Searching for THz Gunn oscillations in GaN planar nanodiodes

A detailed study of GaN-based planar asymmetric nanodiodes, promising devices for the fabrication of room temperature THz Gunn oscillators, is reported. By using Monte Carlo simulations, an analysis of the static I-V curves and the time-domain evolution of the current obtained when varying some simulation parameters in the diodes has been made. Oscillation frequencies of hundreds of GHz are predicted by the simulations in diodes with micrometric channel lengths. Following simulation guidelines, a first batch of diodes was fabricated. It was found that surface charge depletion effects are stronger than expected and inhibit the onset of the oscillations. Indeed, a simple standard constant surface charge model is not able to reproduce experimental measurements and a self-consistent model must be included in the simulations. Using a self-consistent model, it was found that to achieve oscillations, wider channels and improved geometries are necessary.ROOTHz (FP7-243845

Experimental demonstration of direct terahertz detection at room-temperature in AlGaN/GaN asymmetric nanochannels

The potentialities of AlGaN/GaN nanodevices as THz detectors are analyzed. Nanochannels with broken symmetry (so called Self Switching Diodes) have been fabricated for the first time in this material system using both recess-etching and ion implantation technologies. The responsivities of both types of devices have been measured and explained using Monte Carlo simulations and non linear analysis. Sensitivities up to 100 V/W is obtained at 0.3 THz with a 280 pW/sqrt(Hz) Noise Equivalent Power.ROOTHz (FP7-243845

Top-down fabrication of GaN nano-laser arrays by displacement Talbot lithography and selective area sublimation

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Analyzing full-polarized metasurface holograms by vectorial ptychography

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An Etching‐Free Approach Toward Large‐Scale Light‐Emitting Metasurfaces

International audienceA new class of quasi 2D optical components, known as metasurfaces and exhibiting exceptional optical properties have emerged in recent years. The scattering properties of their subwavelength patterns allow molding the wavefront of light in almost any desired manner. While the proof of principle is demonstrated by various approaches, only a handful of low cost and fabrication friendly materials are suitable for practical implementations. To further develop this technology toward broadband application and industrial production, new materials and new fabrication methods are required. In addition, moving from passive to active devices with, for instance, dynamic tuning requires to move from dielectrics to semiconductors. Here, an etching-free process is presented that combines nanoimprint and selective area sublimation of a semiconductor material to realize centimeter-scale metalenses of high optical quality. Use of gallium nitride is chosen for this demonstration, as it is a widespread semiconductor which can be transparent and active in the visible. The sublimation leads to reduced surface roughness and defects compared to reactive ion etching. As a result, the devices show enhanced photoluminescence efficiency with respect to etched devices. Amplification due to gain in the semiconductor based metaoptics could lead to a new type of optoelectronic devices

Leitfaden zur qualitätssicheren Aktenführung nach DIN ISO-15489-1 erschienen

Der Arbeitskreis Schriftgutverwaltung im DIN NABD 15 als verantwortliches Normungsgremium zur Schriftgutverwaltung/ Records Management in Deutschland hat einen Leitfaden zur qualitätssicheren Aktenführung nach DIN ISO-15489-1 veröffentlicht. Dies zeigt prägnant die rechtlichen und fachlichen Rahmenbedingungen, Verantwortlichkeiten und Prozesse sowie notwendigen Schritte zur geeigneten IT-Unterstützung auf. Ergänzt um eine umfangreiche Literaturliste kann der Leitfaden als guter Einstieg in di..

Broadband decoupling of intensity and polarization with vectorial Fourier metasurfaces

International audienceIntensity and polarization are two fundamental components of light. Independently control of them is of tremendous interest in many applications. In this paper, we propose a general vectorial encryption method, which enables arbitrary far-field light distribution with the local polarization, including orientations and ellipticities, decoupling intensity from polarization across a broad bandwidth using geometric phase metasurfaces. By revamping the well-known iterative Fourier transform algorithm, we propose “à la carte” design of far-field intensity and polarization distribution with vectorial Fourier metasurfaces. A series of non-conventional vectorial field distribution, mimicking cylindrical vector beams in the sense that they share the same intensity profile but with different polarization distribution and a speckled phase distribution, is demonstrated. Vectorial Fourier optical metasurfaces may enable important applications in the area of complex light beam generation, secure optical data storage, steganography and optical communications

Metasurface orbital angular momentum holography

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Vectorial Hologram Based on Pixelated Metasurface

International audienceWe report a general method for full-polarization generation based on pixelated metasurface. By encoding the holographic phase profile into such pixels, vectorial holograms are constructed for the application of multidirectional display and cylindrical vector beam (CVB)

Ptychography retrieval of fully polarized holograms from geometric-phase metasurfaces

International audienceControlling light properties with diffractive planar elements requires full-polarization channels and accurate reconstruction of optical signal for real applications. Here, we present a general method that enables wavefront shaping with arbitrary output polarization by encoding both phase and polarization information into pixelated metasurfaces. We apply this concept to convert an input plane wave with linear polarization to a holographic image with arbitrary spatial output polarization. A vectorial ptychography technique is introduced for mapping the Jones matrix to monitor the reconstructed metasurface output field and to compute the full polarization properties of the vectorial far field patterns, confirming that pixelated interfaces can deflect vectorial images to desired directions for accurate targeting and wavefront shaping. Multiplexing pixelated deflectors that address different polarizations have been integrated into a shared aperture to display several arbitrary polarized images, leading topromising new applications in vector beam generation, full color display and augmented/virtual reality imaging