Air-trench splitters for ultra-compact ring resonators in low refractive index contrast waveguides

We demonstrate air-trench splitters in low index contrast perfluorocyclobutyl (PFCB) waveguides. Splitters are fabricated by etching 800 nm wide high aspect ratio (18:1) trenches. The measured optical loss is 0.4 dB/splitter. The reflection/transmission splitting ratio is 0.859/0.141, which closely matches two-dimensional finite difference time domain (2DFDTD) simulation results. Air-trench splitters and bends are used to demonstrate an ultra-compact ring resonator (RR) with a size reduction of 1,700 compared to a RR based on traditional curved waveguides in the same material system. A comparison between the RR's measured and analytically calculated performance shows close agreement when splitter and bend losses are taken into account.