Balanced Detection in Single Photon Counting

We demonstrate balanced InGaAs/InP single photon avalanche diodes (SPADs) operated in both pulse-gated mode and sinusoidal gating mode for data transmission rate up to 20 MHz. The photodiode pair is biased in a balanced configuration with only one of the SPADs illuminated. The common-mode signal cancellation realized with the balanced configuration enables detection of small avalanche pulses. Afterpulsing is significantly suppressed due to the capability of detecting small avalanche pulses at high laser repetition rate. For pulse-gated mode operation and laser repletion rate of 20 MHz at 240 K, the dark count probability for photon detection efficiency of 13% is 1.9×10. The afterpulse probability is 0.3% for 2 ns pulse width, hold off time of 20 ns, and 10% PDE, at 240K. For sinusoidal gating a phase shifter has been incorporated to achieve better synchronization between signals. At laser rate of 20 MHz and 240 K, the dark count probability and photon detection efficiency are 2.8×10 and 10.8% respectively.