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Optics Express

Intradyne coherent receiver with optical decryption for disaggregated PSK Y-00 cipher transceiver architecture

Ken Tanizawa, Fumio Futami

Published Apr 13, 2026• 0 citations
Publisher

Abstract

The Y-00 quantum stream cipher utilizes the effect of quantum noise on optical signals and realizes signal-level symmetric-key encryption to protect interception in optical communication. A transceiver architecture that disaggregates encryption/decryption and modulation/demodulation in the optical domain facilitates the migration of Y-00 cipher to current digital-coherent communication systems. This paper presents a polarization-diversity intradyne Y-00 coherent receiver where local oscillator light is modulated for decryption. Polarization-diversity optical decryption and detection are simultaneously achieved using a typical optical 90-degree hybrid circuit and a conventional polarization-sensitive electro-optic modulator. Penalty-less detection with the decryption is demonstrated in 5-Gbit/s PSK Y-00 cipher transmission over fiber and free-space links, facilitating the disaggregation of decryption and demodulation.

DOI
10.1364/oe.586652

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The Y-00 quantum stream cipher utilizes the effect of quantum noise on optical signals and realizes signal-level symmetric-key encryption to protect interception in optical communication. A transceiver architecture that disaggregates encryption/decryption and modulation/demodulation in the optical domain facilitates the migration of Y-00 cipher to current digital-coherent communication systems. This paper presents a polarization-diversity intradyne Y-00 coherent receiver where local oscillator light is modulated for decryption. Polarization-diversity optical decryption and detection are simultaneously achieved using a typical optical 90-degree hybrid circuit and a conventional polarization-sensitive electro-optic modulator. Penalty-less detection with the decryption is demonstrated in 5-Gbit/s PSK Y-00 cipher transmission over fiber and free-space links, facilitating the disaggregation of decryption and demodulation.
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.
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.