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Optics Express

Single-channel 48-Gbit/s DP PSK Y-00 quantum stream cipher transmission over 400- and 800-km SSMF

Ken Tanizawa, Fumio Futami

Published Aug 22, 2019• 18 citations
Publisher

Abstract

phase levels. Successful transmission of the Y-00 cipher over 400- and 800-km standard single-mode fibers was achieved without significant negative impact on transmission quality. The product of the data rate and distance was 40 Gbit/s (net rate) × 800 km = 32,000 Gbit/s·km. The system achieves masking of 217 phase levels by shot noise, which promises irreducible and unchanged security based on the quantum nature of coherent light.

DOI
10.1364/oe.27.025357

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phase levels. Successful transmission of the Y-00 cipher over 400- and 800-km standard single-mode fibers was achieved without significant negative impact on transmission quality. The product of the data rate and distance was 40 Gbit/s (net rate) × 800 km = 32,000 Gbit/s·km. The system achieves masking of 217 phase levels by shot noise, which promises irreducible and unchanged security based on the quantum nature of coherent light.
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.
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.
We demonstrate the first 40 Gbit/s single-channel polarization-multiplexed, 5 Gsymbol/s, 16 QAM quantum noise stream cipher (QNSC) transmission over 480 km by incorporating ASE quantum noise from EDFAs as well as the quantum shot noise of the coherent state with multiple photons for the random masking of data. By using a multi-bit encoded scheme and digital coherent transmission techniques, secure optical communication with a record data capacity and transmission distance has been successfully realized. In this system, the signal level received by Eve is hidden by both the amplitude and the phase noise. The highest number of masked signals, 7.5 x 10(4), was achieved by using a QAM scheme with FEC, which makes it possible to reduce the output power from the transmitter while maintaining an error free condition for Bob. We have newly measured the noise distribution around I and Q encrypted data and shown experimentally with a data size of as large as 2(25) that the noise has a Gaussian distribution with no correlations. This distribution is suitable for the random masking of data.