A trade-off in polymer waveguides for interfacing PICs

In the datacom and telecom markets, there has been a recent increase in demand for data throughput and processing. The challenge to meet this demand by increasing compute efficiency, can only be tackled with the support of more advanced and faster packaging methods. An optical redistribution layer (ORDL), that routes optical signals between fibers, from fiber to PIC and from PIC to PIC, is needed to provide the processing units with the required data-flow. This solution eliminates the need for pluggable modules that are less flexible and allows the opto-electronic conversion to happen in the same package as the processing unit. The polymer waveguide material platform offers promising characteristics as a foundational element for building an ORDL. In this poster, we present two methods for interfacing a photonic integrated circuit (PIC) with a polymer waveguide: adiabatic coupling and edge coupling, both of which use an inverse taper to expand the mode in the PIC. We compare two commercially available polymer materials for both methods, focusing on dimensions, and coupling efficiency. The modal overlap at different cross-sections is analysed, and time and frequency domain simulations are used to validate the coupling performance. A key material property is the refractive index, as a higher index contrast between the core and cladding of the polymer waveguide results in smaller modes. This can help reduce the taper length and minimize modal mismatch at the interface. However, a trade-off occurs, as it is decreases the alignment tolerance and makes it harder to couple the smaller modes to an optical fiber.