Self-mixing interference (SMI) in terahertz quantum cascade lasers (THz QCLs) is one of the significant approaches for coherent THz imaging and sensing techniques. Here, the output characteristics of SMI in distributed feedback (DFB) THz QCLs from the index-to the gain-coupling regimes are studied using the coupled wave theory and the multi-mode rate equation method. A mode hopping phenomenon is found to occur when the DFB coupling factor changes from index-coupling to gain-coupling, and the characteristics of the self-mixing signals of DFB-QCLs change greatly with this mode hopping. With the modulus of the coupling factor fixed and its argument varied from 0 to π/2, an extreme point of the self-mixing frequency and power signals of DFB-QCLs is found at π/9 due to the mode hopping. For index-coupling dominated DFB-QCLs, both the varying ranges of the self-mixing frequency signals and amplitudes of power signals increase with increasing DFB coupling factor argument. For gain-coupling dominated DFB-QCLs, with increasing argument value, the amplitude of the self-mixing power signal increases, but the varying range of the self-mixing frequency signal decreases. With the argument of the coupling factor fixed, we also found that the varying ranges of the self-mixing frequency signals decrease with increasing modulus for both index-coupling dominated and gain-coupling dominated DFB-QCLs. For index-coupling dominated DFB-QCLs, the amplitudes of the self-mixing power signals decrease with increasing modulus; however, the amplitudes of the self-mixing power signals of gain-coupling dominated DFB-QCLs increase. With the argument of the coupling factor fixed, for index-coupling dominated DFB-QCLs, we found that the varying ranges of the self-mixing frequency signals and amplitudes of power signals decrease with the increasing modulus. For gain-coupling dominated DFB-QCLs, with the coupling factor modulus increasing, the varying ranges of the self-mixing frequency signals decrease, however, the amplitudes of the self-mixing power signals increase. These results may help with the application of DFB-QCLs to self-mixing interferometers.

太赫兹量子级联激光器 (THz QCL) 中的自混合干涉 (SMI) 是相干太赫兹成像和传感技术的重要方法之一。在这里，使用耦合波理论和多模速率方程方法研究了从指数到增益耦合机制的分布式反馈 (DFB) THz QCL 中 SMI 的输出特性。发现当DFB耦合因子从指数耦合变为增益耦合时会出现跳模现象，DFB-QCL的自混信号特性随着这种跳模发生了很大的变化。在耦合因子的模数固定且其参数从 0 到 π/2 变化的情况下，由于模式跳跃，DFB-QCL 的自混频和功率信号的极值点位于 π/9。对于索引耦合主导的 DFB-QCL，自混频信号的变化范围和功率信号的幅度都随着DFB耦合因子参数的增加而增加。对于以增益耦合为主的DFB-QCL，随着参数值的增加，自混功率信号的幅度增加，但自混频率信号的变化范围减小。在耦合系数固定的情况下，我们还发现自混频信号的变化范围随着指数耦合主导和增益耦合主导的 DFB-QCL 模量的增加而减小。对于指数耦合主导的 DFB-QCL，自混合功率信号的幅度随着模量的增加而减小；然而，增益耦合主导的 DFB-QCL 的自混合功率信号的幅度增加。在耦合因子的参数固定的情况下，对于指数耦合主导的DFB-QCLs，我们发现自混频信号的变化范围和功率信号的幅度随着模量的增加而减小。对于以增益耦合为主的DFB-QCLs，随着耦合系数模量的增加，自混频信号的变化范围减小，而自混功率信号的幅度增加。这些结果可能有助于将 DFB-QCL 应用于自混合干涉仪。自混合功率信号的幅度增加。这些结果可能有助于将 DFB-QCL 应用于自混合干涉仪。自混合功率信号的幅度增加。这些结果可能有助于将 DFB-QCL 应用于自混合干涉仪。