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

ABSTRACT 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.