High precision fabrication of deep trenches for photonic communication chips

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In fiber optic networks, customers will apply the re-configurable optical add/drop multiplexing application at traffic nodes carrying optical communication signals using dense wavelength division multiplexing, which is the incumbent technique today and is growing to scale up bandwidth per fiber. Planar lightwave circuit (PLC) platform plays important roles in such photonic network. A PLC formed on a planar substrate can have various functions such as multiplexing/demultiplexing, optical branching, and optical switching, and hence is expected as a practical optical device or component. But weak optical confinement of silica-PLC platform leads to large component footprints to avoid cross-talk between adjacent channels. Deep trenching not only holds its exclusive advantages over other approaches to suppress the cross-talk, but also solves the large bending problem in photonic circuit layouts. The supporting company D&T Photonics is developing PLC VOA (variable optical attenuators) and switches, for which deep trenching would greatly enhance the device performance and reduce the footprint. The current project aims to fabricate such deep trenches using photo-lithography, metal liftoff and dry plasma etching of custom-made silica. The goal is to develop a microfabrication process to achieve controllable trench sidewall taper angle, minimum sidewall surface roughness, and precise control of trench depth. With success, the technology will be transferred to the supporting company for their production of PLC VOA and switches.