Optical transmitter for a quantum key distribution system or quantum random number generator

Abstract

An optical transmitter 101, e.g. for a quantum key distribution (QKD) system or a quantum random number generator (QRNG), comprising a laser source 103, e.g. a gain-switched laser source, to generate pulses of light for output by the transmitter, a pump for the laser source and a light source 117, e.g. an amplified spontaneous emission (ASE) light source, configured to emit photons via spontaneous emission. The light source 117 is coupled into the cavity of the laser 103 such that the photons emitted by the light source 117 will seed the pulses of light generated by the laser 103, each successive pulse having a random phase. In a QKD system or QRNG, each pulse output by the transmitter 101 may be input to an interferometer 107 comprising a first arm and a second arm, the first arm comprising a delay line 109. In the QKD system, the second arm of the interferometer may comprise a phase modulator 111 and an intensity modulator 105 may modulate the intensity of pulses output by the transmitter 101. In the QRNG, a photodiode (203 fig.2) may detect the pulses that travel along the first and second arms of the interferometer 107.

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