Photon-Driven Broadband Emission and Frequency Comb RF Injection Locking in THz Quantum Cascade Lasers
Andres Forrer, Martin Franckié, David Stark, Tudor Olariu, Mattias Beck, Jérôme Faist, Giacomo Scalari
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 ultrabroadband operation exceeding 1.83 THz (Δf/f = 50%) with high phase noise, exhibiting self-sustained, periodic voltage oscillations. The low CW threshold (115 A cm–2) and broadband comb operation (Δf/f = 25%) make these sources extremely appealing for on-chip frequency comb applications.