A novel bipolar pulse electrochemical polishing approach for ultra-precision conformal polishing of microlens arrays

Ultra-precision polishing technology is an effective method for removing mechanical defects, such as knife lines and burrs, from the surfaces of optical microstructure components. The contact polishing method does not satisfy the requirements for conformal polishing of microstructures, as the polishing tool may exceed the size of the microstructure, and excessive mechanical force can easily damage the microstructure. Electrochemical polishing (ECP) is a non-contact polishing technique, and the electrolyte exhibits good fluidity and accessibility, thereby theoretically fulfilling the demands for ultra-precise polishing of microstructures. Initially, the angle between the polished surface and the horizontal plane was varied, and the flow speed of the viscous layer was regulated by manipulating the gravitational field. It was observed that when the microlens array (MLA) was oriented horizontally, the material was removed uniformly. The ECP for MLAs with varying sagittal heights under constant voltage conditions was investigated. Under optimal processing conditions, the average values of ΔSz‾ and ΔPV‾ before and after ECP of the MLA with a sagittal height of 3 μm were recorded as 0.28 μm and 0.12 μm, respectively. The study revealed that the introduction of bipolar pulses increased the thickness of the viscous layer, further diminishing the surface error of the MLA. The ΔSz‾ and ΔPV‾ before and after ECP of the 3 μm microlens array were further reduced to 0.063 μm and 0.0373 μm. Bipolar pulse electrochemical polishing technology effectively meets the requirements for ultra-precision polishing of microstructures and represents a promising avenue for the development of ultra-smooth conformal polishing techniques.