Abstract-Basic phase-locking, noise, and modulation properties of optically mutual-injected terahertz quantum cascade lasers

Yuanyuan Li, Ning Yang, Yan Xie, Weidong Chu, Wei Zhang, Suqing Duan, and Jian Wang

Fig. 2 Time evolution of |EA|, |EB | (first column), the corresponding power spectral density (second column), and instantaneous frequency (third column) with different coupling strength κ and detuning frequency ΔΩ/2π. The coupling strength in the first three rows are set as κ = 9.87 × 10−3, which is the case of moderate coupling. (a)–(c) within the phase-locking regime, ΔΩ/2π = 0.5GHz, (d)–(f) out of the pahse-locking regime, ΔΩ/2π = 5GHz, (g)–(i) out of the pahse-locking regime, ΔΩ/2π = 0.55GHz. The fourth row is the case of strong coupling with κ = 0.247. (j)–(l) out of the pahse-locking regime, ΔΩ/2π = 0.2GHz. The effective injection current is 1.5Ith in all simulations.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-3-3146

The phase-locking, noise, and modulation properties of two face-to-face optically mutual-injected terahertz (THz) quantum cascade lasers (QCLs) are analyzed theoretically. In the phase-locking range, the two THz QCLs are in stationary states working at the same frequency. Outside the phase-locking range, the amplitude and the instantaneous frequency of the optical field oscillate with time, and the power spectrum shows a series of discrete peaks. For strong mutual injection, the optical field of the THz QCL array also exhibits oscillatory behavior. Coherent collapse or chaotic behavior is not observed within the range of the parameters used in this simulation. The spontaneous emission noise of phase-locked THz QCLs is higher than that of THz QCLs at free-running operation, and mutual injection may introduce additional modulation peaks in the noise spectrum. The modulation response of the mutual-injected THz QCLs to an individual modulation is investigated. It is found that the modulation bandwidth and the phase difference are significantly dependent on the modulation parameters. These results are helpful for further understanding the nonlinear dynamic behaviors of THz QCLs under optical injection and provide theoretical support for the development of THz QCL phase-locked arrays.

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

Making Terahertz Lasers More Powerful

By Catherine Meyers

Scanning electron microscope image of the terahertz quantum cascade laser.
CREDIT: Wang, et al/AIP Advances

Researchers in China nearly double the continuous output power of a type of terahertz laser, opening up applications in spectroscopy, imaging, remote sensing and more

https://publishing.aip.org/publishing/journal-highlights/making-terahertz-lasers-more-powerful?TRACK=aipp-china

WASHINGTON, D.C., July 26, 2016 -- Researchers have nearly doubled the continuous output power of a type of laser, called a terahertz quantum cascade laser, with potential applications in medical imaging, airport security and more. Increasing the continuous output power of these lasers is an important step toward increasing the range of practical applications. The researchers report their results in the journal AIP Advances, from AIP Publishing.

Terahertz radiation sits between microwaves and infrared light on the electromagnetic spectrum. It is relatively low-energy and can penetrate materials such as clothing, wood, plastic and ceramics. The unique qualitites of terahertz radiation make it an attractive candidiate for imaging, but the ability to produce and control terahertz waves has lagged behind technology for radio, microwave and visible light.

Recently, scientists have made rapid progress on a technology to produce terahertz light called a quantum cascade laser or QCL. Quantum cascade lasers are made from thin layers of material. The thin layers give the laser the valuble property of tunability, meaning the laser can be designed to emit at a chosen wavelength. The output power of terahertz QCLs is also relatively high compared to other terahertz sources, said Xuemin Wang, a researcher in the China Academy of Engineering Physics and first author on the new paper.

Wang and his colleagues' work focuses on even further increasing the output power of terahertz quantum cascade lasers, especially in the mode in which the laser output power is continuous. "In engineering, biomechanics and medical science, the applications require continuous wave mode," Wang said.

By optimizing the material growth and manufacturing process for terahertz QCLs, Wang and his team made a laser with a record output power of up to 230 milliwatts in continuous wave mode. The previous record was 138 milliwatts.

Wang said the new 230 milliwatt laser could be used in air, a challenge for lower-powered lasers since particles in the air can scatter or absorb the laser light before it reaches its target.

The increase demonstrates that the team's method of precisely controlling the growth of the laser's layers can increase output power, Wang said, and he is hopeful that future improvements could bring the continuous power above 1 watt. The 1 watt level has been reached in terahertz QCLs in pulsed wave mode.

Wang said he thinks scientists and engineers could use the new laser as a flexible source of terahertz radiation for spectroscopy, medicial imaging, remote sensing and other applications.

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Article title: 

High-power terahertz quantum cascade lasers with ~0.23 W in continuous wave mode

Authors: 

Xuemin Wang, Changle Shen, Tao Jiang, Zhiqiang Zhan, Qinghua Deng, Weihua Li, Weidong Wu, Ning Yang, Weidong Chu and Suqing Duan

Author affiliations: 

China Academy of Engineering Physics in Sichuan, China and the Institute of Applied Physics and Computational Mathematics in Beijing, China

Abstract-Mid-infrared-pumped quantum cascade structure for high-sensitive terahertz detection

Mid-infrared-pumped quantum cascade structure for high-sensitive terahertz detectionh

Yan Xie, Ning Yang, Suqing Duan, and Weidong Chu

 

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-14-15180

Based on multiple quantum wells, we design a pumping-detection quantum cascade structure for the detection of terahertz (THz) radiation. In the structure, carriers are first pumped by a mid-infrared (MIR) laser to an excited state, to get enough energy space for the following fast longitudinal optical (LO) phonon extraction. Within the LO-phonon extraction stair, an absorption well is designed for THz detection. Due to the establishment of LO-phonon stair extractor, carriers transport between quantum wells in picosecond range and a high responsivity for THz absorption can be obtained. We also find that doping in both MIR active well and extractor region is significant for high-speed response of the THz detection. Our design is expected to extend the high-sensitive detection of a quantum cascade photodetector from middle wave of MIR to THz region.

© 2016 Optical Society of America

Full Article  |  PDF Article

Abstract-Mid-infrared-pumped quantum cascade structure for high-sensitive terahertz detection

YAN XIE, 1 NING YANG, 1,2 SUQING DUAN, 1 AND WEIDONG CHU1,3 1

Institute of Applied Physics and Computational Mathematics, P.O. Box 8009(28), 100088, Beijing, China

 2yang_ning@iapcm.ac.cn 3chu_weidong@iapcm.ac.cn

https://www.osapublishing.org/view_article.cfm?gotourl=https%3A%2F%2Fwww%2Eosapublishing%2Eorg%2FDirectPDFAccess%2FC6CF91A7-EBF1-4E43-D0A468CD18F17D66_345173%2Foe-24-14-15180%2Epdf%3Fda%3D1%26id%3D345173%26seq%3D0%26mobile%3Dno&org=

Abstract: Based on multiple quantum wells, we design a pumping-detection quantum cascade structure for the detection of terahertz (THz) radiation. In the structure, carriers are first pumped by a mid-infrared (MIR) laser to an excited state, to get enough energy space for the following fast longitudinal optical (LO) phonon extraction. Within the LO-phonon extraction stair, an absorption well is designed for THz detection. Due to the establishment of LO-phonon stair extractor, carriers transport between quantum wells in picosecond range and a high responsivity for THz absorption can be obtained. We also find that doping in both MIR active well and extractor region is significant for high-speed response of the THz detection. Our design is expected to extend the high-sensitive detection of a quantum cascade photodetector from middle wave of MIR to THz region.

© 2016 Optical Society of America

 OCIS codes: (040.4200)

 Multiple quantum well; (040.5160) Photodetectors; (040.2235) Far infrared or terahertz.

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