Deep lithography with protons to prototype pluggable micro-optical out-of-plane coupling structures for multimode waveguides

We present a pluggable micro-optical component fabricated with Deep Lithography with Protons, incorporating a micro-mirror for the out-of-plane coupling of light to or from polymer multimode waveguides integrated on a printed circuit board (PCB). This millimeter-sized mass-reproducible component can then be readily inserted into laser ablated cavities. The roughness of the optical surfaces of the component is measured using a non-contact optical profiler, showing a local average RMS roughness around 30nm. Non-sequential ray-tracing simulations are performed to predict the optical performance of the component, showing coupling efficiencies up to 78% and a rigorous study on misalignment tolerances is performed. These results are then experimentally verified using piezo-motorized positioning equipment with submicron accuracy. As a first step, we characterize the component in a multimode fiber-to-fiber coupling scheme, showing coupling efficiencies up to 56%. As a second testbed, we use multimode waveguides patterned by UV-exposure in Truemode™ polymer, incorporating excimer laser ablated cavities. The size and depth of the cavities can be easily adapted on the design of the coupling structure, whereas alignment marks can be defined in the same processing step. Due to the multimode character of the waveguides, the total internal reflection condition is not always fully satisfied. Therefore, we investigate the application of a metal reflection coating on the micro-mirrors to improve the coupling efficiency. The fabricated coupling components are suitable for low-cost mass production since the compatibility of our prototyping technology with standard replication techniques, such as hot embossing and injection molding, has been shown before.