A novel physical layer data encryption scheme using two-level constellation masking in three-dimensional (3D) carrier-less amplitude and phase modulation (CAP) passive optical network (PON) is proposed in this Letter. The chaotic sequence generated by Chua’s circuit model realizes two-level encryption of displacement masking and constellation rotation for 3D constellations. We successfully conduct an experiment demonstrating 8.7 Gb/s 3D-CAP-8 data transmission over 25 km standard single-mode fib
