Inverse Design of an Ultra-Compact Symmetric 3-dB Optical Power Splitter Based on N-ary Digital Pattern

Inverse design based on high-performance computing ability is an efficient and intuitive design method. In this paper, we employed the digitized adjoint method to design a symmetric 3-dB power splitter based on N-ary digital pattern with an occupied compact footprint of only 3.25 µm × 2.6 µm. The digitized adjoint method is applied to inverse design and continuously adjusts and updates the relative permittivity for a cylindrical material filled with the intermediate material to obtain a quasi-digital pattern and then transforms it into a quaternary digital pattern. Based on this approach, a symmetrical structure with etching cylindrical radius of 45, 37, and 30 nm was obtained, which enables the 3-dB power splitter to achieve a precise 50:50 split ratio in a wide wavelength range from 1.45 to 1.65 µm. And the excess loss (EL) was less than 1 dB with an operating bandwidth of 200 nm. This approach holds significant potential for informing the design of high-performance, compact power splitters.