Design, fabrication and characterization of a distributed Bragg reflector for reducing the étendue of a wavelength converting system

In this work, the design, fabrication and characterization are reported for a distributed Bragg reflector (DBR) filter with a specific wavelength and angular dependency, which aims to improve the light collection from a wavelength-converter-based light source into a smaller angle than the full angle Lambertian emission. The desired design is obtained by optimizing the transmission characteristics of a multi-layer structure. Titania (TiO2) and silica (SiO2) are used as high and low refractive index materials, respectively. The deposition is made by electron beam evaporation without substrate heating, followed by a post-annealing procedure. The optical properties of the evaporated layers are analyzed by ellipsometer and spectrometer measurements. The angular and wavelength dependency of the fabricated DBR is in good agreement with simulations for the designed structure. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Design and realization of a compact efficient beam combiner, based on liquid crystal Pancharatnam-Berry phase gratings

We demonstrate a laser beam combiner based on four photo-patterned Pancharatnam-Berry (PB) phase gratings, which is compact and has high diffraction efficiency for incident circularly polarized light. The nematic liquid crystal mixture E7 is used as anisotropic material, and the thickness of the layer is controlled by spacers. The beam combiner can bring two parallel laser beams closer to each other while remaining parallel. This work shows the potential to realize components based on flat optical LC devices

Liquid Crystal TV and OLED TV : issues and opportunities

There are currently two competing technologies on the TV market: liquid crystal TV and OLED TV. Each of them has its strengths and weaknesses, but at the same time, both technologies also see rapid developments that further improve their quality. In an OLED matrix the pixels are driven by a DC current and emit light proportional to the level of the current. In an LCD matrix the pixels are driven by an AC voltage and the polarization of incident light is modified, which, in combination with a polarizer determines the transmission. In both the OLED and the LCD TV red, green and blue color filters are used to render millions of colors by mixing filtered white light. In this presentation we will discuss differences between the two technologies, and address a number of important advances in the field of OLEDs (multilayer stacks, temperature dependency, quantum dot OLEDs) and LCDs (LEDarray illumination, photoluminescent quantum dots, brightness enhancement films, local dimming). In addition a few contribution of the research group will be highlighted [1-4]

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Hierarchical Matching Algorithm for Relay Selection in MEC-Aided Ultra-Dense UAV Networks

With the rapid development of communication technology, unmanned aerial vehicle–mobile edge computing (UAV-MEC) networks have emerged with powerful capabilities. However, existing research studies have neglected the issues involving user grouping and relay selection structures under UAV cluster-assisted communication. Therefore, in this article, we present a comprehensive communication–computing resource allocation for UAV-MEC networks. In particular, ground users make stable user groups first, and then multiple UAVs act as relays in order to assist these user groups in simultaneously uploading their tasks to the terrestrial base station at the edge server. Moreover, in order to maximize the system’s overall throughput, a more flexible and hierarchical matching relay selection algorithm is proposed in terms of matching the ground user groups and corresponding UAVs. For vulnerable users, we also propose a weighted relay selection algorithm to maximize the system performance. Furthermore, simulation results show that the proposed relay selection algorithm achieves a significant gain in comparison with the other benchmarks, and the stability of the proposed algorithms could be verified

Driving issues of large area liquid crystal devices

The surface area of liquid crystal (LC) devices in different applications, such as displays, signage devices and smart windows is becoming larger and larger. The electrical driving of such devices does not pose many problems when working on centimetre sized devices. Different types of driving issues arise when up-scaling such devices to areas of several square metre, due to the fact that the thin-film transparent conductors used in these devices exhibit a finite sheet conductivity. One of the resulting issues is the non-uniformity of the electric field across the area of the device and the resulting non-uniform optical behaviour. In this work, we present a simulation model that is able to predict the optical and electrical behaviour of large-sized liquid crystal devices with different applied voltage signals, including the power consumption. The simulation results are compared with optical and electrical measurements on a liquid crystal device of 1.5 m by 1.2 m

What Is the point? a Theory of Mind Model of Relevance

Although pointing is sparse, overloaded, and indirect, it allows humans to effectively decode shared information, (ex)change their minds, and plan accordingly. Pointing is an invitation to jointly attend to an object, which triggers the mutual inference between agents of each other’s mind. Relevance is a fundamental assumption underlying all human communication, including pointing. We define relevance as how much a signaler’s belief can make a positive difference to its receiver’s well being. We build a Theory of Mind (ToM) model to test our definition of relevance and use pointing as a case study. In two experiments, we test our relevance model in a classic artificial intelligence (AI) task, the Wumpus world, with the key difference that there is a guide that points to help a hunter. Agents with our relevance model gain significantly higher rewards than agents who ignore signals from the guide. Agents with our model also achieve better performance than agents who receive an additional observation of the environment. The results show that the power of pointing comes from the ToM inference of relevance, rather than providing more precise individual perception