different photonic platforms. In particular, by using 3D printed coupling interfaces active and passive circuit components can be joined for creating chipscale solutions for high-bandwidth photonic computing. I will report recent progress on building photonic tensor core architectures which make use of heterogeneous integration. This way silicon photonic components can be seamlessly merged with active III-V circuits to realize core building blocks for photonic accelerators to machine learning.

Integrated photonics represents a fast-growing market targeting an increasing number of stakeholders and application fields. With its fabrication platform for advanced integrated photonic components in glass, FEMTOprint can produce high-precision optical and opto-mechanical connectors monolithically aligned with micro-optical elements within a single fabrication process. Therefore, no extra alignment is required and all optical elements can be positioned with sub-micron precision. We will present examples of the most common building blocks used for Integrated Photonics Circuits, i.e. fiber inlets for passive alignment, optical 3D waveguides as well as micro-optical elements for beam shaping such as micro-lenses and micro-mirrors.

Volumetric 3D printing has tremendous potential due to its ability to print in static resin vats and produce complicated parts without support structures, and two-photon printing has been tremendously successful in this regard. Here, we utilize a molecular form of upconversion, triplet fusion, to achieve the same quadratic light dependence as two photon absorption at much lower powers. We demonstrate the ability to tune the upconversion threshold across two orders of magnitude and encapsulate the molecules at the nanoscale, providing durability upon addition to a resin. These materials allow us to volumetrically print with less than 4 mW of CW laser power. In this talk we will also discuss future directions of this technology.

The process of computed axial lithography (CAL) has been established as one of the fastest available photopolymer 3D printing methods, offering smooth surfaces (r.m.s. surface roughness as low as 6 nm) and the ability to process high-viscosity precursor materials (100,000 cP demonstrated). Recently we showed successful printing of microscale geometries into dispersions of silica nanoparticles in a refractive-index-matched photopolymer. After exposing the 3D geometry via patterned tomographic illumination the material is debinded and sintered. In this way, external features of 50 µm and internal channels of 150 µm diameter have been achieved. This processing technique offers a promising route to production of 3D glass microfluidic devices and complex monolithic micro-optical devices. We will describe the status of optics fabrication via CAL. We will also consider the influence of light scattering on spatial resolution and possible ways of addressing this effect.

This conference presentation was prepared for SPIE OPTO, Photonics West, 2023.

We present recent advancements in two-photon grayscale lithography (2GL®). In contrast to one-photon grayscale lithography, for 2GL®, the exposed volume pixel is strongly confined to the vicinity of the laser focus allowing for a truly 3-dimensional dose control with very high spatial resolution. Discrete and accurate steps as well as essentially continuous topographies can be printed with increased throughput, on any substrate, and without the need for additional lithography steps or mask fabrication. We update on throughput and quality levels of the method. As demonstrators we fabricate and characterize a variety of microoptics and other benchmark structures.

This conference presentation was prepared for SPIE OPTO, Photonics West, 2023.

The topology of neural networks fundamentally differs from classical computing concepts. They feature a colocation of memory and transformation of information, which makes them ill-suited for implementation in von Neumann architectures. In substrates pursuing in-memory computing, the connection topology of a neural network is encoded in the wiring of a chip, regardless of photonic or electronic, and this approach promises to revolutionize the efficiency of neural network computing. Equally general is that such in memory architectures cannot be implemented in 2D substrates, where their chip real-estate as well as energy consumption increase with an exponent larger unity with the number of neurons. I will discuss our recent work on using additive one and two photon polymerization in order to create 3D integrated photonic chips, that will allow to overcome this scaling bottleneck. Our process is CMOS compatible and hence maps a direct path to a technological implementation.

This conference presentation was prepared for SPIE OPTO, Photonics West, 2023.

We report a new biopolymer resist that uses functionalized N-acetylglucosamine (NAG) as a monomer and is suitable for direct laser writing (DLW). Since NAG is the monomeric unit of chitin, a biopolymer found in the exoskeletons of various arthropods, the resist expands the available DLW-suitable biopolymers from plant- to animal-based. Furthermore, we show that the simultaneous use of two different photoinitiators is advantageous over the use of only one initiator. Here, the first photoinitiator, which acts as a good two-photon absorber (2PA) for the wavelength used, radicalizes the second photoinitiator (poor 2PA), which is more suitable for crosslinking the NAG.

We present on the additive micro-manufacturing of ceramic packaging, containing arbitrarily routed vias with a diameter and pitch as small as 10µm and 20µm, respectively. We accomplish this feat by pairing recently commercialized micro-printers based on digital micromirror devices with our UV curable pre-ceramic resin that enables dielectric ceramic printing. Ceramic interposers with thousands of vias were 3D printed, then metallized and finally indium bump bonded to test chips fabricated by standard semiconductor lithography. This technology enables unprecedented via routing and packaging options for the 3D integration of microelectronic subsystems and focal plane arrays.

We show first steps towards a simple, fast, and easy to implement algorithm to predict the finally printed topography in Direct Laser Writing (DLW). These robust predictions can be used prior to the printing process to minimize undesired deviations between the experimental 3D print and its target. Consequently, this approach can eliminate the need for a multitude of structural optimization loops to produce highly conformal and high-quality microstructures in the future. Moreover, we show first neural networks trained with our prediction algorithm being able to pre-compensate known and foreign structures without the need of performing any iterative correction prints.

2-photon absorption mediated by short laser pulses provides an optical nonlinearity that is highly desirable or even mandatory for various forms of volumetric (3D) laser printing. Here, we review and compare different approaches that replace 2-photon absorption by some sort of cascaded 1-photon absorption processes. Such “(1+1)-photon absorption” processes can be accomplished by inexpensive continuous-wave lasers at comparably low powers. We present recently published and unpublished results, including screening of molecules suitable for one-color and two-color 2-step absorption. In addition, we investigate the possibility of optical depletion processes at a laser wavelength that is distinct from the excitation wavelength.

Computed Axial Lithography is a recently introduced volumetric additive manufacturing technique that is attracting attention due to improvements in print speed, resin properties, and sterile print environment. Print capability depends on the optical system utilized, the algorithm used to compute image sets for a given print target, and the response of the resin. I will describe recent work in our group that couples advances in these three areas. First, I will describe a new image generation algorithm, Object Space Model Optimization (OSMO), that results in improved printing metrics such as voxel errors. The OSMO algorithm enables new printing optics such as tilted resin rotation that reduce striations and may enable new resin packaging. Finally, I will show that the computational and experimental results of extending the OSMO algorithm to include material properties such as inhibition, internal inclusions, phase-change and diffusion.