Combination of binary and analog lithography to fabricate efficient planar-integrated free-space optical interconnects

With its inherent parallelism free-space optics is well-suited for board- and chip-level communication provided that modern microsystems design and fabrication technologies such as planar-integrated free-space optics (PIFSO) are applied. To reduce the substantial diffraction and scattering losses of previous PIFSO modules with staircase-like DOEs based on (multi-mask) binary lithography and reactive ion etching we switch to systems with continuous-profile DOEs fabricated by grey-scale lithography. Theoretical investigations show that a combination of binary and analog technology provides the optimal balance between energetic efficiency and functional reliability. For experimental demonstration an MT-compatible fiber-to-PIFSO-to-fiber interconnect module was designed and fabricated. HEBS glass masks were used to generate a preform of the continuous-profile DOEs in a 40 µm thick layer of photoresist which was then replicated into a thin layer of plastic material that is laminated on the fused silica PIFSO substrate. The experimental performance of this module will be discussed.