Ultra-compact and broadband arbitrary-to-single-mode power divider-based architecture for flexible on-chip mode conversion and routing

We propose a versatile on-chip mode manipulation architecture based on arbitrary-to-single-mode power dividers (ASPDs), enabling flexible mode conversion and routing in multimode photonic systems. The architecture comprises two oppositely cascaded ASPD units arranged in a Mach-Zehnder-interferometer-like configuration, leveraging standard single-mode components such as phase shifters and mode routers to achieve highly flexible multimode manipulation. This approach offers two key advantages: a compact, scalable design based solely on ASPD units and standard single-mode components, and direct decomposition of higher-order modes into the fundamental mode, simplifying routing and removing the need for complex multimode elements. As a proof of concept, several ultra-compact ASPDs were designed using subwavelength grating structures optimized via intelligent algorithms. For commonly used low-order modes (TE₀-TE₃), the devices exhibit footprints below 9.5 µm and maintain excess losses (ELs) below 0.35 dB across a 300 nm bandwidth (1400-1700nm). Notably, TE₀/TE₁ ASPDs achieve ELs < 0.15 dB over a record-wide 500 nm range (1300-1800nm). Based on these ASPDs, we experimentally demonstrate flexible mode conversion and switching, confirming their effectiveness for multimode signal control. Furthermore, numerical results show that the scheme can be extended to higher-order modes (TE₄-TE₇) while maintaining excellent performance and compact footprints (8 µm), and can be combined with standard single-mode crossings for flexible multimode interconnections. These results validate the feasibility and scalability of the proposed ASPD-based platform, offering a promising route toward reconfigurable multimode photonic integrated circuits.