Abstract-Implantable, Degradable, Therapeutic Terahertz Metamaterial Devices

Long Sun, Zhitao Zhou, Junjie Zhong,   Zhifeng Shi, Ying Mao,  Hua Li,  Juncheng Cao, Tiger H. Tao,

https://onlinelibrary.wiley.com/doi/abs/10.1002/smll.202000294

Metamaterial (MM) sensors and devices, usually consisting of artificially structured composite materials with engineered responses that are mainly determined by the unit structure rather than the bulk properties or composition, offer new functionalities not readily available in nature. A set of implantable and resorbable therapeutic MM devices at terahertz (THz) frequencies are designed and fabricated by patterning magnesium split ring resonators on drug‐loaded silk protein substrates with controllable device degradation and drug release rates. To demonstrate proof‐of‐concept, a set of silk‐based, antibiotics‐loaded MM devices, which can serve as degradable antibacterial skin patches with capabilities to monitor drug‐release in real time are fabricated. The extent of drug release, which correlates with the degradation of the MM skin patch, can be monitored by analyzing the resonant responses in reflection during degradation using a portable THz camera. Animal experiments are performed to demonstrate the in vivo degradation process and the efficacy of the devices for antibacterial treatment. Thus, the implantable and resorbable therapeutic MM devices do not need to be retrieved once implanted, providing an appealing alternative for in‐vivo sensing and in situ treatment application

Abstract-Broadband THz to NIR up-converter for photon-type THz imaging

Peng Bai, Yueheng Zhang, Tianmeng Wang, Zhanglong Fu, Dixiang Shao, Ziping Li, Wenjian Wan, Hua Li, Juncheng Cao, Xuguang Guo,  Wenzhong Shen

https://www.nature.com/articles/s41467-019-11465-6

High performance terahertz imaging devices have drawn wide attention due to their significant application in healthcare, security of food and medicine, and nondestructive inspection, as well as national security applications. Here we demonstrate a broadband terahertz photon-type up-conversion imaging device, operating around the liquid helium temperature, based on the gallium arsenide homojunction interfacial workfunction internal photoemission (HIWIP)-detector-LED up-converter and silicon CCD. Such an imaging device achieves broadband response in 4.2–20 THz and can absorb the normal incident light. The peak responsivity is 0.5 AW−1. The light emitting diode leads to a 72.5% external quantum efficiency improvement compared with the one widely used in conventional up-conversion devices. A peak up-conversion efficiency of 1.14 × 10−2 is realized and the optimal noise equivalent power is 29.1 pWHz−1/2. The up-conversion imaging for a 1000 K blackbody pin-hole is demonstrated. This work provides a different imaging scheme in the terahertz band.

Abstract-Graphene‐Coupled Terahertz Semiconductor Lasers for Enhanced Passive Frequency Comb Operation

Ming Yan. Wenjian Wan. Tao Zhou, Kang Zhou, Ziping Li, Juncheng Cao, Qiang Yu, Kai Zhang, Min Li, Junyi Nan, Boqu He. Heping Zeng

https://onlinelibrary.wiley.com/doi/10.1002/advs.201900460

Optical frequency combs, consisting of well‐controlled equidistant frequency lines, have been widely used in precision spectroscopy and metrology. Terahertz combs have been realized in quantum cascade lasers (QCLs) by employing either an active mode‐locking or phase seeding technique, or a dispersion compensator mirror. However, it remains a challenge to achieve the passive comb formation in terahertz semiconductor lasers due to the insufficient nonlinearities of conventional saturable absorbers. Here, a passive terahertz frequency comb is demonstrated by coupling a multilayer graphene sample into a QCL compound cavity. The terahertz modes are self‐stabilized with intermode beat note linewidths down to a record of 700 Hz and the comb operation of graphene‐coupled QCLs is validated by on‐chip dual‐comb measurements. Furthermore, the optical pulse emitted from the graphene‐coupled QCL is directly measured employing a terahertz pump–probe technique. The enhanced passive frequency comb operation is attributed to the saturable absorption behavior of the graphene‐integrated saturable absorber mirror, as well as the dispersion compensation introduced by the graphene sample. The results provide a conceptually different graphene‐based approach for passive comb formation in terahertz QCLs, opening up intriguing opportunities for fast and high‐precision terahertz spectroscopy and nonlinear photonics.

Abstract-Terahertz planar lenses based on plasmonic metasurfaces

Chang Yang, Yun Shen, Yanqiang Xie, Qi Zhou, Xiaohua Deng, Juncheng Cao,


https://www.sciencedirect.com/science/article/abs/pii/S037596011831185X


Plasmonic planar lenses on silicon substrate are designed to realize terahertz (THz) wave focusing. Super-unit-cells containing eight different resonant units are presented to construct eight concentric rings on the silicon substrate. By controlling of the position distribution of the resonant units, it is shown that focusing at 4.3 THz can be achieved. Moreover, due to that the eight units can steer THz wave and keep phase gradient in frequency range of 4.2 to 4.5 THz, the metalenses can realize broadband THz focusing. The results imply the potential applications in THz wave control devices of light collection and multi-channel optical communication.

Abstract-Sideband generation of coupled-cavity terahertz semiconductor lasers under active radio frequency modulation

Ziping Li, Hua Li, Wenjian Wan, Kang Zhou, Juncheng Cao, Gaolei Chang, and Gangyi Xu

Fig. 1 (a) Schematic of the coupled-cavity terahertz QCL. The inset is a scanning electron microscope image of the fabricated short cavity and air gap of the laser. (b) Calculated total propagation losses as a function of eigen mode frequency of the coupled-cavity with material loss (green) and without material loss (black). The scatters are the calculated results and the solid lines are for the guide of eyes. The red stars are the measured lasing frequencies obtained from (d). (c) Measured light-current-voltage (L-I-V) characteristic of the coupled-cavity laser in continuous wave (cw) mode at 20 K. (d) Normalized terahertz emission spectra as a function of drive current without RF modulation at 20 K. Each spectrum is shifted vertically for clarity. The insets of (d) are magnified spectra to clear show the spectral degeneracy.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-25-32675

The radio frequency (RF) modulation is a powerful tool, which is used for generating sidebands in semiconductor lasers for active mode-locking. The two-section coupled-cavity laser geometry shows advantages over traditional Fabry-Pérot cavities in the RF modulation efficiency, because of its reduced device capacitance of short section cavity. Further, it has been widely used for active/passive mode-locking of semiconductor diode lasers. For semiconductor-based quantum cascade lasers (QCLs) emitting in the far-infrared or terahertz frequency bands, the two-section coupled-cavity configuration can strongly prevent the laser from multimode emissions. This is because of its strong mode selection (loss modulation), which the cavity geometry introduces. Here, we experimentally demonstrate that the coupled-cavity terahertz QCL can be actively modulated to generate sidebands. The RF modulation is efficient at the frequency that equals the difference frequency between the fundamental and higher order transverse modes of the laser, and its harmonics. We show for the first time that, when the laser is modulated at the second harmonic of the difference frequency, the sideband generation in coupled-cavity terahertz QCLs and the generated sidebands are equally spaced by the injected microwave frequency. Our results, which are presented here, provide a novel approach for modulating terahertz coupled-cavity lasers for active mode-locking. The coupled-cavity geometry shows advantages in generating dense modes with short cavities for potential high-resolution spectroscopy. Furthermore, the short coupled-cavity laser consumes less electrical power than Fabry-Pérot lasers that generate a similar mode spacing.

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

Abstract-Surface-phonon-polariton-mediated photon response of terahertz quantum-well infrared photodetectors

DiXiang Shao, XuGuang Guo, YiMing Zhu, SongLin Zhuang, ZhangLong Fu,  JunCheng Cao

http://iopscience.iop.org/article/10.1088/1361-6463/aaeb77/meta

A surface-phonon-polariton (SPHP)-mediated photon response near the longitudinal optical (LO) phonon frequency of GaAs is investigated in a terahertz GaAs/AlGaAs quantum-well infrared photodetector, integrated with a one-dimensional metal grating. For a contrast device without a grating coupler, no SPHP-related signature is found in the photocurrent spectrum, because the incident radiation from free space cannot excite the SPHP, due to the mismatch of momentum. The intensity of the electric field component along the growth direction of the device absorption layer is numerically calculated. The results show that the photocurrent response peaks near the LO phonon frequency band (8.8–9.0 THz) are attributed to the local field enhancement induced by SPHP. Our results are useful to realize high performance SPHP-mediated terahertz photodetectors and other related terahertz devices.

Abstract-Multicolor T‐Ray Imaging Using Multispectral Metamaterials

Zhitao Zhou  Tao Zhou  Shaoqing Zhang  Zhifeng Shi  Ying Chen  Wenjian Wan  Xinxin Li Xinzhong Chen  Stephanie N. Gilbert Corder  Zhanglong Fu  Liang Chen  Ying Mao  Juncheng Cao Fiorenzo G. Omenetto  Mengkun Liu  Hua Li,  Tiger H. Tao,

https://onlinelibrary.wiley.com/doi/abs/10.1002/advs.201700982

Recent progress in ultrafast spectroscopy and semiconductor technology is enabling unique applications in screening, detection, and diagnostics in the Terahertz (T‐ray) regime. The promise of efficaciously operation in this spectral region is tempered by the lack of devices that can spectrally analyze samples at sufficient temporal and spatial resolution. Real‐time, multispectral T‐ray (Mul‐T) imaging is reported by designing and demonstrating hyperspectral metamaterial focal plane array (MM‐FPA) interfaces allowing multiband (and individually tunable) responses without compromising on the pixel size. These MM‐FPAs are fully compatible with existing microfabrication technologies and have low noise when operating in the ambient environment. When tested with a set of frequency switchable quantum cascade lasers (QCLs) for multicolor illumination, both MM‐FPAs and QCLs can be tuned to operate at multiple discrete THz frequencies to match analyte “fingerprints.” Versatile imaging capabilities are presented, including unambiguous identification of concealed substances with intrinsic and/or human‐engineered THz characteristics as well as effective diagnosis of cancerous tissues without notable spectral signatures in the THz range, underscoring the utility of applying multispectral approaches in this compelling wavelength range for sensing/identification and medical imaging.

Abstract-Active Modulation of Coupled-Cavity Terahertz Quantum Cascade Lasers for Sideband generation

Ziping Li, Hua Li, Wenjian Wan, Kang Zhou, Tao Zhou, and Juncheng Cao

https://www.osapublishing.org/abstract.cfm?uri=ISUPTW-2018-TuK29

We experimentally demonstrate that the coupled-cavity terahertz quantum cascade lasers can be actively modulated to generate sidebands under injecting frequencies that are equal to the harmonics of the difference frequency between transverse modes.

© 2018 OSA

Abstract-Metamaterials to see in terahertz in “colors”

Zhitao Zhou,  Hua Li,  Tao Zhou,  Zhifeng Shi,  Juncheng Cao,  Hu Tao

https://ieeexplore.ieee.org/document/8346677/

We report real-time, multi-spectrally selective terahertz (THz) imaging using multi-spectral metamaterial focal plane arrays (MM-FPAs) that are fully compatible with standard micro-electro-mechanical systems (MEMS) processes. A set of frequency switchable quantum cascade lasers (QCLs) is used as THz sources for multi-spectral illumination. Both MM-FPAs and QCLs can be readily tuned to operate at multiple discrete THz frequencies to match the “fingerprints” of the analytes. Frequency selective material identification of concealed substances are successfully demonstrated, which promises a great potential of this technique in security sensing applications.

Abstract-Multicolor T‐Ray Imaging Using Multispectral Metamaterials

Zhitao Zhou, Tao Zhou, Shaoqing Zhang, Zhifeng Shi, Ying Chen, Wenjian Wan, Xinxin Li, Xinzhong Chen, Stephanie N. Gilbert Corder, Zhanglong Fu, Liang Chen, Ying Mao, Juncheng Cao, Fiorenzo G. Omenetto, Mengkun Liu, Hua Li, Tiger H. Tao,


https://onlinelibrary.wiley.com/doi/full/10.1002/advs.201700982

Recent progress in ultrafast spectroscopy and semiconductor technology is enabling unique applications in screening, detection, and diagnostics in the Terahertz (T‐ray) regime. The promise of efficaciously operation in this spectral region is tempered by the lack of devices that can spectrally analyze samples at sufficient temporal and spatial resolution. Real‐time, multispectral T‐ray (Mul‐T) imaging is reported by designing and demonstrating hyperspectral metamaterial focal plane array (MM‐FPA) interfaces allowing multiband (and individually tunable) responses without compromising on the pixel size. These MM‐FPAs are fully compatible with existing microfabrication technologies and have low noise when operating in the ambient environment. When tested with a set of frequency switchable quantum cascade lasers (QCLs) for multicolor illumination, both MM‐FPAs and QCLs can be tuned to operate at multiple discrete THz frequencies to match analyte “fingerprints.” Versatile imaging capabilities are presented, including unambiguous identification of concealed substances with intrinsic and/or human‐engineered THz characteristics as well as effective diagnosis of cancerous tissues without notable spectral signatures in the THz range, underscoring the utility of applying multispectral approaches in this compelling wavelength range for sensing/identification and medical imaging.

Abstract-Research on the Terahertz Absorption Spectra of Histidine Enantiomer (L) and its Racemic Compound (DL)

Tao Zhou, Yidong Wu, Juncheng Cao, Liangliang Zou, Jie Yuan, Zhenwei Yao, and Gongjie Xu

https://www.osapublishing.org/as/abstract.cfm?uri=as-71-2-194

Terahertz time-domain spectroscopy (THz-TDS) is used to investigate the absorption spectra of polycrystalline L- and DL-histidine in the frequency range of 10–100 cm-1. The spectra exhibit distinct differences in peak frequencies between the enantiomer (L-histidine) and racemic compound (DL-histidine). The observed spectral differences are attributed to the intermolecular interactions. With the density function theory (DFT) method, the frequencies of vibrational modes of L-histidine and DL-histidine in the THz range are calculated and well assigned according to the measured spectra. The origin of the observed vibrational modes is found to be non-localized and of a collective (phonon-like) nature, which points to the lattice and skeleton vibrations mediated by the hydrogen bond. Furthermore, we propose and demonstrate a method for determining the composition ratio of histidine mixtures based on the THz absorption spectra.

© 2016 The Author(s)

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Abstract-Beat note analysis and spectral modulation of terahertz quantum cascade lasers with radio frequency injection

Yonghao Zhu, Hua Li, Wenjian Wan, Li Gu, Tao Zhou, Stefano Barbieri, and Juncheng Cao

https://www.osapublishing.org/col/abstract.cfm?uri=col-15-1-011404

We demonstrate the electrical beat note analysis and radio frequency (RF) injection locking of a continuous wave (cw) terahertz quantum cascade laser (QCL) emitting around 3 THz (∼100 μm). In free running the beat note frequency of the QCL shows a shift of ∼180 MHz with increasing drive current. The beat note, modulation response, injection pulling, and terahertz emission spectral characteristics in the different current regimes I, II, and III are investigated. The results show that in the current regime I close to the laser threshold we obtain a narrower beat note and flat response to the RF modulation at the cavity round trip frequency. The pulling effect and spectral modulation measurements verify that in the current regime I the RF injection locking is more efficient and a robust tool to modulate the mode number and mode frequency of terahertz QCLs.

© 2016 Chinese Laser Press

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Abstract-20 Mbps wireless communication demonstration using terahertz quantum devices

Li Gu, Zhiyong Tan, Qingzhao Wu,  Chang Wang,  Juncheng Cao, 
http://www.opticsjournal.net/abstract.htm?aid=OJ150729000104w3y6B8

A wireless terahertz (THz) communication link is demonstrated, in which a THz quantum cascade laser and a THz quantum-well photo-detector (QWP) serve as the emitter and receiver, respectively. With the help of the well-matched THz QWP, the optical collection efficiency has greatly been improved. A data signal transmitted over 2.2 m with a low bit error rate (<=1 \times 10-8) and data rate as high as 20 Mbps is achieved, which are almost 1 order of magnitude higher than that previously reported.

Abstract-20 Mbps wireless communication demonstration using terahertz quantum devices

Li Gu, Zhiyong Tan, Qingzhao Wu, Chang Wang, and Juncheng Cao
https://www.osapublishing.org/col/abstract.cfm?URI=col-13-8-081402

A wireless terahertz (THz) communication link is demonstrated, in which a THz quantum cascade laser and a THz quantum-well photo-detector (QWP) serve as the emitter and receiver, respectively. With the help of the well-matched THz QWP, the optical collection efficiency has greatly been improved. A data signal transmitted over 2.2 m with a low bit error rate (≤1×10−8) and data rate as high as 20 Mbps is achieved, which are almost 1 order of magnitude higher than that previously reported.

© 2015 Chinese Laser Press

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