Ultracompact and broadband Si₃N₄ Y-branch splitter using an inverse design method

An effective inverse design method is used to demonstrate an ultracompact and broadband silicon nitride Y-branch 3-dB power splitter. Its topology is determined by a continuously varying function inspired by the universal approximation theorem for neural networks. The proposed model ensures an adiabatic mode transition in an extremely compact area. Our designs are validated on a commercial foundry photonic platform with 248 nm deep UV lithography. Experimental results demonstrate that the fabricated device features an excess loss of less than 0.15 dB (0.17 dB) at 1550 nm wavelength and splitting imbalance of about 0.4 dB (1.47 dB) from 1480 nm to 1640 nm for the TE (TM) mode, covering S+C+L+U band. The device footprint is only 2.3 µm × 5.2 µm, an order of magnitude smaller than typical silicon nitride power splitters.