Study on gas trapping during precision glass molding of microlens array in a nitrogen atmosphere

Microlens arrays will suffer from filling defects due to trapped gas when molded in a nitrogen atmosphere by precision glass molding (PGM). In this paper, a multistep molding method is proposed to avoid gas trapping and improve the accuracy of a microlens array. The defect formation mechanism of the microlens array caused by the trapped gas is investigated, and the effect of the molding pressure on the defect formation is analyzed. A numerical model of the mold-nitrogen-glass interface at high temperature is established to evaluate the defect evolution, and the minimum number of PGM steps required to greatly reduce defects caused by the trapped gas is predicted. The numerical model is validated by a multistep PGM experiment of D-K59 glass material. The results show that a three-step PGM process significantly reduced the height of the defect. The difference between the height of the microlens unit and the depth of the mold is less than 0.4%. The molded microlens array has a peak-to-valley value of 0.38 mu m and a surface roughness Ra of 3.5 nm. This work is instructive for the fabrication of high-precision glass microlens arrays.