Hyperboloid sol gel microlens array fabricated by soft-lithography for optical coupling

摘要

It is known that the best way to correct spherical aberrations is the use of aspheric microlenses in optical systems, where a single aspheric microlens can be employed to replace a compound of spherical microlenses in a compact design. However the fabrication of aspheric microlenses is often complex because expensive high-energy beam-sensitive (HEBS) gray scale mask is needed in the fabrication process. In this paper, we reported a cost-effective fabrication method, with a combination of the sample-inverted reflow technique and the soft lithography replication method, to fabricate hyperboloid refractive microlens arrays (MLAs) in the inorganic-organic hybrid SiO2-ZrO2 sol-gel material. The fabrication procedures involved two basic steps. Firstly, a master of hyperboloid MLA was made in photoresist by the sample-inverted reflow technique. Secondly, a negative mold of the master was built by casting polydimethylsiloxane (PDMS) to a silicone elastomer against the master, and then the profile was impressed onto the sol-gel glass. As a result, the fabricated sol-gel MLAs have been obtained with excellent smooth profiles, having negligible discrepancies from the profiles of the ideal hyperboloid MLAs. The root-mean-square roughness values (Rq) of the surface of MLA were measured as 1.2 nm in the central areas and 2.1 nm in the outskirts of the lens. In an application of coupling a laser diode (LD) to a single-mode fibre (SMF), we proposed a two-MLA coupling scheme where two revolved-hyperboloid MLAs were back to back introduced between the LD and the SMF. In this configuration, the coupling efficiency has achieved 83.4% (-0.79 dB).