Temperature dependence of the coupling loss between polymer optical waveguides and SMF for co-packaging

We theoretically calculate the coupling loss between single-mode fibers (SMFs) and polymer optical waveguides with different refractive index profiles. Temperature resistance is one of the concerns when integrating polymer optical waveguides near the electronics and photonics chips where they are highly likely to dissipate heat. Hence, the calculation focuses on the core size variations due to changes in operating temperature. The calculated results show that the refractive index variation with respect to temperature has a greater impact on coupling loss compared to the temperature-dependent core size variation. Then, polymer optical waveguides are experimentally fabricated and characterized. The temperature dependence of the output light intensity distribution from the fabricated waveguides is observed, as it is estimated by the theoretical calculation. In addition, it is also found that graded-index cores in polymer waveguides demonstrate slightly higher temperature stability in connection with SMF than their step-index counterparts. Such a low coupling loss with SMF could be maintained even in an environment at 100 °C, making polymer optical waveguides promising for the application of co-packaged optics.