A beam splitter or beamsplitter is an optical device that splits a beam of light into a transmitted and a reflected beam. It is a crucial part of many optical experimental and measurement systems, such as interferometers, also finding widespread application in fibre optic telecommunications. These devices are fundamental in a multitude of optical systems, from simple scientific experiments to complex telecommunications. Nowadays, several classical structures used for on-chip beam splitting mainly include y-branch waveguide [35 – 51], splitters based on multimode interference (MMI) coupling [52 – 69], splitters based on directional coupling (DC) [70 – 75], and splitters based on inverse design [76 – 81].