Microwire fibers for low-loss THz transmission

This paper was presented at Smart Structures, Devices, and Systems, which was a sub-conference contained within Smart Materials, Nano- and Micro-Smart Systems Symposium (10-13 December 2006 : Adelaide, South Australia). This paper was published in Smart Structures, Devices, and Systems III, edited by Said F. Al-Sarawi, Proc. of SPIE Vol. 6414, 64140I and is made available as an electronic reprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.In this paper, we will investigate microwire fibers for low-loss terahertz transmission. Microwires, air-clad wire waveguides with diameter smaller than the operating wavelength (a few μm), have an enhanced evanescent field and tight wave confinement resulting in a low loss waveguide structure for the terahertz (T-ray) frequency regime. Based on our experimental data for the bulk material absorption of four glasses (F2, SF6, SF57 and Bismuth) and a polymer (PMMA), we calculate the normalized field distribution, power fraction outside the wire and effective loss. It will be shown that regardless of material, the effective loss of all microwires converges to the same order < 0.01 cm -1.Shaghik Atakaramians, Shahraam Afshar Vahid, Bernd M. Fischer, Heike Ebendorff-Heidepriem, Tanya Monro and Derek Abbotthttp://spie.org/Documents/ConferencesExhibitions/au06-final.pd

Porous fibers: a novel approach to low loss THz waveguides

We propose a novel class of optical fiber with a porous transverse cross-section that is created by arranging sub-wavelength air-holes within the core of the fiber. These fibers can offer a combination of low transmission loss and high mode confinement in the THz regime by exploiting the enhancement of the guided mode field that occurs within these sub-wavelength holes. We evaluate the properties of these porous fibers and quantitatively compare their performance relative to that of a solid core air cladded fiber (microwire). For similar loss values, porous fibers enable improved light confinement and reduced distortion of a broadband pulse compared to microwires.Shaghik Atakaramians, Shahraam Afshar V., Bernd M. Fischer, Derek Abbott, and Tanya M. Monr

Enhanced terahertz magnetic dipole response by subwavelength fiber

Dielectric sub-wavelength particles have opened up a new platform for realization of magnetic light. Recently, we have demonstrated that a dipole emitter by a sub-wavelength fiber leads to an enhanced magnetic response. Here, we experimentally demonstrate an enhanced magnetic dipole source in the terahertz frequency range. By placing the fiber next to the hole in a metal screen, we find that the radiation power can be enhanced more than one order of magnitude. The enhancement is due to the excitation of the Mie-type resonances in the fiber. We demonstrate that such a system is equivalent to a double-fiber system excited by a magnetic source. This coupled magnetic dipole and optical fiber system can be considered a unit cell of metasurfaces for manipulation of terahertz radiation and is a proof-of-concept of a possibility to achieve enhanced radiation of a dipole source in proximity of a sub-wavelength fiber. It can also be scaled down to optical frequencies opening up promising avenues for developing integrated nanophotonic devices such as nanoantennas or lasers on fibers.Shaghik Atakaramians, Ilya V. Shadrivov, Andrey E. Miroshnichenko, Alessio Stefani, Heike Ebendorff-Heidepriem, Tanya M. Monro and Shahraam Afshar V

Silicon Mie Resonators for Highly Directional Light Emission from monolayer MoS2

Controlling light emission from quantum emitters has important applications ranging from solid-state lighting and displays to nanoscale single-photon sources. Optical antennas have emerged as promising tools to achieve such control right at the location of the emitter, without the need for bulky, external optics. Semiconductor nanoantennas are particularly practical for this purpose because simple geometries, such as wires and spheres, support multiple, degenerate optical resonances. Here, we start by modifying Mie scattering theory developed for plane wave illumination to describe scattering of dipole emission. We then use this theory and experiments to demonstrate several pathways to achieve control over the directionality, polarization state, and spectral emission that rely on a coherent coupling of an emitting dipole to optical resonances of a Si nanowire. A forward-to-backward ratio of 20 was demonstrated for the electric dipole emission at 680 nm from a monolayer MoS2 by optically coupling it to a Si nanowire

Compact air-cavity resonators within a metamaterial waveguide

Recent advances in metamaterials have revealed the possibility of overcoming the diffraction limit, opening the door for high-density-integration photonic devices including waveguides and cavities. Here we investigate the condition required to have air cavities within a uniaxial metamaterial clad waveguide. Our work reveals that air-cavity sizes much smaller than the operating wavelength (D2h/λ3 = 1/(352 × 100)) are achievable under specific cladding material conditions, which could have a great impact on the miniaturization of electromagnetic devices. Harnessing metamaterials enables engineering of the required condition at a desired wavelength, unlike plasmonic cavities where the condition is reached at a specific wavelength

Proceedings of SPIE - The International Society for Optical Engineering

Several waveguide solutions based on technologies from both electronics and photonics have been proposed for guiding Terahertz (THz) radiation. Hollow-core dielectric waveguides are one of the best options for guiding THz radiation since the material absorption is almost zero in the air-core. However, these waveguides are usually multimode and have dimensions in the order of a few millimeters. Here we propose a hollow-core waveguide with sub-wavelength scale metallic wires in the cladding for THz guidance. The theoretical studies show that such a hybrid cladding reflects the transverse magnetic (TM) waves and transmits the transverse electric (TE) waves, leading to a waveguide structure that only confines TM modes. The numerical simulations show a pure single mode, single polarization operation window from 0.22 THz to 0.34 THz and 14.8 dB/m propagation loss at 0.29 THz. Compared to a metallic waveguide with similar dimension, the proposed waveguide more than doubles the single mode operation bandwidth with comparable losses. We discuss the effect of optical and structural parameters of the hybrid cladding on the single mode operating window and propagation losses, and suggest methods of fabrication of the waveguide. The design principle of the proposed waveguide can be extended to the mid-inferred spectrum

Dipole-fiber system: from single photon source to metadevices

Radiation of an electric dipole (quantum emitter) in vicinity of optical structures still attracts great interest due to emerging of novel application and technological advances. Here we review our recent work on guided and radiation modes of electric dipole and optical fiber system and its applications from single photon source to metadevices. We demonstrate that the relative position and orientation of the dipole and the core diameter of the optical fiber are the two key defining factors of the coupled system application. We demonstrate that such a coupled system has a vast span of applications in nanophotonics; a single photon source, a high-quality factor sensor and the building block of metadevices

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz

In polarization-sensitive terahertz (THz) communication systems, grating is one of the essential components that filters THz waves at desired frequencies. Based on dielectric rectangular subwavelength waveguide, we propose a THz grating structure to filter two orthogonally polarized states. From numerical simulations, the proposed filter has two passbands with over 20.9 dB extinction ratio and around 21.1 GHz full-width half-maximum. Moreover, by introducing a π-phase shift, the grating can operate as a polarization-maintaining narrow bandpass filter with over 12.3 dB extinction ratio and less than 1.7 GHz full-width half-maximum

IRMMW-THz 2015 - 40th International Conference on Infrared, Millimeter, and Terahertz Waves

We propose a leaky-wave antenna to generate circularly polarized highly directional terahertz beam using metamaterial scatters. A microstrip line is loaded with a series of complementary electric-LC and electric-LC resonators to generate respectively Ex and Ey components. The 900-phase difference and almost unity amplitude ratio of Ex and Ey are achieved by relative positioning of the resonators on and off the stripline and optimizing the gap size. Moreover, the phase front of the radiated wave can be adjusted to a specific direction by controlling the period of the resonator array. These highly directional planar antennas can be utilized in short-range THz communication, sensing and imaging applications

2020 Conference on Lasers and Electro-Optics Pacific Rim, CLEO-PR 2020

© 2019 Early detection of seeds, as a precursor tool for the prevention of Grass Seed Infestation, is analysed. It is demonstrated that terahertz time-domain spectroscopy and imaging techniques can be utilized to identify seeds in sheep-wool