| 摘要 |
This invention addresses the problem of measuring a stream of modulated pulses. The pulses may be optical pulses with J different modulation levels. The invention finds particular application in quantum communication systems. In a first embodiment a control signal Vj used to control the modulator 17 is used in the determination of a gating signal q0, q1, q2 used to bias the detector 19. The detector is gated such that only pulses with a selected modulation level can be detected. The pulses may be grouped into frames and the photodetector gated so that pulses with a first modulation level are detected in a first frame and pulses with a different second modulation level are detected in a second frame (see Fig. 3). In the second embodiment (Fig. 5 and claims 10 and 17), a signal with J different modulation levels is divided into J different frames. The modulation levels have a different known probability distribution in each of the respective frames. The average intensity is monitored in each of the J frames, and J simultaneous equations are solved to determine the intensity of each of the J modulation levels. |
