Ultra-Compact Silicon Nitride Devices for High-Density Integration

Integrated photonic devices made of silicon nitride (SiN), which can be integrated with silicon on insulator and III V platforms, are expected to drive the expansion of silicon photonics technology. SiN offers lower propagation losses and a broad transparency window compared to other platforms, enabling substantial advancements in key photonic devices, including filters, multiplexers, high Q resonators, and nonlinear components. However, the relatively low refractive index contrast of SiN is often considered a limitation for creating compact and efficient devices. Herein, we present three fundamental devices: a coarse wavelength division multiplexer, a five mode mode division multiplexer, and a polarization beam splitter, all with extremely compact footprints. By achieving a reduction in device footprint of up to 1200 times, this work demonstrates the potential for significantly enhancing component density in silicon nitride chips without sacrificing performance. These results show that inverse design techniques can yield state of the art performance on the SiN platform.