We demonstrated a laser ranging experiment obtained with a Geiger-mode silicon avalanche photodiode (Si GAPD). The Surface-to-surface resolution of 15 cm was achieved with the technique of time-correlated single-photon counting. In the experiment, a mode-locked Yb-doped fiber laser at 1036 nm was applied, as the detection efficiency at 1036 nm of Si GAPDs is much higher than that at 1064nm which was widely applied in remote sensing. Due to the single-photon detector, the laser ranging system was able to measure the reflected photon pulses at single-photon level. We realized 32- m laser ranging experiment with a 135-mm diameter Newtonian telescope in daylight. And the system could measure the non-cooperated object longer than 11.3 km far away, which was tested through inserting the optical loss. It presented a potential for hundreds-of-kilometer laser ranging at low-light level.
In our recent experiment, we have designed a novel single-photon detecting module for quantum key distribution using an InGaAs/InP avalanche photodiode with gate-mode quenched photo-detection. At a repetition rate of 100 kHz and the working temperature of -60°C, we obtained the detection efficiency η higher than 10% and 20% at the dark probability Pd about 1.3×10-5 and 1.6×10-5 per nanosecond, respectively. Also at 100 kHz,
we got the best ratio of Pd/η as 1.7×10-3 per pulse (20 ns). And at a lower repetition such as 10 kHz, we obtained
Pd/η as 8.9×10-4 per pulse.
This report proposes a “Plug and Play” quantum key distribution system using differential phase shift, in which any birefringence effects and polarization-dependent losses in the telecom fiber are automatically compensated by using a Faraday mirror. In this system, a light pulse is split into three pulses after traveling through four couplers and a light intensity feedback servosystem is plugged into this system in order to adjust the phase shifter to compensate the variation of these three pulses. The efficiency of key creation in this system is 8/3 higher than the conventional cryptosystem based on the BB84 protocol.