A signal manipulator for a quantum communication system

A signal manipulator, comprising: an input for multiplexed signal, a demultiplexer for separating the multiplexed signal into separate components, a retransmitter unit being configured to receive a first component from the separated components and retransmit said received first component at a higher power than it is received; a bypass channel being configured to receive a second component from the components separated by the demultiplexer; and a multiplexer for multiplexing the first and second components, wherein the retransmitter is configured to regulate the power of the first component such that the power of the multiplexed signal leaving the multiplexer is −5 dBm or less.