QCL Arrays Research Articles

Widely tunable single-mode slot waveguide quantum cascade laser array.

We report designs and experimental demonstrations of a widely tunable single-mode quantum cascade laser array based on slot waveguide structures in the mid-infrared region. The laser array device realized a continuous tuning range of 71 cm-1 from 9.66 μm to 10.37 μm at 300K only using the current tuning without any external heatsink temperature adjustments, in good agreement with the design. Stable single-mode operations free of undesired mode-hops have been obtained over the whole tuning range. Another slot waveguide QCL array with a 41 cm-1 continuous tuning range around 7.3 μm has also been realized with the same design principle, demonstrating the universal applicability of the array design. The broadly continuous tuning with simple processing makes the array device a suitable candidate for mid-infrared sensing and spectroscopy application.

Stability diagrams of two optically mutual-injected quantum cascade lasers

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.

Optically mutual-injected terahertz quantum cascade lasers for self-mixing velocity measurements.

Self-mixing velocity sensor based on a mutual-injected two-element terahertz quantum cascade laser (THz QCL) array is studied theoretically. The working characteristics of mutual-injected THz QCL array with different frequency detunings and self-mixing feedback strengths, as well as their influences on the self-mixing measurements are discussed in detail. Within the phase-locked range, each laser in the array reaches a stable state rapidly and can be used as a self-mixing detector due to the mutual injection coupling. The array will no longer be phase-locked when the frequency detuning of the lasers is too large, and only the laser that receives the feedback light can still be used for self-mixing velocity measurements. It is also found that even for the case of strong feedback, the THz QCLs will not be completely unstable and the self-mixing velocity measurements could also be possible. In addition, the simulation also shows that the array could measure two independent moving targets simultaneously. These results provide the theoretical support for the future applications of THz QCL arrays in self-mixing sensors.