Abstract-Highly-efficient spintronic terahertz emitter enabled by metal-dielectric photonic crystal

Zheng Feng, Rui Yu, Yu Zhou, Hai Lu, Wei Tan, Hu Deng, Quancheng Liu, Zhaohui Zhai, Liguo Zhu, Jianwang Cai, Bingfeng Miao, Haifeng Ding

https://arxiv.org/abs/1807.03069

Spintronic terahertz (THz) emitter provides the advantages such as apparently broader spectrum, significantly lower cost, and more flexibility in compared with the commercial THz emitters, and thus attracts great interests recently. In past few years, efforts have been made in optimizing the material composition and structure geometry, and the conversion efficiency has been improved close to that of ZnTe crystal. One of the drawbacks of the current designs is the rather limited laser absorption - more than 50% energy is wasted and the conversion efficiency is thus limited. Here, we theoretically propose and experimentally demonstrate a novel device that fully utilizes the laser intensity and significantly improves the conversion efficiency. The device, which consists of a metal-dielectric photonic crystal structure, utilizes the interference between the multiple scattering waves to simultaneously suppress the reflection and transmission of the laser, and to reshape the laser field distributions. The experimentally detected laser absorption and THz generations show one-to-one correspondence with the theoretical calculations. We achieve the strongest THz pulse emission that presents a 1.7 times improvement compared to the currently designed spintronic emitter. This work opens a new pathway to improve the performance of spintronic THz emitter from the perspective of optics.

Abstract-A Terahertz Controlled-NOT Gate Based on Asymmetric Rotation of Polarization in Chiral Metamaterials

Wei-Zong Xu, Ya-Ting Shi, Jiandong Ye, Fang-Fang Ren, Ilya V. Shadrivov, Hai Lu, Lanju Liang, Xiaopeng Hu, Biaobing Jin, Rong Zhang, Youdou Zheng, Hark Hoe Tan, Chennupati Jagadish

http://onlinelibrary.wiley.com/doi/10.1002/adom.201700108/abstract

Logical operation based on polarization encoding of light is important for future data transmission and information processing. However, in the terahertz (THz) region, chiral materials with large optical activity are not available in nature, and the effective manipulation of polarization states remains challenging. Here, the authors demonstrate a double-layer bi-anisotropic metamaterial that consists of planar spiral and cut-wire layers separated by a polyimide film. Strong asymmetric polarization rotation of two orthogonal linear polarizations can be observed around 0.53 THz. By investigating the correlation between two linear polarization states before and after the spiral-wire metamaterial at this frequency, a controlled-NOT (CNOT) gate operating on two linear-polarization-based qubits is further exploited. The processing mechanism of the asymmetric rotation and CNOT gate is attributed to the scattering of dipole momentum based on classical multipole theory. This polarization processor's architecture is promising for robust and energy-efficient THz polarization control, and also provides an effective path for the development of future optical supercomputing technology.

Abstract-Anomalous Terahertz Reflection and Scattering by Flexible and Conformal Coding Metamaterials

1. Lanju Liang¹, 
2. Meiqing Qi², 
3. Jing Yang³,
4. Xiaopeng Shen², 
5. Jiquan Zhai¹, 
6. Weizong Xu⁴, 
7. Biaobing Jin^1,5,*, 
8. Weiwei Liu^3,5,*,
9. Yijun Feng⁴, 
10. Caihong Zhang¹, 
11. Hai Lu⁴,
12. Hou-Tong Chen⁶, 
13. Lin Kang¹, 
14. Weiwei Xu¹,
15. Jian Chen^1,5, 
16. Tie Jun Cui^2,5,*, 
17. Peiheng Wu¹ and
18. Shenggang Liu^5,7

Article first published online: 30 JUN 2015

http://onlinelibrary.wiley.com/doi/10.1002/adom.201500206/abstract;jsessionid=75D9087BA4464D14DC4C0EA2F158CD85.f03t01?userIsAuthenticated=false&deniedAccessCustomisedMessage=

DOI: 10.1002/adom.201500206

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Arbitrary control of terahertz (THz) waves remains a significant challenge although it promises many important applications. Here, a method to tailor the reflection and scattering of THz waves in an anomalous manner by using 1-bit coding metamaterials is presented. Specific coding sequences result in various THz far-field reflection and scattering patterns, ranging from a single beam to two, three, and numerous beams, which depart obviously from the ordinary Snell's law of reflection. By optimizing the coding sequences, a wideband THz thin film metamaterial with extremely low specular reflection, due to the scattering of the incident wave into various directions, is demonstrated. As a result, the reflection from a flat and flexible metamaterial can be nearly uniformly distributed in the half space with small intensity at each specific direction, manifesting a diffuse reflection from a rough surface. Both simulation and experimental results show that a reflectivity less than −10 dB is achieved over a wide frequency range from 0.8 to 1.4 THz, and it is insensitive to the polarization of the incident wave. This work reveals new opportunities arising from coding metamaterials in effective manipulation of THz wave propagation and may offer widespread applications.