Fraunhofer-Institut für Optronik, Systemtechnik und Bildauswertung IOSB

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Optimal, blind-search modal wavefront correction in atmospheric turbulence. Part I: Simulations

2021 , Segel, Max , Gladysz, Szymon

Modal control is an established tool in adaptive optics. It allows not only for the reduction in the controllable degrees of freedom, but also for filtering out unseen modes and optimizing gain on a mode-by-mode basis. When Zernike polynomials are employed as the modal basis for correcting atmospheric turbulence, their cross-correlations translate to correction errors. We propose optimal modal decomposition for gradient-descent-based wavefront sensorless adaptive optics, which is free of this problem. We adopt statistically independent Karhunen-Loève functions for iterative blind correction and analyze performance of the algorithm in static as well as in dynamic simulated turbulence conditions.

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SmartSpectrometer - Embedded Optical Spectroscopy for Applications in Agriculture and Industry

2021 , Krause, Julius , Grüger, Heinrich , Gebauer, Lucie , Zheng, Xiaorong , Knobbe, Jens , Pügner, Tino , Kicherer, Anna , Gruna, Robin , Längle, Thomas , Beyerer, Jürgen

The ongoing digitization of industry and agriculture can benefit significantly from optical spectroscopy. In many cases, optical spectroscopy enables the estimation of properties such as substance concentrations and compositions. Spectral data can be acquired and evaluated in real time, and the results can be integrated directly into process and automation units, saving resources and costs. Multivariate data analysis is needed to integrate optical spectrometers as sensors. Therefore, a spectrometer with integrated artificial intelligence (AI) called SmartSpectrometer and its interface is presented. The advantages of the SmartSpectrometer are exemplified by its integration into a harvesting vehicle, where quality is determined by predicting sugar and acid in grapes in the field.

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From Visual Spectrum to Millimeter Wave: A Broad Spectrum of Solutions for Food Inspection

2020 , Becker, Florian , Schwabig, Christopher , Krause, Julius , Leuchs, Sven , Krebs, Christian , Gruna, Robin , Kuter, Andries , Längle, Thomas , Nußler, Dirk , Beyerer, Jürgen

The consequences of food adulteration can be far reaching. In the past, inexpensive adulterants were used to inflate different products, leading to severe health issues. Contamination of food has many causes and can be physical(plant stems in tea), chemical (melamine in infant formula), or biological (bacterial contamination). Employing suitable sensor systems along the production process is a requirement for food safety. In this article, different approaches to food inspection are illustrated, and exemplary scenarios outline the potential of different sensor systems along the spectrum.

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Aspects of a head-mounted eye-tracker based on a bidirectional OLED microdisplay

2012 , Baumgarten, Judith , Schuchert, Tobias , Voth, Sascha , Wartenberg, Philipp , Richter, Bernd , Vogel, Uwe

In today's mobile world, small and lightweight information systems are becoming increasingly important. Microdisplays are the base for several near-to-eye display devices. The addition of an integrated image sensor significantly boosts the range of applications. This paper describes the base-building block for these systems: the bidirectional organic light-emitting diode microdisplay. A small and lightweight optic design, an eye-tracking algorithm, and interaction concepts are also presented.

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Quantum ghost imaging using asynchronous detection

2021 , Pitsch, Carsten , Walter, Dominik , Grosse, Simon , Brockherde, Werner , Bürsing, Helge , Eichhorn, Marc

We present first results of a novel type of setup for quantum ghost imaging based on asynchronous single photon timing using single photon avalanche diode (SPAD) detectors. This scheme enables photon pairing with arbitrary path length difference and does, therefore, obviate the dependence on optical delay lines of current quantum ghost imaging setups [Nat. Commun. 6, 5913 (2015) [CrossRef]]. It is also, to our knowledge, the first quantum ghost imaging setup to allow three-dimensional imaging.

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Adaptable Shack-Hartmann wavefront sensor with diffractive lenslet arrays to mitigate the effects of scintillation

2020 , Lechner, Daniel , Zepp, Andreas , Eichhorn, Marc , Gladysz, Szymon

Adaptive optics systems are used to compensate for distortions of the wavefront of light induced by turbulence in the atmosphere. Shack-Hartmann wavefront sensors are used to measure this wavefront distortion before correction. However, in turbulence conditions where strong scintillation (intensity fluctuation) is present, these sensors show considerably worse performance. This is partly because the lenslet arrays of the sensor are designed without regard to scintillation and are not adaptable to changes in turbulence strength. Therefore, we have developed an adaptable Shack-Hartmann wavefront sensor that can flexibly exchange its lenslet array by relying on diffractive lenses displayed on a spatial light modulator instead of utilizing a physical microlens array. This paper presents the principle of the sensor, the design of a deterministic turbulence simulation test-bed, and an analysis how different lenslet arrays perform in scintillation conditions. Our experiments with different turbulence conditions showed that it is advantageous to increase the lenslet size when scintillation is present. The residual phase variance for an array with 24 lenslets was up to 71% lower than for a 112 lenslet array. This shows that the measurement error of focal spots has a strong influence on the performance of a Shack-Hartmann wavefront sensor and that in many cases it makes sense to increase the lenslet size. With our adaptable wavefront sensor such changes in lenslet configurations can be done very quickly and flexibly.

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55 W actively Q-switched single oscillator Tm3+, Ho3+-codoped silica polarization maintaining 2.09 µm fiber laser

2019 , Dalloz, Nicolas , Robin, Thierry , Cadier, Benoît , Kieleck, Christelle , Eichhorn, Marc , Hildenbrand-Dhollande, Anne

A bidirectional 793 nm diode-pumped actively Q-switched Tm3+, Ho3+-codoped silica polarization-maintaining (PM) double-clad (DC) fiber laser is reported. With this fiber laser, 55 W of average output power with 100 ns pulse width at 200 kHz repetition rate and 2.09 µm wavelength is obtained. The pump power injection with end-caps fusion-spliced on fiber tips provides good power stability (< 1.1%) and beam quality factors (M2 < 1.7). The fiber laser output beam polarization factor is 97.5%. At 55 W, no thermal-induced damage is observed on any optical element, and power scaling of the laser is only pump-power-limited in the range of the total available pump power (180 W).

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Experimental Evaluation of a Novel Sensor-Based Sorting Approach Featuring Predictive Real-Time Multiobject Tracking

2021 , Maier, Georg , Pfaff, Florian , Pieper, Christoph , Gruna, Robin , Noack, Benjamin , Kruggel-Emden, Harald , Längle, Thomas , Hanebeck, Uwe D. , Wirtz, Siegmar , Scherer, Viktor , Beyerer, Jürgen

Sensor-based sorting is a machine vision application that has found industrial application in various fields. An accept-or-reject task is executed by separating a material stream into two fractions. Current systems use line-scanning sensors, which is convenient as the material is perceived during transportation. However, line-scanning sensors yield a single observation of each object and no information about their movement. Due to a delay between localization and separation, assumptions regarding the location and point in time for separation need to be made based on the prior localization. Hence, it is necessary to ensure that all objects are transported at uniform velocities. This is often a complex and costly solution. In this paper, we propose a new method for reliably separating particles at non-uniform velocities. The problem is transferred from a mechanical to an algorithmic level. Our novel advanced image processing approach includes equipping the sorter with an area-scan camera in combination with a real-time multiobject tracking system, which enables predictions of the location of individual objects for separation. For the experimental validation of our approach, we present a modular sorting system, which allows comparing sorting results using a line-scan and area-scan camera. Results show that our approach performs reliable separation and hence increases sorting efficiency.

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Ultra-flat supercontinuum from 1.95 to 2.65 µm in a nanosecond pulsed Thulium-doped fiber laser

2020 , Romano, Clément , Jaouën, Yves , Tench, Robert E. , Delavaux, Jean-Marc

We report on mid-IR supercontinuum generation in an all-silica nanosecond pulsed fiber laser. The laser topology is a master oscillator power amplifier which consists of a two stage Thulium-doped fiber amplifier seeded with a directly modulated semiconductor laser at 1952 nm. The supercontinuum performance is investigated for repetition rate frequencies between 35 kHz and 100 kHz and pulse widths between 6 ns and 21 ns. Supercontinuum average output powers greater than 1.5 W and spectra ranging from 1.95 µm to 2.65 µm are demonstrated.

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Cyber-physical systems in manufacturing

2016 , Monostori, László , Kádár, Botond , Bauernhansl, Thomas , Kondoh, Shinsuke , Kumara, Soundar R. , Reinhart, Gunther , Sauer, Olaf , Schuh, Günther , Sihn, Wilfried , Ueda, Kanji

One of the most significant advances in the development of computer science, information and communication technologies is represented by the cyber-physical systems (CPS). They are systems of collaborating computational entities which are in intensive connection with the surrounding physical world and its on-going processes, providing and using, at the same time, data-accessing and data-processing services available on the Internet. Cyber-physical production systems (CPPS), relying on the latest, and the foreseeable further developments of computer science, information and communication technologies on one hand, and of manufacturing science and technology, on the other, may lead to the 4th industrial revolution, frequently noted as Industrie 4.0. The paper underlines that there are significant roots in general - and in particular to the CIRP community - which point towards CPPS. Expectations towards research in and implementation of CPS and CPPS are outlined and some case studies are introduced. Related new R&D challenges are highlighted.

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