THz optical solitons from dispersion-compensated antenna-coupled planarized ring quantum cascade lasers

TL;DR

This paper demonstrates the generation of THz optical solitons in dispersion-compensated ring quantum cascade lasers, enabling on-chip ultrashort pulse generation and advancing THz photonics research.

Contribution

It introduces defect-less THz ring QCLs with anomalous dispersion and dispersion compensation, leading to the observation of dissipative Kerr solitons in the THz range.

Findings

Observation of sech$^2$-shaped comb spectra in free-running operation

Detection of self-starting 12 ps-long pulses in emission

Good agreement between experiments and numerical simulations

Abstract

Quantum Cascade Lasers (QCL) constitute an intriguing opportunity for the production of on-chip optical Dissipative Kerr Solitons (DKS): self-organized optical waves which can travel while preserving their shape thanks to the interplay between Kerr effect and dispersion. Originally demonstrated in passive microresonators, DKS were recently observed in mid-IR ring QCL paving the way for their achievement even at longer wavelengths. To this end we realized defect-less THz ring QCLs featuring anomalous dispersion leveraging on a technological platform based on waveguide planarization. A concentric coupled-waveguide approach is implemented for dispersion compensation whilst a passive broadband bullseye antenna improves the device power extraction and far field. In these devices, comb spectra featuring sech$^2$ envelopes are presented for free-running operation. This first hint of the presence of solitons is further supported by the observation of highly hysteretic behaviour and by phase-sensitive measurements which show the presence of self-starting 12 ps-long pulses in the reconstructed time profile of the emission intensity. These observations are in very good agreement with our numeric simulations based on a Complex Ginzburg-Landau equation time-domain solver. Such devices constitute a new experimental platform for the study of soliton phenomena in the THz range, allowing as well on-chip, passive ultrashort THz pulse generation appealing for a variety of applications.