Advances in On‐Chip Polarization Multiplexing Devices: From Traditional Designs to Inverse Design and Hybrid Multiplexing

Polarization multiplexing technology achieves double data transmission capacity in photonic integrated devices by utilizing different polarization states of light. The key function of polarization multiplexing devices is to separate and convert the polarization states of light waves using devices such as polarization beam splitters (PBS) and polarization rotators (PR). This paper reviews various design structures for polarization multiplexers, such as directional coupler (DC) structures, multimode interference (MMI) structures, Y‐branch structures, and auxiliary structures like photonic crystals (PC), hybrid plasmonic waveguides (HPW), subwavelength gratings (SWG), and slot waveguides, as well as the applications of various materials, such as silicon, silicon nitride, lithium niobate, and compounds. The paper emphasizes the application of inverse design techniques in polarization multiplexer devices, particularly in improving the design efficiency and performance of devices through the combination of deep learning and optimization algorithms. With the continuous advancement of technology, polarization multiplexing devices will become more compact and efficient, and through hybrid multiplexing technology, combined with wavelength division multiplexing (WDM) and mode division multiplexing (MDM), communication capacity will be significantly increased. Although current devices still face challenges in terms of performance and manufacturing processes, they have great application potential in the future in optical interconnection chips, quantum computing, and biological detection.