Abstract-Generalization of active radar imaging and passive imaging models applied to wide band terahertz array imaging systems

Orges Furxhi,  Lei Zhang, Ronald Driggers,

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11001/110010H/Generalization-of-active-radar-imaging-and-passive-imaging-models-applied/10.1117/12.2519683.short

System solutions for commercial applications such as autonomous driving, augmented reality, medical imaging, and security imaging, exploit active illumination. In these applications, the active source is used to provide photons but also to code and decode relevant information such as range or spectral response. The wavelengths of choice range from visible to millimeter waves depending on the application and associated requirements. Across these wavelengths, the targets range from Lambertian to specular. For single element and scanned systems, ranging is commonly modeled using conventions borrowed from the radar and antenna community. Staring and scanning systems that facilitate resolution in the cross-range are modeled using conventions borrowed from the synthetic aperture radar community or the passive imaging community. All the borrowed conventions, however, make assumptions about the size and nature of the target in relationship to the illumination and wavelength, unresolved versus resolved and Lambertian versus specular. These assumptions are relevant for the calculation of system signal to noise ratio and resolution; therefore, they should be carefully considered when adopting the conventions. Examples of systems where modeling falls between active radar and passive imaging include wide band Terahertz array imaging systems and solid state lidar systems. This paper generalizes and bridges the models used by the active radar community and the passive imaging community. We apply the model to a wide band terahertz array imaging system enabled by terahertz array technology recently developed at imec. The model is validated using simulated measurements from a two-dimensional terahertz array.
© (2019) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Abstract-Performance modeling of terahertz (THz) and millimeter waves (mmW) pupil plane imaging

Nafiseh Mohammadian,  Orges Furxhi,  Lei Zhang,  Peter Offermans,  Galia Ghazi,  Ronald Driggers

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10625/1062511/Performance-modeling-of-terahertz-THz-and-millimeter-waves-mmW-pupil/10.1117/12.2311496.short


Terahertz- (THz) and millimeter-wave sensors are becoming more important in industrial, security, medical, and defense applications. A major problem in these sensing areas is the resolution, sensitivity, and visual acuity of the imaging systems. There are different fundamental parameters in designing a system that have significant effects on the imaging performance. The performance of THz systems can be discussed in terms of two characteristics: sensitivity and spatial resolution. New approaches for design and manufacturing of THz imagers are a vital basis for developing future applications. Photonics solutions have been at the technological forefront in THz band applications. A single scan antenna does not provide reasonable resolution, sensitivity, and speed. An effective approach to imaging is placing a high-performance antenna in a two-dimensional antenna array to achieve higher radiation efficiency and higher resolution in the imaging systems. Here, we present the performance modeling of a pupil plane imaging system to find the resolution and sensitivity efficiency of the imaging system.
© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Abstract-Realization of Full Control of a Terahertz Wave Using Flexible Metasurfaces

• Lei Zhang,

• Min Zhang,

• Huawei Liang

• 
  

http://onlinelibrary.wiley.com/doi/10.1002/adom.201700486/full

Compared with devices controlling microwave and visible light, there is a lack of functional devices for terahertz (THz) wave control. Moreover, the available THz elements are usually manufactured with bulk materials, in contrast to the trend of miniaturization and compact device requirements. Here, full control of both phase and amplitude is achieved experimentally and numerically at 0.14 THz, one of the atmospheric windows, by demonstrating the functionalities such as polarization conversion, metalenses and the generation of a non-diffraction Airy beam. Significantly, the metal structures are fabricated on a flexible substrate with a total thickness of ≈0.063 l via a standard flexible printed circuit technique. Taking into account the considerable manipulation efficiency and cost-efficient sample fabrication technique, the results show solid advances in the development of metasurfaces as a versatile platform for designing practical functional devices in the THz range.

Abstract-Full-State Controls of Terahertz Waves Using Tensor Coding Metasurfaces

Shuo Liu, Hao Chi Zhang, Lei Zhang, Quan Long Yang, Quan Xu, Jian Qiang Gu, Yan Yang, XiaoYang Zhou, Jiaguang Han, Qiang Cheng, Weili Zhang, and Tie Jun Cui

ACS Appl. Mater. Interfaces, Just Accepted Manuscript

DOI: 10.1021/acsami.7b02789

Publication Date (Web): June 5, 2017

Copyright © 2017 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acsami.7b02789?journalCode=aamick

Coding metasurfaces allow us to study metamaterials from a fully-digital perspective, enabling many exotic functionalities such as anomalous reflections, broadband diffusions, and polarization conversion. Here, we propose a tensor coding metasurface at terahertz frequency that could take full-state controls of electromagnetic wave in terms of its polarization state, phase and amplitude distributions, and wave-vector mode. Due to the off-diagonal elements that dominant in the reflection matrix, each coding particle could reflects the normally incident wave to its cross polarization with controllable phases, resulting in different coding digits. A 3-bit tensor coding metasurface with three coding sequences is taken as example to show its full-state controls in reflecting normally incident terahertz beam to anomalous directions with cross polarizations, and making a spatially propagating wave (PW) to surface wave (SW) conversion at the terahertz frequency. We show that the proposed PW-SW convertor based on tensor coding metasurface supports both x and y-polarized normal incidences, producing cross-polarized transverse- magnetic (TM) and transverse-electric (TE) modes of terahertz SWs, respectively.

Abstract-Frequency-Dependent Dual-Functional Coding Metasurfaces at Terahertz Frequencies

http://onlinelibrary.wiley.com/doi/10.1002/adom.201600471/full

A frequency-dependent dual-functional coding metasurface is proposed at terahertz frequencies using two layers of metamaterial structures, each of which is responsible for the independent control of reflection phases at two distinct frequencies. The zero interference between the functionalities at the lower and higher frequencies are promising for possible applications in multicolor holography for color displays or a frequency beam splitter.

Abstract-Dual-wavelength narrow-linewidth linearly polarized seed source and stimulated Brillouin scattering suppression in its high-power fiber amplification

Yaqian Ding, Yuan Liu, Yunfeng Qi, Lei Zhang, Baoling Guo, Rui Wang, Jun Zhou, and Guanghui Chen

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-54-22-6616#Abstract

In this paper, we demonstrate a dual-wavelength narrow-linewidth linearly polarized all-fiber amplifier emitting 1035 and 1030 nm wavelengths with a high power of 80.0 W. The seed source features two sets of fiber Bragg gratings fabricated on polarization maintaining fibers and a ytterbium-doped fiber as the gain medium. Two wavelengths propagate in one overlapping cavity and the power ratio can be tuned by a coiling fiber setup. A master oscillator power amplifier system consisting of a two-stage amplifier is employed. Longitudinally varied strains are applied on the gain fiber to suppress the back-scattered Stokes light in the main amplifier stage. With an appropriate seed power ratio, we are able to generate amplification power to 80.0 W comprised of 1035 and 1030 nm light while achieving an increase of at least six times that of the stimulated Brillouin scattering threshold. Since both frequencies are propagating in one cavity and amplified in one gain medium, the 1035 and 1030 nm lasers have good temporal and spatial overlapping characteristics. This high-power MHz-level linearly polarized structure affords a compact, novel, and high-efficiency approach to different frequency generation of mid-infrared or terahertz emission.

© 2015 Optical Society of America

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Abstract-One- and two-dimensional photo-imprinted diffraction gratings for manipulating terahertz waves

Ioannis Chatzakis^1,a), Philippe Tassin^1,b), Liang Luo¹, Nian-Hai Shen¹, Lei Zhang¹, Jigang Wang^1,c), Thomas Koschny¹ and C. M. Soukoulis^1,2,d)
http://scitation.aip.org/content/aip/journal/apl/103/4/10.1063/1.4813620
a) Present address: Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA.
b) Author to whom correspondence should be addressed: Electronic mail: tassin@ameslab.gov
c) Electronic mail: jgwang@iastate.edu, jwang@ameslab.gov
d) Electronic mail: soukoulis@ameslab.gov
Appl. Phys. Lett. 103, 043101 (2013); http://dx.doi.org/10.1063/1.4813620

Emerging technology based on artificial materials containing metallic structures has raised the prospect for unprecedented control of terahertz waves. The functionality of these devices is static by the very nature of their metallic composition, although some degree of tunability can be achieved by incorporating electrically biased semiconductors. Here, we demonstrate a photonic structure by projecting the optical image of a metal mask onto a thin GaAs substrate using a femtosecond pulsed laser source. We show that the resulting high-contrast pattern of photo-excited carriers can create diffractive elements operating in transmission, potentially providing a route to terahertz components with reconfigurable functionality.