Abstract-Super-resolution reconstruction for terahertz imaging based on sub-pixel gradient field transform

Youdong Guo, Furi Ling, He Li, Siyan Zhou, Jie Ji, and Jianquan Yao

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-58-23-6244

This paper presents the gradient-guided image super-resolution reconstruction for terahertz imaging to improve the image quality, taking advantage of super-resolution reconstruction based on adaptive super-pixel gradient field transform. Moreover, spatial entropy-based enhancement and a bilateral filter are introduced to ensure better performance of the reconstruction. Furthermore, we compare the performance of reconstruction operated on terahertz images with frequencies of 0.1 THz, 0.3 THz, 0.5 THz, and 0.7 THz. Experimental results demonstrate that this method successfully improves the image quality and reconstruct high-resolution images from low-resolution images with the peak signal-to-noise ratio and structural similarity index improved. In addition, the signal frequency and intensity are demonstrated to affect the performance of reconstruction.

© 2019 Optical Society of America

Abstract-Active control of terahertz plasmon-induced transparency in the hybrid metamaterial/monolayer MoS2/Si structure

Jie Ji,  Siyan Zhou,  Weijun Wang,  Furi Ling,  Jianquan Yao

https://pubs.rsc.org/en/Content/ArticleLanding/2019/NR/C8NR08813F#!divAbstract

Active control of terahertz wave is critical to the development of terahertz devices. Two dimensional materials with excellent optical properties provide more choices for opto-electrical devices with the maturity of their preparation technology. We proposed a hybrid structure of metamaterial/monolayer MoS2/Si and investigated its optical properties in terahertz range. The phenomenon of the plasmon-induced transparency (PIT) effect was observed in the transmission spectra, resulting from near-field coupling of two bright modes. According to simulated results, the phenomenon was confirmed its dependency on the length of the cutwire and distance between DSSRs. Furthermore, an external optical field supported by a 1064 nm laser could realized a switch effect on the sample. The resonances of the PIT metamaterial was disappeared when the optical power was further increased, as excited carriers in MoS2/Si substrate blocked the coupling effect. In addition, experimental results inferred that the PIT metamaterial enhanced the interaction of infrared light with monolayer MoS2/Si substrate.

Abstract-Tunable characteristics of the SWCNTs thin film modulator in the THz region

Weijun Wang, Wen Xiong, Jie Ji, Yue Tian, Furi Ling, and Jianquan Yao

Fig. 1 200 nm high interdigitated electrodes grown on silicon substrate.

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-9-4-1776

The modulation characteristics of the polyimide-based film of SWCNTs at room temperature were studied with time-domain terahertz (THz) spectroscopy in the study. The transmission greatly reduced with an increase in the power of the external optical pump. Under the pump power of 300 mW, the transmission even decreased to 3.4% of that of the original SWCNTs sample without illumination. The modulation depth of the film reached 95.6% at 300 mW, indicating the excellent modulation effect. In addition, the optical pump greatly increased the conductivity and caused a blue shift in the real conductivity peak. In order to explore the electric field modulation characteristic of the polyimide-based SWCNTs film, the results of the conductivity at 0 mW and 300 mW under different voltages were discussed. The change in transmission at 300 mW was much more significant than that at 0 mW, indicating that the modulation effect of voltage was more obvious under the condition of illumination. However, even under the pump power of 300 mW, the modulation depth was only 41.11% at 0.7 THz. In terms of the modulation depth of the optic field and electric field, we believed that the optical modulator worked better for the polyimide-based SWCNTs film.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Active multifunctional terahertz modulator based on plasmonic metasurface

Jie Ji, Siyan Zhou, Weijun Wang, Chunya Luo, Yong Liu, Furi Ling, and Jianquan Yao

Fig. 1 (a) The schematic of an efficient light modulator based on a frequency-selective tunable terahertz metasurface. The sample size was 15 mm*15mm. (b) the OM image of the sample when the photo-resist was lift off. (c) Geometry of the unit-cell of the metasurface with parameters: L1 = 120 um, L2 = 80 um, h1 = 30 um, h2 = 25 um, a = 30 um, g = w = 5um. Metal thickness for the metasurface: d = 100 nm (5 nm Ti + 95 nm Al).

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-27-3-2363&id=404331

An active multifunctional terahertz modulator based on plasmon-induced transparency (PIT) metasurface under the effect of external infrared light was investigated theoretically and experimentally. A distinct transparency window, which resulted from the near-field coupling between two resonators, could be observed in the transmission spectra. Experimental results showed a phenomenon infrared light induced blue shift on the both resonator with increasing optical powers. When the optical power was tuned from 0 mW to 400 mW, the amplitude tunability of transmission at transparency window reached to 34.01%, much larger than that at the two resonance frequencies. Moreover, the phase tunability of the transmission at 0.98 THz reached to 31.35%. Meanwhile, the amplitude variation was limited to 10%. Furthermore, a coupled Lorentz oscillator model was adopted to analyze the near-field interaction of the resonances. Experimental results were in good agreement with the analytical fitting results.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Active optical modulator based on a metasurface in the terahertz region

Yue Tian, Jie Ji, Siyan Zhou, Hu Wang, Zhichao Ma, Furi Ling, and Jianquan Yao

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-57-27-7778

The characteristics of the electromagnetically induced transparency (EIT) analog exposed under different illumination powers have been investigated theoretically and experimentally. The EIT analog is composed of a fixed aluminum structure fabricated on the silicon substrate. It was found that the resonance degree of the transparent window displayed a decreasing trend, and a blueshift phenomenon emerged by increasing the powers of the laser. Similarly, the properties of the time delay under different illumination powers have also been researched. The realization of the tuning effect may provide a possible choice for the modulation of the slow light devices.

© 2018 Optical Society of America

Abstract-Electrical terahertz modulator based on photo-excited ferroelectric superlattice

Jie Ji, Siyan Zhou, Jingcheng Zhang, Furi Ling,  Jianquan Yao,

https://www.nature.com/articles/s41598-018-21095-5

The transmission and dielectric spectra of ferroelectric STO/PT superlattice on Si substrate under simultaneous external optical and electric field were investigated and compared at room temperature. Results found that when with an optical field, the electric field realized an effective modulation on the transmission, which displayed a diode property. In addition, a comprehensive model combined with Debye relaxation and Lorentz model was used to analyze the dielectric spectra, variation of the soft mode with external field was put emphasis on exploring.

Abstract-The effect of optical pump on the absorption coefficient of 0.65CaTiO3-0.35NdAlO3 ceramics in terahertz range

Dan Li, Chunya Luo, Yebin Xu, Liang, Wu, Huaixing Wang, Songjie Shi, Furi Ling, Jianquan Yao,

http://www.sciencedirect.com/science/article/pii/S0925346717306729?via%3Dihub

The absorption coefficient of 0.65CaTiO3-0.35NdAlO3 ceramics under external optical fields was investigated by terahertz time-domain spectroscopy in a frequency range of 0.2 THz to 1 THz at room temperature. It could be found that the variation of the absorption coefficient is approximately from 8.95 cm−1 to 26.02 cm−1 in the frequency range of 0.2 THz to 1 THz, and the tuning range is about 3.32 cm−1 at 0.6 THz which almost reaches up to nearly 23.32%. The micromechanism of these results was attributed to the excited free carriers by the external optical pump intensity.

Abstract-Effect of optical pumping on the dielectric properties of 0.6CaTiO3-0.4NdAlO3 ceramics in the terahertz range

Dan Li, Chunya Luo, Yebin Xu, Jing Zhang, Liang Wu, Huaixing Wang, Songjie Shi, Furi Ling, and Jianquan Yao

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-57-1-1&origin=search

The dielectric properties of 0.6CaTiO3-0.4NdAlO3$0.6{\mathrm{CaTiO}}_3\text{-}0.4{\mathrm{NdAlO}}_3$ ceramics under external optical fields were investigated by terahertz time-domain spectroscopy in a frequency range of 0.2 THz to 1 THz at room temperature. It could be found that the variation of the real part of complex permittivity is approximately 0.31 in the frequency range of 0.2 THz to 1 THz. However the imaginary part of the dielectric constant does not change appreciably with the external optical field. The micromechanism of these results was attributed to the built-in electric field caused by the excited free carriers in the ceramics.

© 2017 Optical Society of America

Abstract-Dual-band tunable perfect metamaterial absorber in the THz range

Gang Yao, Furi Ling, Jin Yue, Chunya Luo, Jie Ji, and Jianquan Yao

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-2-1518

In this paper, a dual-band perfect absorber, composed of a periodically patterned elliptical nanodisk graphene structure and a metal ground plane spaced by a thin SiO2 dielectric layer, is proposed and investigated. Numerical results reveal that the absorption spectrum of the graphene-based structure displays two perfect absorption peaks in the terahertz band, corresponding to the absorption value of 99% at 35𝜇𝑚 and 97%at 59𝜇𝑚, respectively. And the resonance frequency of the absorber can be tunned by controlling the Fermi level of graphene layer. Further more, it is insensitive to the polarization and remains very high over a wide angular range of incidence around ±600. Compared with the previous graphene dual-band perfect absorption, our absorber only has one shape which can greatly simplify the manufacturing process.

© 2016 Optical Society of America

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