Self-cancellation single photon detection system

The invention belongs to the technical field of communication, and discloses a self-cancellation single photon detection system. The system comprises a mixer, an avalanche photodiode APD, a trans-impedance amplifier TIA, a sample resistor R and a comparator. A negative electrode of the avalanche photodiode APD is connected with a direct-current bias VD, and a positive electrode is grounded through the sample resistor; a positive electrode of the avalanche photodiode APD is connected with an input end of the trans-impedance amplifier TIA; an output end of the trans-impedance amplifier TIA is connected with a negative electrode of the avalanche photodiode APD and the comparator respectively; a single photon signal to be tested and a local oscillator light signal are mixed by the mixer, then an optical signal is output, and the optical signal is sent to a light input end of the avalanche photodiode APD; an output signal of the trans-impedance amplifier TIA feeds back and adjusts the voltage across two ends of the avalanche photodiode APD; and the comparator counts the pulse of the single photon. The self-cancellation single photon detection system provided by the invention is high efficiency, convenient and reliable.