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IEEE Optoelectronics Global Conference (OGC)

Constellation-Preserving Symbol Encryption with Minimal Impact on Fiber Non-linear Channels

Keiji Shimada, Ryosuke Matsumoto, Takahiro Kodama

Published Sep 5, 2023• 6 citations
Publisher

Abstract

We showed that uniform-QAM constellation-preserving symbol encryption is below the FEC limit Q2in any fiber transmission distance without decryption. 32Gbaud 7ch-WDM-DP-16QAM transmission experiments under the condition of fiber non-linear optics revealed no extreme degradation.
DOI
10.1109/ogc59456.2023.10314588

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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 2^256 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 Q2performance due to stronger interactions with fiber nonlinearities, the Q2values 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 Q2penalty 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.