基于三能级速率方程，研究了独立运行、主从注入和相互注入太赫兹量子级联激光器(THz-QCLs)的相对强度噪声和调制特性。在自由运行情况下， THz-QCL的自发辐射噪声在低频时表现出白噪声特性。与传统的半导体激光器不同，在低频区没有对应于弛豫振荡的共振峰。主从注入可以有效降低 THz-QCLs噪声20 dB，提高 THz-QCLs低噪声工作的效率。对于互注入 THz-QCLs，即使在锁相区，噪声也明显高于自由运行情况。通过应用注入锁定方案，与直接调制方案相比，可以大大增加调制带宽。

Based on the three-level rate equations, the relative intensity noise and modulation characteristics of free-running operation, master-slave injection and optically mutual-injected Terahertz Quantum Cascade Lasers(THz-QCLs) are studied theoretically. In the case of free-running operation, the spontaneous emission noise of THz-QCLs exhibits white noise characteristics at low frequencies. Unlike conventional semiconductor lasers, there is no resonance peak corresponding to relaxation oscillation in the low frequency region. Master-slave injection can effectively reduce the noise of THz-QCLs for nearly 20 dB. It is an effective and practical technology to achieve low noise of THz-QCLs. For optically mutual-injected THz-QCLs，even in the phase -locked region, the noise is significantly higher than that in the case of free operation. In addition, compared with direct modulation scheme, the modulation bandwidth can be greatly increased by using optical injection phase-locking scheme.