Polymer Waveguides for Co-Packaged Optics

This paper demonstrates a low-loss photo patternable polymer waveguide material platform based on benzocyclobutene (BCB) that works in both liquid resins and dry film formats. By precise control of molecule design and refractive index between the core and clad layers, we minimized material absorption at target wavelengths, achieving a propagation loss value of <0.1 dB/cm at 850 nm and <0.3 dB/cm at 1310 nm at the system level based on cutback measurements. We patterned these waveguides on silicon and PCB substrates with laser direct imaging (LDI) or mask aligner, with sub-10 μm accuracy. Moreover, our patterned waveguides maintain thermal stability, with <±5% change in optical loss after multiple reflow processes and 1000 h at 85 °C and 85% humidity (HAST) tests. Lastly, we introduce our modeling framework, predicting transmission, mode profile, and optimal performance of waveguides while considering varying geometries, coupling designs, bend radii, and pitch sizes.