An ultra-compact Si-based beam splitter (BS) with footprint of 1  μm  ×  2  μm has been reported. It can split beams fifty–fifty with a 180-deg separation angle, and it is suit for integrated on a chip. It achieves high efficiency of 94.6% and 93.1% at wavelengths 1310 and 1550 nm, respectively, and more than 91% from 950 to 1600 nm. If Si is replaced with GaN or SiC in this device, it also can split the beam with high efficiency. Based on this, by means of replacing substrate material, different kinds of BSs for suitable wavebands can be fabricated in the same pipeline without changing mask template. This device has been designed by an intelligent method, which combines the method of moving asymptotes and the finite-element method, and GaN-based and SiO₂-based BSs have been designed by this method for near-infrared and visible light, respectively.