Real-time generation of quantum keys between satellite and ground nodes is essential for a scalable and global quantum network. We report the development of a QKD system that operate at gigahertz clock rate with multiplexed classical and quantum channels. This system is tested on a free-space link which is an emulation of the satellite to ground link with dynamic loss and random misalignments. With the assumption of a small satellite in low Earth orbit and a ground station with moderate aperture, we demonstrate the generation of >5 Mbits of quantum keys in a single emulated satellite pass.
We report the development of an optical assembly and driving electronics for a low-SWaP polarization encoder design for use in satellite-to-ground quantum communication. The optical design multiplexes multiple lasers, which are selectively excited to produce a polarization encoded output. This implementation is intrinsically stable due to the use of only polarization maintaining fiber in the combining optics. The transmitter, provides a low-cost, low-power and high-speed platform to produce polarization encoded pulses. We use the transmitter to generate 4 polarization states with 2 intensity levels via multiplexing of 8 pulsed light sources. The module can generate the polarization states H, V, D and A, which correspond to polarization angles of 0, 90, 45 and -45 degrees respectively, forming two mutually unbiased bases. The transmitter is characterized via a polarization decoder over a free-space link within a laboratory setting. We characterize the source for varying optical channel loss which is introduced between the transmitter and receiver. The transmitter employs the T12 decoy-state BB84 protocol. We explore the performance of the system with commercially available single photon detectors for two clock rates of 500 MHz and 1 GHz. We find a similar secure key rate for both repetition rates, despite the expected 3 dB gain at 1 GHz. This is a result of detector jitter hindering the performance of the QKD system, resulting in a larger QBER when detection events leak into the adjacent time bins and ultimately reduces the secure key rate.
The information networks of the future will consist of an all-optical core, with wireless access technologies wherever possible. The fibre networks are extending their reach rapidly, and will further extend to individual spaces within homes and office buildings. The data traffic on networks and the demand for wireless services are also growing exponentially and the nature of services is also evolving with rapid increase in the number of devices. A new generation of 3D displays, with the ability to create Virtual Reality (VR) environments, is being launched. VR technology places significant demands on bandwidth, latency, positioning and mobility. One challenge addressed by our European collaborative project WORTECS is the development of an optical wireless system able to deliver ultra-high throughput (up to Tbps). The first demonstrator focuses on a high density network that can provide > 1 Gbps per user with multi user, but has the potential to provide Tbps per indoor environment. The second demonstrator focuses on ultra-high data rate links with a novel fibre-optical wireless-fibre approach to create Tbps capable links. VR is targeted as a demanding application, however, other applications include wireless data centers and aircraft cabins. In this paper, after introduction on the demand for wireless Terabit/s communication, we will focus on VR use case and the need for multi-Gigabit/s data rates. Then we will present the challenges for the project and propose new optical wireless system architecture and system engineering associated to new approach in space and frequency diversity with OFDM and adaptive bit rate for VR.
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