Terahertz semiconductor laser chaos

TL;DR

This paper demonstrates the first experimental observation of chaos in terahertz quantum cascade lasers (QCLs) without external perturbations, using a multimode THz QCL and validating results with simulations based on semiconductor Maxwell-Bloch equations.

Contribution

It introduces a novel method to generate chaos in THz QCLs intrinsically, supported by experimental evidence and theoretical modeling, advancing the understanding of chaos mechanisms in THz semiconductor lasers.

Findings

First experimental chaos in THz QCLs without external perturbations

Chaos characterized by largest Lyapunov exponent from radio frequency signals

Chaos explained by defect mediated turbulence regime in the system

Abstract

Chaos characterized by its irregularity and high sensitivity to initial conditions finds various applications in secure optical communications, random number generations, light detection and ranging systems, etc. Semiconductor lasers serve as ideal light platforms for chaos generations owing to the advantages in on-chip integration and complex nonlinear effects. In near-infrared wavelengths, semiconductor laser based chaotic light sources have been extensively studied and experimentally demonstrated. However, in the terahertz (THz) spectral range, due to the lack of effective THz light sources and high-speed detectors, chaos generation in THz semiconductor lasers, e.g., quantum cascade lasers (QCLs), is particularly challenging. Due to the fast intersubband carrier transitions, single mode THz QCLs resemble Class A lasers, where chaos can be hardly excited, even with external perturbations. In this work, we experimentally show a THz chaos source based on a sole multimode THz QCL without any external perturbations. Such a dynamical regime is characterized by the largest Lyapunov exponent associated to the temporal traces of the measured radio frequency (intermode beatnote) signal of the laser. The experimental results and chaos validation are confirmed by simulations of our model based on effective semiconductor Maxwell-Bloch Equations. To further understand the physical mechanism of the chaos generation in THz QCLs, a reduced model based on two coupled complex Ginzburg-Landau equations is derived from the full model cited above to systematically investigate the effects of the linewidth enhancement factor and group velocity dispersion on the chaotic regime. This model allows us to show that the chaos generation in the THz QCL can be ascribed to the system attaining the defect mediated turbulence regime.