On-chip replication of micro-optical structures for VCSEL to fiber coupling

We present the design and fabrication of optical microsystems based on UV-replication techniques using Ormocer (R)* materials. An integration of the optical and mechanical structures on chip level is demonstrated for Vertical Surface Emitting Lasers (VCSEL). VCSEL's are of increasing interest for various fields such as telecommunication, optical sensing and optical interconnects. UV-replication techniques using Ormocer (R) materials offer a cost-effective way of integrating micro-optical elements directly on the chip with reduced assembly effort. Structures up to several hundred microns thickness and alignment tolerances in the order of few microns can be produced. The method is suitable for the fabrication of single elements, arrays and is extendable to wafer-scale processing. The presented example is a system for the coupling of VCSEL arrays into multimode optical fibers. Two different approaches are followed: Focussing of the VCSEL output into the fiber using replicated microlenses and fiber butt-coupling of the VCSEL lasers with help of replicated fiber alignment/guiding structures. Origination of the structure elements is accomplished by direct laser writing in photoresist and resist reflow techniques, respectively. Specific limitations of the corresponding fabrication method are already taken into account during element design and modelling. Results for the replicated lenses show a total fiber launch efficiency better than 70% over the laser operational range. This performance can be met by passive fiber alignment with tolerances of approximately +/- 10 mum. In case of the replicated fiber alignment / guiding structures, fiber launch efficiencies better than 50% over the operation range and maximum values better than 80% are reported.