134 research outputs found

    Dielectric Metasurfaces for Complete Control of Phase and Polarization with Subwavelength Spatial Resolution and High Transmission

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    Metasurfaces are planar structures that locally modify the polarization, phase, and amplitude of light in reflection or transmission, thus enabling lithographically patterned flat optical components with functionalities controlled by design. Transmissive metasurfaces are especially important, as most optical systems used in practice operate in transmission. Several types of transmissive metasurfaces have been realized, but with either low transmission efficiencies or limited control over polarization and phase. Here we show a metasurface platform based on high-contrast dielectric elliptical nano-posts which provides complete control of polarization and phase with sub-wavelength spatial resolution and experimentally measured efficiency ranging from 72% to 97%, depending on the exact design. Such complete control enables the realization of most free-space transmissive optical elements such as lenses, phase-plates, wave-plates, polarizers, beam-splitters, as well as polarization switchable phase holograms and arbitrary vector beam generators using the same metamaterial platform.Comment: Nature Nanotechnology (2015

    Photonic Cavity Synchronization of Nanomechanical Oscillators

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    Synchronization in oscillatory systems is a frequent natural phenomenon and is becoming an important concept in modern physics. Nanomechanical resonators are ideal systems for studying synchronization due to their controllable oscillation properties and engineerable nonlinearities. Here we demonstrate synchronization of two nanomechanical oscillators via a photonic resonator, enabling optomechanical synchronization between mechanically isolated nanomechanical resonators. Optical backaction gives rise to both reactive and dissipative coupling of the mechanical resonators, leading to coherent oscillation and mutual locking of resonators with dynamics beyond the widely accepted phase oscillator (Kuramoto) model. Besides the phase difference between the oscillators, also their amplitudes are coupled, resulting in the emergence of sidebands around the synchronized carrier signal.Comment: 23 pages including supplementary materia

    Simultaneous and Complete Control of Light Polarization and Phase using High Contrast Transmitarrays

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    We report an efficient dielectric metasurface platform for complete control over polarization and phase of light with subwavelength spatial resolution. Using this platform, we experimentally demonstrate polarization switchable phase holograms and vector beam generators

    Efficient dielectric metasurface collimating lenses for mid-infrared quantum cascade lasers

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    Light emitted from single-mode semiconductor lasers generally has large divergence angles, and high numerical aperture lenses are required for beam collimation. Visible and near infrared lasers are collimated using aspheric glass or plastic lenses, yet collimation of mid-infrared quantum cascade lasers typically requires more costly aspheric lenses made of germanium, chalcogenide compounds, or other infrared-transparent materials. Here we report mid-infrared dielectric metasurface flat lenses that efficiently collimate the output beam of single-mode quantum cascade lasers. The metasurface lenses are composed of amorphous silicon posts on a flat sapphire substrate and can be fabricated at low cost using a single step conventional UV binary lithography. Mid-infrared radiation from a 4.8 μm distributed-feedback quantum cascade laser is collimated using a polarization insensitive metasurface lens with 0.86 numerical aperture and 79% transmission efficiency. The collimated beam has a half divergence angle of 0.36° and beam quality factor of M^2=1.02

    Efficient high NA flat micro-lenses realized using high contrast transmitarrays

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    We present design, fabrication, and characterization results of high numerical aperture (NA) micro-lenses based on a high contrast transmitarray platform. The high contrast transmitarray is created by periodic arrangement of amorphous silicon posts with different diameters on a fused silica substrate. We report near infrared high NA micro-lenses with spot sizes as small as 0.57λ and focusing efficiencies in excess of 80%. We demonstrate a trade-off relation between NA and efficiency of high contrast array flat micro-lenses, and attribute it to the spatial discretization of their phase profiles

    Subwavelength-thick Lenses with High Numerical Apertures and Large Efficiency Based on High Contrast Transmitarrays

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    We report subwavelength-thick, polarization insensitive micro-lenses operating at telecom wavelength with focal spots as small as 0.57 wavelengths and measured focusing efficiency up to 82%. The lens design is based on high contrast transmitarrays that enable control of optical phase fronts with subwavelength spatial resolution. A rigorous method for ultra-thin lens design, and the trade-off between high efficiency and small spot size (or large numerical aperture) are discussed. The transmitarrays, composed of silicon nano-posts on glass, could be fabricated by high-throughput photo or nanoimprint lithography, thus enabling widespread adoption

    Controlling the phase front of optical fiber beams using high contrast metastructures

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    The phase of optical beams can be modified by high contrast sub-wavelength periodic structures with gradually varying geometrical features. We present design, simulation, fabrication and characterization of planar micro-lenses shaping the beam of optical fibers

    Necessary Indicators for Developing a Hazmat Response Team of the Iranian Health System

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    Introduction: Although some countries have set up predetermined programs and specialized teams to deal with hazardous materials (Hazmat) induced events, in other countries including Iran there are many weaknesses in this regard. Objective: We aimed to develop the necessary indicators for the formation of teams to deal with Hazmat accidents in the health system based on existing standards and resources as well as the indigenous conditions of Iran. Methods: This cross-sectional study was carried out in two stages from 2018 to 2020.  In the first stage, the literature review was performed and the current guidelines, standards, and models presented in other countries were reviewed and related items were extracted. In the second stage, semi-structured and purposeful interviews by managers and physicians specialized in Hazmat incidents working in Iran, were conducted. The interviews were recorded and later the recordings were transcribed and simultaneously the categorizing and coding of the interviews were performed. Results: In the first stage, searching through the available resources for the present study identified 12 published references through which 10 indicators to develop a Hazmat team were ultimately extracted. In the second stage, a total of 10 interviews were conducted and data saturation occurred. Based on the results of the content analysis for the main indicators of designing and developing teams, 8 categories and 19 sub-categories were developed. Conclusions: By interviewing and localizing the 10 main indicators that were achieved in the first stage, we finally reached the 8 indicators including: Training hazmat team’s members, required equipment for team, response plan, medical surveillance program, hazmat team structure, incident command system, hazmat team qualification of different levels, certification and maintenance of the certificate