EXCESS NOISE REDUCTION FOR CONTINUOUS VARIABLE QUANTUM KEY DISTRIBUTION

A transmitter (100A) comprises at least one signal processing circuitry (104) configured to convert random bits into baseband digital signals encoding complex constellation points corresponding to the random bits and to apply a frequency upshift to the baseband digital signals to generate up-converted passband digital signals; at least two digital-to-analog converters (106) configured to convert the up-converted passband digital signals into up-converted passband analog signals; at least two linear driver amplifiers (109) configured to amplify the up-converted passband analog signals to generate amplified analog signals; an electro-optical modulator (107) configured to modulate a laser source signal to generate a coherent optical signal modulated by the amplified analog signals. A receiver (100B), comprises a coherent receiver circuit (112) configured to extract input symbols encoding random bits of a random key from a modulated optical signal and to generate an electrical signal; an analog-to-digital converter, ADC, (113) for generating a digital signal from the electrical signal; at least one digital signal processing circuitry (115) configured to apply a frequency downshift to the digital signal to generate a down-converted digital signal and to extract random bits from the down-converted digital signal.