Low-noise GHz InGaAs/InP single-photon detector (invited)

  Objective  With the development of quantum information science, laser radar and deep space detection, the traditional linear photoelectric detection technology has been unable to meet the needs of sensitive optical signal detection. The single-photon detection technology has gradually become an important research in the fields of weak light detection. InGaAs/InP avalanche photodiodes (APDs) are widely used in near-infrared single-photon detection due to the small size, low power consumption and fast response. The detection rate of most commercial InGaAs/InP detectors is at the level of 100 MHz, which cannot meet the application requirements for high counting rate. Meanwhile, low noise of the APD will bring smaller false counts to the system and further improve the performance. Therefore, a low-noise InGaAs/InP single-photon detector operating at the repetition frequency of GHz was demonstrated. Furthermore, the whole detector is evaluated with the quantum detector tomography technology, providing support for its application in quantum information technology such as quantum communication and quantum computation.

  Methods  In order to determine the detection frequency of gating signals, the response bandwidth of the APD is analyzed in the linear mode, and the bandwidth range is calculated to be 1-2 GHz. The spectral distribution characteristics of APD avalanche and noise signals are analyzed in the Geiger mode. It could be figured out that the noise is mainly distributed in the gating frequency and its harmonic frequencies, while the avalanche signal is mainly distributed below 1 GHz. Therefore, a cascade scheme of sine wave gating combined with low-pass filtering is proposed (Fig.3). The detector comprises high-speed gate generation and delay regulation module, temperature feedback control module, etc. Sine wave gating could be precisely controlled from many parameters which include frequency, amplitude, delay in a wide range. Feedback is added in the temperature control module to improve the stability of the detector. In addition, quantum detector tomography (Fig.2) is introduced to calibrate the detector, which is regarded as a "dark box". The positive operator-value measuring matrix can fully characterize the detector, which is obtained from input states and output results. The Wigner function is employed to describe whether the detector has quantum properties at high input photons.

  Results and Discussions   Sine wave gating combined with low-pass filtering is designed in the system, and signal-to-noise ratio is over 40 dB. The relationship between the detection efficiency and the afterpulse probability at the frequencies of 1-2 GHz is recorded. When the working rate is 1.5 GHz and the detection efficiency is set to be 20.0%, the afterpulse probability is 6.6% with the dark count rate of only 6.7×10⁻⁷ per gate (Fig.4). At constant detection efficiency of 20.0%, the DC bias voltage of the APD increases with temperature, showing a linear trend. While the afterpulse probability decreases, showing a contracting trend. The dark count rate degrades with the decrease of temperature and the trend is reversed at −30 ℃ (Fig.5), which might be related to high afterpulse or the intrinsic defection of APD. During the 12-hour test period, the detector performs perfectly stable and the variance of detection efficiency is 1% (Fig.8). Quantum detector tomography technology is employed to verify that high background noise does not affect the quantum properties (Fig.7).

  Conclusions  A GHz low noise InGaAs/InP detector is designed, and its detection efficiency, false count, saturation count rate and stability are explored. Based on the analysis of the response bandwidth of APD, a cascade scheme of sine wave gating combined with low-pass filtering is determined, realizing a low noise single photon detection below 2 GHz. In addition, quantum detector tomography technology is employed to calibrate the detector and verify its quantum properties. The structure of the detection technology is simple and the detector can run stably in the long term, which provides strong support for the practical application of single photon detector in deep space communication, laser mapping, optical time domain reflection and other fields.