Broadband power splitter for 3D photonic integrated chips

Three-dimensional (3D) photonic integrated circuits have emerged as a promising solution for the miniaturization and integration of chips, offering significant advantages in functional density and spatial scalability. Optical power splitters play a central role in photonic integrated circuits by enabling efficient signal distribution and recombination. However, inter-layer power splitters remain largely unexplored, primarily due to challenges such as strong wavelength dependence and structural configurations sensitivity. Here, we demonstrate the ultra-broadband and high robustness inter-layer power splitters based on spatial adiabatic passage, specifically designed for 3D photonic integrated circuits. The designed 3-dB power splitter exhibits outstanding performance across a 370 nm bandwidth (1260–1630 nm), with an imbalance of less than 0.11 dB and excess loss below 0.70 dB, which is further experimentally validated on a polymer waveguide platform. Notably, the proposed scheme shows a considerable tolerance to significant structural deviations. We also demonstrate a 2:8 inter-layer splitter with similarly broadband operation. This work provides a route toward ultra-broadband and fabrication-tolerant inter-layer power splitting, offering great potential for advancing high-performance 3D photonic integrated circuits.