OPTIDOC - Optimum Quantum Detectors for Communications

With increasing digitalisation, the demands on wireless high-speed data transmission are growing. Traditional systems are reaching their limits because they require high light output on the transmitter side.

Quantum communication offers a promising solution here, as it operates with minimal light output and requires only a few photons. However, a major problem with wireless optical transmission is multipath propagation. This leads to interference and can significantly impair transmission quality.

OPTIDOC solves this problem with a novel receiving device that was developed specifically for optical quantum communication. This device includes a channel estimation unit that determines the relevant channel parameters based on the number of photons received. Based on this, another unit calculates probability increments, which are further processed in a transition metric calculation unit. The special feature is that the calculation is based on a modified Laguerre-based transition metric. This takes into account the physical properties of quantum transmission and is specially adapted for the case of multipath propagation. 

The receiver combines proven methods from digital communication, such as the Viterbi algorithm or the BCJR algorithm, with this new metric, ensuring reliable data transmission, especially under difficult conditions. In addition, multiple receiver strands can be operated in parallel if necessary to further increase robustness through diversity reception. The device is flexibly designed for use in single-mode and multi-mode operation.