Fabrication and Characterization of Small Optical Ridge Waveguides Based on SU-8 Polymer

Small SU-8 ridge optical waveguides with an air cladding and a SiO₂ buffer on Si substrate have been realized by using a direct ultraviolet (UV) photolithography technology. The propagation loss measured by the cut-back method is about 0.1 dB/mm (@1550 nm) when the core width is 2.8 ??m. The bending losses of the present SU-8 optical ridge waveguides are also characterized. The measured results show that the bending loss decreases exponentially as the bending radius increases and the total loss can be reduced effectively by introducing an appropriate offset between two connected sections with different curvatures. A small bending radius (as small as 75 ??m) is still allowed for the requirement of a small bending loss (< 0.1 dB) when an offset of 0.1 ??m is introduced. Finally, by using this kind of waveguide, a small 1 ?? 2 Y-branch power splitter is fabricated and characterized.