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arXiv:2203.08726 · IEEE Journal of Selected Topics in Quantum Electronics

Differential Phase-Shift QKD in a 2:16-Split Lit PON with 19 Carrier-Grade Channels

Nemanja Vokić, Dinka Milovančev, Bernhard Schrenk, Michael Hentschel, Hannes Hübel

Published Apr 1, 2020• 17 citations
arXivHTMLPDF

Abstract

We investigate the practical network integration of differential phase shift quantum key distribution following a cost-optimized deployment scheme where complexity is off-loaded to a centralized location. User terminal equipment for quantum state preparation at 1 GHz symbol rate is kept technologically lean through use of a directly-modulated laser as optical encoder. Integration in a passive optical network infrastructure is experimentally studied for legacy and modern optical access standards. We analyze the implications that result from Raman scattering arising from different spectral allocations of the classical channels in the O-, S-, C- and L-band, and prove that the quantum channel can co-exist with up to 19 classical channels of a fully-loaded modern access standard. Secure-key generation at a rate of 5.1×10-7bits/pulse at a quantum bit error ratio of 3.28% is obtained over a 13.5 km reach, 2:16 split passive network configuration. The high power difference of 93.8 dB between launched classical and quantum signals in the lit access network leads to a low penalty of 0.52% in terms of error ratio.

DOI
10.1109/jstqe.2020.2983592

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We investigate the practical network integration of differential phase shift quantum key distribution following a cost-optimized deployment scheme where complexity is off-loaded to a centralized location. User terminal equipment for quantum state preparation at 1 GHz symbol rate is kept technologically lean through use of a directly-modulated laser as optical encoder. Integration in a passive optical network infrastructure is experimentally studied for legacy and modern optical access standards. We analyze the implications that result from Raman scattering arising from different spectral allocations of the classical channels in the O-, S-, C- and L-band, and prove that the quantum channel can co-exist with up to 19 classical channels of a fully-loaded modern access standard. Secure-key generation at a rate of 5.1×10-7bits/pulse at a quantum bit error ratio of 3.28% is obtained over a 13.5 km reach, 2:16 split passive network configuration. The high power difference of 93.8 dB between launched classical and quantum signals in the lit access network leads to a low penalty of 0.52% in terms of error ratio.
We provide design guidelines for the integration of quantum key distribution (QKD) into legacy passive optical networks (PONs). Our study addresses the challenge of quantum coexistence with various PON standards in different network topologies. We develop a novel theoretical model to assess the impact of the passive optical distribution network on both the quantum signal and the generation of scattered Raman photons from classical signals. This work also includes an extensive Raman efficiency experimental evaluation over a wide frequency range. The study evaluates the integration of upstream QKD systems in 32- or 64-user PON scenarios, determining quantum-available bandwidths and maximum supported PON lengths. In single-fibre architectures the coexistence with standards having upstream and downstream classical channels in different telecommunication fibre windows (e.g. XG-PON) is extremely challenging due to the pervasive spectrum placement of the spontaneous Raman scattering noise. However dual-feeder architectures (i.e., placing the QKD receiver at the OLT-side of the protection feeder fibre) can significantly enhance QKD performance and support the key-exchange over the entire standardized PON length for most PON standards and even in case of two-PON standard presence. Finally, the dual-fibre topology allows the quantum coexistence in access networks where three classical standards share the same infrastructure.
We present the first demonstration of quantum key distribution (QKD) on a multi-user wavelength division multiplexed passive optical network (WDM-PON) with simultaneous, bidirectional 10Gb/s classical channel transmission. The C-Band QKD system operates at a clock rate of 10GHz and employs differential phase shift keying (DPSK). A dual feeder fiber and band filtering scheme is used to suppress classical to quantum channel cross-talk generated by spontaneous Raman scattering, which would otherwise prevent secure key distribution. Quantum keys were distributed to 4 users with negligible Raman cross-talk penalties. The mean QBER value for 4 users was 3.5% with a mean raw key distribution rate of 1.3Mb/s, which decreased to 696kb/s after temporal windowing to reduce inter-symbol interference due to single photon detector timing jitter.
It is well known that optical access networks are able to provide high data rates over long distances and to a reasonable number of users. Security and privacy are always a challenge for public accessible network infrastructures. Especially in time-division multiplexing passive optical networks (TDM-PONs), in which the downstream signal is broadcasted to all users connected via the same wavelength channel in a shared fiber link, privacy can be a critical concern. Although encryption at the application layer can provide a high level of security, this can be achieved only if the encryption key distribution is perfectly save. On the other hand, encryption on the physical layer such as quantum cryptography or, more precisely, quantum key distribution (QKD) is a very promising approach to achieve secure communication. However, there remain several issues that have to be solved before the quantum cryptography reaches the maturity level needed for a cost effective implementation in practical networks. In this paper, we address quantum key distribution (QKD) over passive optical access networks, which is an enabling technology required to cost efficiently deploy practical quantum encrypted data communication in the access area. We study different methods to integrate QKD systems in conventional optical access networks and quantitatively evaluate their suitability for a potential implementation.
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The integration of quantum key distribution (QKD) into passive optical networks (PONs) poses new challenges due to the specific characteristics of the access network, as the high losses from passive splitters and the spontaneous Raman scattering noise generated by classical channels co-propagating in the same optical fiber. In this paper, different QKD technologies and implementations are compared, taking into account both discrete-variable and continuous-variable QKD systems to maximize the achievable secret key rate performance in single-fiber bidirectional PONs.