Link technology for all-optical satellite-based quantum key distribution system in C-/L-band

Abstract

Satellite based quantum key distribution (QKD) enables the delivery of keys for quantum secure communications over long distances. Maturity of the technology as well as industrial interest keep increasing. So does the technology readiness of satellite free-space optical communications. A satellite QKD system comprises a quantum communication subsystem and a classical communication subsystem (public channel). Both are implemented with freespace optics. Thus, in satellite QKD system design, there are strong synergies that should be exploited as much as possible and lead to an all-optical satellite QKD system. In this paper, we present a system like this locating all optical channels in ITU DWDM C-band. We focus on the overall conceptual design and the setup of the optical channels for quantum and classical signal transmission. The system description addresses the breadboards of a transmitter laser terminal (Alice terminal), a receiver laser terminal, (Bob terminal), the public channel implementation, the interfaced QKD system and the deployed encryption system. The design basis for the Alice terminal is the laser terminal development OSIRISv3. The design basis for the Bob terminal is the ground station development THRUST. The later contains an adaptive optics correction to enable single mode fiber coupling. This enables the interfacing to almost arbitrary quantum receivers such as the Bob modules used in the described experiment. The public channel is composed of a bi-directional 1 Gbps IM/DD system and a MODEM that implements a proprietary waveform optimized for free-space channels.The system was experimentally analyzed in a field test in the framework of the German initiative QuNET which addresses the use case of quantum secure communication for authorities. The results of the experiment are used to model a feasible LEO satellite-ground link. Performance indicators such as quantum bit error rate and secure key rate of a potential mission are estimated analytically.

Optical satellite links at DLR

“…In 2021, a large scale technology demonstration was conducted in Bonn where a quantum secure video conference was demonstrated between the German Ministry of Education and Research and the Federal Office for Information Security. In this experiment, the group contributed to the setting up of the free-space photonic link which was used for different QKD connections [32], [33].…”

Development of a cascaded fine pointing and tracking control loop for quantum key distribution via free-space optical communications

“…This development was part of a demonstration campaign between two public authorities in Bonn, Germany. For this purpose, a system was built 4 incorporating the previously discussed controls to establish a 300 m quantumsecure link. Figure 8 shows the resulting error in normalized 4QD space, which has an absolute range of [0;1].…”