Objective Single-photon detection technology has attracted attention of researchers increasingly in recent years. The development of negative feedback avalanche diode (NFAD) which integrates a quenching resistor for fast quenching has greatly lessened the afterpulsing effects in InGaAs/InP based near-infrared single-photon detectors. Moreover, the integration of the thermal-electric cooler (TEC) with the NFAD has made the detector small in size and low in power consumption. However, the integration of the quenching resistor with large resistance reduces the amplitude of the avalanche current output to tens of μA. Though it can be read out using a broadband pre-amplifier, the long bonding wire of the TEC-integrated NFAD makes it prone to electro-magnetic interference. In addition, the large parasitic inductance and capacitance of the long bonding wire, combined with the low amplitude of the avalanche signal, makes it hard to cancel the noise induced by the capacitive response of the recovery signal of the NFAD, and hence it is difficult to use active-quenching circuits for better performance. Therefore, it is required to design a sophisticated circuit to solve the problems above to facilitate the application of the NFAD-based single-photon detector.
Methods An integrated free-running InGaAs near-infrared single-photon detector was developed based on negative feedback avalanche diode (NFAD). In order to tackle with the problem that the readout of the avalanche current is prone to interference when using an amplifier, a high-impedance differential circuit without pre-amplifier was proposed for avalanche signal extraction. By introducing a specially designed resistive-capacitive network and signaling, the active-quenching technique was successfully combined with NFAD and was able to work stably. In addition, shielding material was applied to the amplifier-free readout circuitry for further interference shielding. The design above enhanced the quenching performance and stability of the detector at the same time. Moreover, in order to lower the dark-count rate, the circuit and the heat-dissipation structure of the detector was optimized to maximize the thermal contact area, and hence the high heat from the integrated thermal-electric cooler of the NFAD and the high-speed quenching circuit can be quickly dissipated to achieve lower cooling temperature.
Results and Discussions The performance of the quenching circuit, the thermal design, and the anti-interference were verified through experiments. Waveforms at the inputs of the comparator (in Fig. 3) showed that the performance of the detector without pre-amplifier was stable. The maximum detection efficiency for 1550 nm wavelength reached 33%, and the minimum dead time available was 120 ns at the detection efficiency of 10%, at −50 ℃, where the dark-count rate and afterpulse probability were as low as 890 Hz and 10.6%, respectively. The heat-dissipation performance was good enough to maintain the temperature of the NFAD at −58 ℃ with fan cooling when the ambient temperature was 20 ℃. At −30 ℃, the afterpulse probability was approximately 70% of the value at −58 ℃, at the cost of a higher dark count rate of 13.2 times of the value at −58 ℃.
Conclusions The proposed amplifier-free avalanche extraction and active-quenching circuit was able to work with the NFAD stably with a threshold of 9 mV, showing an excellent anti-interference performance. The afterpulse probability was as low as 10.6% at 10% detection efficiency, 120 ns dead time, −50 ℃, indicating that the hybrid quenching performance of the active-quenching circuit with NFAD was sufficient for low-dead-time free-running operation of the detector. In addition, good heat-dissipation performance was achieved by the large-thermal-contact-area design, where the temperature of the NFAD reached −58 ℃ with fan cooling at an ambient temperature of 20 ℃. It is indicated that this highly integrated low-noise near-infrared single-photon detector for communication wavelengths is especially suitable for use in the applications where high performance and minimum space usage are required.
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