The requirements of the mass consumer and educational market impose great restrictions on the cost of hardware-software demonstrators with relatively low requirements for the characteristics of the quantum key distribution process. This means that these devices do not have to be advanced and, as such, can provide a dramatic reduction in size, weight, and power compared to other quantum key distribution systems. The article presents the stages of development and creation of an experimental prototype of a hardware-software demonstrator of a universal quantum key distribution system that implements existing methods based on amplitude and phase modulation, as well as the proposed method of tandem amplitude-phase modulation of an optical carrier. The evaluation of the technical, economic and operational characteristics of the hardware-software demonstrator was carried out; practical recommendations were formulated for its development, creation and operation, as well as for the choice of an import-substituting element base, which ensured its low cost and the possibility of wide use at various research and educational sites, including World Skills youth championships and Future Skills process. In addition, the proposed demonstrator, embedded in a desktop computer, can act as access devices that can be connected to a terminal combined with a quantum network node to replenish a secret key store, which can then be used to encrypt daily activities on conventional platforms such as the Internet.
A high-precision symmetric optical vector analyzer (OVA) based on amplitude-phase double sideband (DSB) modulation with suppression of an optical carrier is proposed and numerically simulated. Accurate and stable frequency characteristics are achieved by the formation and minimization of such higher-order components in the probe radiation, the difference frequency of which does not coincide with the difference frequency of the two main measuring components of the first order. In comparison with the known solutions, the processing of spectral information is carried out at the modulation frequency, and not at the doubled frequency; the operating range of OVA has been increased by 2 times in terms of the bandwidth of the tested devices; instead of the standard Pound-Drever-Hall technique used to stabilize the laser wavelength with an additional modulator, the technique of controlling the amplitude and phase of the beating envelope of the main probing components is used; the relative error in the reconstruction of the frequency response of the high-Q optical structure at each point does not exceed 5×10–5. The obtained characteristics are confirmed by numerical modeling of the developed OVA when characterizing the spectral parameters of a narrow-band fiber Bragg grating. The presented method is structurally simple, does not require the use of various generators to perform its main functions and monitoring functions, and can be used to characterize both selective fiber-optic structures and high-Q optical Fabry-Perot resonators, resonators based on whispering modes, ring active and passive resonators, transparency windows of nonlinear crystals, plasmon resonances, etc.
In this paper, we propose the option of constructing a multi-channel system of quantum key distribution with frequency coding based on the AMPM-PMAM electro-optical scheme, using a Comb generator, multiplexer and demultiplexer to form a set of parallel quantum subchannels. The AMPM-PMAM work of the QKD system is based on the modulation conversion of the photon carrier based on the Ilyin-Morozov method and its one- and two-modulator implementations. The application of this scheme will significantly increase the transmission speed of the quantum key, allow the use of several levels of cryptographic protection, reduce the likelihood of achieving a positive result in PNS attacks of Eve (illegal subscriber) by eliminating the carrier from the structure of the signal transmitted through the quantum key distribution channel, and splitting information about key to different independent quantum channels.
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. In this paper, we present the results of constructing a frequency coding system of quantum key distribution (QKD) based on the serial electro-optical photon amplitude modulation and phase commutation. The possibility of reducing the probability of achieving a positive result in PNS attacks by Eva is shown by eliminating the carrier of the signal transmitted via the quantum channel from the structure of the key distribution. It was early 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, that is realized in considering. Additionally it is not necessary to form a notch filter system, which is usually carried out using fiber Bragg gratings (FBG) or arrayed waveguide gratings (AWG) for discrimination the photon carrier and its sideband components.
Design principals of universal microwave photonics system for quantum key distribution with frequency coding are concerned. Its concept is based on the possibility of creating the multi-functional units to implement the most commonly used technologies of frequency coding: amplitude, phase and combined amplitude-phase modulation and re-modulation of optical carrier. The characteristics of advanced systems based on classical approaches and prospects of their development using a combination of amplitude modulation and phase commutation are discussed. These are the valuations how to build advanced systems with frequency coding quantum key distribution, including at their symmetric and asymmetric constructions, using of the mechanisms of the photon polarization states passive detection, based on the filters for wavelength division multiplexing of modulated optical carrier side components.
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