This study enhances optical wireless atto-cell networks by introducing network-coordinated beam steering for seamless handover and interference-free spatial multiplexing. Experimental results confirm increased coverage, stable mobility, and capacity improvement, demonstrating the feasibility of ultra-reliable, high-speed optical wireless communication for future 6G networks in dense environments. © 2025 IEEE.

We present an experimental demonstration of a physical-layer encryption scheme for high-speed optical communication, focusing on cipher block chaining (CBC)-mode symbol-block phase encryption applied to 100 Gbaud dual-polarization quadrature phase-shift keying (DP-QPSK) signals within a 1.6 Tbps optical waveband. In the proposed approach, each of the two 100 Gbaud subchannels is independently encrypted using distinct 128-bit AES keys, yielding a combined key space of 2256 and ensuring strong security without key interdependence. Unlike conventional bit-level operations, encryption is performed directly on symbol blocks, which increases confidentiality while remaining compatible with high-baud-rate DSP implementations. Experimental transmission over 560 km of standard single-mode fiber with multiple ROADM nodes confirms the feasibility of this scheme. The results show that, although CBC-mode encryption introduces additional phase variations and slightly degrades Q2 performance due to stronger interactions with fiber nonlinearities, the Q2 values consistently remained above the FEC threshold, demonstrating reliable transmission. Furthermore, the proposed method benefits from practical integration with forward error correction and exhibits tolerance to cascaded ROADM traversals, with only a modest Q2 penalty of ~0.9 dB after 10 nodes. These findings indicate that CBC-mode symbol-block encryption can effectively enhance the confidentiality of high-capacity optical networks while maintaining transmission performance, thereby advancing the physical-layer security of next-generation waveband-based optical transport systems. © 2025 IEICE.

A twin-beam WDM-TDHP optical wireless system using flat-narrow beams is proposed for high-capacity underwater transmission. By optimizing adaptive modulation and beam design, the system achieves up to 2.5 Gbps across varying distances, demonstrating robustness against scattering and offering scalable, efficient communication for next-generation networks. © 2025 IEEE.