Dynamics of Optically Mutual-injected Terahertz Quantum Cascade Lasers

Based on the rate equation model, we study the phase locking and self-mixing properties of optically mutual-injected terahertz quantum cascade lasers. Within the phase-locked range, the laser array works steadily at the same frequency, and the electric field amplitudes are stable. Out of the phase-locked range, the instantaneous frequencies and electric field amplitudes oscillate with time. The spontaneous emission noise of mutual-injected QCLs is higher than that of free-running lasers with the same parameters. Mutual-injected QCLs for self-mixing velocity measurement are also analyzed and simulated. When the array works in the phase-locked range, simulation with a moving target shows that self-mixing signals can be observed from each laser. These results are helpful for further understanding the nonlinear dynamic behaviors of THz QCLs under optical injection and provide theoretical support for the development of self-mixing measurement techniques using QCL arrays.