Spiral transformation boosted by inverse design for a compact multi-core optical vortex mode sorter

Orbital angular momentum (OAM)-based dense space-division multiplexing technology has emerged as a promising candidate to break through the Shannon limit of single-mode fibers. While optical coordinate transformation offers potential for high-resolution OAM mode sorting, current implementations face critical limitations: the paraxial approximation constrains mode density scalability, and the plane wave approximation introduces beam quality degradation during transformation processes. We address these challenges by developing a transmissive optical vortex sorter through spiral coordinate transformation boosted by inverse-design approaches, achieving simultaneous sorting of 21 OAM modes with improved fidelity. Furthermore, we extend this advancement to a 19-core array implementation, thereby demonstrating its potential compatibility and scalability. The proposed scheme may pave the way for future ultrahigh capacity dense OAM fiber-optic communications with a large number of OAM modes while minimizing spatial resource requirements.