Abstract
This article reports on a symmetric-key direct-data encryption technique that directly protects the interception of optical and microwave signals from physical layer in a coherent analog radio-over-fiber (RoF) system. Secrecy is realized by signal masking by quantum (shot) noise. The quantum noise masking for the encryption is achieved by converting data into extremely high-order signals at an optical frequency. After signal transmission over an optical fronthaul link, the frequency of the encrypted signal is shifted to a microwave frequency via an optical heterodyne process using a local oscillator for wireless transmission. The effect of the quantum noise masking is naturally and seamlessly kept in the heterodyne process. We experimentally demonstrate 12 Gbit/s coherent RoF cipher systems utilizing the quantum noise masking for a 30 GHz wireless band. Adequate signal quality and high security against interception with sufficient quantum noise masking are simultaneously achieved in the optical fronthaul and microwave wireless links.
Highlights
H IGH security is a critical value in communication networks for transmission of important/private information
We demonstrated a quantum noise-assisted 12 Gbit/s RoF cipher system based on quadrature phase shift keying (QPSK) data for 30 GHz wireless transmission
We have experimentally demonstrated a proof-of-concept 12 Gbit/s coherent RoF cipher system using optical heterodyne frequency shift for secure optical fronthaul and 30 GHz-band wireless links
Summary
H IGH security is a critical value in communication networks for transmission of important/private information. We focus on symmetric-key direct-data encryption utilizing signal masking by quantum (shot) noise [6] This cipher system was originally demonstrated as AlphaEta [7] or the Y-00 quantum stream cipher [8] for fiber-optic transmission. We have recently proposed photonic generation of the quantum noise-masking cipher at microwave frequencies [17]. An optical heterodyne with a local oscillator (LO) was utilized to achieve sufficient signal masking by quantum noise at microwave frequencies. Generation of a 12 Gbit/s quantum noise-masking cipher at a center frequency of 30 GHz was demonstrated. The paper is organized as follows: In Section II, operating principles of the quantum noise-masking cipher and our proposed photonic generation of the cipher at microwave frequencies are explained.
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