Compact angled MMI utilizing subwavelength gratings

We present the first silicon photonic Multimode Interferometer (MMI) that integrates angled subwavelength grating (SWG) access waveguides with a compact, uniform SWG-based multimode region. The angled input/output geometry suppresses direct path coupling between ports, minimizing crosstalk without increasing the device width. Meanwhile, the SWG-based MMI region enables effective index reduction, allowing a shorter self-imaging length compared to conventional MMIs. The structure is fully compatible with CMOS processes and supports compact footprint integration. 3D finite-difference time-domain (FDTD) simulations confirm accurate operation, including direct imaging, inverse imaging, and balanced power splitting. This work introduces a novel hybrid approach for realizing ultra-compact, low-crosstalk MMI devices by combining angled access and SWG engineering. The proposed structure offers strong potential for dense photonic integration in switching, routing, and sensing applications.