退相关现象制约散斑干涉测量的实现。为了增加散斑场的相关性，抑制退相关，提出一种使用三次相位板进行相位调制的方法。通过分析散斑场相关性与散斑尺寸的关系，阐述了相位调制通过扩展散斑尺寸而抑制退相关的机理，仿真验证了方法的有效性。在此基础上设计了相位调制散斑干涉测量系统，其物光光路采用4f 系统结构，可在相位面处放置三次相位板方便地进行相位调制。对比实验结果表明：经相位调制的散斑场横向相关尺寸提升约1.7 倍，纵向相关尺寸提升约2.5 倍，有效抑制了散斑干涉测量中退相关的发生，能够获得良好干涉条纹的纵向相干区域扩展约2.5 倍，提升了散斑干涉条纹局部对比度。

Decorrelation of speckle patterns restricts the implementation of speckle pattern interferometry. A method to increase the speckle correlation and to suppress the decorrelation phenomena is proposed by using a cubic phase mask for the phase modulation. The relationship between the speckle correlation and speckle sizes is analyzed, and the mechanism is elaborated that the phase modulation suppresses the decorrelation of speckle patterns. The feasibility of the method of phase modulation is verified by simulation. Then the measurement system of phase modulation speckle pattern interferometry is setup. Object lights transmit through a 4f system with a cubic phase mask on the phase surface, therefore the phase modulation can be conveniently achieved. The results of contrast experiments show that the transverse correlation size and the longitudinal correlation size of modulated speckle patterns can be increased by about 1.7 and 2.5 times, respectively. The decorrelation of speckle patterns can be effectively suppressed. Moreover, the correlation area of speckle pattern interferometry, in which well-observable fringes are obtained, can be increased by about 2.5 times, and the partial contrast of fringes in speckle pattern interferometry can be enhanced.