Fraunhofer Institute for Applied Optics and Precision Engineering

Multi-core fibers have emerged as a promising solution for high-power fiber laser systems, which allow for the simultaneous mitigation of thermal and nonlinear effects through core-count scaling. This makes them highly attractive for high-average-power applications. However, there has been no demonstration of a multi-kilowatt, multi-core fiber laser system to date. In this work, we present a Yb-doped, multi-core fiber laser system, delivering up to 3.2 kW of average power (over all cores) with excellent short- and long-term stability. The system exhibited a slope efficiency with respect to launched power of 86.3%, and the output power was limited only by the available pump power.

We present a femtosecond laser system based on a 49-core, Ytterbium-doped fiber. Phase control of the individual beams enables fast beam-shaping up to the kHz frequency range at 150 W total average power after compression.

ABSTRACT This paper proposes an output‐feedback tracking controller for non‐minimum phase nonlinear systems with unknown uncertainties and external disturbances, where not all states are measurable, and the zero dynamics are unstable. The approach combines a backstepping‐based stabilizing state‐feedback law with a cascade extended high‐gain observer (EHGO): A fast observer estimates the measured output and its derivatives to generate a virtual output, while a slower observer estimates the unmeasured controlled output, its derivatives, and the lumped disturbance and uncertainty. For relative‐degree‐two systems, the controller exhibits a PID‐like control. This feature is rarely achieved for non‐minimum phase systems. Simulations of a wafer‐handling robot modeled as a flexible‐joint robot demonstrate accurate tracking, rapid disturbance rejection, smooth inputs, and improved robustness compared to existing methods.

Quasi-2D halide perovskites are chemically synthesized realizations of quantum well stacks with giant exciton oscillator strengths, tunable emission spectra, and very large exciton binding energies. While these features render quasi-2D halide perovskites a promising platform for room-temperature polaritonics, bosonic condensation and polariton lasing in quasi-2D perovskites have so far remained elusive at ambient conditions. Here, we demonstrate room-temperature cavity exciton-polariton condensation in mechanically exfoliated crystals of the quasi-2D Ruddlesden-Popper iodide perovskite (BA)2(MA)2Pb3I10 in an open optical microcavity. We observe a polariton condensation threshold of 0.41 µJ cm−2 per pulse and detect a strong non-linear response. Interferometric measurements confirm the spontaneous emergence of spatial coherence across the condensate with an associated first-order autocorrelation reaching 0.6 with 1 ps coherence time and an effective de Broglie wavelength of 13 µm. Our results lay the foundation for a new class of room-temperature polariton lasers based on quasi-2D halide perovskites with great potential for hetero-integration with other van-der-Waals materials and combination with photonic crystals or waveguides.

ABSTRACT Biphotons from spontaneous parametric down conversion with broad bandwidth are highly wanted in many quantum technologies. However, achieving broad bandwidth in both frequency and momentum while keeping a high rate remains a challenge for both conventional nonlinear crystals and recently emerging nonlinear metasurfaces. Here, we address this challenge by introducing a periodically poled Brillouin zone folding (PP‐BZF) metasurface incorporating a periodically perturbed silica grating atop a periodically poled lithium niobate film. PP‐BZF metasurfaces support high‐Q guided mode resonances at pump, signal and idler wavelengths while enabling quasi‐phase matching between three guided modes in a broad frequency/momentum range. The predicted biphoton rate is over 100 MHz/mW with a frequency bandwidth of 20.5 THz (1472.5–1637.8 nm) and a momentum bandwidth of , improving the state‐of‐the‐art for metasurface biphoton sources by over three orders of magnitude in rate and one order of magnitude in bandwidths. This ultrathin broadband bright biphoton source could stimulate system‐level miniaturization of various free‐space quantum photonic technologies.

ABSTRACT This study presents a detailed comparative study of lactone‐based electrolytes (γ‐valerolactone, GVL and γ‐butyrolactone, GBL) combined with lithium imide‐based salts, namely lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluoromethanesulfonyl)imide (LiFSI). Propylene carbonate is employed as a reference electrolyte solvent. The physicochemical properties of these electrolyte systems are determined experimentally and further calculated using our developed computational model. Besides, in‐silico investigations are used to reveal valuable insights into the molecular interactions of the electrolyte components, such as self‐diffusion coefficients and radial distribution functions. Furthermore, the suitability of lactone‐based electrolytes for electrochemical applications is demonstrated by their promising rate capability and cycling stability over 200 cycles in graphite half‐cells, especially with 1 M LiTFSI and 2 wt% vinylene carbonate, together with their favorable performance on lithium iron phosphate. An excellent capacity retention achieved in a full‐cell configuration (> 80% after 200 cycles) further validates the potential of lactones as battery solvent alternatives, with GVL standing out due to its bio‐based origin.

Person-centered care, a gold standard in serious illness care and palliative care, emphasizes the importance of understanding a patient's personhood and values. Nurses are uniquely suited to provide high-quality, person-centered care and to support patients as they communicate their worries, goals, hopes for the future, and sources of support. By assessing and understanding an individual's health-related values, nurses are better able to complete their nursing responsibilities, advocate for their patients, and confidently encourage shared decision-making. Nurses have strong communication skills but may benefit from additional education to develop the interpersonal skills needed to empathically explore patients' health-related values.

For the development of photonic (quantum) computing, ultra-low loss fiber coupling is one of the crucial aspects for scalability of the systems and efficiency. For high efficiencies in fiber coupling, mode field matching between fiber and waveguide is highly important, but also high precision alignment and bonding of fibers. Currently the state-of-the-art fiber coupling technology for high fiber counts is using fiber array. While this technique allows easier packaging, the efficiency suffers due to positioning inaccuracies. Therefore, single fiber coupling is the solution for the highest accuracy fiber placement and highest fiber coupling efficiency. As the packaging process of single fibers is time consuming and hence expensive, we present a novel parallel fiber alignment system for packaging

Abstract Future gravitational wave observatories require significant advances in all aspects of their seismic isolation; inertial sensors being a pressing example. Inertial sensors using gram-scale high mechanical Q factor ( Q ) glass resonators combined with compact interferometric readout are promising alternatives to kilogram-scale conventional inertial sensors. We have produced fused silica resonators suitable for low frequency inertial sensing and demonstrated that Q s of over 150 000 are possible. One resonator we produced was combined with a homodyne quadrature interferometer (HoQI) to read out the test mass displacement to form an inertial sensor. This is the first time a HoQI was used with a high Q resonator. The resulting sensor was tested against other commercial, kilogram scale inertial sensors at the AEI 10 m Prototype facility. Despite the dynamic range challenges induced by the test mass motion, we can match the excellent noise floors HoQIs have achieved so far with slow-moving or stationary test masses, showing HoQIs as an excellent candidate for the readout of such sensors. We evaluate the setup as an inertial sensor, showing the best performance demonstrated by any gram-scale sensor to date, with comparable sensitivity to the significantly bulkier sensors used in gravitational wave detectors today. These sensors’ compact size, self-calibration, and vacuum compatibility make them ideal candidates for the inertial sensing requirements in future gravitational wave detectors.

Placing nanowire lasers on top of metallic substrates can shorten the duration of emitted pulses if coupling between lasing modes and Surface Plasmon Polaritons (SPPs) can be achieved. In this article, we perform time-resolved double-pump measurements of ZnO nanowires of varying diameters on aluminum substrates to investigate the relationship between nanowire diameter and emitted pulse duration. We find that nanowires with diameters below 190 nm emit pulses longer in duration than nanowires with a diameter above 190 nm. This suggests that the coupling between ZnO nanowire modes and SPPs of an aluminum substrate is suppressed for nanowires with diameters below 190 nm. We explain this behavior with the switching of the dominant lasing mode between azimuthal and linear polarization around a nanowire diameter of 190 nm. Thus, these findings highlight the importance of rigorous mode engineering in optimizing SPP coupling for low-loss metallic substrates, fostering future research on resonator design to achieve faster lasing dynamics.