Practical integration of a quantum channel for QKD in commercial WDM systems : simulation and setup of a quantum channel

Abstract

The problem of distributing keys for encryption and decryption of sensitive data can be solved on the physical layer by means of quantum physics. Quantum key distribution (QKD) is the application of quantum theory to facilitate secure key transmission over an insecure channel. By performing key data transmission in the quantum regime, the possibility of eavesdropping information or man-in-the-middle attacks are made impossible based on physical properties rather than mathematical or computational complexity. Transparent optical networks are capable of providing a flexible and dynamic data transport via transparency regarding both data rate and format of transmitted signals, which is achieved by implementing data transmission and forwarding in the optical domain. While supporting all-optical end-to-end paths, transparent optical networks are in principle suitable to integrate end-to-end quantum cryptography. However, quantum signals are extremely sensitive to loss and noise, which is a particular issue because of the cascaded passive and active components along signal paths, common with transparent optical networks. This thesis analyzes different options for integrating quantum key distribution (QKD) in wavelengthdivision multiplexed (WDM) transparent optical networks where QKD signals are transmitted along with conventional WDM signals. Realistic simulations were implemented in VPItransmissionMaker with the goal to find applicable wavelength bands for the uninterrupted operation of a quantum channel. Metropolitan area network links with typical lengths of 20 km to 60 km and 40 WDM channels were simulated in scenarios with a direct point-to-point connection, using an intermediate amplifier (EDFA) and an intermediate optical switch node (OXC). Additionally, passive optical access networks (PONs) were examined considering standard options such as EPON, GPON, 10GPON, XGPON, PtP-GbE, PtP-10GbE, WDM-PON andWDM/TDM-PON. Finally, the background noise spectra at QKD receiver sites are presented. This data was further post-processed using analytical models of a well-known commercially available QKD system to estimate the quantum bit error rate (QBER) and final secure key rate (Rsec) for BB84 and SARG protocols across all wavelengths. The main conclusion is that QKD operation may be possible for fiber lengths up to 30 km, if the quantum channel is allocated in the O-Band, active nodes such as EDFA and OXC are bypassed and conventional data channels are restricted to the C-band.