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Metro and Data Center Optical Networks and Short-Reach Links

Digital-coherent PSK Y-00 quantum stream cipher for secure fiber-optic transmission

Ken Tanizawa, Fumio Futami

Published Feb 1, 2019• 2 citations
Publisher

Abstract

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.

DOI
10.1117/12.2506835

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IEICE Communications Express•Oct 18, 2017•7 citations
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.
A record-long 10,118-km fiber transmission with physical layer encryption is demonstrated utilizing a Y-00 cipher based on signal masking by quantum (shot) noise. The Y-00 cipher enables symmetric-key data encryption to ensure the security of the physical layer of optical communications. Irreducible secrecy without significant negative impact on transmission performance is achieved by the synergistic effect of combining seed-key-based high-order modulation and truly random shot noise inevitable in optical detection. This paper reports a comprehensive study of applying a phase-shift-keying (PSK) Y-00 cipher for ultra-long haul fiber transmission. Theoretical analysis shows that security-enhanced transmission over transoceanic-distance (>10,000 km) fiber is feasible when the quadrature PSK data signal is encrypted by converting to a PSK signal with 218 levels. Subsequently, 10,118-km standard single-mode fiber transmission of 48-Gbit/s line-rate dual-polarization PSK Y-00 cipher with 218 levels is experimentally demonstrated. An adequate signal quality above the Q-factor threshold of soft decision forward error correction is achieved together with sufficient signal masking by shot noise, yielding balanced transmission performance and high security in an ultra-long-haul PSK Y-00 cipher transmission system.
A 100-km fiber transmission with 10 Gbit/s is demonstrated based on Y-00 quantum noise randomized stream cipher (QNRC) utilizing cascaded phase shift keying (PSK). The proposed of the experimental scheme is to break the limitation of high-resolution and high-speed digital-to-analog converter (DAC) in the QNRC systems. In this paper, a 10 Gbit/s encrypted signal generated by employing seven cascaded phase modulators (PM) which are driven by designed electrical voltage signals at the transmitter side. The encrypted signal is successfully decrypted by the same six cascaded PMs and digital coherent detection. The experimental results show that the power penalties between back to back (B2B) and 50 km transmission and between B2B and 100 km transmission are 1.2 dB and 2 dB, respectively. The proposed PSK-QNRC system can realize error-free transmission. Meanwhile, the bit error rate (BER) performance of the proposed scheme is well below the forward error correction (FEC) threshold. However, the DAC sampling rate of the traditional scheme is not enough to recover the complete waveform. This proposed scheme greatly improves the security of the system.
Encryption in fiber-optic transmission is one of remaining issues in modern communication systems. One of the solutions is to use Y-00 quantum-noise randomized stream cipher. In this paper, we propose feedforward carrier phase estimation (CPE) with Y-00 decryption process for digital-coherent detection of phase-shift keying (PSK) Y-00 signal. After decryption of Y-00 signal in a digital domain, carrier phase is estimated by calculating Mth power of signal complex amplitude. Numerical simulations for 10-Gbaud PSK Y-00 signal show that the feedforward CPE with decryption process, which is used by a legitimate receiver who shares keys, successfully tracks phase noise. Consequently, penalty-less demodulation of Y-00 signal is achieved.