Coexisting frequency combs spaced by an octave in a monolithic quantum cascade laser
Abstract
Quantum cascade lasers are proving to be instrumental in the development of compact frequency comb sources at mid-infrared and terahertz frequencies. Here we demonstrate a heterogeneous terahertz quantum cascade laser with two active regions spaced exactly by one octave. Both active regions are based on a four-quantum well laser design and they emit a combined 3~mW peak power at 15~K in pulsed mode. The two central frequencies are 2.3~THz (bandwidth 300~GHz) and 4.6~THz (bandwidth 270~GHz). The structure is engineered in a way that allows simultaneous operation of the two active regions in the comb regime, serving as a double comb source as well as a test bench structure for all waveguide internal self-referencing techniques. Narrow RF beatnotes ( 15~kHz) are recorded showing the simultaneous operation of the two combs, whose free-running coherence properties are investigated by means of beatnote spectroscopy performed both with an external detector and via self-mixing. Comb operation in a highly dispersive region (4.6~THz) relying only on gain bandwidth engineering shows the potential for broad spectral coverage with compact comb sources.
Cite
@article{arxiv.1810.10203,
title = {Coexisting frequency combs spaced by an octave in a monolithic quantum cascade laser},
author = {Andres Forrer and Markus Roesch and Matthew Singleton and Mattias Beck and Jerome Faist and Giacomo Scalari},
journal= {arXiv preprint arXiv:1810.10203},
year = {2018}
}