Abstract
The dynamic properties and stability of optically mutual-injected arrays composed of terahertz quantum cascade lasers (THz QCLs) were investigated and compared with those of diode laser (DL) arrays. The influences of the coupling strength and frequency detuning on the working states of the arrays were analyzed using numerical simulations of the time evolutions of the electric fields and their corresponding Fourier-transform spectra. It was found that when the frequency detuning between individual lasers was zero, the QCL arrays could always maintain phase-locked operation. In contrast, the DLs were only able to function in a stable state with weak coupling strengths. With increasing coupling strength, periodic, quasi-periodic, multi-periodic, and aperiodic oscillations appeared. When the frequency detuning of the array lasers was nonzero, the QCL array could not be phase-locked at low coupling strengths, and it only entered the phase-locked region if the coupling strength was increased. However, the DL array could only work stably at low coupling strengths and quickly entered the aperiodic oscillation region as the coupling strength was increased. When we fixed the coupling strength and changed the frequency detuning, with large frequency detunings, both the QCL and DL arrays exhibited periodic oscillations. However, the QCLs were phase-locked at low frequency detunings, while the DLs exhibited periodic and multi-periodic oscillations across a broader frequency range. The results indicate that QCL arrays are more stable than DL arrays across a wide range of coupling strengths and frequency detuning parameters.
Highlights
Terahertz (THz) technology has significant applications in the fields of security imaging,1 non-destructive inspection,2 biomedical sciences,3 gas monitoring,4 communication technology,5 and materials analysis.6 Quantum cascade lasers (QCLs) are important light sources in the mid-infrared and THz bands.7,8 After the development of the first THz QCL in 2002, with the continuous improvement of structural design, material quality, and manufacturing technology, the performances of THz QCLs have been greatly improved.9 Terahertz QCLs have become compact light sources with high-power,10–12 high operational temperatures,13,14 high spectral purity,15 and wide tunability.16,17 Currently, THz QCLs are ideal laser sources in the fields of gas sensing, medical diagnostics, and security imaging.Delay-coupled systems in fields, including quasi-optical oscillator arrays,18 chemical oscillations,19,20 biological clocks,21 and neural networks,22 have attracted much attention, both experimentally and theoretically
Studying the dynamic behavior of THz QCL arrays is of great significance for developing devices using this technology
It is found that the electric field amplitude of a QCL with high frequency detuning shows a single-periodic oscillation of the detuning frequency
Summary
Terahertz (THz) technology has significant applications in the fields of security imaging, non-destructive inspection, biomedical sciences, gas monitoring, communication technology, and materials analysis. Quantum cascade lasers (QCLs) are important light sources in the mid-infrared and THz bands. After the development of the first THz QCL in 2002, with the continuous improvement of structural design, material quality, and manufacturing technology, the performances of THz QCLs have been greatly improved. Terahertz QCLs have become compact light sources with high-power, high operational temperatures, high spectral purity, and wide tunability. Currently, THz QCLs are ideal laser sources in the fields of gas sensing, medical diagnostics, and security imaging. As typical delay-coupled systems with rich dynamic behaviors, phase-locked laser arrays are an important means for producing high-power, low-divergence output beams. Studying the dynamic behavior of THz QCL arrays is of great significance for developing devices using this technology. A basic experimental method for measuring the nonlinear stability of a specific laser is analyzing its dynamic behavior under external optical injection. The dynamic behaviors of typical optical injection laser systems, including master–slave injection lasers, mutual-injected phase-locked arrays, and laser self-mixing sensing systems, have been intensively studied.. Studying the behavior of optically mutual-injected THz QCLs can help deepen the understanding of the dynamics of QCL arrays. There have as yet been few comprehensive studies on the dynamic behavior of mutual-injected THz QCL arrays or comparisons of THz QCL arrays with semiconductor laser arrays. It is found that the electric field amplitude of a QCL with high frequency detuning shows a single-periodic oscillation of the detuning frequency
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