<title>On-chip replication of micro-optical structures for VCSEL to fiber coupling</title>

We present an approach towards design and fabrication of optical microsystems based on UV-replication techniques using Ormocer materials. An integration of the structures on chip level is demonstrated for Vertical Surface Emitting Lasers (VCSEL). VCSEL's are of increasing interest for various fields such as telecommunications, optical sensing and optical interconnects. In terms of optical system integration, high technological requirements are imposed. UV-replication techniques using Ormocer 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. Here, we give an example for the coupling of VCSEL arrays into multimode optical fibers using two different approaches: Focusing 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 into photoresist and resist reflow techniques, respectively. Specific limitations of the corresponding fabrication method are already taken into account during element design and modeling. Results for the replicated lenses show a total fiber launch efficiency better than 70% over the laser operational range with alignment tolerances of approximately +/- 10 micrometers , which can be met by passive fiber alignment. In case of the replicated fiber alignment/guiding structures, fiber launch efficiencies better than 50% over the operation range and peak values better than 80% are reported.