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Proceedings Paper

All-dielectric metasurface for wavefront control at terahertz frequencies
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Paper Abstract

Recently, metasurfaces have gained popularity due to their ability to offer a spatially varying phase response, low intrinsic losses and high transmittance. Here, we demonstrate numerically and experimentally a silicon meta-surface at THz frequencies that converts a Gaussian beam into a Vortex beam independent of the polarization of the incident beam. The metasurface consists of an array of sub-wavelength silicon cross resonators made of a high refractive index material on substrates such as sapphire and CaF2 that are transparent at IR-THz spectral range. With these substrates, it is possible to create phase elements for a specific spectral range including at the molecular finger printing around 10 μm as well as at longer THz wavelengths where secondary molecular structures can be revealed. This device offers high transmittance and a phase coverage of 0 to 2π. The transmittance phase is tuned by varying the dimensions of the meta-atoms. To demonstrate wavefront engineering, we used a discretized spiraling phase profile to convert the incident Gaussian beam to vortex beam. To realize this, we divided the metasurface surface into eight angular sectors and chose eight different dimensions for the crosses providing successive phase shifts spaced by π/4 radians for each of these sectors. Photolithography and reactive ion etching (RIE) were used to fabricate these silicon crosses as the dimensions of these cylinders range up to few hundreds of micrometers. Large 1-cm-diameter optical elements were successfully fabricated and characterised by optical profilometry.

Paper Details

Date Published: 5 January 2018
PDF: 6 pages
Proc. SPIE 10456, Nanophotonics Australasia 2017, 104561W (5 January 2018); doi: 10.1117/12.2283090
Show Author Affiliations
Raghu Dharmavarapu, Swinburne Univ. of Technology (Australia)
Indian Institute of Technology Madras (India)
Australian National Fabrication Facility (Australia)
Soon Hock Ng, Swinburne Univ. of Technology (Australia)
Australian National Fabrication Facility (Australia)
Shanti Bhattacharya, Indian Institute of Technology Madras (India)
Saulius Juodkazis, Swinburne Univ. of Technology (Australia)
Australian National Fabrication Facility (Australia)

Published in SPIE Proceedings Vol. 10456:
Nanophotonics Australasia 2017
James W. M. Chon; Baohua Jia, Editor(s)

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