When using a fly’s eye lens system for illumination homogenization of a highly coherent light source, interference effects between the sub-beams result in a periodic speckle distribution of illumination intensity, which disrupts illumination uniformity. It has been shown that using a rotating optical phase-shift plate behind the fly’s eye lens can eliminate interference patterns, but it only demonstrated engineering realizations. There is still a lack of detailed theoretical analysis and technical guidance on the methods of phase modulation and statistical averaging for fly’s eye lens homogenization systems. In this paper, a simulation model of fly’s eye random phase modulation homogenization system is developed and fully researched. Each sub-beam of the fly’s eye lens is randomly phase-modulated to break the coherence condition, and the illumination intensity of multiple independent modulations is cumulated to eliminate the interference pattern. The more times the intensity is cumulated, the better the homogenization is. Meanwhile, this paper analyzes the influence of the diffraction effect on homogenization, and explores the influence of the sub-lens size and focal length on the homogenization results in the diffracting-type and imaging-type systems. For an imaging type system, it is necessary to ensure that the first fly’s eye lens is on the front focal plane of the second fly’s eye lens By optimizing the parameters of the fly’s eye lens, a gaussian beam with a non-uniformity of 117% is homogenized into a flat-topped beam with a non-uniformity of 1.2 % in a square illumination area of 100 mm<sup>2</sup> using an imaging-type system with <i>p</i>=1.8 mm and <i>f<sub>A</sub></i>=9mm. This fly’s eye lens random phase modulation homogenization system has a simple structure, low energy loss and good illumination uniformity, and can be used in systems with high coherent laser input and high resolution requirements. This technology can be used in the field of deep-ultraviolet mask defect detection.
