Abstract-Photonic Engineering Technology for the Development of Terahertz Quantum Cascade Lasers

Yongquan Zeng, Bo Qiang, Qi Jie Wang,

https://onlinelibrary.wiley.com/doi/10.1002/adom.201900573

A terahertz (THz) quantum cascade laser (QCL) is an electrically pumped semiconductor laser based on the inter‐subband electron transitions in a multiple‐quantum‐well heterostructure. Comparing with many other THz wave generation methods, THz QCL is mostly developed with compact fingerprint, high power, and high efficiency in the demanding frequency range of 0.8–5.4 THz with the aid of advanced electronic engineering technology of the active materials. This triggers various important applications including nonlinear optics, astronomy, imaging, sensing, and spectroscopy. However, the applications of THz QCL require good output characteristics in terms of the emission spectrum, beam quality, power efficiency, and polarization control, which are beyond the reach of the electronic engineering techniques. The main focus here is placed on photonic engineering of the THz QCLs with attention to the significant improvement of THz QCL output characteristics. Various photonic solutions to manipulate the laser output are thoroughly reviewed. Some innovative photonic designs with impressive achievements are highlighted. Nonconventional cavities with exotic physics and special functionalities are also discussed in the end, which may be exploited for potential applications in the future.

Abstract-Optomechanical response with nanometer resolution in the self-mixing signal of a terahertz quantum cascade laser

Andrea Ottomaniello, James Keeley, Pierluigi Rubino, Lianhe Li, Marco Cecchini, Edmund H. Linfield, A. Giles Davies, Paul Dean, Alessandro Pitanti, Alessandro Tredicucci,

(a) Sketch of the two configurations of the SM apparatus. (b) Calculated Δ𝑁$\mathrm{\Delta }N$ (blue curve), and measured 𝑉SM$V_{\mathrm{S}\mathrm{M}}$ (red points) as a function of Δ𝐿$\mathrm{\Delta }L$ using configuration 1

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-44-23-5663

Owing to their intrinsic stability against optical feedback (OF), quantum cascade lasers (QCLs) represent a uniquely versatile source to further improve self-mixing interferometry at mid-infrared and terahertz (THz) frequencies. Here, we show the feasibility of detecting with nanometer precision, the deeply subwavelength (<𝜆/6000$<\lambda /6000$) mechanical vibrations of a suspended Si3N4${\mathrm{S}\mathrm{i}}_3{\mathrm{N}}_4$ membrane used as the external element of a THz QCL feedback interferometer. Besides representing an extension of the applicability of vibrometric characterization at THz frequencies, our system can be exploited for the realization of optomechanical applications, such as dynamical switching between different OF regimes and a still-lacking THz master-slave configuration.

Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Abstract-Sub-terahertz and terahertz generation in long-wavelength quantum cascade lasers

Kazuue Fujita, Shohei Hayashi, Akio Ito, Masahiro Hitaka, Tatsuo Dougakiuchi

https://www.degruyter.com/view/j/nanoph.ahead-of-print/nanoph-2019-0238/nanoph-2019-0238.xml

Terahertz quantum cascade laser sources with intra-cavity non-linear frequency mixing are the first room-temperature electrically pumped monolithic semiconductor sources that operate in the 1.2–5.9 THz spectral range. However, high performance in low-frequency range is difficult because converted terahertz waves suffer from significantly high absorption in waveguides. Here, we report a sub-terahertz electrically pumped monolithic semiconductor laser. This sub-terahertz source is based on a high-performance, long-wavelength (λ ≈ 13.7 μm) quantum cascade laser in which high-efficiency terahertz generation occurs. The device produces peak output power of 11 μW within the 615–788 GHz frequency range at room temperature. Additionally, a source emitting at 1.5 THz provides peak output power of 287 μW at 110 K. The generated terahertz radiation of <2 THz is mostly attributable to the optical rectification process in long-wavelength infrared quantum cascade lasers.

Abstract-Gain measurement of terahertz quantum cascade laser via a master-oscillator power-amplifier configuration

Chenren Yu, Huan Zhu, Fangfang, Wang, Gaolei Chang, Haiqing Zhu, Jianxin Chen, Gangyi Xu, Li He,



https://www.sciencedirect.com/science/article/pii/S0022024819301551

We report a method to measure the net loss and gain of a terahertz quantum cascade laser (THz-QCL), which is based on a master-oscillator power-amplifier (MOPA) configuration. In the measurement, the master-oscillator (MO) section and power-amplifier (PA) section are separately biased. With the fixed seed power from the MO section, the output power of the device is measured at various bias voltage applied on the PA section, from which the net loss and gain is deduced as a function of bias. We demonstrate that gain clamping and gain saturation can be avoided in our measurement, which allow a complete evolution of the loss and gain characteristics. For a THz-QCL with the bound-to-continuum active region and the metal-metal waveguide, the measured maximal net gain is about 13.0-16.5 cm-1 at 2.58 THz at a 20 K, which is in qualitative agreement with the theoretical analysis.