Xiuliang Chen

Low-Timing-Jitter Single-Photon Detection Using 1-GHz Sinusoidally Gated InGaAs/InP Avalanche Photodiode

We demonstrate an efficient way to improve the timing jitter of sine-wave gated InGaAs/InP avalanche photo diode (APD) by combining sinusoidally balanced differencing and low-pass filtering techniques to minimize detrimental waveform distortion of the avalanche signal, and realize a 1-GHz gated InGaAs/InP single-photon detector with the timing jitter as low as 60 ps. The detection efficiency could reach 10.4% at 1550 nm with the maximum count rate ~100 MHz, after pulse probability ~3.0%, and dark count rate ~6.1 × 10-6 per gate. Such low timing jitter single-photon detectors offer facility for quantum key distribution at gigahertz clock rate.

1550-nm time-of-flight ranging system employing laser with multiple repetition rates for reducing the range ambiguity.

We demonstrated a time-of-flight (TOF) ranging system employing laser pulses at 1550 nm with multiple repetition rates to decrease the range ambiguity, which was usually found in high-repetition TOF systems. The time-correlated single-photon counting technique with an InGaAs/InP avalanche photodiode based single-photon detector, was applied to record different arrival time of the scattered return photons from the non-cooperative target at different repetition rates to determine the measured distance, providing an effective and convenient method to increase the absolute range capacity of the whole system. We attained hundreds of meters range with millimeter accuracy by using laser pulses of approximately 10-MHz repetition rates.

Room-Temperature Single-Photon Detector Based on InGaAs/InP Avalanche Photodiode With Multichannel Counting Ability

Using a capacitance balancing circuit, we achieved infrared single-photon detection based on an InGaAs/InP avalanche photodiode (APD) with a low dark count rate and negligible afterpulse effect at room temperature of 290 K. Detection efficiency of 9.80% was attained with the dark count rate of 6.62 × 10-4 per gate, showing that the detector could work efficiently even at room temperature without Peltier cooling. Moreover, the detector was operated in an arbitrary gated mode, meaning that more than one gating pulse was applied on the APD during one period. The single-photon detector working in this mode was capable of multichannel photon counting for practical quantum key distribution.

Low-noise high-speed InGaAs/InP-based single-photon detector.

A low-noise high-speed InGaAs/InP-based single-photon detector was demonstrated with a double-self-differencing spike signal cancellation technique. A photon-number resolving method was used to analyze the ratio of avalanche signal to background noise. By adding a post-self-differencing circuit to the pre-self-differencing circuit, the signal to noise ratio was improved by 11.0 dB. The typical error count probability was as low as 2.1% and 6.4% at the detection efficiency of 20.6% and 30.5%, respectively.

Photon-number resolving performance of the InGaAs/InP avalanche photodiode with short gates

By using a self-differencing circuit to achieve efficient spike cancellation for the near-infrared single-photon detector based on InGaAs/InP avalanche photodiode, we verified that shortening the gate duration enforced the detection efficiency to saturate at an increased voltage, while increasing the avalanche gain favored the discrimination of the avalanche signals caused by different photon-number states. Photon-number resolving detection was realized by measuring the weak current at the avalanche built-up. The photon-number resolving performance could be improved by shortening the gating pulse duration.

“Plug and play” quantum key distribution system with differential phase shift

We propose a “plug and play” scheme for the long-distance fiber-based cryptosystem based on the differential phase shift quantum key distribution, where any birefringence effects and polarization-dependent losses in the transmission fiber are automatically compensated by using a Faraday mirror. This system not only has stable performance but also creates keys 8/3 times more efficiently than the conventional cryptosystem based on the BB84 protocol.

Phonon mode and phase transition behaviors of (1-x)PbSc1/2Ta1/2O3-xPbHfO3 relaxor ferroelectric ceramics determined by temperature-dependent Raman spectra

The composition dependence of phase transition temperature in (1-x)PbSc1/2 Ta 1/2O3-xPbHfO3 (PSTH) ceramics ( 0 ≤ x ≤ 0 . 2 ) has been investigated by Raman spectra. From the typical phonon mode variations, the PSTH ceramics unambiguously undergoes three structural transformations with increasing the temperature from 82 to 673 K. It was found that the F 2 g phonon mode disappears above the Curie temperature. Moreover, the PSTH ceramics exhibited the paraelectric to ferroelectric phase transitions at 287, 293, 313, 320, and 330 K with the composition. The phenomena can be ascribed to the enhanced length of Pb-O-Ta bonds induced by the incorporation of Hf4+ ions.

Stable differential phase shift quantum key distribution with a key creation efficiency of 3/4

In this letter, we demonstrate that a high key creation efficiency can be achieved in a stable differential phase shift quantum key distribution system by using three cascaded Mach–Zehnder interferometers. A pulse is split into four independent pulses, and the bit information is carried by one of the three phase differences between the sequential pulses. Any birefringence effects and polarization-dependent losses in the long-distance fiber are automatically compensated with a Faraday mirror. Due to the neatly use of three cascaded interferometers, the key creation efficiency reaches 3/4.

Efficient quantum key distribution with stable and expansible differential phase shift schemes

Efficient quantum key distribution can be achieved by using a stable differential phase shift scheme, with an expansible setup mainly composed of several parallel Mach–Zehnder interferometers, a serial Mach–Zehnder interferometer, and a Faraday mirror. An expansion of the scheme by adding more parallel Mach–Zehnder interferometers can conveniently increase the key creation efficiencies, and the energies of the interfering pulses can be equalized easily without changing the phase shifts in the serial interferometer. The long-term stabilities are guaranteed by using a multifeedback servo-system and Faraday mirror. And the sensibilities of the scheme to the disturbance of eavesdropping are improved by increasing the key creation efficiencies. The security of the scheme against some possible attacks, such as intercept/resend attack and Trojan horse attack, are discussed.

Time-dependent photon number discrimination of InGaAs/InP avalanche photodiode single-photon detector

We investigated the photon-number-resolving (PNR) performance of the InGaAs/InP avalanche photodiode (APD) as a function of the electric gate width and the photon arrival time. The optimal electric gate width was around 1 ns for PNR measurements in our experiment, which provided a PNR capability up to three photons per pulse when the detection efficiency was ~20%. And the dependence of the PNR performance on the arrival time of the photons showed that the photon number could be better resolved if the photons arrived on the rising edge of the electric gate than on the falling edge. In addition, we found that with the increase of the electric gate width, PNR performance got worse. The observation would be helpful for improving the PNR performance of the InGaAs/InP APD in the gated mode.