| In this paper, the stability of optical phase conjugation mirror (PCM) with the application background of nonlinear optical phase conjugation technique which operated by acoustic-optic interaction have been discussed and its intrinsic reasons have been explained.Stimulated Brillouin scattering (SBS) and Brillouin-Enhanced Four-wave mixing (BEFWM) are two typical means to realize phase conjugation. Because of their small frequency shift and easy realization, they have been researched deep for a long time. But in practice, stability is one of the most important factors that decide the practicability of this kind of PCM included SBS-PCM, BEFWM-PCM and composite PCM.In this paper, some problems about the stability of PCM have been discussed as below. Firstly, we considered Langevin term which describes noise initiation in SBS coupling wave equations and found complete equations. In the simulation, we set initial Stokes and Langevin term as random numbers. It is demonstrated that, the randomicity of noise lead to random establishment of initial Stokes, and its different established speed and intensity make conjugation wave shapes and energy transfer efficiency different. Secondly, we established complete acoustic mathematic model, simulated temporal and spacial evolvement characteristics of the acoustic field, so as to explain the phenomenon of BEFWM. Thirdly, we did numerical simulation to find out how these three PCM respond to and transfer the temporal profile of signal wave, and compared their each character. The results indicated that, SBS-PCM can't respond to or transfer signal wave profiles well, BEFWM-PCM has good output wave shapes, and composite PCM has good conjugation fidelity to modulate signal waves and can restrain transient peak on signal waves well. Lastly, the wave shapes fidelity and reflectivity of these three PCM has been investigated through experiment. The experimental results demonstrated the trend that obtained in numerical simulation.
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