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Conference on Lasers and Electro-Optics

214 (=16,384) Level Intensity Modulation at 10 Gbaud for Y-00 Quantum Stream Cipher

Ken Tanizawa, Fumio Futami

Published Jan 1, 2018• 4 citations
Publisher

Abstract

Coarse-to-fine driving of an MZI is proposed for multilevel intensity modulation beyond a resolution limit of a D/A converter. We demonstrate noise masking with record-high 214 (=16,384) intensity levels in 10-Gbaud Y-00 quantum stream cipher.
DOI
10.1364/cleo_at.2018.jtu2a.57

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We present a symmetric-key direct data encryption technique utilizing signal masking by quantum noise, called Y-00 quantum stream cipher. Physical encryption of phase-shift-keying (PSK) Y-00 quantum stream cipher is achieved by our proposed extremely high-order phase modulation. Two cascaded phase modulators are driven with two synchronized digital-to-analog converters for coarse-to-fine modulations, resulting in a record 217 phase levels for the quantum noise masking. Decryption of the cipher is implemented in digital signal processing after intra-dyne coherent detection with a free-running local oscillator. We experimentally demonstrate transmission of 10-Gbaud digital-coherent PSK Y-00 cipher with 217 levels over a 240-km field-installed single-mode fiber.
The Internet plays an essential role in modern societies and in the amount of sensitive data transported over the optical networks that shows its' importance has increased drastically. Therefore, it is critical to develop data protection schemes for optical fiber communications to provide user security. The Y-00 quantum-noise randomized stream cipher that employs extremely high-order modulation and restricts an attacker's interception of ciphertext is a practical candidate for providing data protection. In this article, we introduce the operation principle of the Y-00 cipher with respect to data encryption and decryption. The Y-00 cipher combines the mathematical encryption of multi-level signaling and physical randomness, and provides a high level of security to the physical layer of optical communications and a high communication performance. We also present the noise masking phenomenon of the Y-00 cipher with intensity modulation (IM). This noise masking is generated by shot noise, i.e., quantum noise and additive noise such as amplified spontaneous emission noise. The noise masking phenomenon fails an attacker's interception of the ciphertext. The secrecy of the IM Y-00 cipher is also discussed, and an approximate analytical solution is introduced for evaluating the probability of the attackers accurately guessing the ciphertext. Finally, the secrecy of a 1,000-km transmission system is experimentally demonstrated with the Y-00 cipher transceiver at data rate of 1.5-Gb/s using the derived analytical solution to deduce the high secrecy of the entire transmission system.