Nanoporosity effect in optical loss of single-mode polymer waveguides

We fabricate single-mode polymer waveguide structures exhibiting polarization-independent ultra-low loss of 0.04 and 0.05 dB/cm at the 1310 and 1550 nm bands, respectively, with a Deltan of 1.6%. A porous structure that arises during the fabrication process is studied by considering its implications in the propagation loss based on the Rayleigh-Mie scattering loss mechanism. We demonstrate that the porous structure is to be reduced to the nanoscale (i.e., <10 nm) to realize waveguide structures with ultra-low propagation losses based on fabrications and measurements of morphologies with various degrees of porosity. Further, the bending loss and its respective polarization-dependent propagation loss behavior are analyzed to realize compact devices with ultra-low-loss and polarization-independent features, where a 4 mm bending radius is found to be adequate for such a performance over the 1550 nm band.