Homogeneous quantum cascade lasers operating as terahertz frequency combs over their entire operational regime

Alessandra Di Gaspare,David D Ritchie,Leonardo Viti,Miriam S Vitiello,Harvey E Beere

doi:10.1515/nanoph-2020-0378

Alessandra Di Gaspare, David D Ritchie + Show 3 more

Open Access

https://doi.org/10.1515/nanoph-2020-0378

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Journal: Nanophotonics	Publication Date: Sep 28, 2020
Citations: 13	License type: CC BY 4.0

Affiliation: Scuola Normale Superiore, University of Cambridge

Abstract

AbstractWe report a homogeneous quantum cascade laser (QCL) emitting at terahertz (THz) frequencies, with a total spectral emission of about 0.6 THz, centered around 3.3 THz, a current density dynamic range Jdr = 1.53, and a continuous wave output power of 7 mW. The analysis of the intermode beatnote unveils that the devised laser operates as an optical frequency comb (FC) synthesizer over the whole laser operational regime, with up to 36 optically active laser modes delivering ∼200 µW of optical power per optical mode, a power level unreached so far in any THz QCL FC. A stable and narrow single beatnote, reaching a minimum linewidth of about 500 Hz, is observed over a current density range of 240 A/cm2 and even across the negative differential resistance region. We further prove that the QCL FC can be injection locked with moderate radio frequency power at the intermode beatnote frequency, covering a locking range of 1.2 MHz. The demonstration of stable FC operation, in a QCL, over the full current density dynamic range, and without any external dispersion compensation mechanism, makes our proposed homogenous THz QCL an ideal tool for metrological applications requiring mode-hop electrical tunability and a tight control of the frequency and phase jitter.

Highlights

We report a homogeneous quantum cascade laser (QCL) emitting at terahertz (THz) frequencies, with a total spectral emission of about 0.6 THz, centered around 3.3 THz, a current density dynamic range Jdr = 1.53, and a continuous wave output power of 7 mW
We further prove that the QCL frequency comb (FC) can be injection locked with moderate radio frequency power at the intermode beatnote frequency, covering a locking range of 1.2 MHz
We demonstrate a THz QCL based on a homogenous active region design with an emission bandwidth of 600 GHz, a CW optical output power of 7 mW, operating as a FC synthesizer over the entire laser operation range, including the negative differential resistance (NDR) regime

Summary

Introduction

The terahertz (THz) region of the electromagnetic spectrum, loosely defined in the frequency range between 0.1 and 10 THz [1], attracted a renewed attention, in recent years, for targeting far-infrared applications requiring a tight control of the frequency and phase jitter of the laser modes, such as high-resolution and high-sensitivity spectroscopy [2, 3], telecommunications [4, 5], and quantum metrology [6], amongst many others. relevant models for gigahertz–terahertz generation exploiting nonlinearity in semiconductor superlattices have been recently proposed [7], electrically pumped quantum cascade lasers (QCLs) are the most efficient on-chip sources of optical frequency comb (FC) synthesizers at THz frequencies [8–11], thanks to the wide frequency coverage [10, 12] and the inherently high optical power levels [13, 14], which allow continuous-wave (CW) emitting powers per comb tooth in the 3 μW [12] to 60 μW [8] range and the high spectral purity (intrinsic linewidths of ∼100 Hz) [15]. Abstract: We report a homogeneous quantum cascade laser (QCL) emitting at terahertz (THz) frequencies, with a total spectral emission of about 0.6 THz, centered around 3.3 THz, a current density dynamic range Jdr = 1.53, and a continuous wave output power of 7 mW.

Results

Conclusion