Glass Interposer Assisted Edge Coupling to SiN Photonic Integrated Circuits

Scaling the fiber-to-chip interface is a critical bottleneck for modern photonic interconnect solutions, which must support the growing density and bandwidth demands of high-performance photonic integrated circuit (PIC) applications. In this study, we present a novel, high-density edge coupling solution that enables low-loss, simultaneous multichannel coupling to a silicon nitride (SiN) chip, utilizing a glass-based waveguide array to fiber (WAFT) interposer. The WAFT interposer efficiently bridges single-mode fibers to the SiN chip, providing mode-field matching and supporting an exceptional density of up to 67 input/output (I/O) channels per millimeter for robust, scalable integration. We designed and fabricated SiN edge couplers optimized for the WAFT-coupled fibers and characterized the full coupling interfacefrom fiber through the WAFT to the SiN chip across the O and C optical bands. Measured fiber-to-chip coupling loss (CL) per optical port ranged from 1.55-1.81 dB (TE)/1.55-1.93 dB (TM) in the O band and 1.67-1.86 dB (TE)/1.58-1.69 dB (TM) in the C band. Furthermore, polarization-dependent loss (PDL) tests showed low CL of 1.42-1.62 dB/optical port at 1310 nm and 1.35-1.83 dB/optical port at 1550 nm. These results indicate that the WAFT-based edge coupling solution holds significant promise as an effective, scalable, and bandwidth-flexible approach, potentially addressing a critical packaging bottleneck for advanced, high-density PIC integration.