Implementation of a micro ball lens on a silicon optical bench using insoluble two-phase liquid immersion technology

Abstract

This paper presents a two-phase liquid micro lens formation technology to implement a polymer micro ball lens. A UV-curable polymer is dispensed into a buffer liquid to form the ball lens. The buffer liquid provides a gravity-free condition so that the ball lens has a highly symmetric shape. The diameter of the ball lens is controlled by the volume of the dispensed polymer. This technology implements either a discrete optical component, or a ball lens integrated with a MEMS (micro electrical mechanical system) structure to form a SiOB (silicon optical bench). To demonstrate the feasibility of this study, ball lenses with diameters ranging from 200 to 600 µm and root mean square (RMS) surface roughness of about 10 nm are fabricated using a commercial UV-curable polymer. The average roundness of a 550 µm diameter ball lens observed from different angles is 3.3 ± 0.4 µm. The peak-to-valley and RMS wavefront errors of a 550 µm diameter ball lens measured by a Mach–Zehnder interferometer are 0.3744 waves (237 nm) and 0.0766 waves (48 nm), respectively. The measured back focal length is about 99 µm, and the associated effective focal length is about 351 µm. The integration of such polymer micro ball lenses with suspended micromachined Si3N4 structures to form the SiOB is also demonstrated.