High Dynamic Range, Heterogeneous, Terahertz Quantum Cascade Lasers Featuring Thermally Tunable Frequency Comb Operation over a Broad Current Range

Year: 2019

Authors: Garrasi K., Mezzapesa F.P., Salemi L., Li L., Consolino L., Bartalini S., De Natale P., Davies A.G., Linfield E.H., Vitiello M.S.

Autors Affiliation: NEST, CNR – Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, Pisa, 56127, Italy; School of Electronic and Electrical Engineering, University of Leeds, Leeds, LS2 9JT, United Kingdom; CNR-Istituto Nazionale di Ottica and LENS (European Laboratory for Non-linear Spectroscopy), Via Carrara 1, Sesto Fiorentino (FI), 50019, Italy

Abstract: We report on the engineering of broadband quantum cascade lasers (QCLs) emitting at Terahertz (THz) frequencies, which exploit a heterogeneous active region scheme and have a current density dynamic range (Jdr) of 3.2, significantly larger than the state-of-the-art, over a 1.3 THz bandwidth. We demonstrate that the devised broadband lasers operate as THz optical frequency comb synthesizers, in continuous-wave, with a maximum optical output power of 4 mW (0.73 mW in the comb regime). Measurement of the intermode beatnote map reveals a clear dispersion-compensated frequency comb regime extending over a continuous 106 mA current range (current density dynamic range of 1.24), significantly broader than the state-of-the-art at similar geometries, with a corresponding emission bandwidth of ˜1.05 THz and a stable and narrow (4.15 kHz) beatnote detected with a signal-to-noise ratio of 34 dB. Analysis of the electrical and thermal beatnote tuning reveals a current-tuning coefficient ranging between 5 and 2.1 MHz/mA and a temperature-tuning coefficient of -4 MHz/K. The ability to tune the THz QCL combs over their full operating dynamic range, by temperature and current, paves the way for their use as a powerful spectroscopy tool that can provide broad frequency coverage combined with high precision spectral accuracy.

Journal/Review: ACS PHOTONICS

Volume: 6 (1)      Pages from: 73  to: 78

More Information: We acknowledge financial support from the EC Project 665158 (ULTRAQCL), and the ERC Project 681379 (SPRINT), the EPSRC Programme Grant EP/P021859/1 (HyperTerahertz) and the Royal Society Project IEC/NSFC/170384. E.H.L. acknowledges the support of the Royal Society and Wolfson Foundation.
KeyWords: Bandwidth; Continuous wave lasers; Quantum cascade lasers; Quantum optics; Signal to noise ratio; Terahertz waves; Tuning, Broad-band lasers; Frequency combs; Optical frequency combs; Optical output power; Quantum cascade lasers (QCLs); Tera Hertz; Terahertz frequencies; Terahertz quantum-cascade lasers, Terahertz spectroscopy
DOI: 10.1021/acsphotonics.8b01483

Citations: 37
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