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APL Photonics

Cryptography in coherent optical information networks using dissipative metamaterial gates

Angelos Xomalis, Iosif Demirtzioglou, Yongmin Jung, Eric Plum, Cosimo Lacava, Periklis Petropoulos, David John Richardson, Nikolay I. Zheludev

Published Apr 1, 2019• 11 citations

Abstract

All-optical encryption of information in fibre telecommunication networks offers lower complexity and far higher data rates than electronic encryption can deliver. However, existing optical layer encryption methods, which are compatible with keys of unlimited length, are based on nonlinear processes that require intense optical fields. Here, we introduce an optical layer secure communication protocol that does not rely on nonlinear optical processes but instead uses energy redistribution of coherent optical waves interacting on a plasmonic metamaterial absorber. We implement the protocol in a telecommunication optical fibre information network, where signal and key distribution lines use a common coherent information carrier. We investigate and demonstrate different encryption modes, including a scheme providing perfect secrecy. All-optical cryptography, as demonstrated here, exploits signal processing mechanisms that can satisfy optical telecom data rate requirements in any current or next-generation frequency band with bandwidth exceeding 100 THz and a switching energy of a few photons per bit. This is the first demonstration of an optical telecommunications application of metamaterial technology.

DOI: 10.1063/1.5092216

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The growing awareness of the vulnerability of information transmitted on communication systems within the government, military and commercial sectors, has stimulated a number of areas of research within the optical community to design optical hardware encryption systems providing inherent immunity to espionage techniques. This paper describes a hardware optical encryption technique that utilises off the shelf telecommunication equipment and negates the necessity for an independent key distribution system with respect to the data transmission system, as is common with alternative encryption system implementations. This method also lends itself easily to fiber optic or free space communication and is applicable within any optical waveband. The encryption-decryption of the optical signal is achieved through low coherence optical interferometry. This requires the instantaneous processing and analysis of the signal, optically, to retrieve the relevant optical phase information hidden in the transmitted optical noise. This technology allows an authorised user to transmit encrypted information at a high data rate securely, while maintaining opaqueness to an unauthorised observer that data transmission is occurring. As the instantaneous optical field properties of the signals present in the system are essential to the optical encryption - decryption process, the system is inherently protected against electronic recording and advances in computational decryption algorithms. For organisations wishing to protect sensitive data and levels of communication activity these are highly desirable features.

The optical network supporting emerging bandwidth-intensive services has become the cornerstone of the 5G era. However, the development of optical fiber eavesdropping and quantum computing has brought huge security challenges to traditional cryptography. As an effective approach to improving optical layer transmission security, all-optical logic gate encryption has important research significance. This paper proposes a high-speed coherent optical encryption and decryption system based on phase encoding with all-optical logic gates. The system ingeniously designs the phase encoding and decoding scheme between two quadrature phase-shift keying (QPSK) signals, which doubles the encryption and decryption efficiency. In addition, the integration of physical-layer key distribution (PLKD) and physical-layer encryption (PLE) contributes to a reduction in overall system complexity. By adopting real-time signal processing in an all-optical domain, the single-wavelength rate of system security communication can reach 100 Gbps. The system is also applicable to other phase-modulated signals and provides a feasible scheme to enhance transmission security in wavelength division multiplexing (WDM) optical networks featuring high speed, low latency, and high flexibility.