Space-division multiplexing (SDM) technology can effec-tively expand the capacity of optical fiber communication networks, but few-mode fiber (FMF) for SDM must use multiple-input multiple-output (MIMO) signal processing to withstand the induced cross talk, resulting in system complexity and cost rise. Zhou Bingkun academician's research team from Tsinghua University designed a po-larization-maintaining PANDA ring-core fiber with a ring-core structure and two stress-applying rods to solve the problem.