**5. Conclusions**

In this paper, a new type of large-field microscopic speckle interferometry system based on Mach-Zehnder structure is proposed. By introducing doublet lens groups, the new system expands the field of view from a circular area with a diameter of 2.4 mm to a rectangular area of 6 mm × 8 mm. Additionally, our system effectively reduces the reflected light beam in the optical path, thereby reducing the reflected coherent noise. The experimental results show that our improved measurement system can achieve large-field and high-precision dynamic measurement of MEMS.

There are still some details that need to be further improved. The first limitation of our system is the need to obtain proper field of view with different sizes of measured object. To achieve this purpose, we can combine different microscope objectives and doublet lenses, which require a series of experiments to summarize. At the same time, the measurement accuracy is not very high. We can improve the measurement accuracy by optimizing the algorithm (such as phase subdivision) and adding the anti-reflection film on the surface of optical components to further reduce the coherent noise.

**Author Contributions:** Study design, data analysis, and writing—original draft preparation: C.G.; project administration, writing—review and editing: Z.G.; software: Y.N.; visualization: X.W.; supervision: J.Z.; investigation: L.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Natural Science Foundation of China, gran<sup>t</sup> number 52075034.

**Informed Consent Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
