Optical systems are constantly becoming smaller. This requires innovative approaches to integrate multiple optical functionalities into single components. A promising way forward is to combine a diffraction grating onto the curved surface of a lens. However, established diffraction grating inscription techniques face challenges when applied to curved surfaces. In this article, we present a proof-of-concept method to combine a diffraction grating, lithographically inscribed on a planar wafer, with a bi-convex cylindrical lens through hydrophilic direct bonding. We characterize the resulting novel hybrid lens by measuring the line width in the focus position. Our findings demonstrate the potential for enhancing the performance of optical systems in terms of improved aberration correction and new optical functionalities while minimizing their size and weight.

Single-photon avalanche diode (SPAD) sensors are versatile candidates for applications in low-light imaging and scenarios where high temporal resolution is crucial, like quantum imaging, fluorescence lifetime imaging, and (direct) time-of-flight methods. We demonstrate the improvement in light sensitivity by a factor of 7x for LiDAR (Light Detection and Ranging) by molding application-specific filling factor enhancing microlenses directly onto backside-illuminated SPADs. An 8"-wafer-level process is presented utilizing a mask aligner device for selective UV-curing of highly transparent polymer lenslets only in areas where SPADs are located and rinse uncured material from areas being compatible with postprocessing steps like chip dicing and electrical bonding. In addition to the optical benefits of chip-integrated lenslets, advantages arise from less system integration efforts of separately realized microlenses, especially with respect to tolerance conditions.

Light-absorbing black coatings are indispensable for many different optical applications. Thin-film interference coatings can be flexibly adapted to different wavelengths. To generate an effective (> 99 %) light absorption of an interference coating, the interference effect needs to be combined with a well-defined absorption of the layer's material. On this basis, different black absorber coatings were developed and deposited on optical components for actual applications. A wideband black absorber for 400 -1000 nm wavelength on a space spectrometer slit, a bi-directional black coating for a single wavelength in the VIS, which can be wet-chemically etched for micro-patterning, and a black aperture for NIR and SWIR light on the exit face of a dispersion prism are presented.

Recently the first automotive vehicles with micro-optical headlights entered the market as series production models. Besides aesthetics, multi aperture micro-optics bring the advantage of a reduced axial length of the system due to the much shorter focal length of each channel. However, the currently implemented low-beam systems suffer from low transmission and notable cost for the micro-optics elements. Both problems can be traced back to the buried micro-slides within the micro lens arrays, (MLA) which shape the distribution. To overcome these issues, we developed a micro-optical solution for a low-beam without mask layers, thereby significantly increasing transmission to a very competitive level and enabling more cost-effective manufacturing processes. Our design follows the general principle of a fly's eye condenser (FEC) but comprises of a multitude of differently shaped lenslets, which form the beam collectively. The design process includes the generation of the overall distribution as well as detailed features such as the sharp and specially shaped cut-off and a smooth distribution within the beam. Particular effort is necessary to control stray light which is caused by imperfect manufacturing of the MLAs. A first LED-illuminated demonstrator showed that the shape and the required sharpness of the cut-off can be achieved even without the use of absorbing masks with a single optical module. Stray light control and fine tuning of the distribution makes it possible to manufacture a maskless polymer-on-glass micro-optical component and generate a beam pattern in accordance with UNECE safety regulations.

Maskless microlens arrays (MLA) for multi-aperture projection offer high transmission due to absence of buried absorbing mask structures for shaping the pattern. Arbitrary shaped lenslets arranged in a high fill-factor array form the entrance MLA, the apertures of each entrance lenslet are projected towards the far-field by regularly shaped lenslets of the exit array. Resulting tandem MLA is arranged in a fly's eye homogenizer (FEH) configuration. Such MLAs are mastered by grayscale photolithography and replicated as UV-molded polymer-on-glass (POG) elements. Furthermore, such maskless projectors can be realized using alternative replication technologies, primarily - injection molding (IM), which offers low cost for large area replication. MLA designed for POG replication can be adapted for IM replication by adjustment of certain parameters, e.g., thickness due to material substitution. Since the shape of the lenslets remain same for both processes, the same MLA masters can be used to generate the tooling molds necessary for IM replication. However, unlike POG replication, IM technology lacks active alignment of the entrance and exit arrays which makes IM replicated MLAs more vulnerable to crosstalk and stray light. Hence, a trade-off between ease of manufacturing (low costs) and projected image quality (sharpness, contrast, stray light) should be considered when dealing with IM replication. In this work we describe an exemplary IM replicated maskless MLA, based on masters of a previously realized POG replicated MLA for an automotive projected blinker. We discuss the design adaptation to IM and present profilometric and photometric characterization of the IM replicated MLA. We also compare the characterization results of the IM MLA samples with that of 'gold-standard' POG replicated MLA and discuss performance, quality of projection and limitations of IM technology.

The monitoring of anthropogenic CO2 by satellites (part of Copernicus, the European Union's Earth Observation and Monitoring program) requires a special dispersive spectrometer.As a highly efficient light dispersing element, a Prism-Grating Prism (PG-P) optical element will operate in the program, mentioned above.Anti-reflection (AR) coatings and light blocking apertures are requested to suppress optical losses, to reduce stray light and to shape the beam.Beside the AR-coatings, deposition of "black" aperture as a coating directly on the PG-P element, allows to abstain a mechanical aperture.Thereby, reduced number of elements in the optical setup and therefore reduced payload of the satellite can be achieved.For this purpose, an antireflective coating inside a clear aperture combined with a light blocking and absorbing aperture-coating outside the clear aperture was realized.The developments shown in this contribution were performed for the application wavelength of 1590 -1675 nm.

Micro-optical projectors consist of a double-sided, aligned microlens array (MLA) with an absorptive slide mask array buried under the entrance condenser lenslets. While the exit lenslets project the slides, the condenser lenslets realize Kohler illumination of the multiple projector channels. To achieve high system transmission, the condenser lenslets have to be positioned in a space-filling arrangement. For arbitrary projected shapes, the slide further reduces the effective fill-factor of a channel. We propose to increase fill-factor and simplify architecture of the MLA by replacing the buried slides by condenser lenslets with certain elementary shapes, building an irregular entrance array with space-filling parqueting. The condenser lenslets´ apertures are imaged by the projector lenslets towards certain positions in the far-field, controlled by the decentration between condenser contour and projector vertex. This enables for optional ‘jigsawing’ of the intended pattern from elementary images. Any residual MLA regions, that cannot be covered by condenser lenslet apertures, can be excluded from projection by patterning with diffusor structures, which scatter away incident light under large angles. Now, that we have excluded the buried mask array, such double-sided MLA can be replicated not only as precise polymer-on-glass elements (POG), but also by cheaper high-volume techniques like injection molding (IM), making the latter attractive for the automotive industry. An automotive projecting chase light blinker based on this concept, employing controlled channel crosstalk, replicated as POG is presented. IM replication of MLA is currently underway. We evaluate the performance and present a brief outlook of mask-less, multi-aperture microoptics.

A tandem microlens array with arbitrary shaped lenslets projects patterns towards the far-field. Employing intentional channel crosstalk enables dynamic steering of the projected pattern. The micro-optics is mastered by grayscale lithography and replicated as polymer-on-glass element.

Snapshot multispectral imaging is a rising non-invasive and contact-free analysis method and technology to discriminate or identify objects based on their spectral characteristics. We demonstrate a versatile system approach for compact and real-time capable snapshot cameras for the visible (VIS) and the near-infrared (NIR) or the short-wave infrared (SWIR) wavelength range based on a micro-optical multi-aperture system and various spectral filter approaches. In addition, the manufacturing, the calibration, and the limitations of the demonstration systems are described.

This paper discusses a collaborative effort of two Fraunhofer institutes to develop a lithography model that simulates the fabrication of blazed gratings using grayscale lithography. The model is calibrated with experimental data of blazed grating profiles. The complete process of modeling and calibration has been performed using the research and development lithography simulator Dr.LiTHO. To emulate the grayscale exposure of blazed gratings in a LED-based micro-image stepper with Dr.LiTHO a thin mask with a linear variation of the mask transmission and corresponding distribution of exposure dose was used. The resulting photoresist profiles are obtained with a standard model for Diazonaphthoquinone (DNQ) photoresists. The calibration of simulated and experimental profile data of blazed gratings is performed using Dr.LiTHO's inbuilt optimizer - Pythmea. The difference between experimental and simulated profile shapes is expressed by an areaFit. Minimization of this areaFit versus photoresist parameters and correlation analysis help to identify the most appropriate model parameters.

A UV LED-based photolithography system combines grayscale technology with a digital reticle and stepper to produce freeform micro-optics on a 300 mm wafer, while enabling processing time and resolution to be tailored to specific applications.

An array of micro spectrometers for parallel spectral sensing is designed, set up and tested. It utilizes a planar prism grating combination to obtain an almost linear optical system of 6 mm length only. Arranging such micro spectrometers in an array configuration yields 2'000 spectrometers when utilizing a common 4/3" CCD image sensor well adapted to e.g. microscopic image dimensions. The application in microscopic imaging in the 450-900 nm spectral range is demonstrated as proof of concept, which can be adapted to massively parallel sensing in the frame of integrated sensor concepts.

We describe the design and set-up an array of micro-spectrometers for parallel sensing. The approach utilizes a prism - grating combination to obtain a linear light path and to achieve a high packing density. This yields 2'000 micro spectrometers of 6 mm length only when working with a 4/3 '' CCD image sensor.

Micro-optical array projectors are discussed as replacement for structured illumination in applications with critical space requirements. The concept bases on the fly’s eye condenser principle and a well-defined buried array of micro-dia. Their optical performance benefits from etendue conservation and the large depth of field of applied short focal lenses. As an established technique to generate microlens profiles, thermal reflow of binary patterned photoresist is known for more than three decades. This approach leads to lens arrays with filling factors up to ~90% when used in hexagonal arrangement. Further increment requires direct writing methods such as grayscale lithography. Recently a LED based projection stepper-like lithography system became competitive, because it allows structure depths beyond 50 microns. It utilizes an LCoS micro-imager as variable 8-bit reticle and a high dynamic dosage controlled illumination. This paper represents the evaluation of the technique for the generation of refractive lens profiles by means of metrology and optical performance of micro-optical array projectors. Micro-array projectors based on circular lenslets will be compared, followed by the analysis of closely packed square-shaped lenslets. The aim is to understand the impact of lens shape deviation, conical constant or statistical distribution of lens properties like sag height, radius of curvature on the projection. A correlation of imperfections and quality loss due to scattering, aberrations, and mismatch of images in the overlay of different projectorlets will be given. The work concludes with an outlook on further developments in mastering micro-optical profiles for illumination application.

We developed a novel LED projection based direct write grayscale lithography system for the generation of optical surface profiles such as micro-lenses, diffractive elements, diffusors, and micro freeforms. The image formation is realized by a LCoS micro-display which is illuminated by a 405 nm UV High Power LED. The image on the display can be demagnified from factors 5x to 100x with an exchangeable lens. By controlling exposure time and LED power, the presented technique enables a highly dynamic dosage control for the exposure of h-line sensitive photo resist. In addition, the LCoS micro-display allows for an intensity control within the micro-image which is particularly advantageous to eliminate surface profile errors from stitching and limited homogeneity from LED illumination. Together with an accurate calibration of the resist response this leads to a superior low surface error of realized profiles below <0.2% RMS. The micro-display is mounted on a 3-axis (XYθ) stage for precise alignment. The substrate is brought into position with an air bearing stage which addresses an area of 500 × 500 mm2 with a positioning accuracy of <100 nm. As the exposure setup performs controlled motion in the z-direction the system to maintain the focal distance and lithographic patterning on non-planar surfaces to some extent. The exposure concept allows a high structure depth of more than 100 μm and a spatial resolution below 1 μm as well as the possibility of very steep sidewalls with angles larger than >80°. Another benefit of the approach is a patterning speed up to 100 cm2/h, which allows fabricating large-scale optics and microstructures in an acceptable time. We present the setup and show examples of micro-structures to demonstrate the performance of the system, namely a refractive freeform array, where the RMS surface deviation does not exceed 0.2% of the total structure depth of 75 μm. Furthermore, we show that this exposure tool is suitable to generate diffractive optical elements as well as freeform optics and arrays with a high aspect ratio and structure depth showing a superior optical performance. Lastly we demonstrate a multi-level diffraction grating on a curved substrate.

The combination of a 10.6 μm main pulse CO2 laser and a 1064 nm pre-pulse Nd:YAG laser in EUV source concepts for HVM would require collector mirrors with an integrated spectral purity filter that suppresses both laser wavelengths. This paper discusses a new approach of a dual-wavelength spectral purity filter to suppress 10.6 μm and 1064 nm IR radiation at the same time. The dual-wavelength spectral purity filter combines two binary phase gratings that are optimized for 10.6 μm and 1064 nm, respectively. The dual phase grating structure has been realized on spherical sub-aperture EUV collector mirrors having an outer diameter of 150 mm. IR suppression factors of 260 at 10.6 μm and 620 at 1064 nm have been measured on the sub-aperture EUV collector while its EUV reflectance exceeded 64 % at 13.5 nm.

In this study, a miniature artificial compound eye (15 mm in diameter) called the curved artificial compound eye (CurvACE) was endowed for the first time with hyperacuity, using similar micro-movements to those occurring in the fly’s compound eye. A periodic micro-scanning movement of only a few degrees enables the vibrating compound eye to locate contrasting objects with a 40-fold greater resolution than that imposed by the interommatidial angle. In this study, we developed a new algorithm merging the output of 35 local processing units consisting of adjacent pairs of artificial ommatidia. The local measurements performed by each pair are processed in parallel with very few computational resources, which makes it possible to reach a high refresh rate of 500 Hz. An aerial robotic platform with two degrees of freedom equipped with the active CurvACE placed over naturally textured panels was able to assess its linear position accurately with respect to the environment thanks to its efficient gaze stabilization system. The algorithm was found to perform robustly at different light conditions as well as distance variations relative to the ground and featured small closed-loop positioning errors of the robot in the range of 45 mm. In addition, three tasks of interest were performed without having to change the algorithm: short-range odometry, visual stabilization, and tracking contrasting objects (hands) moving over a textured background.

We describe a 2 mg artificial elementary eye whose structure and functionality is inspired by compound eye ommatidia. Its optical sensitivity and electronic architecture are sufficient to generate the required signals for the measurement of local optic flow vectors in multiple directions. Multiple elementary eyes can be assembled to create a compound vision system of desired shape and curvature spanning large fields of view. The system configurability is validated with the fabrication of a flexible linear array of artificial elementary eyes capable of extracting optic flow over multiple visual directions.