Abstract-Single-walled carbon nanotubes assisted THz silicon grating modulator

Yang Liu, Tianxiang Zhu, Jijun Feng, Shuai Yuan, Xinluo Zhao, Tengfei Wu, and Heping Zeng

https://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=6457046985648642545

Single-walled carbon nanotubes (SWCNTs) are applied to realize an enhanced frequency modulation for a suspended THz silicon grating, which is fabricated by a nanosecond laser direct writing and coated with the synthetic SWCNTs/polyacrylic emulsion composite. With terahertz time domain spectroscopy system, the transmission spectra of the bare and SWCNTs coated silicon grating are measured and compared. The SWCNTs coated silicon grating can realize an improved extinction ratio and quality factor, which is due to the SWCNTs caused local field enhancement and can be explained by the theoretical simulation with finite element method. Besides the effective modulation of the grating transmittance, SWCNTs can also be integrated with other platforms and applied in future THz imaging and communication systems.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Tunable multi-band terahertz absorber based on a one-dimensional heterostructure containing semiconductor

Yang Liu,  Sheng-Qiu Xu, Ming Liu, Xin-Guang Hu, Yong-Fa Duan, Lin Yi

https://www.sciencedirect.com/science/article/pii/S0030402618307502

The absorption properties of a simple layered heterostructure composed of semiconductor and dielectric are analyzed by transfer matrix method. The numerical results indicate that such a structure can serve as a tunable multi-band terahertz perfect absorber. This phenomenon is due to the photon localization in the semiconductor layer at particular wavelengths and the presence of the damping factor of semiconductor layer. The number of the absorption peaks can be tuned by changing the thickness of the semiconductor layer. Moreover, the influences coming from the incident angle and the temperature of semiconductor on the absorption properties are also numerically studied.

Abstract-Ultrafast PM fiber ring laser mode-locked by nonlinear polarization evolution with short NPE section segments

Wenchao Zhang, Yang Liu, Chao Wang, Zhiwei Zhu, Daping Luo, Chenlin Gu, and Wenxue Li

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-7-7934&origin=search

We demonstrate a nonlinear polarization evolution (NPE) mode-locked polarization maintaining (PM) Yb-doped fiber laser with short NPE section segments by setting proper splicing angle. With a theoretical analysis, we propose that an appropriate deviation splicing angle exists to maximize the adjustable range of transmission modulation. The simulation results are highly consistent with theoretical conclusions. Experimentally, using the optimal splicing angle predicted by the theoretical calculation, we have achieved an environmentally stable mode-locking fiber laser at 111-MHz repetition rate with corresponding pulse energy of 0.47 nJ. Additionally, the noise performance of this PM fiber laser is characterized. The measured RMS timing jitter and amplitude noise are 6.41 fs and 0.0052% respectively (1 kHz-10 MHz), which are competitive to the low phase noise performance of the typical fiber laser.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Compact and stable high-repetition-rate terahertz generation based on an efficient coaxially pumped dual-wavelength laser

Yang Liu, Kai Zhong, Jialin Mei, Chu Liu, Jie Shi, Xin Ding, Degang Xu, Wei Shi, Jianquan Yao

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-25-31988

A compact and stable terahertz (THz) source is demonstrated based on difference frequency generation (DFG) pumped by an efficient dual-wavelength acousto-optic (AO) Q-switched solid-state Nd:YLF laser with composite gain media (a-cut and c-cut) in the coaxial pumping configuration. Optimal power ratio and pulse synchronization of the orthogonal polarized 1047/1053 nm dual-wavelength laser could be realized by varying the pump focusing depth and/or pump wavelength. The total power of 2.92 W was obtained at 5 kHz pumped by 10-W laser-diode power at 803 nm. Such an efficient dual-wavelength laser demonstrated good stability and inconspicuous timing jitter benefiting from the suppressed gain competition between two resonating wavelengths. An 8-mm-long GaSe crystal was employed to generate THz waves at 1.64 THz by DFG and the maximum THz average output power was about 0.93 μW. This compact coaxial pumping method can be extended to all kinds of neodymium (Nd) doped laser crystals to produce different dual-wavelength lasers for various THz wavelength generation, which have good prospects for portable and costless applications like imaging, non-destructive inspection, etc.

© 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz High-Gain Offset Reflector Antennas Using SiC and CFRP Material

Hongjian Wang,  Xingchao Dong, Min Yi, Fei Xue, Yang Liu, Guang Liu

http://ieeexplore.ieee.org/document/7972966/

Two high-gain terahertz (THz) offset reflector antennas are proposed. The silicon carbide material and thermally stable carbon fiber-reinforced plastic are selected as reflectors for high specific stiffness and low thermal expansion coefficient which are helpful for space use. Dual polarization is achieved by introducing a wire-grid polarizer which can separate the two THz polarization waves provided by multimode horns fabricated in electroforming technology. Furthermore, three-coordinate test system and theodolites are employed to detect the surface error of dishes and alignment of antenna subsystem. The physical optics analysis based on the measured reflector surface data is introduced referring to the large aperture antenna patterns by virtue of its accuracy and high efficiency. The results of this novel method are compared to that of the near-field test. Measurements show that the sidelobe levels (SLLs) of the single polarization silicon-based reflector are below −32 dB while the gain is 55.3 dB at 330 GHz, and the dual polarization carbon fiber-reinforced plastic reflector antenna suppresses the SLLs to −28 and −29 dB in two principal planes while the gain is 57.2 dB at the same frequency, respectively. The good performances of the proposed antennas indicate the potential for the application of space THz radiometer.

Abstract-Terahertz High Gain Offset Reflector Antennas Using SiC and CFRP Material

Hongjian Wang,  Xingchao Dong,  Min Yi, Fei Xue, Yang Liu, Guang Liu

http://ieeexplore.ieee.org/document/7972966/
Two high gain terahertz offset reflector antennas are proposed. The silicon carbide material and thermally stable carbon fiber-reinforced plastic are selected as reflectors for high specific stiffness and low thermal expansion coefficient which are helpful for space use. Dual polarization is achieved by introducing a wire-grid polarizer which can separate the two terahertz polarization waves provided by multimode horns fabricated in electroforming technology. Furthermore, three-coordinate test system and theodolites are employed to detect the surface error of dishes and alignment of antenna subsystem. The physical optics analysis based on the measured reflector surface data is introduced referring to the large aperture antenna patterns by virtue of its accuracy and high efficiency. The results of this novel method are compared to that of the near field test. Measurements show that the side lobe levels of the single polarization silicon based reflector are below -32dB while the gain is 55.3dB at 330GHz, and the dual polarization carbon fiber-reinforced plastic reflector antenna suppresses the side lobe levels to -28dB and -29dB in two principal planes while the gain is 57.2dB at the same frequency, respectively. The good performances of the proposed antennas indicate the potential for the application of space terahertz radiometer.

Abstract-High-Performance THz Emitters Based on Ferromagnetic/Nonmagnetic Heterostructures

http://onlinelibrary.wiley.com/doi/10.1002/adma.201603031/full

A low-cost, intense, broadband, noise resistive, magnetic field controllable, flexible, and low power driven THz emitter based on thin nonmagnetic/ferromagnetic metallic heterostructures is demonstrated. The THz emission origins from the inverse spin Hall Effect. The proposed devices are not only promising for a wide range of THz equipment, but also offer an alternative approach to characterize the spin-orbit interaction in nonmagnetic/ferromagnetic bilayers.

Abstract-Widely-tunable high-repetition-rate terahertz generation in GaSe with a compact dual-wavelength KTP OPO around 2 μm

Jialin Mei, Kai Zhong, Maorong Wang, Yang Liu, Degang Xu, Wei Shi, Yuye Wang, Jianquan Yao, Robert A. Norwood, and Nasser Peyghambarian

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-20-23368

A compact efficient high-repetition-rate doubly-resonant dual-wavelength KTP optical parametric oscillator (OPO), with output power up to 3.65 W and tuning ranges of 2.088-2.133 μm/2.171-2.122 μm for signal/idler waves, was deployed for terahertz (THz) generation in a GaSe crystal. Based on difference frequency generation (DFG), the THz wave was continuously tunable from 730.9 μm (0.41 THz) to 80.8 μm (3.71 THz), believed to be the first report of a compact high-repetition-rate widely-tunable THz source. The maximum THz average power reached 1.2 μW at 1.54 THz and the corresponding DFG efficiency was 7.8 × 10−7, entirely suitable for portable applications. The utility of the THz source was also demonstrated through spectroscopy and imaging experiments.

© 2016 Optical Society of America

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