Beam splitters are an indispensable part of optical measurements and applications. We propose a dynamic beam splitter incorporating all-dielectric metasurface in an elastic substrate under external mechanical stimulus of stretching. The optical behavior at 720 nm wavelength shows that it can be changed from a pure optical-diode-like behavior to a dynamic beam splitter. Although the structure is designed running at 720 nm, the design approach with appropriate materials can be used at any wavelength. Various cases, including wavelength and polarization dependencies, are thoroughly investigated to demonstrate the principles of operating conditions of two different regimes of the designed metasurface.
High electron mobility transistors (HEMTs) based on gallium nitride (GaN) with a wide range of application potentials need to be rigorously examined for reliability to take advantage of their intrinsically extraordinary properties. The most vital parameter of the reliability, the hotspot, or Tmax, resides in the two-dimensional electron gas (2DEG) temperature profile inside the device where optical access is often restricted. The device surface temperature can be measured by widespread IR thermography with the limitation of diffraction-based IR transmission losses. However, Tmax on the sub-surface cannot be reached thermographically. Although finite element analysis (FEA)-based thermal simulations can easily reveal the 2DEG temperature profile, accuracy is tightly dependent on the realistic modeling of material/structure parameters. Because these parameters are rather sensitive to fabrication and processing, it is quite difficult to specify them accurately. To overcome these drawbacks, a method integrating both IR thermography and FEA thermal analysis is demonstrated on a fabricated high-power 40 × 360 μm packaged GaN HEMT as a proof-of-concept. Utilizing the simulation and measurement temperature profiles, a correlation algorithm is developed so that accuracy of the FEA thermal simulation is improved by calibrating the parameters specific to fabrication/process conditions by thermographic measurement. Then, it is quantitatively shown that the proposed method is able to find the 2DEG temperature profile and Tmax with an accuracy that best suits the intrinsic and extrinsic characteristics of the device under test. The method sheds light on GaN reliability engineering by providing a feasible and reliable alternative to realistically reveal hotspot information for device lifetime assessments.
This study proposes a novel binocular pupil and gaze detection system utilizing a remote full high definition (full HD) camera and employing LabVIEW. LabVIEW is inherently parallel and has fewer time-consuming algorithms. Many eye tracker applications are monocular and use low resolution cameras due to real-time image processing difficulties. We utilized the computer's direct access memory channel for rapid data transmission and processed full HD images with LabVIEW. Full HD images make easier determinations of center coordinates/sizes of pupil and corneal reflection. We modified the camera so that the camera sensor passed only infrared (IR) images. Glints were taken as reference points for region of interest (ROI) area selection of the eye region in the face image. A morphologic filter was applied for erosion of noise, and a weighted average technique was used for center detection. To test system accuracy with 11 participants, we produced a visual stimulus set up to analyze each eye's movement. Nonlinear mapping function was utilized for gaze estimation. Pupil size, pupil position, glint position and gaze point coordinates were obtained with free natural head movements in our system. This system also works at 2046 × 1086 resolution at 40 frames per second. It is assumed that 280 frames per second for 640 × 480 pixel images is the case. Experimental results show that the average gaze detection error for 11 participants was 0.76 • for the left eye, 0.89 • for right eye and 0.83 • for the mean of two eyes.
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