We propose a chaotic spatial symbol transforming encryption method for enhancing the physical layer security in fiber-optic systems based on space-division multiplexed (SDM) transmission. The designed 3-D chaotic sequences are used to scramble the real and imaginary part of quadrature amplitude modulation (QAM) symbols. permute the symbol-to-space mapping. and control iteration times ... https://jalyttlers.shop/product-category/pen-holder/