Form-factor and light efficiency are important issues Head-Mounted Displays face, since they both restrict their usage. Improving the form-factor means that for a defined visual stimulus, the system is smaller in volume. The light efficiency issue is linked to power consumption and time of use as well as the device’s ability to deliver, within a specific environment, enough luminance for the virtual image to be seen. This trade-off can also be found in imaging systems and Christophe Gaschet previously explored the optical design of onaxis imaging systems using curved sensors and particularly diopters number reduction thanks to Petzval shaped image plane. However, the behavior of an optical system changes dramatically when the design is off-axis. This paper focuses on demonstrating how using a curved microdisplay helps to improve the form-factor of a HMD system optimized using freeform optical design on a practical example. Curvature can also plays a great role in reducing the losses of light, but this imposes more constraints on the shapes to be given to the microdisplay. We discuss the trade-offs between these two advantages given by curved microdisplays. The mechanical feasibility of curved micro-displays will also be discussed, as well as the process to make a curved microdisplay, which is compatible with current mass-production CMOS displays. For OLED technology, the main resistance to curvature is the silicon substrate. The case for GaN technologies shows other mechanical limitations. We can predict the highest reachable curvature values, depending on microdisplay size and technology.
Flow cytometry is the main technology used in hematology analyzers. However, this technology requires bulky and complex hardware systems. Lens-free imaging is an emerging microscopy technique based on a simple and compact inline holography setup. This technique enables to image a large field-of-view (≈30mm²) leading to statistical counting (>10 000 cells) in a single-shot acquisition consistent with performances required in hematology. We report high accuracy platelet count in 54 platelet-rich plasma samples. This accuracy can be achieved through a wise choice of the illumination spectral properties and an optimized algorithmic chain dedicated to small pure phase objects.
Decreasing turnaround time is a paramount objective in clinical diagnosis. We evaluated the discrimination power of Raman spectroscopy when analyzing colonies from 80 strains belonging to nine bacterial and one yeast species directly on solid culture medium after 24-h (macrocolonies) and 6-h (microcolonies) incubation. This approach, that minimizes sample preparation and culture time, would allow resuming culture after identification to perform downstream antibiotic susceptibility testing. Correct identification rates measured for macrocolonies and microcolonies reached 94.1% and 91.5%, respectively, in a leave-one-strain-out cross-validation mode without any correction for possible medium interference. Large spectral differences were observed between macrocolonies and microcolonies, that were attributed to true biological differences. Our results, conducted on a very diversified panel of species and strains, were obtained by using simple and robust sample preparation and preprocessing procedures, while still confirming published results obtained by using more complex elaborated protocols. Instrumentation is simplified by the use of 532-nm laser excitation yielding a Raman signal in the visible range. It is, to our knowledge, the first side-by-side full classification study of microorganisms in the exponential and stationary phases confirming the excellent performance of Raman spectroscopy for early species-level identification of microorganisms directly from an agar culture.
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