Simulation design and experimental study of low-loss couplers for integrated optical gyroscopes based on Si3N4 waveguides

Si3N4 waveguides have been posited as vital photonic devices for next-gen photonic integrated circuits (PICs) due to their excellent properties of broad transparency, low loss, thermal stability, and Complementary Metal Oxide Semiconductor (CMOS) compatibility. In this work, we focused on the simulation design and experimental studies of Si3N4 waveguides based splitters and couplers at 850nm, ensuring the optimized single-mode operation, minimizing dispersion, and highly-efficient transmission of light. A major challenge, inefficient fiber-waveguide coupling, was addressed by developing a special optimized taper waveguide, achieving a theoretical coupling efficiency boost from 11.21% to 99.7%. By meticulously tuning the width and height of the multimode interference (MMI) region to 18.26μm and 4μm, respectively, and positioning the output single-mode waveguides at an optimized distance of 2.05μm, we achieved a remarkable single-end transmission of over 49.8%, ensuring balanced and efficient signal distribution crucial for complex networks. The coupling loss of fiber to waveguide was calculated to be as low as 0.013dB compared to that of 9.5dB, and the insertion loss of MMI was calculated to be as low as 0.09dB. In summary, our work realized Si3N4-based waveguides for the enhanced coupling efficiency and optimized MMI splitters with excellent performance improvements to form the backbone of more efficient, compact, and high-performance photonic systems, such as the integrated optical gyroscope, on-chip optical sensors, etc.