采用具有高重复频率的连续变量脉冲量子态进行量子通信，不仅可利用单个脉冲编码信息，还可进行波分复用和时分复用，因而有助于提高量子通信系统的速度和容量。为了消除脉冲光重复频率信号对探测系统的饱和效应，设计制作了一种适用于测量脉冲光正交分量或强度噪声起伏的差分探测系统。对于利用变压器耦合的两个光电二极管的差分光电流交流分量，在采用低噪声放大器放大之前，先利用高隔离度的低通滤波器抑制脉冲光重复频率的拍频。该探测系统共模抑制比可达54 dB。入射的总光功率约为0.32 mW时，测得的光电流散粒噪声比电子噪声基底高8.7 dB。通过平衡零拍探测对散粒噪声基准进行标定，结果说明该系统适于测量脉冲光的量子噪声。

Speed and capacity of the quantum communication system can be increased by using the pulsed continuous variable entanglements with short pulse durations and high repetition rates, because the information can be encoded with individual pulses, and wavelength-division and time-division multiplexing can be applied. To avoid the saturation caused by the repetition rate of light pulses, we experimentally demonstrate a differential detection system, which is suitable for measuring the noise of pulsed lights. The photon-current difference of the two photo-diodes coupled by a transformer is passed through low pass filters to reject the repetition beat signal of pulsed light. Then it is amplified by the cascaded low-noise electronic amplifiers. The common mode reject ratio of the system is about 54 dB, and the noise of the photon-current difference is beyond that of the electronic background up to 8.7 dB when the sum of the total optical power incident to the two photo-diodes is about 0.32 mW. When the pulsed laser serves as the local oscillator, we successfully calibrate the shot noise limit by using balanced homodyne detection, showing that the detection system can be used to measure the quantum noise of pulsed optical fields.