Photon-driven broadband emission and RF injection locking of THz quantum cascade laser frequency combs

TL;DR

This paper demonstrates broadband terahertz quantum cascade lasers with stable frequency combs, RF injection locking, and ultra-broadband operation exceeding 1.83 THz, suitable for integrated frequency comb applications.

Contribution

It introduces homogeneous THz QCLs with up to 950 GHz bandwidth, RF injection locking at very low power, and ultra-broadband operation in the negative differential resistance region.

Findings

Devices operate in harmonic and dense mode regimes.

RF injection locking achieved with -55 dBm power.

Ultra-broadband emission exceeds 1.83 THz.

Abstract

We present homogeneous quantum cascade lasers (QCLs) emitting around 3 THz which display bandwidths up to 950 GHz with a single stable beatnote. Devices are spontaneously operating in a harmonic comb state, and when in a dense mode regime they can be injection locked at the cavity roundtrip frequency with very small RF powers down to -55 dBm. When operated in the electrically unstable region of negative differential resistance, the device displays ultra-broadband operation exceeding 1.83 THz ($\Delta f/f=50\%$) with high phase noise, exhibiting self-sustained, periodic voltage oscillations. The low CW threshold (115 A$\cdot$ cm$^{-2}$) and broadband comb operation ($\Delta f/f=25\%$) make these sources extremely appealing for on-chip frequency comb applications.