Frequency coded quantum key distribution channel based on photon amplitude-phase modulation
Ildaris M. Gabdulhakov, Oleg G. Morozov · 2017
The technology of frequency coding in channels of quantum key distribution allows to determine the ground state of photons through the value of the amplitude of its carrier, frequency modulated in phase (PM) or amplitude (AM) by a radio-frequency signal, and the resulting side components. Over the past twenty years, it has been substantially modified and improved. At the same time, in recent works, an expanded understanding of the frequency coding principle is used, in which each photon state is associated not with the phase of the modulating signal at a certain frequency, but with one or more sideband frequencies or the carrier frequency of the photon itself. The known schemes of electro-optical modulation and remodulation are described by the symmetric pairs PM-PM, AM-AM and AM-PM (PM-AM), where the first component determines the modulator type on the Alice side (legal subscriber - transmitter), and the second one on the side of Bob legal subscriber - receiver). It is noted, that the smallest value of QBER is achieved in schemes with a passive definition of one or two basic states of a photon, i.e. without the use of remodulation processes. The formation of a filter system is carried out using fiber Bragg gratings (FBG) or arrayed waveguide gratings (AWG), tuned to the photon carrier or it sideband components. In this paper, we present the results of constructing a universal system of quantum key distribution (QKD) based on the electro-optical AMPM-PMAM scheme, which makes it possible to realize all the above-mentioned schemes and additionally combined version. At the heart of the AMPMPMAM system of the QKD system is the modulation transformation of the photon carrier based on the Il'inMorozov's method and its one- and two-modulator realizations. For the mathematical description of the scheme, the principles of constructing a single-port modulation microwave photonic link of a sequential type and photon modeling of electro-optical modulators were used. The use of the universal scheme will allow using several levels of cryptographic protection, including switching schemes and protocols, with remodulation and only passive detection. In addition, it should be noted the high spectral efficiency of the Il'in-Morozov's modulation conversion, its spectral purity and the stability of the received characteristics of the output radiation when the conversion parameters deviate from the optimal ones. The possibility of reducing the probability of achieving a positive result in PNS attacks by Eva (illegal subscriber) is shown by eliminating the carrier of the signal transmitted via the quantum channel from the structure of the key distribution.