Method for detecting gigahertz single photon with low time jitter and low noise

[0017] Example: such as Figure 1-2 As shown, the numbers 1-13 respectively indicate: detection circuit 1, noise suppression circuit 2, signal processing circuit 3, phase shifter 4, radio frequency amplifier 5, low pass filter 6, radio frequency amplifier 7, comparator 8, adjustable attenuation Detector 9, power splitter 10, sinusoidal signal generator 11, high power amplifier 12, band pass filter 13.

[0018] Such as figure 1 As shown, the detection circuit converts the single-photon signal into an electrical signal through the APD. In the converted electrical signal, the avalanche signal is annihilated in the spike noise caused by the capacitive effect of the APD, and the avalanche signal is extracted by the noise suppression circuit. The noise suppression circuit is composed of a low-pass filter and a balance circuit. The signal is first passed through the low-pass filter and then balanced with the attenuated sinusoidal signal to remove noise and extract the avalanche signal. Finally, the extracted avalanche signal is converted into a digital signal through a signal processing circuit, and the count is output.

[0019] The specific analog circuit principle of this embodiment is as follows figure 2 Shown. The sinusoidal signal generator 11 generates a sinusoidal signal with a repetition frequency of ω, which is divided into two equal parts by the power splitter 10. One of the sinusoidal signals is amplified by the high-power amplifier 12, and then loaded on the APD as a gate pulse after passing through a band-pass filter 13. The amplitude of the sinusoidal signal generated by the sinusoidal signal generator is limited. After a high-power amplifier 12, the amplitude adjustment range of the sinusoidal signal is larger, which can fully meet the gate pulse amplitude required by the optimal operating point of the detector. After passing through the high power amplifier 12, bypass noise and resonance noise of other frequencies will be generated, which are filtered out by a bandpass filter 13 with a center frequency of ω. Adjust the bias voltage at both ends of the APD to work in avalanche mode to convert the optical signal into an avalanche signal. The avalanche signal output by the APD is annihilated in the spike noise, and the spike noise is filtered through a low-pass filter 2 with a cut-off frequency of ω. The filtered APD output signal is input to the power combiner 3 for balance. The reference signal of the balance circuit is an attenuated sinusoidal signal, the amplitude of which is the same as the filtered spike noise through the adjustable attenuator 9, and the phase difference between the two is 180° through the phase shifter 4. After the power combiner 3, the peak noise is basically reduced to the thermal noise level, which can be ignored, and the avalanche signal is extracted. The avalanche signal amplified by the two radio frequency amplifiers 5 and 7 is converted into a digital signal after the comparator 8 is buffered, and then sent to a counter for counting to realize single photon detection. Adding a low-pass filter 6 with a cutoff frequency of 2ω between the two radio frequency amplifiers 5 and 7 can prevent the crosstalk between the two amplifiers 5 and 7 from affecting the signal.

[0020] The present invention is composed of a signal detection circuit 1, a noise suppression circuit 2, and a signal processing circuit 3. The signal detection circuit 1 uses the APD to convert the detected optical signal into an avalanche electrical signal and sends it to the noise suppression circuit 2. The noise suppression circuit 2 suppresses the spike noise, extracts the avalanche signal, and finally the extracted avalanche signal enters the signal processing circuit 3. Convert analog signals into digital signals for counting. Due to the capacitive effect of the APD, while converting the optical signal into an avalanche electrical signal, spike noise is also generated. By using a low-pass filter 2, the noise can be filtered out to extract the avalanche signal. However, only one low-pass filter 2 is used, and the peak noise suppression ratio is not enough. Therefore, the sinusoidal gate signal is divided into two channels, and the amplitude of one channel is attenuated to the same amplitude as the low-pass filtered peak noise, and then sent to the balance circuit and After low-pass filtering, the spike noise is balanced and the avalanche signal is extracted. The signal processing circuit is composed of signal amplification, comparison, buffering, and counting. The avalanche signal enters the comparator 8 after being amplified, and the signal from the comparator 8 enters the counter to count after being buffered.