Microlens arrays (MLAs) have a variety of applications in, e.g., display systems, projection optics, and sensors. They can be manufactured by various fabrication methods. Among all, inkjet printing stands out because it offers a straightforward, versatile, and low‐cost fabrication route. However, extra manufacturing steps such as photolithography are so far involved to pre‐structure the substrate in order to improve the uniformity of the printed MLAs and achieve a high fill factor (FF). In this study, the fabrication of MLAs is reported on unstructured substrates by inkjet printing using an optimized UV‐curable ink on top of self‐assembled monolayers (SAMs). The latter allows for tuning the surface free energy and thus the aspect ratio of the microlenses. The high uniformity of the printed MLAs is demonstrated by the automatic quantitative evaluations, where the standard deviations of the radii are below 2.5% and of the sag heights are less than 3.9%. An unprecedented FF of 88% amongst all inkjet‐printed MLAs on unstructured substrates is achieved. Digitally controlled large area fabrication is demonstrated, both, on rigid as well as on flexible substrates, opening a pathway for customized microoptics by additive manufacturing.

We quantitatively investigate multiple algorithms for microlens array grid estimation for microlens array-based light field cameras. Explicitly taking into account natural and mechanical vignetting effects, we propose a new method for microlens array grid estimation that outperforms the ones previously discussed in the literature. To quantify the performance of the algorithms, we propose an evaluation pipeline utilizing application-specific ray-traced white images with known microlens positions. Using a large dataset of synthesized white images, we thoroughly compare the performance of the different estimation algorithms. As an example, we apply our results to the decoding and calibration of light fields taken with a Lytro Illum camera. We observe that decoding as well as calibration benefit from a more accurate, vignetting-aware grid estimation, especially in peripheral subapertures of the light field.Since the ML grid parameters are application-specific, we make the source code for a full evaluation pipeline (image

In the emerging field of computational imaging, rapid prototyping of new camera concepts becomes increasingly difficult since the signal processing is intertwined with the physical design of a camera. As novel computational cameras capture information other than the traditional two-dimensional information, ground truth data, which can be used to thoroughly benchmark a new system design, is also hard to acquire. We propose to bridge this gap by using simulation. In this article, we present a raytracing framework tailored for the design and evaluation of computational imaging systems. We show that, depending on the application, the image formation on a sensor and phenomena like image noise have to be simulated accurately in order to achieve meaningful results while other aspects, such as photorealistic scene modeling, can be omitted. Therefore, we focus on accurately simulating the mandatory components of computational cameras, namely apertures, lenses, spectral filters and sensors. Besides the simulation of the imaging process, the framework is capable of generating various ground truth data, which can be used to evaluate and optimize the performance of a particular imaging system. Due to its modularity, it is easy to further extend the framework to the needs of other fields of application. We make the source code of our simulation framework publicly available and encourage other researchers to use it to design and evaluate their own camera designs. 1

We investigate the classical and quantum Proca field (a massive vector potential) of mass m > 0 in arbitrary globally hyperbolic spacetimes and in the presence of external sources. We motivate a notion of continuity in the mass for families of observables {O m } m>0 and we investigate the massless limit m → 0. Our limiting procedure is local and covariant and it does not require a choice of reference state. We find that the limit exists only on a subset of observables, which automatically implements a gauge equivalence on the massless vector potential. For topologically non-trivial spacetimes, one may consider several inequivalent choices of gauge equivalence and our procedure selects the one which is expected from considerations involving the Aharonov-Bohm effect and Gauss' law.We note that the limiting theory does not automatically reproduce Maxwell's equation, but it can be imposed consistently when the external current is conserved. To recover the correct Maxwell dynamics from the limiting procedure would require an additional control on limits of states. We illustrate this only in the classical case, where the dynamics is recovered when the Lorenz constraint remains well behaved in the limit.

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