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Optics Express

Experimental investigation of heterodyne quantum key distribution in the S-band or L-band embedded in a commercial C-band DWDM system

Sebastian Kleis, Joachim Steinmayer, Rainer H. Derksen, Christian G. Schaeffer

Published May 29, 2019• 24 citations
Publisher

Abstract

The tolerance of continuous-variable quantum key distribution to co-propagating DWDM channels is investigated. The quantum channel is operated in the S-band or L-band and multiplexed with a commercial C-band DWDM system. The results show that, compared to previously proposed configurations, the number of co-propagating channels can be doubled. At a fiber length of 25 km, 56 DWDM channels with a total launch power of 14.5 dBm are tolerated by the quantum channel.

DOI
10.1364/oe.27.016540

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The tolerance of continuous-variable quantum key distribution to co-propagating DWDM channels is investigated. The quantum channel is operated in the S-band or L-band and multiplexed with a commercial C-band DWDM system. The results show that, compared to previously proposed configurations, the number of co-propagating channels can be doubled. At a fiber length of 25 km, 56 DWDM channels with a total launch power of 14.5 dBm are tolerated by the quantum channel.
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We report co-propagation experiments of the quantum channel (at 1310 nm) of a Quantum Key Distribution (QKD) system with Dense Wavelength Division Multiplexing (DWDM) data channels in the 1550 nm range. Two configurations are assessed. The first one is a single span configuration where various lengths of Standard Single Mode Fiber (SSMF) (from 20 to 70 km) are used and the total WDM channels power is varied. The Secure Key Rate (SKR) and the Quantum Bit Error Ratio (QBER) are recorded showing that up to ∼17 dBm total power of 30 or 60 channels at 100 Gb/s can coexist with the quantum channel. A metric to evaluate the co-propagation efficiency is also proposed to better evaluate the ability of a QKD system to provide secure keys in a co-propagation regime. The second experiment is a three spans link with a cascade of three QKD systems and two trusted nodes in a 184 km total link length. We report the transmission of a coherent 400 Gb/s Dual Polarization DP-16QAM (Quadrature Amplitude Modulation) channel that transports a QKD secured 100 GbE data stream, with other fifty-four 100 Gb/s WDM channels. Encryption is demonstrated at the same time as co-propagation.
Abstract Quantum key distribution (QKD) can offer communication with unconditional security and is a promising technology to protect next generation communication systems. For QKD to see commercial success, several key challenges have to be solved, such as integrating QKD signals into existing fiber optical networks. In this paper, we present experimental verification of QKD co-propagating with a large number of wavelength division multiplexing (WDM) coherent data channels. We show successful secret key generation over 24 h for a continuous-variable QKD channel jointly transmitted with 100 WDM channels of erbium doped fiber amplified polarization multiplexed 16-ary quadrature amplitude modulation signals amounting to a datarate of 18.3 Tbit/s. Compared to previous co-propagation results in the C-band, we demonstrate more than a factor of 10 increase in the number of WDM channels and more than 90 times higher classical bitrate, showing the co-propagation with Tbit/s data-carrying channels.
Network integration of quantum key distribution is crucial for its future widespread deployment due to the high cost of using optical fibers dedicated for the quantum channel only. We studied the performance of a system running a simplified BB84 protocol at 2.5 GHz repetition rate, operating in the original wavelength band, the short O-band, when multiplexed with communication channels in the conventional wavelength band, and the short C-band. Our system could successfully generate secret keys over a single-mode fiber with a length of 95.5 km and with co-propagating classical signals at a launch power of 8.9 dBm. Furthermore, we discuss the performance of an ideal system under the same conditions, showing the limits of what is possible with a discrete variable system in the O-band. We also considered a short and lossy link with 51 km optical fiber resembling a real link in a metropolitan area network. In this scenario, we could exchange a secret key with a launch power up to 16.7 dBm in the classical channels.
Abstract Integration of quantum key distribution (QKD) into existing optical transport network is one of the important problems that should be solved to expand the applicability of QKD systems and to develop quantum networks. When multiplexing a quantum channel with classical ones, researchers and engineers are faced with a high background count rate caused by spontaneous Raman scattering. This paper presents the results of Raman noise measurement in the O-band at different distances and launched power of the C-Band channels. Based on this data, the 1310 nm QKD system capable to integrate into DWDM optical network was developed. Its performance has been experimentally confirmed in testing on coexistence with intense C-band signals. The experiments were carried out on the propagation of classical and quantum signals in the same fiber as well as in the opposite directions. As a result, the stable QKD over a distance up to 60 km with a total launched power of classical channels up to 20 mW has been demonstrated.