This PDF file contains the front matter associated with SPIE Proceedings Volume 12898, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

In this paper we demonstrate the development and optimization of an 800 nm-thick Plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SiN) photonic platform on a 300-mm silicon wafer. The implementation of ArF immersion lithography contributes to superior manufacturing processes, as it provides excellent critical dimension (CD) uniformity inter- and intra-wafers, make it an optimal platform of production of integrated circuits and nanoscale devices.

Micro lens array (MLA) is an optical element used in various purposes. For MLA industrial lighting device, such as uniform illumination diffuser or super wide-angle diffuser, it is required to achieve high quality illumination control. When we process MLA mold by ordinary diamond milling, error factors including tool wear, cause the same distribution of shape errors in each micro lens. The MLA lighting device produced using this mold will have an illuminance irregularity on the light distribution corresponding to the shape error distribution. In this study, we have investigated a processing method to vary the distribution of the shape error of each micro lens comprising the MLA for improve illumination quality. This method can be applied to various MLA design, for example, MLA consisting of aspheric micro lens with a maximum tangent angle of more than 60° or non-rotationally symmetric micro lens such as polynomial freeform surface.

This work demonstrates the effectiveness of advanced manufacturing strategies in multi-photon lithography, utilizing smart hatching and slicing strategies alongside laser power modulation. These techniques enable the high-fidelity printing of spherical structures, producing micro-spheres of the quality necessary for standard optical applications and even for advanced optical applications, such as micro-sphere-assisted microscopy. Additionally, these advancements are shown to positively impact the fabrication time, offering a more efficient way to use MPL.

We report on wavelength independent laser direct writing 3D nanolithography using both amplified and non-amplified laser sources. Ultra-precise and truly three-dimensional optical printing technique known as two-photon or multi-photon polymerization (TPP and MPP, respectively) is experimentally validated without the use of any photo-initiators and applying various wavelengths ranging from 515 to 1250 nm. The novel approach is achieved in hybrid organic-inorganic SZ2080^TM and other hybrid polymer materials showing its versatility. Linear writing speeds up to 100 mm/s are realized without compromising the spatial resolution or quality of the structures reaching reproducible line structures with ≈270 nm in lateral dimensions. Therefore, here we demonstrate that various light-matter interactions mechanisms can trigger photopolymerization enabling optical 3D nanoscale printing using x-photon absorption.

Recent results from numerical studies suggest that transversely distributed structures can be used to design nanoscale, binary phase, pseudo-randomly distributed structured surfaces (PDnS) that enhance transmission through dielectric optical windows. The PDnS are designed using deterministic rules, which allows minimumfeature dimensional control, repeatable uniformity, and some selection rules for transmitted intensity scatter profiles. Although the redistributed features within the PDnS unit cells are subwavelength in scale, numerical results indicate that the unit cells are not required to be subwavelength in size. This allows for customized surface correlated structures, with nearly zero root-mean-square surface (height) roughness. PDnS are in direct contrast to periodic subwavelength binary grating structures, which have constant periods, a single-phase transition within their unit cell, and are at least deep enough to result in π-phase shifted emerging wavefront segments. We chose a series of PDnS patterns to realize optical transmission enhancement above Fresnel limits, within a limited 2 μm wavelength bandwidth centered at 4 μm. To ease fabrication requirements, the designs used were restricted to a binary phase depth close to quarter-wave, and unit cell dimensions ranging from 4 µm to 6 µm. PDnS patterns were prototyped using two-photon-absorption direct laser-writing in a photosensitive polymer film supported by a silicon substrate. To investigate fidelity and tolerance of the candidate design, the PDnS patterns were characterized using a UV-laser confocal microscope. Unpolarized spectral transmission of the structure depth was measured using a spectrophotometer. The experimental results were compared to numerical predictions using rigorous coupled-wave analysis simulations.

We report on fabrication of form birefringent phase retarder structures for visible wavelengths using 3D laser printing technique. The structures use 3D photonic crystal architecture modified to enhance structural anisotropy and birefringence, and exhibit a high phase retardation while retaining a low optical geometrical thickness of less than ten wavelengths. This architecture is used for realization of spatially-variant form birefringent Q-plate structures having spatially variant prentation of the local optical axis. Optical characteristics of the laser-printed Q-plates providing the evidence for their capability to convert optical spin orbital momentum into orbital angular momentum at optical wavelengths are also presented.

Optical fiber coupling plays a critical role in various fields, particularly when fibers are utilized in alignment stations. The efficiency of coupling is greatly influenced by the incident angles of the transmitting and receiving fibers. To enhance the coupling efficiency, one effective approach involves employing optical elements at the ends of one or both fibers. In this paper, we introduce a method for manufacturing lenses on optical fibers using a liquid polymer and strong electric fields to deform the liquid polymer into a defined shape. Our experimental setup includes cameras, linear axes, LEDs, electrodes, and a high voltage supply, enabling precise control of the deformation process. By applying an electrical field, we deform a liquid polymer droplet on the fiber tip, allowing us to create lenses of various shapes based on the electrode configuration. These lenses are fabricated using a UV-curable polymer which can be subsequently cured with UV light. We evaluate the quality and performance of the lensed fibers by reconstructing the 3D shape of the droplet and then utilizing raytracing. Furthermore, we present an innovative approach to calculate the electric field during in-situ deformation of the polymer droplet. This numerical method utilizes data and images obtained from the linear axes. By combining experimental observations with computational modeling, we gain valuable insights into the behavior and characteristics of the electric field. Our research offers a practical technique for manufacturing optical fibers with customized lenses and provides a comprehensive understanding of the electrical field dynamics involved. This approach has the potential to significantly improve coupling efficiency and advance the field of photonics.

Nanoimprint lithography (NIL) is nowadays the most popular and effective method to develop new environmentally-friendly and low-cost photonic nanodevices. Combined with titanium dioxide (TiO₂) in the form of sol-gel, photonic nanostructures with low absorption and high refractive index can be produced, which can be of interest for many applications for which sustainability becomes increasingly important. In this paper, we present a patterning process based on soft NIL of TiO₂ sol-gel, and show that the pattern transfer is almost perfect independently from the feature size, shape and height of the patterns. We also propose a low-temperature (400°C) calcination process to crystallize the TiO₂ nanostructures, which leads to very similar crystalline structures to higher-temperature processes, and a vertical shrinkage of about 61% compared to the imprinted pattern. Using this environmentally-friendly combined soft-NIL + calcination process, we show that submicron patterns with heights above 300 nm can be obtained. Such a large pattern height, combined with the wide range of pattern shapes and dimensions that can be fabricated, opens the possibility of a wide diversity of designs for the eco-friendly fabrication of TiO₂ nanostructures with highly-interesting photonic properties.

Typically, conventional micro-nano fabrication methods are applied to flat surfaces, ensuring precise alignment and resolution at the nanoscale. Nevertheless, when dealing with curved or multi-oriented substrates, the task becomes considerably more intricate, necessitating complex equipment for sample positioning, lithographic alignment, and focusing. This often results in significantly reduced fabrication capabilities compared to standard processes. Recently, our group introduced a straight method to handle micro-structures fabricated by two photon lithography and conformably place them on curved surface target objects by exploiting Van der Walls adhesion of ultra-thin polymeric film used as temporary freestanding support. In this invited lecture, we will review the most recent results of our group with this approach applied to the field of optical meta-surfaces and sensors, highlighting the future directions and the possible extension of the technology to other fields.

Selective laser etching (SLE) enables highly precise 3-dimensional structuring of glasses with a resolution of a few µm. The procedure requires two main process steps. First, the desired structure design created beforehand is transferred inside the glass by a fs-pulsed laser. Subsequently, the glass is placed in acid or a lye, respectively, to etch the modified area. Hereby, the required liquid for the post-processing step depends on the used glass type. In our work, we performed a detailed investigation of the structuring of fused silica with subsequent etching by KOH solution. We studied the influence of different writing parameters such as laser power, repetition rate, polarization, stage motion speed and hatching distance towards an optimized surface roughness which is crucial for optical applications. Hereby, we were able to reliably achieve surface roughness values of ~40 nm and realize first waveguiding structures. Additionally, we also structured the glass periodically with feature sizes of less than 1 µm. The process developed is not limited to the structuring of flat glass substrates. Also standard glass fibers were employed to realize free access to the fiber core and create integrated optical structures for sensing. We will present our latest results of structuring and etching different types of glasses and geometries achieved by varying the laser parameters with and without a subsequent tempering step. Various optical structures were created and characterized as well as their feasibility for utilization as optical sensors demonstrated.

We present a monolithically 3D nanoprinted micro-optomechanical switch with electromagnetic actuation. The bistable actuator moves a microlens between two distinct positions along the optical axis, thereby shifting the image plane and attaining different numerical apertures. The sub-millimeter-size device achieves an average displacement of 163.9 µm between the two stable positions, with positioning and orientation errors below 3 µm and 0.5 degrees, respectively. An electromagnetic actuation system consisting of a polymer magnet and an external coil allows for rapid switching. We characterized the resonance behavior of the microlens actuator and demonstrated its capability for both DC and AC driving between stable positions.

Direct laser writing of surface relief microstructures on azopolymer films using structured polarization is an emerging technology for the fabrication of diffractive optics. Films are photopatterned with 488 nm laser light and a spatial light modulator (SLM) configured as a polarization modulator. The structures require no post-exposure processing, and can be replicated using nanoimprint lithography. A limitation of this method is that typical exposure areas are of order 1 mm². Larger areas require XY stepping of the film, degrading the diffractive functionality due to the stitched boundaries between exposures. Here we report that continuous scanning of the film in the structured polarized illumination reduces boundary structure effects. This has been previously demonstrated in photochemical materials such as photoresist, and it is effective in photomechanical azopolymers since the characteristically slow response enables a surface-averaging that results in relief gratings of highly uniform amplitude. Additionally, the surface relief amplitude and period can be continuously varied via direct programming of the SLM and scan rate. We use the system to fabricate a variety of sinusoidal surface relief gratings of area 25 mm2 which were replicated via nanoimprint lithography and which exhibited first order diffraction efficiencies approaching 33% at 633 nm. We also fabricated chirped gratings designed to diffract RGB along a common direction in first order, with custom color generation based on grating area.

As a recently developed 3D printing technique, tomographic volumetric additive manufacturing (VAM) enables rapid printing of freeform objects by parallelizing photopolymerization through tomographic exposure. In this tomographic exposure process, patterning resolution and conversion accuracy crucially depend on the design of tomographic projections. In this nascent field, there are only a few optimization algorithms and each proposed to cater certain special cases of the general inverse design problem. Yet, there is no comprehensive and rigorous treatment to simultaneously address the larger class of design problems involving a mix of greyscale targets, non-linear material response, spatially variant tolerance, arbitrary tomographic configuration, and complex propagation media. This paper outlines two contributions to the mathematical and computational foundation for volumetric 3D printing, namely, a general band constraint optimization model and a ray-tracing light propagation model. These advancements are crucial for VAM in creating accurate functionally graded objects in heterogeneous media. Beyond 3D printing, the findings in this work are relevant to synthesis of spatiotemporal irradiation profiles in other contexts, such as those in photografting of biological constructs, 3D neural photostimulation, and intensity-modulated radiation therapy (IMRT).

Volumetric additive manufacturing based on the principles of tomographic reconstruction has seen inspiring advancements in the past three years. Here we discuss the desirability and challenges associated with using more than one color in computed axial lithography to realize multiple functionalities. We first recap the implementation of a dual color system for spatial control of workpiece stiffness. The orthogonal polymerization of two independent yet interlaced networks allows fine tuning of the end product’s mechanical property from hydrogel-like to thermoset-like. The challenge in maximizing achievable property contrast led us to develop a sinogram computation strategy that differentially prioritize voxels. However, such a strategy puts a stringent requirement on the projecting resolution. We discuss the feasibility of alleviating such a requirement by lifting the non-negativity constraint for tomographic printing. We laid out the theoretical framework for a binary photoinhibitory system, which creates a stationary state with controllable stability on the phase diagram. We show that if illumination of two wavelengths are coordinated to steer a system such that it revolves counterclockwise about the origin, the two wavelengths become effectively negative to each other in the context of polymerization initiation. We further explain why creating negative illumination helps alleviate the resolution requirement. Combined, these efforts lead us to a hypothetically tri-color system that holds the potential of realizing full orthogonality between geometric control and property modulation.

In regenerative medicine, layer-by-layer additive manufacturing has been pivotal in developing intricate 3D tissue scaffolds, yet challenges remain in the fast production of cell-laden structures of clinically relevant (centimeter-scale) sizes. Volumetric Bioprinting (VBP) is a recent optical additive manufacturing technique which facilitates rapid creation of such structures by using spatial light modulation to deliver precise tomographic patterns into a rotating volume of cellladen photoresin, thus allowing for rapid, volumetric crosslinking of materials. Our research enhances VBP by integrating extrusion and electrohydrodynamic printing, thus optimizing multi-cell and multi-material constructs. Using photoresponsive biopolymers and polycaprolactone-based meshes, we have crafted complex cell-laden 3D forms with VBP, introducing diverse features unseen with conventional techniques. With applications for multi-walled blood vessel engineering and specialized cell growth platforms, our findings emphasize the transformative role of optics in biofabrication, suggesting VBP's potential in replicating tissue intricacies and advancing regenerative medicine.

HoloTile is our novel and recently patent-filed approach [1,2] to obtain very fast reconfigurable and strongly speckle-reduced digital holography. Using HoloTile we have experimentally demonstrated more than 90 % photon-efficient phase-only projected dynamic and static far field diffraction both with and without a lens. A key aim for inventing and innovating HoloTile has been to effectively solve the challenge of rapid and speckle-free coherent or semi-coherent light sculpting without the need for time-averaging techniques - a challenge that exists in several fields of optics and photonics. In particular, HoloTile provides four new unique key features as CGH-modality for high-resolution spatial light modulators, reconfigurable DOEs or new meta-surface MOEs: • A 100x speed improvement over standard CGH-modalities • Substantial speckle reduction by matched tiling and PSF-shaping • Real-time dynamic and output 'pixel' discretized digital holograms • Lens-free scaling or zoom by software adapted HoloTile phase-encoding.

Computed Axial Lithography (CAL) is a 3D additive manufacturing process that is able to form all points within a geometry simultaneously by delivering a light dose to a photopolymer via tomographic reconstruction. CAL can avoid hydrodynamic rate limitations, allowing for higher-viscosity precursors, and fast manufacturing speeds. Hydrogel Infusion Additive Manufacturing (HIAM) is a recent additive manufacturing process that allows for the production of metallic parts but has only been demonstrated with traditional layer-by-layer additive manufacturing. This research demonstrates a modified HIAM process utilizing CAL, in which a higher-viscosity precursor material with additives is used.

The fabrication of optical filters whose reflection/transmission response is spatially-graded has been the object of numerous research studies over the past decades given their applications in areas including multi- and hyperspectral imaging, structural colouring and even holographic encryption. In this context, the key enabling feature is the ability to tailor the thickness profile of at least one layer of the optical coating multilayer stack. To-date, this 3-dimensional structuration has been achieved either at the deposition stage or as an additional post-deposition process step. In the former case, the technique relies on the shaping of the material deposition flux thanks to the insertion of a (moving) mask inside the evaporation or sputtering machine. As such, the method is usually limited to the implementation of centimetre-scale variations. A contrario, to reach sub-millimeter-scale features, the preferred approach is based on postdeposition layer structuration, which is performed using grayscale lithography in the form of multi-(mask-)level optical lithography, or using e-beam or laser lithography. All these approaches are nevertheless relatively complex since they involve either multiple steps or need a very precise calibration of the exposition curve. In this paper, we report that the evaporation through re-usable shadow masks can be used to create optical filters whose spatial variations can be controlled with a ~70-µm-resolution. Using metal-mirror Fabry-Pérot interferometer structures as representative optical filters, we demonstrate the ability to adjust the resonance wavelength, the filter bandwidth and extinction ratio, and the coupling strength and splitting in cascaded resonators.

UV-replication is well known from wafer level optics, where supporting glass wafers remain in the final lens severely limiting the degrees of freedom of the optical design. In addition, material shrinkage occurring during the curing of the polymer limits reasonable sag heights of the lenses, so that only low-resolution imaging optics are possible. In our UVreplication process, the glass substrate in the individual lenses can now be omitted and a compensation of the shrinkage is achieved with minimum form error. As a result, monolithic components with double-sided aspherical lens profiles of large sag height can be manufactured, as required in high-resolution imaging optics, which previously could only be realized by injection molding. Unlike injection molding, the replication is carried out at room temperature saving large portions of energy required. In combination with a high degree of parallelization as in wafer-level-optics, which is the key to large-scale production, a more environmental-friendly production is possible, since the number of replication machines and thus the required clean room space are significantly reduced. As a further advantage, the used materials meet high temperature requirements and even withstand reflow-soldering performed at 260°C. We present details of our new technology at the example of realized demo systems for 3D-sensing applications using nano-optical structures and imaging use-cases aiming at high-volume, low-cost and high-performance solutions.

In this study, we present a novel approach combining nano-scale imprint lithography (NIL) and reactive ion etching (RIE) to fabricate high-quality surface relief gratings (SRGs). This study provides valuable insights into the challenges and optimizations in fabricating SRGs from TiO₂ layers using the combination of NIL and RIE. The work was performed with SCHOTT RealView® substrates coated with a 100 nm TiO₂ layer and a NIL mask with pattern widths of 200 nm and a pitch of 400 nm. The substrates were processed using the SmartNIL® method to prepare the NIL mask. The advantage of removing the residual layer before the actual structuring of the TiO₂ using argon plasma was demonstrated in our research. This led to a significant increase in the selectivity between TiO₂ and the NIL resist UV/OA R18. Through the employment of a two-step etching process, which involved the removal of the residual layer with argon plasma and the use of a BCl₃-based reactive process with high ion energy, TiO₂ structures with a height of 100 nm and a sidewall angle of 75° were successfully created. An effective selectivity of 0.84 was achieved for this two-step process.

In the field of optics, Nanoimprint Lithography (NIL) is frequently discussed as a cost-effective manufacturing technology for diffractive elements. Using polymer-based NIL structures, it is interesting to quantify their fidelity in the imprinting process. Electron microscopy images are commonly used for measurement purposes. However, there are several other measurement techniques suitable for assessing NIL structures. Each measurement technology has its specific advantages and disadvantages, which can complement the evaluation of NIL structures. Here alternative measurement methods such as white-light interferometry, atomic force microscopy, optical coherent tomography, micro-computed tomography, and environmental scanning electron microscope are investigated to evaluate NIL structures non-destructively and with respect to multiple parameters (e.g. topological, optical). The evaluation criteria include resolution, aspect ratio, and fidelity. Using the discussed measurement technologies makes it possible to choose an appropriate measurement method based on the structure type and research question. Additionally, this enables non-destructive measurement of NIL structures and their continued utilization in the NIL process. Consequently, new insights into the behavior of stamp materials during the imprinting process can be gained and the manufacturing process of diffractive elements can be optimized.

In our research, we are investigating the manufacturing of phase gratings using soft nanoimprint lithography (NIL). NIL is a nanostructuring process in which a master structure is replicated via a stamp. In the soft NIL method, the stamp structure is molded from the master structure using liquid photoresist followed by ultraviolet (UV) light curing. Once a working stamp is created, it can be used to directly stamp multiple replicas. This makes the nanostructuring process time and cost efficient. The quality and reproducibility of the replicated structures are critical for the application of the nanostructures. Here, for the evaluation of the resolution, a test pattern (grating structures in the shape of a USAF 1951 Resolution Test Chart) is used as master structure. For stamp production, we use various polymers (Micro Resist Technology, EV Group and DELO) as stamp materials, spin coated on 4-inch wafers. These photoresists differ in their properties, such as the refractive index, which affects the quality of the nanostructures. The imprinted phase gratings are investigated with respect to their shape deviations and surface properties. We present a comprehensive analysis of the different stamp materials. Based on our evaluation, an optimal material can be selected to fulfill specific requirements of an application. This work provides insights into the manufacturing of nanostructures with soft NIL. Our research contributes to the further development of the NIL process and thus the fabrication of precise phase gratings.

The increasing concerns regarding the health risks and economic impact of food adulteration, particularly in honey, have sparked significant attention. Ensuring the quality and authenticity of honey relies on the ability to effectively detect adulterants such as glucose. This research focuses on the utilization of etched fiber Bragg Grating (eFBG)-based sensors for monitoring honey quality and detecting cases of glucose adulteration. FBG sensors offer numerous advantages in detecting food adulteration, including their exceptional sensitivity, real-time monitoring capability, and non-invasive nature. This paper provides a comprehensive account of the experimental design and data collection procedures employed to develop FBG sensors optimized for glucose detection in honey. Furthermore, coating the eFBG sensor with reduced graphene oxide (rGO) has shown better sensitivity due to its unique properties. The achieved sensitivity found is 43.56 nm/RIU with rGO-coated eFBG sensors. The results demonstrate the ability of FBG sensors to identify honey adulterated with glucose, highlighting their potential in enhancing food safety and quality control measures.

Overlay in upper layer with respect to lower layer need to be measured and controlled with sub-nanometer-level accuracy in semiconductor manufacturing process. However, as the Metrology To Device (MTD) deviation continues to increase, there is a growing need to maintain and improve MTD variation. In this study, we propose a methodology utilizing COMSOL Multiphysics to directly track process changes and quantify their impact. It can realize actual measurement equipment setting and modify optical property. We will introduce device matching methods that can improve MTD on product wafers through optical simulations.

A new approach named “place and bend assembly” for the efficient integration of complex optical systems in high volume has been developed by Fraunhofer IPMS. The concept has been proven using 3D printed components. Recent developments aim at applying injection molding for the fabrication of substrates optionally in high volume, as well as the integration of functional and optical active surfaces into the substrate. Design, material, process parameters and their optimization for the injection molding have to be analyzed in fine detail. Results of the substrate characterization and system integration will be presented.

3D-printed lens by two photon polymerization is promising technology in the filed of optics thanks to its free-form writing with sub-micron accuracy. However, reflection loss on the lens surface is problematic due to Fresnel reflection. In order to solve the problem, we have demonstrated a 3D-printed aspherical lens with moth-eye anti-reflection structure. An aspherical lens with submicron stripe was printed on fiber end face. Reflectance on the lens surface was reduced from 4.4% to 0.005% at 1550 nm wavelength, and furthermore, coupling efficiency to another fiber is improved from -0.52 dB to -0.33 dB thanks to the reduction of Fresnel reflection.

Recently, there has been growing interest in integrating metasurfaces with fiber-optic technology, which offers high functionality and design flexibility in handling optical properties. However, existing approaches of integrating optical fiber with Huygen’s metasurfaces are based on techniques such as Focused Ion Beam (FIB) or Multiphoton lithography which directly draw the desired metasurface on optical fiber, resulting in high fabrication complexity and difficulty in transferring multilayered metasurfaces for multifunctionality. In this study, we propose the punching-method, a simple technique to transfer prefabricated Huygen’s metasurfaces onto fiber apex.