Microfabrication of microlens array by focused ion beam technology

Microfabrication process of plano-convex microlens arrays with continuous relief for refractive and diffractive usage by focused ion beam (FIB) technology is introduced in detail in this paper. Two functions of FIB – milling and deposition of SiO2 are used for the fabrication. A 9×9 micro-diffractive optical elements (DOEs) array with singlet f-number of 2 and NA value of 0.25, and a 9×9 refractive microlens array with singlet diameter of 60 μm, NA value of 0.1, and f-number of 5 are designed and fabricated by the milling method. In addition, the other method of FIB induced SiO2 deposition for microlens is introduced. The lens profile and focusing characteristics are measured by WYKO NT2000 interferometer and BeamScope-5 PTM beam scanner respectively. Focused spot size is about 6.7 μm (at site of 50%) and 5.1 μm (at site of 1/e2: 13.5%) for diffractive lens and refractive lens array respectively. The RMS thickness error within a diameter of 27 μm DOEs and 60 μm of refractive lens (by the way of milling) is 11 nm, and 15 nm respectively. Wave aberration for both of them are 1.7 wave and 1.5 wave respectively.