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Polarisation insensitive multifunctional metasurfaces based on all-dielectric nanowaveguides
Mahmood, Nasir,Kim, Inki,Mehmood, Muhammad Qasim,Jeong, Heonyeong,Akbar, Ali,Lee, Dasol,Saleem, Murtaza,Zubair, Muhammad,Anwar, Muhammad Sabieh,Tahir, Farooq Ahmad,Rho, Junsuk The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.38
<P>Metasurfaces, two dimensional (2D) metamaterials comprised of subwavelength features, can be used to tailor the amplitude, phase and polarisation of an incident electromagnetic wave propagating at an interface. Though many novel metasurfaces have been explored, the hunt for cost-effective, highly efficient, low-loss and polarisation insensitive applications is ongoing. In this work, we utilise an efficient and cost-effective dielectric material, hydrogenated amorphous silicon (a-Si:H), to create a ultra-thin transmissive surface that simultaneously controls phase. This material exhibits significantly lower absorption in the visible regime compared to standard amorphous silicon, making it an ideal candidate for various on-chip applications. Our proposed design, which works on the principle of index waveguiding, integrates two distinct phase profiles, that of a lens and of a helical beam, and is versatile due to its polarisation-insensitivity. We show how this metasurface can lead to highly concentrated optical vortices in the visible domain, whose focused ring-shaped profiles carry orbital angular momentum at the miniaturised scale.</P>
Twisted non-diffracting beams through all dielectric meta-axicons
Mahmood, Nasir,Jeong, Heonyeong,Kim, Inki,Mehmood, Muhammad Qasim,Zubair, Muhammad,Akbar, Ali,Saleem, Murtaza,Anwar, Muhammad Sabieh,Tahir, Farooq Ahmad,Rho, Junsuk The Royal Society of Chemistry 2019 Nanoscale Vol.11 No.43
<P>We demonstrate transmission-based all-dielectric, highly efficient (≈73.4%) and polarization-insensitive meta-axicons (for the visible wavelength of 633 nm) to generate zero and higher order Bessel beams without using additional components. The Bessel beams, owing to their diverse applications and non-diffractive properties, attract great interest from the scientific community. It is shown that the propagation length can be increased through a lower numerical aperture (∼2600 <I>λ</I> for NA = 0.1) whereas a higher full width at half maximum (< 0.5 <I>λ</I>) can be obtained for a higher numerical aperture (for NA ≥ 0.7). Our dielectric material, hydrogenated amorphous silicon (a-Si:H), provides a significant efficiency advantage over plasmonic and other high-index all-dielectric (<I>e.g.</I>, TiO2 and GaN) metasurfaces in terms of cost, ease of fabrication, and CMOS compatibility. The finite difference time domain (FDTD) technique based numerically simulated and experimental results show excellent agreement. Due to the technological and scientific importance of the Bessel beams, the recommended material and meta-axicons provide an efficient and compact platform for realizing various advanced applications like optical manipulation, optical alignment, laser fabrication, imaging, and laser machining.</P>
Sarir Uddin,Abid Zaman,Imtiaz Rasool,Sadiq Akbar,Muhammad Kamran,Nasir Mehboob,Asad Ali,Abid Ahmad,Muhammad Farooq Nasir,Zafar Iqbal 한양대학교 세라믹연구소 2020 Journal of Ceramic Processing Research Vol.21 No.6
The effects of Ba substitution on the phase analysis, microstructure and microwave dielectric properties of Ca1-xBaxTiO3ceramics were prepared through conventional solid state reaction route. The X-ray diffraction analysis of the samples showedthat the specimens Ca1-xBaxTiO3 presented single phase compound with orthorhombic structure in the range of x=0.0 to 0.7when sintered at 1300oC for 3hrs in air. From the morphological point of view, it consists of round and rod shaped grains withporous microstructure. The substitution of Ba2+ ions over Ca2+, the microwave dielectric constant (εr) diminishes from 145 to52 whereas the quality factor (Qxf) will increases from 8105 to 24305 GHz and temperature coefficient of resonant frequencydecreases from 705 to 80 ppm/oC (at 3 GHz).