Investigation of diffractive-refractive microlens array fabricated by focused ion beam technology

A microfabrication process for piano-convex microlens arrays with continuou s relief for refractive and diffractive usage by focused ion beam (FIB) tec hnology is introduced in detail. Two FIB techniques--milling and deposition of SiO2--are used for the fabrication. A 9x9 array of micro diffractive op tical elements (DOEs) with a singlet f number of 2 and a numerical aperture (NA) of 0.25, and a 9x9 refractive microlens array with a singlet diameter of 60 mum, NA of 0.1, and f number of 5 were designed and fabricated by th e milling method. In addition, the method of FIB-induced SiO2 deposition fo r microlenses is utilized. The lens profile and focusing characteristics we re measured with a WYKO NT2000 interferometer and a BeamScope-5PTM beam sca nner, respectively. The focused spot size is about 6.7 mum (full width at h alf maximum) and 5.1 mum (at 1/e(2)) for the diffractive lens and the refra ctive lens array, respectively. The rms thickness errors within a diameter of 27 mum for the DOEs and within 60 mum for the refractive lenses (produce d by milling) are 11 nm, and 15 nm, respectively. The wave aberrations are 1.7 and 1.5 waves, respectively. (C) 2001 Society of Photo-Optical instrume ntation Engineers.