Abstract-Thermally controllable filter at terahertz region

 Hee Jun Shin, Min-Cheol Lim, Sae-Hyung Kim, Kisang Park, Sung-Wook Choi, Gyeongsik Ok

https://www.sciencedirect.com/science/article/pii/S1350449517306722

We experimentally investigated terahertz (THz) filters fabricated using dodecanoic acid (DDA) particles and polyethylene (PE) by performing THz time-domain spectroscopy. Since the refractive indices of DDA and PE are the same in the THz range, no optical scattering occurred when they were mixed. However, heating caused air voids to replace the DDA particles, and the DDA melted into the spaces between the PE particles. Furthermore, as the DDA particle size, heating time, and DDA content increased, the THz band width became narrower. Based on the results, we propose a new, low-cost type of THz filter with a simple manufacturing method.

Abstract-Broad- and Narrow-Line Terahertz Filtering in Frequency-Selective Surfaces Patterned on Thin Low-Loss Polymer Substrates

 Antonio Ferraro,  Dimitrios C. Zografopoulos,  Roberto Caputo,   Romeo Beccherell

http://ieeexplore.ieee.org/document/7847400/

A new class of frequency-selective surface filters (FSS) for terahertz (THz) applications is proposed and investigated both numerically and experimentally. A periodic FSS array of cross-shaped apertures is patterned on aluminum, deposited on thin foils of the low-loss cyclo-olefin polymer Zeonor. Apart from the fundamental filtering response of the FSS elements, we also observe very narrow-linewidth peaks with high transmittance, associated with guided-mode resonances in the dielectric substrate. The effect of the filter's geometrical parameters on its performance is systematically studied via finite-element method simulation and confirmed by time-domain spectroscopy characterization of the fabricated samples. Finally, thanks to the flexibility of the employed substrates, THz-FSS filters are also characterized in bent configuration, revealing a robust response in terms of the fundamental FSS passband filter and a high sensitivity of the GMR peaks. These features can be exploited in the design of novel THz filters or sensors.

Abstract-Single and cascaded, magnetically controllable metasurfaces as terahertz filters

Andriy E. Serebryannikov, Akhlesh Lakhtakia, and Ekmel Ozbay
https://www.osapublishing.org/josab/abstract.cfm?uri=josab-33-5-834

Transmission of a normally incident, linearly polarized, plane wave through either a single electrically thin metasurface comprising H-shaped subwavelength resonating elements made of magnetostatically controllable InAs or a cascade of several such metasurfaces was simulated in the terahertz regime. Stop bands that are either weakly or strongly controllable can be exhibited by a single metasurface by proper choice of the orientation of the magnetostatic field, and a ∼19% downshift of stop bands in the 0.1–5.5 THz spectral regime is possible on increasing the magnetostatic field strength from 0 to 1 T. Better controllability and wider bandwidths are possible by increasing the number of metasurfaces in a cascade, although increase of the total losses can lead to some restrictions. ON/OFF switching regimes, realizable either by applying/removing the magnetostatic field or just by changing its orientation, exist.

© 2016 Optical Society of America

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Abstract-Design of terahertz narrowband filter based on surface plasmon polaritons of metal–dielectric–metal structure with circular loop arrays

Xiang Liu, Wei Wang, Yinlong Zhao

Zhejiang University, College of Information Science and Electronic Engineering, Hangzhou, Zhejiang 310027, China

Dongxiao Yang

Zhejiang University, College of Information Science and Electronic Engineering, Hangzhou, Zhejiang 310027, China

Zhejiang University, Research Center for Terahertz Technology, Hangzhou, Zhejiang 310027, China

Opt. Eng. 54(12), 127107 (Dec 29, 2015). doi:10.1117/1.OE.54.12.127107

http://opticalengineering.spiedigitallibrary.org/article.aspx?articleid=2480140

Abstract.  A narrowband terahertz (THz) filter based on metal–dielectric–metal structure with a circular loop array patterned on metallic films was proposed. The transmission properties in the THz range of the structure were experimentally and theoretically analyzed. The structure’s transmission spectrum has two narrow bands of which band 1 in the lower frequency range was dominated by the transmission mode due to localized plasmon polaritons and band 2 in the higher frequency range was dominated by propagated plasmon polaritons mode and guided mode. Both band 1 and band 2 have high Q$Q$-factors. By designing an asymmetry periodic constant in orthogonal directions, band 2 exhibits potentials as a narrowband polarizer. Furthermore, the transmittance of band 2 can be promoted to 100% by laterally shifting the metallic arrays.

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Abstract-Terahertz filter integrated with a subwavelength structured antireflection coating

Jeong Min Woo¹, Dae-Seon Kim¹, Dong-Ju Kim¹ and Jae-Hyung Jang^1,a)
http://scitation.aip.org/content/aip/journal/adva/5/12/10.1063/1.4939571
a) Electronic mail: jjang@gist.ac.kr.
AIP Advances 5, 127238 (2015); http://dx.doi.org/10.1063/1.4939571

Micro-pyramid shaped subwavelength structures (SWSs) were integrated on both sides of a terahertz (THz) filter by means of stamping methods. Two silicon-based stamping molds fabricated via crystallographic wet etching were utilized to replicate SWSs onto cyclo-olefin copolymer (COC) films coated onto both sides of a THz filter at the same time. The SWSs act as an broadband antireflection coating to reduce the surfacereflection loss in a frequency range of 0.2 THz to 1.4 THz. Compared to a THz filter without SWSs, the filter integrated with double-sided SWSs exhibits a low standing wave ratio inside the substrate and THz signal transmission enhancement of up to 10.8%.

Abstract- A Tunable Terahertz Photonic Crystal Narrow-Band Filter

Li, S. Liu, H. ; Sun, Q. ; Huang, N.
State Key Laboratory of Transient Optics and Photonics Technology, Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an, China 
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?reload=true&arnumber=7017510&filter%3DAND%28p_IS_Number%3A7051313%29

We theoretically propose and investigate a magnetically tunable narrow-band terahertz filter based on a triangular lattice silicon photonic crystal with a point and two line defects. The optical properties of the filter have been analyzed in detail. It is found that a single resonant peak with the central frequency of$sim 1$ THz is existed in the transmission spectrum, which has a narrow full width at half maximum of <2 GHz. Moreover, under the control of an external magnetic field, transmission frequency and width of passband are adjustable, which reveals that the 2-D silicon photonic crystal waveguide with point and line defects can serve as a continuously tunable bandpass filter at the terahertz waveband.