Recent developments in terahertz quantum cascade lasers for practical applications

Abstract

Terahertz (THz) quantum cascade laser (QCL) is an electrically pumped unipolar photonic device in which light emission takes place due to electronic transitions between subbands formed by multiple strongly coupled quantum wells. THz QCL is arguably the most promising solid-state source to realize various THz applications, such as high-resolution spectroscopy, real-time imaging, chemical and biological sensing, and high-speed wireless communication. To date, THz QCLs have covered emitting frequency from 1.2 to 5.4 THz when operating without the assistance of an external magnetic field. The highest output power is in hundreds milliwatt and watt levels continuous-mode and pulsed-mode operations, respectively. THz QCL-based local oscillators have been implemented in astronomy for the identification of atoms and ions. However, there are also limitations, including under room-temperature operation, large divergent beam, narrow single-mode frequency tuning range, incomplete polarization control, and narrow-range frequency comb operation that hinder the widespread applications of THz QCLs. Continuous efforts have been made to improve those THz QCL properties in order to satisfy the requirements of different THz applications. This report will review the key output characteristic developments of THz QCLs in the past few years, which aim to speed up THz QCLs toward practical applications.

Field-dependent THz transport nonlinearities in semiconductor nano structures

“…Tunable and intense THz sources e.g. from laser difference frequency mixing, 70,71 plasms, 72 on chip nonlinear mixing 73 or quantum cascade lasers 74 are interesting for implementation into future 6G communication systems with carrier frequencies operating in frequency ranges of ∼300 GHz to 10 THz. 75,76 Nonlinear frequency conversion and gain in semiconductor nanostructures, like demonstrated in this paper may provide the needed functionalities for signal mixing and amplification.…”

Performance of a High-Speed Pyroelectric Receiver as Cryogen-Free Detector for Terahertz Absorption Spectroscopy Measurements

“…The first QCL with an emission frequency in the THz range was reported in 2002 by Köhler et al [4]. THz QCLs cover, at present, the emission frequency range of about 1 THz to 5.5 THz [5][6][7]. In this spectral region, QCLs are the only available powerful cw radiation sources, with optical output powers of up to a few mW and extremely narrow linewidths of a few MHz down to kHz.…”